RFC 3126
Electronic Signature Formats for long term electronic signatures
RFC 3126 ✨ Electronic Signature Formats for long term electronic signatures
Okay bestie, let's get into it 🎀 This is RFC 3126, written by D. Pinkas (Integris), J. Ross, and N. Pope (Security & Standards), and it came out in September 2001. It's Informational, which means it shares info with the internet community and doesn't set an internet standard. The title block doesn't list anything it obsoletes or updates. It's giving "here's how to make an e-signature that still holds up years later" 💅
Status of This Memo
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
Okay so this doc defines the format of an electronic signature that can stay valid for a really long time 🦋 It also includes evidence of its validity, even if the signer or the verifying party later tries to deny it (aka repudiates the validity of the signature). Main character energy for sure ✨
The format can be thought of as an extension to RFC 2630 and RFC 2634, where extra signed and unsigned attributes get added when they make sense 🧚
Also, the contents of this Informational RFC are technically equivalent to ETSI TS 101 733 V.1.2.2. That ETSI TS is under the ETSI Copyright (C), and you can download individual copies of the ETSI deliverable from http://www.etsi.org 💜
Table of Contents
1. Introduction 4
2 Overview 5
2.1 Aim 5
2.2 Basis of Present Document 5
2.3 Major Parties 6
2.4 Electronic Signatures and Validation Data 7
2.5 Forms of Validation Data 8
2.6 Extended Forms of Validation Data 11
2.7 Archive Validation Data 13
2.8 Arbitration 15
2.9 Validation Process 15
2.10 Example Validation Sequence 16
2.11 Additional optional features 21
3. Data structure of an Electronic Signature 22
3.1 General Syntax 22
3.2 Data Content Type 22
3.3 Signed-data Content Type 22
3.4 SignedData Type 22
3.5 EncapsulatedContentInfo Type 23
3.6 SignerInfo Type 23
3.6.1 Message Digest Calculation Process 23
3.6.2 Message Signature Generation Process 24
3.6.3 Message Signature Verification Process 24
3.7 CMS Imported Mandatory Present Attributes 24
3.7.1 Content Type 24
3.7.2 Message Digest 24
3.7.3 Signing Time 24
3.8 Alternative Signing Certificate Attributes 24
3.8.1 ESS Signing Certificate Attribute Definition 25
3.8.2 Other Signing Certificate Attribute Definition 25
3.9 Additional Mandatory Attributes 26
3.9.1 Signature policy Identifier 26
3.10 CMS Imported Optional Attributes 28
3.10.1 Countersignature 29
3.11 ESS Imported Optional Attributes 29
3.11.1 Content Reference Attribute 29
3.11.2 Content Identifier Attribute 29
3.11.3 Content Hints Attribute 29
3.12 Additional Optional Attributes 30
3.12.1 Commitment Type Indication Attribute 30
3.12.2 Signer Location attribute 32
3.12.3 Signer Attributes attribute 33
3.12.4 Content Time-Stamp attribute 34
3.13 Support for Multiple Signatures 34
3.13.1 Independent Signatures 34
3.13.2 Embedded Signatures 34
4. Validation Data 35
4.1 Electronic Signature Time-Stamp 36
4.1.1 Signature Time-Stamp Attribute Definition 36
4.2 Complete Validation Data 37
4.2.1 Complete Certificate Refs Attribute Definition 38
4.2.2 Complete Revocation Refs Attribute Definition 38
4.3 Extended Validation Data 40
4.3.1 Certificate Values Attribute Definition 40
4.3.2 Revocation Values Attribute Definition 41
4.3.3 ES-C Time-Stamp Attribute Definition 42
4.3.4 Time-Stamped Certificates and CRLs Attribute Definition 42
4.4 Archive Validation Data 43
4.4.1 Archive Time-Stamp Attribute Definition 43
5. Security Considerations 44
5.1 Protection of Private Key 44
5.2 Choice of Algorithms 44
6. Conformance Requirements 45
6.1 Signer 45
6.2 Verifier using time-stamping 46
6.3 Verifier using secure records 46
7. References 47
8. Authors' Addresses 48
Annex A (normative): ASN.1 Definitions 49
A.1 Definitions Using X.208 (1988) ASN.1 Syntax 49
A.2 Definitions Using X.680 1997 ASN.1 Syntax 57
Annex B (informative): General Description 66
B.1 The Signature Policy 66
B.2 Signed Information 67
B.3 Components of an Electronic Signature 68
B.3.1 Reference to the Signature Policy 68
B.3.2 Commitment Type Indication 69
B.3.3 Certificate Identifier from the Signer 69
B.3.4. Role Attributes 70
B.3.4.1 Claimed Role 71
B.3.4.2 Certified Role 71
B.3.5 Signer Location 72
B.3.6 Signing Time 72
B.3.7 Content Format 73
B.4 Components of Validation Data 73
B.4.1 Revocation Status Information 73
B.4.2 CRL Information 74
B.4.3 OCSP Information 74
B.4.4 Certification Path 75
B.4.5 Time-Stamping for Long Life of Signature 76
B.4.6 Time-Stamping before CA Key Compromises 77
B.4.6.1 Time-Stamping the ES with Complete validation data 77
B.4.6.2 Time-Stamping Certificates and Revocation Information 78
B.4.7 Time-Stamping for Long Life of Signature 79
B.4.8 Reference to Additional Data 80
B.4.9 Time-Stamping for Mutual Recognition 80
B.4.10 TSA Key Compromise 81
B.5 Multiple Signatures 81
Annex C (informative): Identifiers and roles 82
C.1 Signer Name Forms 82
C.2 TSP Name Forms 82
C.3 Roles and Signer Attributes 83
Full Copyright Statement 841. Introduction ✨
Okay so this doc is meant to cover electronic signatures for all kinds of transactions 💼 Think business stuff like purchase requisitions, contracts, and invoices, where it really matters that the signature stays valid for a long time 🍓 It also includes evidence of validity, even if the signer or verifying party later tries to deny it (aka repudiates it, see [ISONR]) 🙈
E-signatures can be used for any transaction you can think of: individual to company, company to company, individual to government, the works 🌈 This doc is independent of any environment, so it can be applied anywhere, like smart cards, GSM SIM cards, or special e-signature programs, etc. 💅
An electronic signature made under this document gives you evidence you can process to get confidence that some commitment was explicitly endorsed under a signature policy, at a given time, by a signer under an identifier (like a name or a pseudonym), and optionally a role 🎀
The European Directive on a community framework for Electronic Signatures defines an electronic signature as: "data in electronic form which is attached to or logically associated with other electronic data and which serves as a method of authentication". An electronic signature as used in this document is a form of advanced electronic signature as defined in the Directive 🦋
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase, as shown) are to be interpreted as described in [RFC2119] 👑
2. Overview 💖
2.1. Aim 🔥
The aim of this doc is to define an Electronic Signature (ES) that stays valid over long periods 🫶 It includes evidence of its validity, even if the signer or verifying party later tries to deny (repudiates) the validity of the signature. Iconic behaviour from a signature honestly 💅
This document specifies the use of trusted service providers (e.g., Time-Stamping Authorities (TSA)) and the data that needs to be archived (e.g., cross certificates and revocation lists) to meet the requirements of long term electronic signatures 🧚 An ES defined by this document can be used for arbitration if there's a dispute between the signer and verifier, even if that happens years later 😭 Also, this document uses a signature policy, referenced by the signer, as the basis for establishing the validity of an electronic signature 🌸
2.2 Basis of Present Document 💖
okay so this whole document is built on public key cryptography 🔐, which is what lets us make digital signatures, and those signatures are backed up by public key certificates 🎀
A Public key certificate is a public keys of a user, together with some other information, rendered unforgeable by encipherment with the private key of the Certification Authority (CA) which issued it (ITU-T Recommendation X.509 [1]). ✨
This document also covers using time-stamping services to prove a signature is still valid long after the normal lifetime of the critical parts of an electronic signature, and to support non-repudiation 🫶. As an option, it also defines the use of additional time-stamps for very long-term protection against key compromise or weakened algorithms 🔥.
This document builds on existing standards that are already widely adopted. This includes:
- RFC 2459 [RFC2459] Internet X.509 Public Key Infrastructure Certificate and CRL Profile (PKIX); 🌸
- RFC 2630 [CMS] Crytographic Message Syntax (CMS); 🦋
- RFC 2634 [ESS] Enhanced Security Services (ESS); 💜
- RFC 2439 [OCSP] One-line Certificate Status Protocol (OCSP); 🧚
- ITU-T Recommendation X.509 [1] Authentication framework; 🍓
- RFC (to be published) [TSP] PKIX Time Stamping protocol (TSP). 👑
NOTE: See clause 8 for a full set of references 📚
2.3 Major Parties 🎀
okay the major parties involved in a business transaction backed by electronic signatures (as defined in this document) are:
- the Signer;
- the Verifier;
- the Arbitrator;
- Trusted Service Providers (TSP).
A Signer is an entity that initially creates the electronic signature. When the signer digitally signs over data using the prescribed format, that's a commitment on behalf of the signing entity to the data being signed. main character energy 💅
A verifier is an entity that verifies an evidence. (ISO/IEC 13888-1 [13]). Within the context of this document, this is an entity that validates an electronic signature. ✨ An arbitrator, is an entity which arbitrates disputes between a signer and a verifier when there is a disagreement on the validity of a digital signature. ⚖️
Trusted Service Providers (TSPs) are one or more entities that help to build trust relationships between the signer and verifier 🤝. Use of some specific TSP services MAY be mandated by signature policy. TSP supporting services may provide the following information: user certificates, cross-certificates, time-stamping tokens, CRLs, ARLs, OCSP responses.
The following TSPs are used to support the validation or the verification of electronic signatures:
- Certification Authorities;
- Registration Authorities;
- Repository Authorities (e.g., a Directory);
- Time-Stamping Authorities;
- One-line Certificate Status Protocol responders;
- Attribute Authorities;
- Signature Policy Issuers.
Certification Authorities provide users with public key certificates 🔑
Registration Authorities allow the registration of entities before a CA generates certificates 📝
Repository Authorities publish CRLs issued by CAs, cross-certificates (i.e., CA certificates) issued by CAs, signature policies issued by Signature Policy Issuers and optionally public key certificates (i.e., leaf certificates) issued by CAs 📚
Time-Stamping Authorities attest that some data was formed before a given trusted time ⏰
One-line Certificate Status Protocol responders (OSCP responders) provide information about the status (i.e., revoked, not revoked, unknown) of a particular certificate 🚦
A Signature Policy Issuer issues signatures policies that define the technical and procedural requirements for electronic signature creation, validation and verification, in order to meet a particular business need 📜
Attributes Authorities provide users with attributes linked to public key certificates 🏷️
2.4 Electronic Signatures and Validation Data 🌈
okay so validating an electronic signature under this document requires:
- The electronic signature; this includes:
- the signature policy;
- the signed user data;
- the digital signature;
- other signed attributes provided by the signer;
- other unsigned attributes provided by the signer.
Validation data, which is the additional data needed to validate the electronic signature; this includes:
- certificates references;
- certificates;
- revocation status information references;
- revocation status information;
- time-stamps from Time Stamping Authorities (TSAs).
- The signature policy specifies the technical requirements on signature creation and validation in order to meet a particular business need. A given legal/contractual context may recognize a particular signature policy as meeting its requirements 👀
For example: a specific signature policy may be recognized by a court of law as meeting the requirements of the European Directive for electronic commerce ⚖️ A signature policy may be written using a formal notation like ASN.1 or in an informal free text form, provided the rules of the policy are clearly identified. However, for a given signature policy there shall be one definitive form which has a unique binary encoded value 🤓
Signed user data is the user's data that is signed 💌
The Digital Signature is the digital signature applied over the following attributes provided by the signer:
- hash of the user data (message digest);
- signature Policy Identifier;
- other signed attributes
The other signed attributes include any additional information which must be signed to conform to the signature policy or this document (e.g., signing time) ⏱️
According to the requirements of a specific signature policy in use, various Validation Data shall be collected and attached to or associated with the signature structure by the signer and/or the verifier 🗂️ The validation data includes CA certificates as well as revocation status information in the form of certificate revocation lists (CRLs) or certificate status information provided by an on-line service. Additional data also includes time-stamps and other time related data used to provide evidence of the timing of given events ⏳ It is required, as a minimum, that either the signer or verifier obtains a time-stamp over the signer's signature, or a secure time record of the electronic signature must be maintained. Such secure records must not be undetectably modified and must record the time close to when the signature was first validated 🔒
2.5 Forms of Validation Data 💫
An electronic signature may exist in many forms, including:
- the Electronic Signature (ES), which includes the digital signature and other basic information provided by the signer;
- the ES with Time-Stamp (ES-T), which adds a time-stamp to the Electronic Signature, to take initial steps towards providing long term validity;
- the ES with Complete validation data (ES-C), which adds to the ES-T references to the complete set of data supporting the validity of the electronic signature (i.e., revocation status information).
