RFC 3628
Policy Requirements for Time-Stamping Authorities (TSAs)
RFC 3628: Policy Requirements for Time-Stamping Authorities (TSAs) 🎀
Authors: D. Pinkas (Bull), N. Pope and J. Ross (Security & Standards) Category: Informational 🌸 Date: November 2003 Obsoletes / Updates: nothing listed, so this one doesn't replace or update any earlier RFC 💅 Series: Network Working Group, Request for Comments: 3628
Status of This Memo ✨
okay bestie, this memo is just here to give the Internet community information. it does NOT specify an Internet standard of any kind 🙈 distribution is unlimited, so share it with everyone 💖
Copyright Notice 🦋
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract 🔥
this doc lays out requirements for a baseline time-stamp policy for Time-Stamping Authorities (TSAs) that issue time-stamp tokens. those tokens are backed by public key certificates and are accurate to one second or better ⏱️ a TSA is allowed to write its own policy that builds on this one, but that policy shall incorporate or further constrain the requirements in this document, so the baseline is always there underneath 👑
Table of Contents 📖
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definitions and Abbreviations . . . . . . . . . . . . . . . . 5
3.1. Definitions. . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Abbreviations. . . . . . . . . . . . . . . . . . . . . . 6
4. General Concepts. . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Time-Stamping Services . . . . . . . . . . . . . . . . . 6
4.2. Time-Stamping Authority. . . . . . . . . . . . . . . . . 7
4.3. Subscriber . . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Time-Stamp Policy and TSA Practice Statement . . . . . . 8
4.4.1. Purpose. . . . . . . . . . . . . . . . . . . . . 8
4.4.2. Level of Specificity . . . . . . . . . . . . . . 8
4.4.3. Approach . . . . . . . . . . . . . . . . . . . . 8
5. Time-Stamp Policies . . . . . . . . . . . . . . . . . . . . . 9
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Identification . . . . . . . . . . . . . . . . . . . . . 9
5.3. User Community and Applicability . . . . . . . . . . . . 10
5.4. Conformance. . . . . . . . . . . . . . . . . . . . . . . 10
6. Obligations and Liability . . . . . . . . . . . . . . . . . . 10
6.1. TSA Obligations. . . . . . . . . . . . . . . . . . . . . 10
6.1.1. General. . . . . . . . . . . . . . . . . . . . . 10
6.1.2. TSA Obligations Towards Subscribers. . . . . . . 11
6.2. Subscriber Obligations . . . . . . . . . . . . . . . . . 11
6.3. Relying Party Obligations. . . . . . . . . . . . . . . . 11
6.4. Liability. . . . . . . . . . . . . . . . . . . . . . . . 11
7. Requirements on TSA Practices . . . . . . . . . . . . . . . . 12
7.1. Practice and Disclosure Statements . . . . . . . . . . . 12
7.1.1. TSA Practice Statement . . . . . . . . . . . . . 12
7.1.2. TSA Disclosure Statement . . . . . . . . . . . . 13
7.2. Key Management Life Cycle. . . . . . . . . . . . . . . . 15
7.2.1. TSU Key Generation . . . . . . . . . . . . . . . 15
7.2.2. TSU Private Key Protection . . . . . . . . . . . 15
7.2.3. TSU Public Key Distribution. . . . . . . . . . . 16
7.2.4. Rekeying TSU's Key . . . . . . . . . . . . . . . 17
7.2.5. End of TSU Key Life Cycle. . . . . . . . . . . . 17
7.2.6. Life Cycle Management of the Cryptographic Module
used to Sign Time-Stamps . . . . . . . . . . . . 17
7.3. Time-Stamping. . . . . . . . . . . . . . . . . . . . . . 18
7.3.1. Time-Stamp Token . . . . . . . . . . . . . . . . 18
7.3.2. Clock Synchronization with UTC . . . . . . . . . 19
7.4. TSA Management and Operation . . . . . . . . . . . . . . 20
7.4.1. Security Management. . . . . . . . . . . . . . . 20
7.4.2. Asset Classification and Management. . . . . . . 21
7.4.3. Personnel Security . . . . . . . . . . . . . . . 22
7.4.4. Physical and Environmental Security. . . . . . . 23
7.4.5. Operations Management. . . . . . . . . . . . . . 25
7.4.6. System Access Management . . . . . . . . . . . . 26
7.4.7. Trustworthy Systems Deployment and Maintenance . 27
7.4.8. Compromise of TSA Services . . . . . . . . . . . 28
7.4.9. TSA Termination. . . . . . . . . . . . . . . . . 29
7.4.10. Compliance with Legal Requirements . . . . . . . 29
7.4.11. Recording of Information Concerning Operation
of Time-Stamping Services. . . . . . . . . . . . 30
7.5. Organizational . . . . . . . . . . . . . . . . . . . . . 31
8. Security Considerations . . . . . . . . . . . . . . . . . . . 32
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.1. Normative References. . . . . . . . . . . . . . . . . . 33
10.2. Informative References. . . . . . . . . . . . . . . . . 34
Annex A (informative): Coordinated Universal Time . . . . . . . . 35
Annex B (informative): Possible for Implementation Architectures
and Time-Stamping Services . . . . . . . . 36
Annex C (informative): Long Term Verification of Time-Stamp
Tokens . . . . . . . . . . . . . . . . . . 38
Annex D (informative): Model TSA Disclosure Statement . . . . . . 39
Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 42
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 431. Introduction 🌈
okay so this Informational RFC is technically equivalent to ETSI TS 102 023 V 1.2.1 (2002-06) [TS 102023] 🧚 the ETSI TS is under the ETSI Copyright (C), and you can grab individual copies of that ETSI deliverable from http://www.etsi.org
so here's the vibe: reliable digital evidence needs an agreed-upon way to attach time data to a transaction, so you can compare them later on ⏳ how good that evidence is depends on the data structures that represent the events and on the parametric data points that anchor those events to the real world. in this case, that means the time data and how it was applied 🫶
a typical transaction is a digitally signed document, and it's super important to prove that the signer's signature was applied while the signer's certificate was valid 💅
a timestamp (or time mark, which is an audit record kept in a secure audit trail from a trusted third party) applied to a digital signature value proves that the digital signature was created before the date in the time-stamp or time mark 🔥
to prove a digital signature was generated while the signer's certificate was valid, the digital signature must be verified AND these conditions must be satisfied:
- the time-stamp (or time mark) was applied before the end of the validity period of the signer's certificate,
- the time-stamp (or time mark) was applied either while the signer's certificate was not revoked or before the revocation date of the certificate.