The signer must provide at least the ES form, but in some cases may decide to provide the ES-T form, and in the extreme case could provide the ES-C form 🦋 If the signer does not provide ES-T, the verifier must either create the ES-T on first receipt of an electronic signature or shall keep a secure time record of the ES. Either of these two approaches provides independent evidence of the existence of the signature at the time it was first verified, which should be near the time it was created, and so protects against later repudiation of the existence of the signature 🫶 If the signer does not provide ES-C, the verifier must create the ES-C when the complete set of revocation and other validation data is available.
The ES satisfies the legal requirements for electronic signatures as defined in the European Directive on electronic signatures. See Annex C for further discussion on the relationship of this document to the Directive 🇪🇺 It provides basic authentication and integrity protection and can be created without accessing on-line (time-stamping) services. However, without the addition of a time-stamp or a secure time record, the electronic signature does not protect against the threat that the signer later denies having created the electronic signature (i.e., does not provide non-repudiation of its existence) 😬
The ES-T time-stamp or time record should be created close to the time that ES was created, to provide protection against repudiation. At this time all the data needed to complete the validation may not be available, but what information is readily available may be used to carry out some of the initial checks. For example, only part of the revocation information may be available for verification at that point in time. Generally, the ES-C form cannot be created at the same time as the ES, as it is necessary to allow time for any revocation information to be captured. Also, if a certificate is found to be temporarily suspended, it will be necessary to wait until the end of the suspension period ⏳
The signer should only create the ES-C in situations where it was prepared to wait for a sufficient length of time after creating the ES form before dispatching the ES-C. This, however, has the advantage that the verifier can be presented with the complete set of data supporting the validity of the ES 🎁
Support for ES-C by the verifier is mandated (see clause 6 for specific conformance requirements) 👑
An Electronic Signature (ES), with the additional validation data forming the ES-T and ES-C, is illustrated in Figure 1 ✨
+------------------------------------------------------------ES-C-----+
|+--------------------------------------------ES-T-----+ |
||+------Elect.Signature (ES)----------+ +------------+| +-----------+|
|||+---------+ +----------+ +---------+| |Time-Stamp || |Complete ||
||||Signature| | Other | | Digital || |over digital|| |certificate||
||||Policy ID| | Signed | |Signature|| |signature || |and ||
|||| | |Attributes| | || +------------+| |revocation ||
|||+---------+ +----------+ +---------+| | |references ||
||+------------------------------------+ | +-----------+|
|+-----------------------------------------------------+ | +---------------------------------------------------------------------+
Figure 1: Illustration of an ES, ES-T and ES-Cokay so the verifier's conformance requirements for an ES with a time-stamp on the digital signature are in subclause 6.2 🕰️✨ It's giving "the timestamp is the receipt" energy.
The ES on its own already satisfies the legal requirements for electronic signatures under the European Directive on electronic signatures 💅 The signer's conformance requirements for an ES are in subclause 6.1, and they're met with a structure like this one 🎀
+------Elect.Signature (ES)-----------|
|+---------+ +----------+ +---------+ |
||Signature| | Other | | Digital | |
||Policy ID| | Signed | |Signature| |
|| | |Attributes| | | |
|+---------+ +----------+ +---------+ |
|+-----------------------------------+|
Figure 2: Illustration of an ESNow, if you want long-term signatures but you aren't time-stamping the digital signature, you need a secure record of when verification happened, tied to the electronic signature (so both have to be securely recorded) 🔐 On top of that, the certificates and revocation info used during verification should be recorded too, as shown in figure 3. That's called an ES-C(bis) 🦋
+-------------------------------------------------------ES-C-----+
| |
| +------Elect.Signature (ES)----------+| +-----------+|
| |+---------+ +----------+ +---------+|| |Complete ||
| ||Signature| | Other | | Digital ||| |certificate||
| ||Policy ID| | Signed | |Signature||| |and ||
| || | |Attributes| | ||| |revocation ||
| |+---------+ +----------+ +---------+|| |references ||
| +------------------------------------+| +-----------+|
| |
+----------------------------------------------------------------+
Figure 3: Illustration of an ES-C(bis)The verifier's conformance requirements for an ES-C(bis) are in subclause 6.3 🌸
Note: A time-stamp attached to the electronic signature or a secure time record helps to protect the validity of the signature even if some of the verification data associated with the signature become compromised AFTER the signature was generated. The time-stamp or a secure time record provides evidence that the signature was generated BEFORE the event of compromise; hence the signature will maintain its validity status. 🫶
2.6. Extended Forms of Validation Data ✨
The complete validation data (ES-C) described above can be extended into an ES with eXtended validation data (ES-X) 🧚 It covers these extra requirements:
First up, when the verifier doesn't have access to:
- the signer's certificate,
- all the CA certificates that make up the full certification path,
- all the associated revocation status information, as referenced in the ES-C.
then those certificates and revocation info can be added to the ES-C. This extended validation data is called an X-Long 💜
Second, if there's a risk that any CA keys in the certificate chain might get compromised, you need to time-stamp the validation data too, either by:
- time-stamping all the validation data held with the ES(ES-C). This extended validation data is called a Type 1 X-Time-Stamp; or
- time-stamping individual reference data used for complete validation.
This extended validation data is called a Type 2 X-Time-Stamp 🔥
NOTE: The advantages and drawbacks of Type 1 and Type 2 X-Time-Stamp are discussed in this document (see clause B.4.6.)
If all of the above conditions happen, you can combine the two formats above. That's called an X-Long-Time-Stamped 👑
Support for the extended forms of validation data is optional. 🌈
An Electronic Signature (ES), with the additional validation data forming the ES-X long, is illustrated in Figure 4:
+-------------------------------------------------------- ES-X Long--+
|+---------------------------------------- EC-C --------+ |
||+---- Elect.Signature (ES)----+ +--------+| +--------+ |
|||+-------+-+-------+-+-------+| +----------+|Complete|| |Complete| |
||||Signa- | |Other | |Digital|| |Time-Stamp||certi- || |certi- | |
||||ture | |Signed | |Signa- || |over ||ficate || |ficate | |
||||Policy | |Attri- | |ture || |digital ||and || |and | |
||||ID | |butes | | || |signature ||revoc. || |revoc. | |
|||+-------+ +-------+ +-------+| +----------+|refs || |data | |
||+-----------------------------+ +--------+| +--------+ |
|+------------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure 4: Illustration of an ES and ES-X long.An Electronic Signature (ES), with the additional validation data forming the eXtended Validation Data - Type 1, is illustrated in Figure 5:
+----------------------------------------------------------- ES-X 1 -+
|+----------------------------------------- EC-C --------+ |
|| +---- Elect.Signature (ES)----+ +--------+| +-------+ |
|| |+-------+ +-------+ +-------+| +----------+|Complete|| | | |
|| ||Signa- | |Other | |Digital|| |Time-Stamp||certifi-|| | Time- | |
|| ||ture | |Signed | |Signa- || |over ||cate and|| | stamp | |
|| ||Policy | |Attri- | |ture || |digital ||revoc. || | over | |
|| ||ID | |butes | | || |signature ||refs || | CES | |
|| |+-------+ +-------+ +-------+| +----------+| || | | |
|| +-----------------------------+ +--------+| +-------+ |
|+-------------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure 5: Illustration of ES with ES-X Type 1An Electronic Signature (ES), with the additional validation data forming the eXtended Validation Data - Type 2, is illustrated in Figure 6:
+--------------------------------------------------------- ES-X 2 ---+
|+---------------------------------------- EC-C --------+ |
||+---- Elect.Signature (ES)----+ +--------+| +--------+ |
|||+-------+ +-------+ +-------+| +----------+|Complete|| |Times | |
||||Signa- | |Other | |Digital|| |Time-Stamp||certs || |Stamp | |
||||ture | |Signed | |Signa- || |over ||and || |over | |
||||Policy | |Attri- | |ture || |digital ||revoc. || |Complete| |
||||ID | |butes | | || |signature ||refs || |certs | |
|||+-------+ +-------+ +-------+| +----------+| || |and | |
||+-----------------------------+ +--------+| |revoc. | |
|| | |refs | |
|+------------------------------------------------------+ +--------+ |
+--------------------------------------------------------------------+
Figure 6: Illustration of ES with ES-X Type 22.7. Archive Validation Data 🗄️
Before the algorithms, keys and other cryptographic data used when the ES-C was built become weak and the cryptographic functions become vulnerable, or the certificates supporting previous time-stamps expire, the signed data, the ES-C and any additional information (ES-X) should be time-stamped 💀 If possible, this should use stronger algorithms (or longer key lengths) than the original time-stamp.
This additional data and time-stamp is called Archive Validation Data (ES-A) 🌟 The time-stamping process may be repeated every time the protection used to time-stamp a previous ES-A becomes weak. So an ES-A may end up with multiple embedded time stamps 🧁
An example of an Electronic Signature (ES), with the additional validation data for the ES-C and ES-X forming the ES-A, is illustrated in Figure 7.
+-------------------------------- ES-A --------- ----------+
| +-------------------- ES-A -----------------+ |
| | +--------- ES-X -------------- + | |
| | |..............................| +-----+ | +-----+ |
| | |..............................| |Time | | |Time | |
| | |..............................| |Stamp| | |Stamp| |
| | | | +-----+ | +-----+ |
| | +----------------------------- + | |
| +-------------------------------------------+ |
+----------------------------------------------------------+
Figure 7: Illustration of ES -ASupport for ES-A is optional. 🎀
2.8. Arbitration ⚖️
The ES-C may be used for arbitration if there's a dispute between the signer and verifier, provided that:
- a copy of the signature policy referenced by the signer is available;
- the arbitrator knows where to retrieve the signer's certificate (if not already present), all the cross-certificates and the required CRLs and/or OCSPs responses referenced in the ES-C;
- none of the issuing keys from the certificate chain have ever been compromised;
- the cryptography used when the ES-C was built has not been broken at the time the arbitration is performed.
If the second condition isn't met, then the plaintiff must provide an ES-X Long 😭
If it's known by some external means that the third condition isn't met, then the plaintiff must provide an ES-X Time-Stamped 🙈
If the two previous conditions aren't met, the plaintiff must provide both of the above (i.e., an ES-X Time-Stamped and Long) 🍓
If the last condition isn't met, the plaintiff must provide an ES-A 👑
It should be noticed that a verifier may need two time stamps at two different instants: one soon after the generation of the ES, and one soon after some grace period that allows any entity in the certification chain to declare a key compromise 🦋 Okay that's the arbitration part, bestie, more coming up next 💖
2.9. Validation Process ✨
okay so the Validation Process is the part that checks an electronic signature against the signature policy 🔍💅 the output status can be one of three things:
- valid;
- invalid;
- incomplete verification.
A Valid result means the signature passed verification and follows the signature validation policy 🎀 ✅
A signature validation policy is the bit of the signature policy that spells out the technical requirements for the signer when they create a signature, and for the verifier when they check one 🧐📜
An Invalid result means either the signature format is wrong, or the digital signature value fails verification 💀 (for example, the integrity checks on the digital signature value fail, or any of the certificates the digital signature verification depends on is known to be invalid or revoked). rip 😭
An Incomplete Validation result means the format and digital signature checks haven't failed, but there isn't enough info to decide whether the electronic signature is valid under the signature policy 🤔 this can happen when extra information is around that doesn't affect the validity of the digital signature value, but that extra info is invalid. it's giving "not enough tea to call it" 🫖🙈
with incomplete validation, it may be possible to ask for the electronic signature to be checked again at a later date, once more validation information might be available 🔁🌸 and the application or user can also be given that extra information, so they get to decide what to do with partially correct electronic signatures. main character decision-making energy 👑
The validation process may also output validation data:
- a signature time-stamp;
- the complete validation data;
- the archive validation data.
2.10. Example Validation Sequence
okay bestie, Figure 8 (plus the explanation after it) shows how the validation process can build up a complete electronic signature over time 🧚✨ watch the numbers!
soon after the electronic signature (ES) arrives from the signer (1), the digital signature value may be checked, and the validation process must at least add a time-stamp (2), unless the signer already provided one that the verifier trusts 🕰️💖 the validation process may also validate the electronic signature, as required under the identified signature policy, using extra data (e.g., certificates, CRL, etc.) from trusted service providers 🫶 if the validation process isn't finished at this stage, the output is the ES-T 🌈
when all the extra data needed to validate the electronic signature (e.g., the complete certificate and revocation information) finally shows up, the validation process:
- obtains all the necessary additional certificate and revocation status information;
- completes all the validation checks on the ES, using the complete certificate and revocation information (if a time-stamp isn't already there, one may be added at this same stage, combining the ES-T and ES-C process);
- records the complete certificate and revocation references (3);
- indicates the validity status to the user (4).
+----------------------------------------- ES-C ----------+
|+----------------------------- ES-T --------+ |
||+--- Elect.Signature (ES) ----+ | +--------+ |
|||+-------+ +-------+ +-------+|+----------+| |Complete| |
||||Signa- | |Other | |Digital|||Time-Stamp|| |certifi-| |
||||ture | |Signed | |Signa- |||over || |cate and| |
||||Policy | |Attri- | |ture |||digital || |revoca- | |
||||ID | |butes | | |||signature || |tion | |
|||+-------+ +-------+ +-------+|+----------+| |referen-| |
||+------------\----------------+ ^ | |ces | |
|| \ | | +--------+ |
|| \ 1 / | ^ |
|+----------------\----------------/---------+ | |
+------------------\--------------/--------------- /------+
\ /2 ----3------/
+----------+ | / /
| Signed |\ v / |
|User data | \ +--------------------+ +------------+
+----------+ \--->| Validation Process |---> |- Valid |
+---|--^-------|--^--+ 4 |- Invalid |
| | | | |- Validation|
v | v | | Incomplete|
+---------+ +--------+ +------------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+Figure 8: Illustration of an ES with Complete validation data (ES-C)
at the same time the validation process creates the ES-C, it may also provide and/or record the values of the certificates and revocation status information it used in the ES-C, which is called the ES-X Long (5) 📚✨ here's Figure 9:
+----------------------------------------------------- ES-X ---------+
|+---------------------------------------- ES-C --------+ +--------+ |
||+--- Elect.Signature (ES) ----+ +--------+ | |Complete| |
|||+-------+ +-------+ +-------+|+----------+|Complete| | |certifi-| |
||||Signa- | |Other | |Digital|||Time-Stamp||certifi-| | |cate | |
||||ture | |Signed | |Signa- |||over ||cate and| | |and | |
||||Policy | |Attri- | |ture |||digital ||revoca- | | |revoca- | |
||||ID | |butes | | |||signature ||tion | | |tion | |
|||+-------+ +---|---+ +-------+|+----------+|referen-| | |Data | |
||+--------------\--------------+ ^ |ces | | +--------+ |
|| \ | +--------+ | ^ |
|| \ 1 2/ ^ | | |
|+------------------\--------------/------------|-------+ / |
+--------------------\------------/------------/-------------/-------+
\ / ---3----/ /
+----------+ | / / ------------5-----/
| Signed |\ v | | /
|User data | \ +--------------------+ +-----------+
+----------+ \--->| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+Figure 9: Illustration ES with eXtended validation data (Long)
when the validation process creates the ES-C, it may also create extended forms of validation data 🦋 the first option is to time-stamp all the data that forms the Type 1 X-Time-Stamp (6) 🕰️🔥 here's Figure 10:
+----------------------------------------------------- ES-X -------+
|+---------------------------------------- ES-C --------+ +------+ |
||+--- Elect.Signature (ES) ----+ +--------+ | |Time- | |
|||+-------+ +-------+ +-------+|+----------+|Complete| | |Stamp | |
||||Signa- | |Other | |Digital|||Time-Stamp||certifi-| | |over | |
||||ture | |Signed | |Signa- |||over ||cate and| | |CES | |
||||Policy | |Attri- | |ture |||digital ||revoca- | | +------+ |
||||ID | |butes | | |||signature ||tion | | ^ |
|||+-------+ +--|----+ +-------+|+----------+|referen-| | | |
||+-------------|---------------+ ^ |ces | | | |
|| | | +--------+ | | |
|| \ 1 2/ ^ | | |
|+----------------\------------------/----------|-------+ | |
+------------------\----------------/-----------/-------------/----+
\ / ----3---/ /
+----------+ | / / ---------------6---/
| Signed |\ v | | /
|User data | \ +--------------------+ +-----------+
+----------+ \--->| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+Figure 10: Illustration of ES with eXtended validation data - Type 1 X-Time-Stamp
another option is to time-stamp the certificate and revocation information references used to validate the electronic signature (but not the signature) (6'); this is called Type 2 X-Time-Stamped 🎀 here's Figure 11:
+----------------------------------------------------- ES-X -----------+
|+---------------------------------------- ES-C --------+ +----------+ |
||+--- Elect.Signature (ES) ----+ +--------+ | |Time-Stamp| |
|||+-------+ +-------+ +-------+|+----------+|Complete| | |over | |
||||Signa- | |Other | |Digital|||Time-Stamp||certifi-| | |Complete | |
||||ture | |Signed | |Signa- |||over ||cate and| | |Certifi- | |
||||Policy | |Attri- | |ture |||digital ||revoc. | | |cate and | |
||||ID | |butes | | |||signature ||refs | | |revoc. | |
|||+-------+ +---^---+ +-------+|+----^-----++---^----+ | |refs | |
||+--------------\--------------+ | | | +----------+ |
|+----------------\------------------/-----------|------+ ^ |
+----------------1-\----------------/-----------/--------------|-------+
\ / -----3---/ |
+----------+ | 2/ / ---------------6'-----/
| Signed |\ v | | /
|User data | \ +--------------------+ +-----------+
+----------+ \--->| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+Figure 11: Illustration of ES with eXtended validation data - Type 2 X-Time-Stamp
before the algorithms used in any of the electronic signatures become, or are likely, to be compromised or made vulnerable in the future, it is necessary to time-stamp the entire electronic signature, including all the values of the validation and user data 🔐💜 this gives an ES with Archive validation data (ES-A), which is illustrated in figure 12:
2.11. Additional optional features of an ES 🎀
Okay so this document also defines some extra optional features an electronic signature can have, bestie 🦋 Here they are:
- indicate a commitment type being made by the signer;
- indicate the role under which a signature was created;
- support multiple signatures.
3. Data structure of an Electronic Signature ✨
This clause uses and builds on the Cryptographic Message Syntax (CMS), as defined in RFC 2630 [CMS], and Enhanced Security Services (ESS), as defined in RFC 2634 [ESS]. The overall structure of Electronic Signature is as defined in [CMS]. The Electronic Signature (ES) uses attributes defined in [CMS], [ESS] and this document. This document defines in full the ES attributes which it uses and which are not defined elsewhere 💅
The mandated set of attributes and the digital signature value is defined as the minimum Electronic Signature (ES) required by this document. A signature policy MAY mandate other signed attributes to be present. 🌸
3.1. General Syntax
The general syntax of the ES is as defined in [CMS] 🧚
3.2. Data Content Type
The data content type of the ES is as defined in [CMS].
The data content type is intended to refer to arbitrary octet strings, such as ASCII text files, and the interpretation is left to the application. Such strings need not have any internal structure (although they could have their own ASN.1 definition or other structure) ✨
3.3. Signed-data Content Type
The Signed-data content type of the ES is as defined in [CMS].
The signed-data content type consists of a content of any type and zero or more signature values. Any number of signers in parallel can sign any type of content. The typical application of the signed-data content type represents one signer's digital signature on content of the data content type 🫶
To make sure that the verifier uses the right certificate, this document mandates that the hash of the signer's certificate is always included in the Signing Certificate signed attribute. 🔥
3.4. SignedData Type
The syntax of the SignedData type of the ES is as defined in [CMS].
The fields of type SignedData have the meanings defined [CMS] except that:
- version is the syntax version number. The value of version must be 3.
- The identification of signer's certificate used to create the signature is always present as a signed attribute.
- The degenerate case where there are no signers is not valid in this document.
3.5. EncapsulatedContentInfo Type
The syntax of the EncapsulatedContentInfo a type of the ES is as defined in [CMS].
For the purpose of long term validation as defined by this document, it is advisable that either the eContent is present, or the data which is signed is archived in such a way as to preserve any data encoding. It is important that the OCTET STRING used to generate the signature remains the same every time either the verifier or an arbitrator validates the signature 🔍
The degenerate case where there are no signers is not valid in this document.
3.6. SignerInfo Type
The syntax of the SignerInfo a type of the ES is as defined in [CMS].
Per-signer information is represented in the type SignerInfo. In the case of multiple independent signatures, there is an instance of this field for each signer 👑
The fields of type SignerInfo have the meanings defined in [CMS] except that signedAttributes must, as a minimum, contain the following attributes:
- ContentType as defined in clause 3.7.1.
- MessageDigest as defined in clause 3.7.2.
- SigningTime as defined in clause 3.7.3.
- SigningCertificate as defined in clause 3.8.1.
- SignaturePolicyId as defined in clause 3.9.1.
3.6.1. Message Digest Calculation Process
The message digest calculation process is as defined in [CMS].
3.6.2. Message Signature Generation Process
The input to the digital signature generation process is as defined in [CMS].
3.6.3. Message Signature Verification Process
The procedures for CMS signed data validation are as defined in [CMS] and enhanced in this document.
The input to the signature verification process includes the signer's public key, verified as correct using either the ESS Signing Certificate attribute or the Other Signing Certificate attribute 🦋
3.7. CMS Imported Mandatory Present Attributes
The following attributes MUST be present with the signed-data defined by this document. The attributes are defined in [CMS] 💖
3.7.1. Content Type
The syntax of the content-type attribute type of the ES is as defined in [CMS].
3.7.2. Message Digest
The syntax of the message-digest attribute type of the ES is as defined in [CMS].
3.7.3. Signing Time
The syntax of the message-digest attribute type of the ES is as defined in [CMS] and further qualified by this document.
The signing-time attribute type specifies the time at which the signer claims to have performed the signing process ⭐
This present document recommends the use of GeneralizedTime. 🍓
3.8. Alternative Signing Certificate Attributes
One, and only one, of the following two alternative attributes MUST be present with the signed-data defined by this document to identify the signing certificate. Both attributes include an identifier and a hash of the signing certificate. The first, which is adopted in existing standards, may be only used with the SHA-1 hashing algorithm. The other shall be used when other hashing algorithms are to be supported 🌈
The signing certificate attribute is designed to prevent the simple substitution and re-issue attacks, and to allow for a restricted set of authorization certificates to be used in verifying a signature. It's giving security, no cap 🙈
3.8.1. ESS Signing Certificate Attribute Definition
The syntax of the signing certificate attribute type of the ES is as defined in [ESS], and further qualified and profiled in this document.
The ESS signing certificate attribute must be a signed attribute.
This document mandates the presence of this attribute as a signed CMS attribute, and the sequence must not be empty. The certificate used to verify the signature must be identified in the sequence. The Signature Validation Policy may mandate other certificate references to be present, which may include all the certificates up to the point of trust. The encoding of the ESSCertID for this certificate must include the issuerSerial field 🔐
The issuerAndSerialNumber present in the SignerInfo must be consistent with the issuerSerial field. The certificate identified must be used during the signature verification process. If the hash of the certificate does not match the certificate used to verify the signature, the signature must be considered invalid 💀
The sequence of policy information field is not used in this document.
NOTE: Where an attribute certificate is used by the signer to associate a role, or other attributes of the signer, with the electronic signature, this is placed in the Signer Attribute attribute as defined in clause 3.12.3. 🎀
3.8.2. Other Signing Certificate Attribute Definition
The following attribute is identical to the ESS SigningCertificate defined above, except that this attribute can be used with hashing algorithms other than SHA-1 🧁
This attribute must be used in the same manner as defined above for the ESS SigningCertificate attribute.
The following object identifier identifies the signing certificate attribute:
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }The signing certificate attribute value has the ASN.1 syntax OtherSigningCertificate:
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THIS DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL
}
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue
}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}3.9. Additional Mandatory Attributes 🦄
3.9.1 Signature policy Identifier ✨
okay so this doc says the signedData has to include a reference to the signature policy 📜. That reference can be spelled out explicitly, or it can just be implied by the semantics of the signed content and other external data 🫶. A signature policy is basically the rulebook for creating and validating an electronic signature 💅, and it gets included as a signed attribute with every signature. The signature policy identifier must be a signed attribute 🔥.