so a time-stamp (or time mark) applied this way proves the digital signature was created while the signer's certificate was valid. this concept proves the validity of a digital signature over the whole of any certificate chain 💖
covering that case is the main reason this document exists 🎀 BUT these policy requirements can also be used for other needs, so don't sleep on that 👀
the electronic time stamp is getting major attention from the business sector as an important component of electronic signatures ✨ it's also featured by the ETSI Electronic Signature Format standard [TS 101733] or Electronic Signature Formats for long term electronic signatures [RFC 3126], both built upon the Time-Stamp Protocol [RFC 3161]. agreed minimum security and quality requirements are needed so that long-term electronic signatures can be validated in a trustworthy way 🦋
the European Directive 1999/93/EC [Dir 99/93/EC] defines a certification service provider as "an entity or a legal or natural person who issues certificates or provides other services related to electronic signatures". one example of a certification-service-provider is a Time-Stamping Authority 🌸
the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC 2119] 🔑
2. Overview 🍓
these policy requirements target time-stamping services used to support qualified electronic signatures (i.e., in line with article 5.1 of the European Directive on a community framework for electronic signatures) 💅 but they may be applied to any application that needs to prove a datum existed before a particular time ⏰
these policy requirements are based on public key cryptography, public key certificates and reliable time sources 🔐 this present document may be used by independent bodies as the basis for confirming that a TSA may be trusted to provide time-stamping services 👑
this document covers requirements for synchronizing TSAs that issue time-stamp tokens with Coordinated Universal Time (UTC) and that are digitally signed by TSUs 🕰️
subscribers and relying parties should consult the TSA's practice statement to get more details on exactly how this time-stamp policy is implemented by the particular TSA (e.g., protocols used in providing this service) 🧐
this document does not specify:
- protocols used to access the TSUs;
NOTE 1: A time-stamping protocol is defined in RFC 3161 [RFC 3161] and profiled in TS 101 861 [TS 101861]. 📝
- how the requirements identified herein may be assessed by an independent body;
- requirements for information to be made available to such independent bodies;
- requirements on such independent bodies.
NOTE 2: See CEN Workshop Agreement 14172 "EESSI Conformity Assessment Guidance" [CWA 14172]. 📚
3. Definitions and Abbreviations 💅
3.1. Definitions
okay so these are the definitions that apply everywhere in this doc, so bookmark them 🔖💖
NOTE: whenever a definition is copied from a referenced document, the reference identifier number shows up at the very end of it, so you can always trace where it came from 🧚
relying party: the recipient of a time-stamp token who relies on that token 🫶
subscriber: an entity that needs the services a TSA provides, and that has explicitly or implicitly agreed to the TSA's terms and conditions 💅
time-stamp token: a data object that binds a representation of a datum to a particular time. so it's evidence that the datum already existed before that time ✨
time-stamping authority: the authority that issues time-stamp tokens 👑
TSA Disclosure statement: a set of statements about a TSA's policies and practices that really need emphasis or disclosure to subscribers and relying parties, for example to meet regulatory requirements 📢
TSA practice statement: a statement of the practices a TSA uses when it issues time-stamp tokens 🎀
TSA system: a composition of IT products and components put together to support the provision of time-stamping services 🖥️
time-stamp policy: a named set of rules that shows where a time-stamp token applies, meaning which community and/or class of application it's for, given the common security requirements 🦋
time-stamping unit: a set of hardware and software that's managed as one unit and has a single time-stamp token signing key active at a time 🔑
Coordinated Universal Time (UTC): a time scale based on the second, as defined in ITU-R Recommendation TF.460-5 [TF.460-5] 🌍
NOTE: for most practical purposes, UTC is the same as mean solar time at the prime meridian. more specifically, UTC is a compromise