The object identifier for the signature policy identifier attribute is:
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }Signature-policy-identifier attribute values have the ASN.1 type SignaturePolicyIdentifier, and it's giving very structured 🎀:
SignaturePolicyIdentifier ::= CHOICE{
SignaturePolicyId SignaturePolicyId,
SignaturePolicyImplied SignaturePolicyImplied }
SignaturePolicyId ::= SEQUENCE {
sigPolicyIdentifier SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULLThe NULL type is the "implied" option. If you see it, that means the signature policy is implied by the semantics of the signed data and other external data 🙈.
The sigPolicyId field holds an object identifier that uniquely identifies one specific version of the signature policy. Its syntax is:
SigPolicyId ::= OBJECT IDENTIFIERThe sigPolicyHash field holds the identifier of the hash algorithm plus the hash of the value of the signature policy 🧚.
If the signature policy is defined using a computer processable notation like ASN.1, the hash is calculated on the value without the outer type and length fields, and the hashing algorithm must be the one specified in the field signPolicyHshAlg 🍓.
If the signature policy is defined using some other structure, then the type of structure and the hashing algorithm must either be specified as part of the signature policy, or be indicated using a signature policy qualifier 🦋.
SigPolicyHash ::= OtherHashAlgAndValueA signature policy identifier can be qualified with other information about the qualifier 💜. The semantics and syntax of the qualifier are associated with the object identifier in the sigPolicyQualifierId field. The general syntax of this qualifier looks like this:
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId
}This document specifies the following qualifiers:
- spuri: this contains the web URI or URL reference to the signature policy 🌸
- spUserNotice: this contains a user notice that should be displayed whenever the signature is validated 📣
Here's the full set of qualifier IDs and their structures, straight from the document:
-- sigpolicyQualifierIds defined in this document
SigPolicyQualifierId ::= OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL
}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER
}
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200))
}3.10 CMS Imported Optional Attributes
The following attributes MAY be present with the signed-data defined by this document 💖. They're defined in ref [CMS], they get imported into this spec, and they were appropriately qualified and profiled by this document 🎀.
3.10.1 Countersignature
The syntax of the countersignature attribute type of the ES is as defined in [CMS] 🧁. The countersignature attribute must be an unsigned attribute 🙅♀️.
3.11 ESS Imported Optional Attributes
The following attributes MAY be present with the signed-data defined by this document ✨. They're defined in ref [ESS], they get imported into this spec, and they were appropriately qualified and profiled by this document 🌈.
3.11.1 Content Reference Attribute
The content reference attribute is a link from one SignedData to another 🔗. You can use it to link a reply back to the original message it refers to, or to pull one SignedData into another by reference 💅.
The content reference attribute MUST be used as defined in [ESS]. The content reference MUST be a signed attribute 🫶.
The syntax of the content reference attribute type of the ES is as defined in [ESS] 📝.
3.11.2 Content Identifier Attribute
The content identifier attribute gives the signed content an identifier 🪪. It's for when you might need to point back to that content later, like in a content reference attribute on signed data sent afterwards 🦋.
The content identifier must be a signed attribute 🔐.
The syntax of the content identifier attribute type of the ES is as defined in [ESS] 💜.
The minimal signedContentIdentifier should contain a concatenation of user-specific identification information (such as a user name or public keying material identification information), a GeneralizedTime string, and a random number 🎲.
3.11.3 Content Hints Attribute
The content hints attribute describes the format of the signed content 🖼️. The signer can use it to tell a verifier the precise format that MUST be used to present the data (e.g., text, voice, video) 🎙️. This attribute MUST be present when it is mandatory to present the signed data to human users on verification 👑.
The syntax of the content hints attribute type of the ES is as defined in ESS (RFC 2634, section 2.9 [9]) 📚.
When it's used to indicate the precise format of the data to be presented to the user, the following rules apply 💌:
The contentType (defined in RFC 2630 [8]) indicates the type of the associated content. It's an object identifier (i.e., a unique string of integers) assigned by an authority that defines the content type 🌸.
The UTF8String shall define the presentation format. The format may be defined by MIME types as indicated below 🍓.
Note 1: The contentType can be id-data defined in CMS (RFC 2630 [8]). The UTF8String can be used to indicate the encoding of the data, like MIME type. RFC 2045 [25] provides a common structure for encoding a range of electronic documents and other multi-media types, see annex B for further information, a system supporting verification of electronic signature may present information to users in the form identified by the MIME type 🧚.
id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs7(7) 1 }3.12 Additional Optional Attributes
3.12.1 Commitment Type Indication Attribute
There may be situations where a signer wants to explicitly tell a verifier that by signing the data, they're making a type of commitment on the signer's behalf 🤝. The commitmentTypeIndication attribute carries that information 💅.
The commitmentTypeIndication attribute must be a signed attribute 🔥.
The commitment type may be:
- defined as part of the signature policy, in which case the commitment type has precise semantics that are defined as part of the signature policy 📜.
- be a registered type, in which case the commitment type has precise semantics defined by registration, under the rules of the registration authority 🏛️. That registration authority may be a trading association or a legislative authority 👑.
The signature policy specifies a set of attributes that it "recognizes" 👀. This "recognized" set includes all the commitment types defined as part of the signature policy, plus any externally defined commitment types that the policy chooses to recognize 🌈. Only recognized commitment types are allowed in this field 🚫.
The object identifier for the commitment type indication attribute is:
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}Commitment-Type-Indication attribute values have the ASN.1 type CommitmentTypeIndication 🧸:
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL
}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY
commitmentTypeIdentifier
}The use of any qualifiers to the commitment type is outside the scope of this document 🙈.
The following generic commitment types are defined in this document 🎀:
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 6}Here's what these generic commitment types mean 🧠:
- Proof of origin indicates that the signer recognizes they created, approved and sent the message 💌.
- Proof of receipt indicates that the signer recognizes they received the content of the message 📬.
- Proof of delivery indicates that the TSP providing that indication has delivered a message in a local store accessible to the recipient of the message 📦.
- Proof of sender indicates that the entity providing that indication has sent the message (but not necessarily created it) 📤.
- Proof of approval indicates that the signer has approved the content of the message ✅.
- Proof of creation indicates that the signer has created the message (but not necessarily approved, nor sent it) 🎨.
3.12.2 Signer Location attribute
The signer-location attribute specifies a mnemonic for an address associated with the signer at a particular geographical (e.g., city) location 🗺️. The mnemonic is registered in the country where the signer is located, and it's used in the provision of the Public Telegram Service (according to ITU-T Recommendation F.1 [PTS]) 📠.
The signer-location attribute must be a signed attribute 🔏.
The object identifier for the signer-location attribute is:
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}Signer-location attribute values have ASN.1 type SignerLocation, bestie 💖
SignerLocation ::= SEQUENCE {
-- at least one of the following must be present
countryName [0] DirectoryString OPTIONAL,
-- as used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- as used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL
}PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString3.12.3 Signer Attributes attribute ✨
The signer-attributes attribute is the one that tells you extra stuff about the signer, like their role. It's giving "here's who I am at work" 💼
It may be either:
- claimed attributes of the signer; or
- certified attributes of the signer;
The signer-attributes attribute must be a signed attribute. Lowkey important, so don't skip it 🫶
The following object identifier identifies the signer-attribute attribute:
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}Signer-attribute attribute values have ASN.1 type SignerAttribute. Here's how it's shaped 🎀
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes
}ClaimedAttributes ::= SEQUENCE OF AttributeCertifiedAttributes ::= AttributeCertificate
-- as defined in X.509 : see section 10.3NOTE: The claimed and certified attribute are imported from ITU-T Recommendations X.501 [16] and ITU-T Recommendation X.509:Draft Amendment on Certificate Extensions, October 1999. Bestie, these come from somewhere else, so go check the source 📚
3.12.4 Content Time-Stamp attribute ⏰
The content time-stamp attribute is the time-stamp of the signed data content, taken before it gets signed. Main character timing 💅
The content time-stamp attribute must be a signed attribute.
The following object identifier identifies the signer-attribute attribute:
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}Content time-stamp attribute values have ASN.1 type ContentTimestamp:
ContentTimestamp::= TimeStampTokenThe value of messageImprint field within TimeStampToken must be a hash of the value of eContent field within encapContentInfo within the signedData.
For further information and definition of TimeStampToken see [TSP]. 📖
3.13 Support for Multiple Signatures 👯
3.13.1 Independent Signatures
Multiple independent signatures are supported by independent SignerInfo from each signer. Everyone gets their own lane 🛣️
Each SignerInfo must include all the attributes required under this document and must be processed independently by the verifier. No shortcuts, periodt 💅
3.13.2 Embedded Signatures
Multiple embedded signatures are supported using the counter-signature unsigned attribute (see clause 3.10.1). Each counter signature is carried in Countersignature held as an unsigned attribute to the SignerInfo to which the counter-signature is applied. Like a signature with a little sticky note on it 🌸
4. Validation Data 🔥
This clause specifies the validation data structures which builds on the electronic signature specified in clause 3. Basically the extra receipts that make a signature easier to check later. This includes:
- Time-Stamp applied to the electronic signature value.
- Complete validation data which comprises the time-stamp of the signature value, plus references to all the certificates and revocation information used for full validation of the electronic signature.
The following optional eXtended forms of validation data are also defined:
- X-timestamp: There are two types of time-stamp used in extended validation data defined by this document.
- Type 1 -Time-Stamp which comprises a time-stamp over the ES with Complete validation data (ES-C).
- Type 2 X-Time-Stamp which comprises of a time-stamp over the certification path references and the revocation information references used to support the ES-C.
- X-Long: This comprises a Complete validation data plus the actual values of all the certificates and revocation information used in the ES-C.
- X-Long-Time-Stamp: This comprises a Type 1 or Type 2 X-Timestamp plus the actual values of all the certificates and revocation information used in the ES-C.
This clause also specifies the data structures used in Archive validation data:
- Archive validation data comprises a Complete validation data, the certificate and revocation values (as in a X-Long validation data), any other existing X-timestamps, plus the Signed User data and an additional archive time-stamp over all that data. An archive time-stamp may be repeatedly applied after long periods to maintain validity when electronic signature and timestamping algorithms weaken. Future-proofing era 🦋
The additional data required to create the forms of electronic signature identified above is carried as unsigned attributes associated with an individual signature by being placed in the unsignedAttrs field of SignerInfo. Thus all the attributes defined in clause 4 are unsigned attributes.
NOTE: Where multiple signatures are to be supported, as described in clause 3.13, each signature has a separate SignerInfo. Thus, each signature requires its own unsigned attribute values to create ES-T, ES-C etc. 🫶
4.1 Electronic Signature Timestamp ⏱️
An Electronic Signature with Timestamp is an Electronic Signature for which part, but not all, of the additional data required for validation is available (e.g., some certificates and revocation information is available but not all). Halfway there, no cap 🧚
The minimum structure Timestamp validation data is the Signature Timestamp Attribute as defined in clause 4.1.1 over the ES signature value.
4.1.1 Signature Timestamp Attribute Definition
The Signature Timestamp attribute is timestamp of the signature value. It is an unsigned attribute. Several instances of this attribute from different TSAs may occur with an electronic signature.
The Signature Validation Policy specifies, in the signatureTimestampDelay field of TimestampTrustConditions, a maximum acceptable time difference which is allowed between the time indicated in the signing time attribute and the time indicated by the Signature Timestamp attribute. If this delay is exceeded then the electronic signature must be considered as invalid. That's a hard no, bestie 🙈
The following object identifier identifies the Signature Timestamp attribute:
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 14}The Signature timestamp attribute value has ASN.1 type SignatureTimeStampToken.
SignatureTimeStampToken ::= TimeStampTokenThe value of messageImprint field within TimeStampToken must be a hash of the value of signature field within SignerInfo for the signedData being timestamped.
For further information and definition of TimeStampToken see [TSP]. 📖
4.2 Complete Validation Data 💎
An electronic signature with complete validation data is an Electronic Signature for which all the additional data required for validation (i.e., all certificates and revocation information) is available. Complete validation data (ES-C) build on the electronic signature Time-Stamp as defined above. The full glam version 💖
The minimum structure of a Complete validation data is:
- the Signature Time-Stamp Attribute, as defined in clause 4.1.1;
- Complete Certificate Refs, as defined in clause 4.2.1;
- Complete Revocation Refs, as defined in clause 4.2.2.
The Complete validation data MAY also include the following additional information, forming a X-Long validation data, for use if later validation processes may not have access to this information:
- Complete Certificate Values, as defined in clause 4.2.3;
- Complete Revocation Values, as defined in clause 4.2.4.
The Complete validation data MAY also include one of the following additional attributes, forming a X-Time-Stamp validation data, to provide additional protection against later CA compromise and provide integrity of the validation data used:
- ES-C Time-Stamp, as defined in clause 4.2.5; or
- Time-Stamped Certificates and CRLs references, as defined in clause 4.2.6.
NOTE 1: As long as the CA's are trusted such that these keys cannot be compromised or the cryptography used broken, the ES-C provides long term proof of a valid electronic signature. Long-term receipts, iykyk 🔐
A valid electronic signature is an electronic signature which passes validation according to a signature validation policy.
NOTE 2: The ES-C provides the following important property for long standing signatures; that is having been found once to be valid, must continue to be so months or years later. Long after the validity period of the certificates have expired, or after the user key has been compromised. Ageless, literally 👑
4.2.1 Complete Certificate Refs Attribute Definition 🎀
The Complete Certificate Refs attribute is an unsigned attribute. It references the full set of CA certificates that have been used to validate a ES with Complete validation data (ES-C) up to (but not including) the signer's certificate. Only a single instance of this attribute must occur with an electronic signature.
Note: The signer's certified is referenced in the signing certificate attribute (see clause 3.1).
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}The complete certificate refs attribute value has the ASN.1 syntax CompleteCertificateRefs.
CompleteCertificateRefs ::= SEQUENCE OF OTHERCertIDOTHERCertID is defined in clause 3.8.2.
The IssuerSerial that must be present in OTHERCertID. The certHash must match the hash of the certificate referenced.
NOTE: Copies of the certificate values may be held using the Certificate Values attribute defined in clause 4.3.1.
4.2.2 Complete Revocation Refs Attribute Definition 🦄
The Complete Revocation Refs attribute is an unsigned attribute. Only a single instance of this attribute must occur with an electronic signature. It references the full set of the CRL or OCSP responses that have been used in the validation of the signer and CA certificates used in ES with Complete validation data. Receipts for the revocation checks, basically 🧾
The following object identifier identifies the CompleteRevocationRefs attribute:
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}okay so this is the OID for the complete revocation refs attribute 🦋 the value is typed as CompleteRevocationRefs, and it's a whole SEQUENCE OF CrlOcspRef entries 💅
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}bestie, the ordering rules are where it gets spicy 🌶️ CompleteRevocationRefs MUST contain one CrlOcspRef for the signing certificate, and then one more for each OTHERCertID in the CompleteCertificateRefs attribute. The second and later CrlOcspRef fields MUST be in the same order as the OTHERCertID they belong to 🎀 And at least one of CRLListID, OcspListID or OtherRevRefs SHOULD be present for every certificate except the "trusted" CA of the certificate path ✨
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}when you're making a crlValidatedID, the crlHash is computed over the entire DER encoded CRL, signature and all 🔐 The crlIdentifier would normally be there, unless the CRL can be figured out from other info 🧚
the crlIdentifier identifies the CRL using the issuer name plus the CRL issued time, and that time MUST correspond to the "thisUpdate" time inside the issued CRL 🕰️ The crlListID attribute is an unsigned attribute 💜 If the CRL you're pointing at is a Delta CRL, then you MUST also include references to the set of CRLs that together make up a complete revocation list 🍓
the OcspIdentifier identifies the OCSP response using the issuer name and the time of issue, and that time MUST correspond to the "producedAt" time in the issued OCSP response ⭐ Two OCSP responses can land in the same second, so the hash of the response inside the OcspResponsesID might be needed to sort out the ambiguity 🙈
NOTE: Copies of the CRL and OCSP response values may be held using the Revocation Values attribute defined in clause 4.3.2. 🫶
OtherRevRefs ::= SEQUENCE {
otherRevRefType OtherRevRefType,
otherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIERthe syntax and meaning of other revocation references is outside the scope of this document 🙃 The syntax for that other form of revocation info is whatever OtherRevRefType points to ✨
4.3. Extended Validation Data 🌸
4.3.1. Certificate Values Attribute Definition
the Certificate Values attribute is an unsigned attribute 💖 Only a single instance of this attribute MUST occur with an electronic signature. It holds the values of the certificates referenced in the CompleteCertificateRefs attribute 🎀
Note: If an Attribute Certificate is used, it isn't included in this structure. Instead, the signer MUST provide it as a signer-attributes attribute (see clause 12.3) 👑
here's the OID that identifies the CertificateValues attribute:
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}the certificate values attribute value has the ASN.1 syntax CertificateValues:
CertificateValues ::= SEQUENCE OF CertificateCertificate is defined in RFC2459 and ITU-T Recommendation X.509 [1]) 📚
4.3.2. Revocation Values Attribute Definition
the Revocation Values attribute is also an unsigned attribute 🦋 Only a single instance of this attribute MUST occur with an electronic signature. It holds the values of the CRLs and OCSP responses referenced in the CompleteRevocationRefs attribute 🌈
here's the OID for the Revocation Values attribute:
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 24}the revocation values attribute value has the ASN.1 syntax RevocationValues:
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals
}
OtherRevVals ::= SEQUENCE {
otherRevValType OtherRevValType,
otherRevVals ANY DEFINED BY otherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIERthe syntax and meaning of the other revocation values is outside the scope of this document 🌷 The syntax for that other form of revocation info is whatever OtherRevRefType points to 🫧
CertificateList is defined in RFC 2459 [RFC2459] and in ITU-T Recommendation X.509 [X509]) 🎀
BasicOCSPResponse is defined in RFC 2560 [OCSP] 💅
4.3.3. ES-C Time-Stamp Attribute Definition
this attribute is used for the Type 1 X-Time-Stamped validation data ⏰ The ES-C Time-Stamp attribute is an unsigned attribute. It's a time-stamp of a hash of the electronic signature and the complete validation data (ES-C). It's a special purpose TimeStampToken attribute that time-stamps the ES-C. Several instances of this attribute MAY occur with an electronic signature, from different TSAs 🌟
here's the OID that identifies the ES-C Time-Stamp attribute:
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 25}the ES-C time-stamp attribute value has the ASN.1 syntax ESCTimeStampToken:
ESCTimeStampToken ::= TimeStampTokenthe messageImprint field within the TimeStampToken MUST be a hash of the concatenated values (without the type or length encoding for that value) of the following data objects, as they're present in the ES with Complete validation data (ES-C):
- signature field within SignerInfo;
- SignatureTimeStampToken attribute;
- CompleteCertificateRefs attribute;
- CompleteRevocationRefs attribute.
for more info and the definition of the Time Stamp Token, check out [TSP] 🧚
4.3.4. Time-Stamped Certificates and CRLs Attribute Definition
this attribute is used for the Type 2 X-Time-Stamp validation data 🔒 A TimestampedCertsCRLsRef attribute is an unsigned attribute. It's a list of referenced certificates and OCSP responses/CRLs that have been time-stamped to protect against certain CA compromises 🛡️ Its syntax goes like this:
the OID that identifies the TimestampedCertsCRLsRef attribute:
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 26}the attribute value has the ASN.1 syntax TimestampedCertsCRLs:
TimestampedCertsCRLs ::= TimeStampTokenthe messageImprint field within the TimeStampToken MUST be a hash of the concatenated values (without the type or length encoding for that value) of the following data objects, as they're present in the ES with Complete validation data (ES-C):
- CompleteCertificateRefs attribute;
- CompleteRevocationRefs attribute.
4.4. Archive Validation Data 🗄️
if an electronic signature has to last for a very long time, and the time-stamp on it is at risk of being invalidated because of algorithm weakness or limits on the validity period of the TSA certificate, then it MAY be required to time-stamp the electronic signature several times 💫 When that's needed, an archive time-stamp attribute MAY be required too. This time-stamp MAY be applied repeatedly over a period of time ⏳
4.4.1. Archive Time-Stamp Attribute Definition
the Archive Time-Stamp attribute is a time-stamp of the user data and the entire electronic signature 🌸 If the Certificate Values and Revocation Values attributes aren't present, these attributes MUST be added to the electronic signature before the time-stamp. The Archive Time-Stamp attribute is an unsigned attribute. Several instances of this attribute MAY occur with an electronic signature, both over time and from different TSAs 🦋
here's the OID that identifies the Nested Archive Time-Stamp attribute:
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 27}archive time-stamp attribute values have the ASN.1 syntax ArchiveTimeStampToken:
ArchiveTimeStampToken ::= TimeStampTokenthe messageImprint field within the Time-StampToken MUST be a hash of the concatenated values (without the type or length encoding for that value) of the following data objects, as they're present in the electronic signature:
- encapContentInfo eContent OCTET STRING;
- signedAttributes;
- signature field within SignerInfo;
- SignatureTimeStampToken attribute;
- CompleteCertificateRefs attribute;
- CompleteRevocationData attribute;
- CertificateValues attribute (If not already present, this information MUST be included in the ES-A);
- RevocationValues attribute (If not already present, this information MUST be included in the ES-A);
- ESCTimeStampToken attribute if present;
- TimestampedCertsCRLs attribute if present;
- any previous ArchiveTimeStampToken attributes.
for more info and the definition of TimeStampToken, see [TSP] 🧚
the time-stamp SHOULD be created using stronger algorithms (or longer key lengths) than the ones used in the original electronic signatures 💪
5. Security Considerations 🔐
5.1. Protection of Private Key
the security of the electronic signature mechanism defined in this document depends on the privacy of the signer's private key 😭 Implementations MUST take steps to ensure that private keys cannot be compromised. Stay paranoid, bestie 🙈
5.2. Choice of Algorithms
implementers SHOULD be aware that cryptographic algorithms get weaker over time 💀 As new cryptanalysis techniques are developed and computing performance improves, the work factor to break a particular algorithm goes down. So cryptographic algorithm implementations SHOULD be modular, so new algorithms can be slotted in easily. In other words, implementers SHOULD be prepared for the set of mandatory-to-implement algorithms to change over time 🔄✨
6. Conformance Requirements 📋
this document only defines conformance requirements up to an ES with Complete validation data (ES-C). That means none of the extended and archive forms of Electronic Signature (ES-X, ES-A) need to be implemented to get conformance to this standard 🎀
this document mandates support for elements of the signature policy 👑
6.1. Signer 🎀
okay so bestie, a system that supports signers under this doc MUST, at minimum, be able to generate an electronic signature with these pieces 💅
- The general CMS syntax and content type from RFC 2630 (see clauses 4.1 and 4.2) 🌸
- CMS SignedData from RFC 2630 with version set to 3, and at least one SignerInfo MUST be present (see clauses 4.3, 4.4, 4.5, 4.6) ✨
- These CMS Attributes from RFC 2630:
- ContentType: MUST always be present (see clause 3.7.1) 💖
- MessageDigest: MUST always be present (see clause 3.7.2) 💖
- SigningTime: MUST always be present (see clause 3.7.3) 💖
- These ESS Attributes from RFC 2634:
- SigningCertificate: this MUST be set as defined in clauses 3.8.1 and 3.8.2 🦋
- These Attributes from clause 3.9:
- SignaturePolicyIdentifier: MUST always be present. 👑
- Public Key Certificates as defined in ITU-T Recommendation X.509 [1] and profiled in RFC 2459 [7] (see clause 9.1) 🧚
6.2. Verifier using time-stamping ⏰
so a verifier that has time-stamping facilities MUST, at minimum, support all of this 🫶
- Verification of the mandated components of an electronic signature, as defined in clause 5.1 🔍
- Signature Time-Stamp attribute, as defined in clause 4.1.1 ⏰
- Complete Certificate Refs attribute, as defined in clause 4.2.1 📜
- Complete Revocation Refs Attribute, as defined in clause 4.2.2 📜
- Public Key Certificates, as defined in ITU-T Recommendation X.509 and profiled in RFC 2459 🔐
- Either of the following:
6.3. Verifier using secure records 🔒
ngl this one is so serious bestie. A verifier that follows this document SHALL, at minimum, support all of this 💀
- Verification of the mandated components of an electronic signature, as defined in subclause 5.1 🔍
- Complete Certificate Refs attribute, as defined in subclause 4.2.1 📜
- Complete Revocation Refs Attribute, as defined in subclause 9.2.2 📜
- A record SHALL be maintained, which cannot be undetectably modified, of the electronic signature and the time when the signature was first validated using the referenced certificates and revocation information. 🗂️✨
- Public Key Certificates, as defined in ITU-T Recommendation X.509 [1] and profiled in RFC 2459 [7] (see subclause 10.1) 🔐
- Either of the following:
7. References 📚
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
- [ESS] Hoffman, P., "Enhanced Security Services for S/MIME", RFC 2634, June 1999.
- [CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630, June 1999.
- [OCSP] Myers, M., Ankney, R., Malpani, A., Galperin, S. and C. Adams, "On-line Status Certificate Protocol", RFC 2560, June 1999.
- [TSP] Adams, C., Cain, P., Pinkas, D. and R. Zuccherato, "Internet X.509 Public Key Infrastructure Time-Stamp Protocol (TSP)", RFC 3161, August 2001.
- [PTS] Public Telegram Service. ITU-T Recommendation F1.
- [RFC2459] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet X.509 Public Key Infrastructure, Certificate and CRL Profile", RFC 2459, January 1999.
- [PKCS9] RSA Laboratories, "The Public-Key Cryptography Standards (PKCS)", RSA Data Security Inc., Redwood City, California, November 1993 Release.
- [ISONR] ISO/IEC 10181-5: Security Frameworks in Open Systems. Non-Repudiation Framework. April 1997.
- [TS101733] ETSI Standard TS 101 733 V.1.2.2 (2000-12) Electronic Signature Formats. Note: copies of ETSI TS 101 733 can be freely downloaded from the ETSI web site www.etsi.org.
8. Authors' Addresses 🌷
this Informational RFC was produced in ETSI TC-SEC 💕
ETSI
F-06921 Sophia Antipolis, Cedex - FRANCE
650 Route des Lucioles - Sophia Antipolis
Valbonne - France
Tel: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16
secretariat@etsi.fr
http://www.etsi.org
Contact Point
Harri Rasilainen
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis, Cedex
FRANCE
EMail: harri.rasilainen@etsi.fr
Denis Pinkas
Integris
68, Route de Versailles
78434 Louveciennes CEDEX
FRANCE
EMail: Denis.Pinkas@bull.net
John Ross
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: ross@secstan.com
Nick Pope
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: pope@secstan.comAnnex A (normative): ASN.1 Definitions 🧾
this annex is the big summary of every ASN.1 syntax definition for the new syntax this document defines 🤓
A.1. Definitions Using X.208 (1988) ASN.1 Syntax
📝 quick heads up: if the ASN.1 module in clause A.1 ever conflicts with the one in Annex A-2, clause A.1 has precedence 👑
NOTE: The ASN.1 module defined in clause A.1 has precedence over
that defined in Annex A-2 in the case of any conflict.
ETS-ElectronicSignatureFormats-88syntax { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 5}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All -
IMPORTS
-- Crypographic Message Syntax (CMS): RFC 2630
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime, SigningTime,
id-countersignature, Countersignature
FROM CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms(1) }
-- ESS Defined attributes: RFC 2634
-- (Enhanced Security Services for S/MIME)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference,
id-aa-contentIdentifier, ContentIdentifier
FROM ExtendedSecurityServices
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }
-- Internet X.509 Public Key Infrastructure
-- Certificate and CRL Profile: RFC 2459
Certificate, AlgorithmIdentifier, CertificateList, Name,
GeneralNames, GeneralName, DirectoryString,Attribute,
AttributeTypeAndValue, AttributeType, AttributeValue,
PolicyInformation, BMPString, UTF8String
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit-
88(1)}
-- X.509 '97 Authentication Framework
AttributeCertificate
FROM AuthenticationFramework
{joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}
-- The imported AttributeCertificate is defined using the X.680 1997
-- ASN.1 Syntax,
-- an equivalent using the 88 ASN.1 syntax may be used.
-- OCSP 2560
BasicOCSPResponse, ResponderID
FROM OCSP {-- OID not assigned -- }
-- Time Stamp Protocol Work in Progress
TimeStampToken
FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
-- S/MIME Object Identifier arcs used in this document
-- ===================================================
-- S/MIME OID arc used in this document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
-- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }
-- S/MIME Arcs
-- id-mod OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier
-- Definitions of Object Identifier arcs used in this document
-- ===========================================================
-- The allocation of OIDs to specific objects are given below with the
-- associated ASN.1 syntax definition
-- OID used referencing electronic signature mechanisms based on this
-- standard for use with the IDUP API (see annex D)
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1)
idupMechanism (4)etsiESv1(1) }
-- CMS Attributes Defined in this document
-- =======================================
-- Mandatory Electronic Signature Attributes
-- OtherSigningCertificate
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THIS DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL
}
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue
}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
"SignaturePolicy CHOICE {
SignaturePolicyId SignaturePolicyId,
SignaturePolicyImplied SignaturePolicyImplied
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyIdentifier SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= OtherHashAlgAndValue
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId
}
SigPolicyQualifierId ::=
OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL
}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER
}
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200))
}
-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}Okay, the commitment types are literally so cute 🎀 Here's the next bit of the ASN.1 💅
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL
}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier
}
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following must be present
countryName [0] DirectoryString OPTIONAL,
-- as used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- as used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL
}
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes
}
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate -- as defined in X.509 :
see section 10.3
-- Content Time-Stamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 20}
ContentTimestamp::= TimeStampToken
-- Validation Data
-- Signature Time-Stamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID
-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL
}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- as in OCSP response data
producedAt GeneralizedTime
-- as in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OtherRevRefType,
otherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIER
-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals
}
OtherRevVals ::= SEQUENCE {
otherRevValType OtherRevValType,
otherRevVals ANY DEFINED BY otherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIER
-- ES-C Time-Stamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Time-Stamp
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 27}
ArchiveTimeStampToken ::= TimeStampToken
END -- ETS-ElectronicSignatureFormats-88syntax --A.2. Definitions Using X.680 1997 ASN.1 Syntax ✨
NOTE: The ASN.1 module defined in clause A.1 has precedence over that defined in clause A.2 in the case of any conflict.
ETS-ElectronicSignatureFormats-97Syntax { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 6}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All -
IMPORTS
-- Cryptographic Message Syntax (CMS): RFC 2630
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime,
SigningTime, id-countersignature, Countersignature
FROM CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms(1) }
-- ESS Defined attributes: RFC 2634 (Enhanced Security Services
-- for S/MIME)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference,
id-aa-contentIdentifier, ContentIdentifier
FROM ExtendedSecurityServices
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }
-- Internet X.509 Public Key Infrastructure
- - Certificate and CRL Profile:RFC 2459
Certificate, AlgorithmIdentifier, CertificateList, Name,
GeneralNames, GeneralName, DirectoryString, Attribute,
AttributeTypeAndValue, AttributeType, AttributeValue,
PolicyInformation.
FROM PKIX1Explicit93
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit-88(1)}
-- X.509 '97 Authentication Framework
AttributeCertificate
FROM AuthenticationFramework
{joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}
-- OCSP 2560
BasicOCSPResponse, ResponderID
FROM OCSP
-- { OID not assigned }
-- Time Stamp Protocol Work in Progress TimeStampToken
FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
-- S/MIME Object Identifier arcs used in this document
-- ===================================================
-- S/MIME OID arc used in this document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
-- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }
-- S/MIME Arcs
-- id-mod OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier
-- Definitions of Object Identifier arcs used in this document
-- ===========================================================
-- The allocation of OIDs to specific objects are given below with the
-- associated ASN.1 syntax definition
-- OID used referencing electronic signature mechanisms based on this
-- standard for use with the IDUP API (see annex D)
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1)
idupMechanism (4)etsiESv1(1) }
-- CMS Attributes Defined in this document
-- =======================================
-- Mandatory Electronic Signature Attributes
-- OtherSigningCertificate
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THIS DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL
}
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue
}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
"SignaturePolicy CHOICE {
SignaturePolicyId SignaturePolicyId,
SignaturePolicyImplied SignaturePolicyImplied
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyIdentifier SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= OtherHashAlgAndValue
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SIG-POLICY-QUALIFIER.&id
({SupportedSigPolicyQualifiers}),
qualifier SIG-POLICY-QUALIFIER.&Qualifier
({SupportedSigPolicyQualifiers}
{@sigPolicyQualifierId})OPTIONAL }
SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::=
{ noticeToUser | pointerToSigPolSpec }
SIG-POLICY-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
SIG-POLICY-QUALIFIER-ID &id
[SIG-QUALIFIER-TYPE &Qualifier] }
noticeToUser SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-sqt-unotice SIG-QUALIFIER-TYPE
SPUserNotice
}pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-sqt-uri SIG-QUALIFIER-TYPE SPuri }
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL
}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER
}
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200))
}
-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier
OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentQualifierId COMMITMENT-QUALIFIER.&id,
qualifier COMMITMENT-QUALIFIER.&Qualifier
OPTIONAL }
COMMITMENT-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
COMMITMENT-QUALIFIER-ID &id
[COMMITMENT-TYPE &Qualifier] }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following must be present
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- As defined in X.509 : see section 10.3
-- Content Time-Stamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
ContentTimestamp::= TimeStampToken
-- Validation Data
-- Signature Time-Stamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID
-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OTHER-REVOCATION-REF.&id,
otherRevRefs OTHER-REVOCATION-REF.&Type
}
OTHER-REVOCATION-REF ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
&Type ID &id }
-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals }
OtherRevVals ::= SEQUENCE {
otherRevValType OTHER-REVOCATION-VAL.&id,
otherRevVals OTHER-REVOCATION-VAL.&Type
}
OTHER-REVOCATION-VAL ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
&Type ID &id }
-- ES-C Time-Stamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Time-Stamp
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 27}
ArchiveTimeStampToken ::= TimeStampToken
END -- ETS-ElectronicSignatureFormats-97SyntaxAnnex B (informative): General Description ✨
okay so this annex is the big-picture "why" 🧚 it covers the concepts that apply to this document and the reasoning behind the ASN.1 pieces in the main text. for each component, it explains why it's needed, plus the vulnerabilities and threats it's dealing with and how they get countered 🛡️
B.1 The Signature Policy 💜
a signature policy is a set of rules for creating and validating an electronic signature, and if you follow them, the signature can be determined to be valid 💅 a given legal or contract setting might recognise a particular signature policy as meeting its requirements. a policy can be issued by a party that relies on the signatures, and the signer picks it to use with that relying party. or an electronic trading association can set one up for its members to share 🤝 either way, the signer and the verifier both use the same signature policy.
the policy might be explicitly identified, or it might just be implied by the semantics of the data being signed plus other external data, like a contract that points to a signature policy 📜
an explicit signature policy has a globally unique reference, and the signer binds it to the electronic signature as part of the signature calculation 🔐
the signature policy needs to be readable by humans so people can check that it meets the legal and contractual requirements it's being applied under 👀 the parts that spell out the electronic rules for creating and validating the signature also need to be in a computer processable form 🤖
so the signature policy includes the following:
- Information about the signature policy that can be displayed to the signer or the verifiers.
- Rules, which apply to functionality, covered by this document (referred to as the Signature Validation Policy).
- Rules which may be implied through adoption of Certificate Policies that apply to the electronic signature (e.g., rules for ensuring the secrecy of the private signing key).
- Rules, which relate to the environment used by the signer, e.g., the use of an agreed CAD (Card Accepting Device) used in conjunction with a smart card.
an explicit Signature Validation Policy may be structured so that it can be computer processable 🧠 any format of the signature validation policy is allowed by this document, so it's super flexible 💜 however, for a given explicit signature policy there must be one definitive form that has a unique binary encoded value 🔒
the Signature Validation Policy includes rules about using TSPs (CA, Attribute Authorities, Time Stamping Authorities) 🏛️ it also includes rules defining the components of the electronic signature that must be provided by the signer, along with the data the verifier needs to provide long term proof ⏳
B.2 Signed Information 🎀
the information being signed may be defined as a MIME-encapsulated message, which can be used to signal the format of the content so the right display or application gets picked 🖥️ it can be made of formatted text (e.g., EDIFACT), free text, or fields from an electronic form (e-form). for example, the Adobe(tm) format "pdf" may be used, or the eXtensible Mark up Language (XML) 🦋
B.3 Components of an Electronic Signature 🌸
B.3.1 Reference to the Signature Policy 📜✨
okay so the definition of electronic signature goes: "a commitment has been explicitly endorsed under a "Signature policy", at a given time, by a signer under an identifier, e.g., a name or a pseudonym, and optionally a role". 💅
bestie, when two totally independent parties check the same signature, they need to get the same answer 🥹 that's the whole point. so the same signature policy must be used by the signer and the verifier. 🔥
the policy can be named outright, or it can be implied by what the data means plus other external data that points at the policy you're supposed to use. 🧚
by signing over the signature policy identifier, the signer explicitly shows they applied that policy when making the signature. so they take on any explicit or implied commitments that come with it. 💖
to uniquely identify an explicit signature policy that will be used to verify the signature, an identifier and hash of the "Signature policy" shall be part of the signed data. extra info about the policy (like a web reference to the document) can ride along as "qualifiers" on the signature policy identifier. 🎀
when the signature policy isn't explicitly identified but is implied by the semantics of the data being signed, the signature will include a signature policy identifier that says the policy is implied. 🌸 in this case, the verification rules must be figured out using other external data that designates the policy to use. if it's clear from the context that all the documents being verified refer to the same signature policy, then that policy may be predetermined or fixed inside the application. 👑
to uniquely identify the "Signature Validation Policy" used to verify the signature, an identifier and hash of the "Signature policy" must be part of the signed data. extra info about the policy (like a web reference to the document) may be carried as "qualifiers" on the signature policy identifier. 🦋
B.3.2 Commitment Type Indication 💌
the definition of electronic signature says: "a commitment has been explicitly endorsed under a signature policy, at a given time, by a signer under an identifier, e.g., a name or a pseudonym, and optionally a role". 🫶
the commitment type can be shown in the electronic signature either:
- explicitly, using a "commitment type indication" in the electronic signature;
- implicitly or explicitly, from the semantics of the signed data.
if the commitment type is explicit, using a "commitment type indication" in the electronic signature, then accepting a verified signature means accepting the semantics of that commitment type. the semantics of explicit commitment type indications must be specified either as part of the signature policy, or they may be registered for generic use across multiple policies. 🍓
if a signature includes a commitment type indication that isn't one of those recognized under the signature policy, the signature must be treated as invalid. 💀
how commitment is indicated through the semantics of the data being signed is outside the scope of this document. 🙈
NOTE: Examples of commitment indicated through the semantics of the data being signed are: - An explicit commitment made by the signer, indicated by the type of data being signed over. So the data structure being signed can have an explicit commitment within the context of the application (e.g., EDIFACT purchase order). - An implicit commitment, which is a commitment made by the signer because the data being signed over has specific semantics (meaning) that only humans can interpret (i.e., free text).
B.3.3 Certificate Identifier from the Signer 🪪
the definition of the ETSI electronic signature says: "a commitment has been explicitly endorsed under a signature policy, at a given time, by a signer under an identifier, e.g., a name or a pseudonym, and optionally a role." 🌈
in lots of real-life environments, users can get different certificates containing the same public key for different names, from different CAs or even from the same CA. the big perk is that one user can use the same private key for different purposes. that multi-use thing is a real win when a smart card protects the private key, since a smart card's storage is always limited. 💜 when several CAs are involved, each certificate can contain a different identity, e.g., as a national or as an employee of a company. so when a private key gets used for various purposes, the certificate is needed to clarify the context the private key was used in when the signature was generated. where a private key could be used in multiple ways, the signer has to tell the verifier the precise certificate to be used. 🔑
a lot of current schemes just tack the certificate on after the signed data, which leaves them open to various substitution attacks. 😭 one example of a substitution attack is a "bad" CA that issues a certificate to someone with somebody else's public key. if the signer's certificate is simply appended to the signature and isn't protected by the signature, anyone could swap one certificate for another, and the message would look like it was signed by someone else. 🙀
to counter this kind of attack, the signer's identifier has to be protected by the signer's digital signature. ✨
there's another technique to counter that threat, although it doesn't give the same advantages as the one above. it requires all CAs to perform a Proof Of Possession of the private key at registration time. the problem is that it doesn't guarantee anything at verification time, and you can only get some "after the event" proof, and only if the CA keeps the Proof Of Possession in an audit trail. 🥀
to uniquely identify the certificate used to verify the signature, an identifier of the certificate from the signer must be part of the signed data. 🎯
B.3.4 Role Attributes 👔
the definition of electronic signature says: "a commitment has been explicitly endorsed under a non repudiation security policy, at a given time, by a signer under an identifier, e.g., a name or a pseudonym, and optionally a role." 🧠
the signer's name matters, but their position inside a company or organization can matter even more. some contracts are only valid if a user in a particular role signs them, e.g., a Sales Director. in lots of cases, who the Sales Director really is isn't that important. what's fundamental is being sure the signer has been empowered by their company to be the Sales Director. 💼✨
this document defines two different ways to provide this feature:
- by placing a claimed role name in the CMS signed attributes field;
- by placing an attribute certificate containing a certified role name in the CMS signed attributes field.
NOTE: Another possible approach would have been to use additional attributes containing the role name(s) in the signer's certificate. However, it was decided not to follow this approach, because it breaks the basic philosophy of a certificate being issued for one primary purpose. Also, using separate certificates to manage the signer's identity certificate and to manage additional roles can simplify management, since new identity keys don't need to be issued if the use of a role is changed. 🙌
B.3.4.1 Claimed Role 🗣️
the signer may be trusted to state their own role without any certificate to back up that claim. 🥰 in that case, the claimed role can be added to the signature as a signed attribute. 💅
B.3.4.2 Certified Role 🏅
unlike public key certificates, which bind an identifier to a public key, Attribute Certificates bind the identifier of a certificate to some attributes, like a role. an Attribute Certificate is NOT issued by a CA. it's issued by an Attribute Authority (AA). most of the time, the Attribute Authority is under the control of an organization or company that's best placed to know which attributes are relevant for which individual. 🏢💖
the Attribute Authority may use or point to public key certificates issued by any CA, as long as the appropriate trust can be placed in that CA. Attribute Certificates can have various validity periods, and that period can be quite short, e.g., one day. 🌞 that means a new Attribute Certificate has to be obtained every day, valid just for that day, but this can be a real advantage, since revocation of such certificates may not be needed. 🙌 when signing, the signer has to specify which Attribute Certificate they're selecting. to do that, a reference to the Attribute Certificate has to be included in the signed data, so it's protected by the signer's digital signature. 🔐
to uniquely identify the attribute certificate(s) used to verify the signature, an identifier of the attribute certificate(s) from the signer must be part of the signed data. 🎀
B.3.5 Signer Location 📍
in some transactions, the purported location of the signer at the time they apply their signature may need to be indicated. for this reason, an optional location indicator must be able to be included. 🌍
to indicate where the signer was when they applied their signature, a location attribute may be included in the signature. 🦋
B.3.6 Signing Time ⏰
okay so the definition of electronic signature literally says: "a commitment has been explicitly endorsed under a signature policy, at a given time, by a signer under an identifier, e.g., a name or a pseudonym, and optionally a role." 🎀
There are a few ways to deal with the time part. The approach this document picks is to sign over a time that the signer claims is the signing time (the claimed signing time), and to require a trusted time stamp to be obtained when building an ES with Time-Stamp. When a verifier accepts a signature, the two times have to be within acceptable limits. 💅
The big win here is that electronic signatures can be generated without any on-line connection to a trusted time source, which means they can be made off-line. 🦋
So two dates and two signatures are needed:
- a signing time indicated by the signer, which is part of the data signed by the signer (i.e., part of the basic electronic signature);
- a time indicated by a Time-Stamping Authority (TSA), which is signed over the digital signature value of the basic electronic signature. The signer, verifier or both may obtain the TSA time-stamp. 🌸
For an electronic signature to be valid under a signature policy, it must be time-stamped by a TSA, and the signing time indicated by the signer and the time of time stamping indicated by a TSA must be "close enough" to meet the requirements of the signature validation policy. ✨
"Close enough" means a few minutes, hours or even days, depending on the "Signature Validation Policy". 🫶
NOTE: The need for Time-Stamping is further explained in clause B.4.5. A further optional attribute is defined in this document to time-stamp the content, to provide proof of the existence of the content, at the time indicated by the time-stamp. 💀
Using this optional attribute, a trusted secure time may be obtained before the document is signed and included under the digital signature. This needs an on-line connection to a trusted time-stamping service before the signature is generated, and it may not represent the precise signing time, since the time can be obtained in advance. Still, the signer can use this optional attribute to prove that the signed object existed before the date included in the time-stamp (see 3.12.3, Content Time-Stamp). 🔥
Also, the signing time should be between the time indicated by this time-stamp and the time indicated by the ES-T time-stamp. 👑
B.3.7 Content Format 🌈
When signed data is presented to a human user, it may be important that there is no ambiguity about how the signed information is shown to the relying party. So the signer can indicate a content hint, which lets the relying party pick the right representation (text, sound or video). 🧚 If a relying party system does not use the format specified in the content hints to present the data to the relying party, the electronic signature may not be valid. 🙈
B.4 Components of Validation Data 🍓
B.4.1 Revocation Status Information 💜
A verifier will have to prove that the signer's certificate was valid at the time of the signature. This can be done by either:
- using Certificate Revocation Lists (CRLs);
- using responses from an on-line certificate status server (for example, obtained through the OCSP protocol). 🦋
B.4.2 CRL Information 📜
When using CRLs for revocation information, a verifier will have to make sure that, at the time of the first verification, they get the appropriate certificate revocation information from the signer's CA. This should be done as soon as possible, to minimize the time delay between the generation and verification of the signature. It involves checking that the signer certificate serial number is not included in the CRL. The signer, the verifier or any other third party may obtain this CRL. If it is obtained by the signer, then it must be conveyed to the verifier. It may be convenient to archive the CRL for ease of subsequent verification or arbitration. 🗂️
Alternatively, as long as the CRL is archived somewhere that is accessible for the purpose of arbitration, the serial number of the CRL used may be archived together with the verified electronic signature. ✨
Here's the tricky bit: the certificate serial number might show up in the CRL with the status "suspended" (i.e., on hold). In that case, the electronic signature is not yet valid, since it is not possible to know whether the certificate will or will not be revoked at the end of the suspension period. If a decision has to be taken immediately, then the signature has to be considered as invalid. If a decision can wait until the end of the suspension period, then two cases are possible: 😭
- the certificate serial number has disappeared from the list, so the certificate can be considered as valid, and that CRL must be captured and archived either by the verifier or elsewhere, and be kept accessible for the purpose of arbitration.
- the certificate serial number has been kept on the list with the status definitively revoked, so the electronic signature must be considered as invalid and discarded. 💅
At this point the verifier may be convinced that they got a valid signature, but they are not yet in a position to prove at a later time that the signature was verified as valid. Before getting into that, an alternative to CRL is to use OCSP responses. 🌸
B.4.3 OCSP Information 🧾
When using OCSP for revocation information, a verifier will have to make sure that, at the time of the first verification, they get an OCSP response that contains the status "valid". This should be done as soon as possible after the generation of the signature. The signer, the verifier or any other third party may fetch this OCSP response. Since OSCP responses are transient and are therefore not archived by any TSP, including CA, it is the responsibility of every verifier to make sure that it is stored in a safe place. The simplest way is to store them associated with the electronic signature. An alternative would be to store them in some storage so that they can then be easily retrieved. 🫶
Same as with CRLs, it may happen that the certificate is declared as invalid but with the secondary status "suspended". 🙈
In such a case, the electronic signature is not yet valid, since it is not possible to know whether the certificate will or will not be revoked at the end of the suspension period. If a decision has to be taken immediately, then the electronic signature has to be considered as invalid. If a decision can wait until the end of the suspension period, then two cases are possible: 🌈
- An OCSP response with a valid status is obtained at a later date, so the certificate can be considered as valid, and that OCSP response must be captured.
- An OCSP response with an invalid status is obtained, with a secondary status indicating that the certificate is definitively revoked, so the electronic signature must be considered as invalid and discarded. 💀
As in the CRL case, at this point the verifier may be convinced that they got a valid signature, but they are not yet in a position to prove at a later time that the signature was verified as valid. 🔥
B.4.4 Certification Path 🛤️
A verifier will have to prove that the certification path was valid at the time of the signature, up to a trust point, according to the naming constraints and the certificate policy constraints from the "Signature Validation Policy". It will be necessary to capture all the certificates from the certification path, starting with those from the signer and ending with those of the self-signed certificate from one trusted root of the "Signature Validation Policy". On top of that, it will be necessary to capture the Authority Revocation Lists (ARLs) to prove than none of the CAs from the chain was revoked at the time of the signature. 👑
As in the OCSP case, at this point the verifier may be convinced that they got a valid signature, but they are not yet in a position to prove at a later time that the signature was verified as valid. 🦋
B.4.5 Time-Stamping for Long Life of Signature ⏳
An important property for long-standing signatures is that a signature, having been found once to be valid, must continue to be so months or years later. 💖
A signer, verifier or both may be required to provide, on request, proof that a digital signature was created or verified during the validity period of all the certificates that make up the certificate path. In this case, the signer, verifier or both will also be required to provide proof that all the user and CA certificates used were not revoked when the signature was created or verified. 🌸
It would be quite unacceptable to consider a signature as invalid even if the keys or certificates were later compromised. So there is a need to be able to demonstrate that the signature keys was valid around the time that the signature was created, to provide long-term evidence of the validity of a signature. 😭
It could be the case that a certificate was valid at the time of the signature but revoked some time later. In this event, evidence must be provided that the document was signed before the signing key was revoked. 🔥
Time-Stamping by a Time Stamping Authority (TSA) can provide such evidence. A time stamp is obtained by sending the hash value of the given data to the TSA. The returned "time-stamp" is a signed document that contains the hash value, the identity of the TSA, and the time of stamping. This proves that the given data existed before the time of stamping. Time-Stamping a digital signature (by sending a hash of the signature to the TSA) before the revocation of the signer's private key provides evidence that the signature has been created before the key was revoked. 🧚
If a recipient wants to hold a valid electronic signature, they will have to ensure that they have obtained a valid time stamp for it before that key (and any key involved in the validation) is revoked. The sooner the time-stamp is obtained after the signing time, the better. ⭐
It is important to note that signatures may be generated "off-line" and time-stamped at a later time by anyone, for example by the signer or by any recipient interested in the value of the signature. The time stamp can thus be provided by the signer together with the signed document, or obtained by the recipient following receipt of the signed document. 🎀
The time stamp is NOT a component of the Electronic Signature, but it is the essential component of the ES with Time-Stamp. 🫶
It is required in this document that the signer's digital signature value is time-stamped by a trusted source, known as a Time-Stamping Authority. 💅
This document requires that the signer's digital signature value is time-stamped by a trusted source before the electronic signature can become an ES with Complete validation data (ES-C). The acceptable TSAs are specified in the Signature Validation Policy. 🌈
If both the signer and the verifier are required to time-stamp the signature value to meet the requirements of the signature policy, the signature policy MAY specify a permitted time delay between the two time stamps. 👑
B.4.6. Time-Stamping before CA Key Compromises ✨
Okay so, Time-Stamped extended electronic signatures are needed when there's a requirement to protect against the possibility of a CA key in the certificate chain ever getting compromised 😭 A verifier may be required to provide, on request, proof that the certification path and the revocation information used at the time of the signature were valid, even if one of the issuing keys or OCSP responder keys is compromised later 🫶
This document has two ways of using time-stamps to guard against that compromise 🦋
- Time-Stamp the ES with Complete validation data, when an OCSP response is used to get the status of the certificate from the signer.
- Time-Stamp only the certification path and revocation information references when a CRL is used to get the status of the certificate from the signer.
NOTE: the signer, verifier or both may obtain the time-stamp.
B.4.6.1. Time-Stamping the ES with Complete validation data 💜
When an OCSP response is used, it's necessary to time-stamp that response specifically, in case the responder's key ever gets compromised 🙈 The info in an OCSP response is user specific and time specific, so every signature received needs its own individual time-stamp 🍓 Instead of time-stamping only the certification path references and the revocation information references (which include the OCSP response), the time-stamp goes on the ES-C. Since the certification path and revocation information references are part of the ES with Complete validation data, they're protected too ✨ For the same cryptographic cost, this gives you an integrity mechanism over the ES with Complete validation data, so any modification can be detected immediately 👑 Other ways of protecting or detecting the integrity of the ES with Complete Validation Data do exist, and they could be used instead 💅
This technique does need a time-stamp for every signature, but it's a great fit for individual users who want an integrity-protected copy of every validated signature they've received 🌸
By time-stamping the complete electronic signature, meaning the digital signature plus the references to the certificates and revocation status information used to support validating it, the time-stamp makes sure there's no ambiguity about how that signature was validated 🔥
This technique is called ES with eXtended validation data (ES-X), type 1 Time-Stamped in this document 🎀
NOTE: Trust is achieved in the references by including a hash of the data being referenced.
If you want to keep a copy of the additional data being referenced for any reason, that data can be attached to the electronic signature. When you do that, the electronic signature becomes an ES-X Long, as defined in this document 🧚
An ES-X Long Time-Stamped is simply the concatenation of an ES-X Time-Stamped with a copy of the additional data being referenced 💖
B.4.6.2. Time-Stamping Certificates and Revocation Information 🌈
Time-stamping each ES with Complete validation data the way we just described might not be efficient 🙈 That's especially true when the same set of CA certificates and CRL information is used to validate lots of signatures 😭
Time-stamping CA certificates stops an attacker from issuing bogus CA certificates that could be claimed to have existed before the CA key was compromised 🛑 Any bogus time-stamped CA certificates will show that the certificate was created after the legitimate CA key was compromised. In the same way, time-stamping CA CRLs stops an attacker from issuing bogus CA CRLs that could be claimed to have existed before the CA key was compromised 💀
Time-stamping commonly used certificates and CRLs can be done centrally, e.g., inside a company or by a service provider 🏢 This reduces the amount of data the verifier has to time-stamp. For example, it could come down to just one time-stamp per day, in the case where all the signers use the same CA and the CRL applies for the whole day 🌞 What needs to be time-stamped isn't the actual certificates and CRLs, but the unambiguous references to those certificates and CRLs ✨
To comply with extended validation data, type 2 Time-Stamped, this document requires the following:
- All the CA certificate references and revocation information references (i.e., CRLs) used in validating the ES-C are covered by one or more time-stamps.
So an ES-C with a time-stamp signature value at time T1 can be proved valid if all the CA and CRL references are time-stamped at time T1+ 🎯
B.4.7. Time-Stamping for Long Life of Signature ⏳
Advances in computing make it more likely that algorithms can be broken and keys compromised 🧠 So there's a requirement to be able to protect electronic signatures against that possibility 🛡️
Over time, weaknesses can show up in the cryptographic algorithms used to create an electronic signature (for example, because of the time available for cryptanalysis, or better cryptanalytic techniques) 📈 Before those weaknesses become likely, a verifier should take extra steps to keep the electronic signature valid 💪 Several techniques could do this depending on the nature of the weakened cryptography. To keep things simple, this document uses a single technique that covers all the cases, called Archive validation data 🌟
Archive validation data consists of the Complete validation data and the complete certificate and revocation data, time-stamped together with the electronic signature 📦 Archive validation data is necessary if the hash function and the crypto algorithms used to create the signature are no longer secure. Also, if it can't be assumed that the hash function used by the Time Stamping Authority is secure, then nested time-stamps of the Archived Electronic Signature are required 🪆
Trusted Service Provider (TSP) key compromise should be a lot less likely than user key compromise, because TSPs are expected to use stronger cryptography and better key protection 💜 It can be expected that new algorithms (or old ones with longer key lengths) will be used. In that case, a sequence of time-stamps will protect against forgery. Each time-stamp needs to be put in place before either the compromise of the signing key or the cracking of the algorithms used by the TSA happens ⏰ TSAs (Time-Stamping Authorities) should have long keys (for example, at the time this document was drafted, 2048 bits for the signing RSA algorithm was the figure given) and/or a "good" or different algorithm 🔑
Nested time-stamps will also protect the verifier against key compromise, or against cracking of the algorithm, on the old electronic signatures 🫶
This process needs to be performed and repeated before the cryptographic algorithms used for generating the previous time-stamp stop being secure. So Archive validation data may end up carrying multiple embedded time-stamps 🎀
B.4.8. Reference to Additional Data 🗂️
Even when you use type 1 or type 2 Time-Stamped extended validation data, verifiers still need to keep track of all the components that were used to validate the signature, so they can retrieve them again later 🔍 These components may be archived by an external source, like a trusted service provider. In that case, the referenced information provided as part of the ES with Complete validation data (ES-C) is good enough 💅 The actual certificates and CRL information references in the ES-C can be gathered when they're needed for arbitration ⚖️
B.4.9. Time-Stamping for Mutual Recognition 🤝
In some business scenarios, both the signer and the verifier need to time-stamp their own copy of the signature value. Ideally, the two time-stamps should be as close to each other as possible 💞
Example: A contract is signed by two parties, A and B, each representing their own organization. There are two possible approaches to time-stamping the signer and verifier data 📝
- Under the terms of the contract, a pre-defined common "trusted" TSA may be used.
- If both organizations run their own time-stamping services, A and B can have the transaction time-stamped by those two services. In this case, the electronic signature will only be considered valid if both time-stamps were obtained in due time (i.e., there should not be a long delay between obtaining the two time-stamps). That way, neither A nor B can repudiate the signing time indicated by their own time-stamping service 🙅♀️
So A and B don't need to agree on a common "trusted" TSA in order to get a valid transaction 🥰
It's important to note that signatures may be generated "off-line" and time-stamped later by anyone, e.g., by the signer or by any recipient who wants to validate the signature 📬 The time-stamp over the signature from the signer can therefore be provided by the signer together with the signed document, and/or obtained by the verifier after receiving the signed document ✨
The business scenarios may therefore dictate that one or more of the long-term signature time-stamping methods described above be used. This will need to be part of a mutually agreed Signature Validation Policy, which is part of the overall signature policy under which digital signatures may be used to support the business relationship between the two parties 🧾
B.4.10. TSA Key Compromise 🔐
TSA servers should be built so that once the private signature key is installed, there's minimal likelihood of compromise for as long as possible. So the validity period for the TSA's keys should be as long as possible ⏳
Both the ES-T and the ES-C contain at least one time-stamp over the signer's signature. To protect against compromise of the private signature key used to produce that time-stamp, the Archive validation data can be used when a different Time-Stamping Authority key is involved in producing the additional time-stamp 🔄 If it's believed that the TSA key used for an earlier time-stamp may ever be compromised (e.g., outside its validity period), then the ES-A should be used. For extremely long periods, this may be applied repeatedly using new TSA keys 🌌
B.5. Multiple Signatures ✨
okay so some e-signatures only count if they carry more than one signature 💅 this is super common when a contract gets signed by two parties 🫶 sometimes the order matters and sometimes it doesn't. there are two main flavours of multiple signatures that need to be supported, and they fall into two buckets:
- independent signatures 🦋
- embedded signatures 🧚
independent signatures are parallel, so the order they go on doesn't matter at all. the capability to have more than one independent signature over the same data must be provided 💖
embedded signatures get applied one after the other, and the order does matter here 👑 the capability to sign over signed data must be provided 🔥
these forms are described in clause 3.13 ✨ and every other multi-signature scheme (a signed doc with a countersignature, double countersignatures, or multiple signatures) can be broken down into one or more of those two cases 💅
Annex C (informative): Identifiers and roles 🎀
C.1. Signer Name Forms
the name the signer uses, held as the subject in their certificate, must uniquely identify the entity 🔍 the name has to be allocated and verified when they register with the Certification Authority, either directly or through a Registration Authority, before a certificate gets issued 🪪
this document doesn't put any restrictions on the form of the name 🙌 the subject's name can be a distinguished name (as defined in [RFC2459]) held in the subject field of the certificate, or any other name form held in the X.509 subjectAltName certificate extension field. if the subject doesn't have a distinguished name, the subject name can be an empty sequence and the subjectAltName extension must be critical 🫣
C.2. TSP Name Forms
all TSP name forms (Certification Authorities, Attribute Authorities and Time-Stamping Authorities) must be a distinguished name held in the subject field of the certificate 📋
the TSP name form must include the legal jurisdiction (aka the country) it operates under, plus an identification for the organization providing the service 🌍
C.3. Roles and Signer Attributes
sometimes a signer signs as an individual but also wants to say they're acting on behalf of an organization 💼 in that case it may be necessary to provide two independent forms of identification. the first identity is directly tied to the signing key and identifies them as an individual 🧍♀️. the second one is managed independently and identifies that person acting as part of the organization, possibly with a given role 🎭
in this case the first identity is carried in the subject/subjectAltName field of the signer's certificate, as described above ✨
this document supports the following ways of providing a second form of identification:
- by placing a secondary name field containing a claimed role in the CMS signed attributes field 🏷️
- by placing an attribute certificate containing a certified role in the CMS signed attributes field 📜
Full Copyright Statement 📜
ok the legal bit, verbatim, because it's important 🙈
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📦 where this page comes from
- ietf: rfc3126 2001-09
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms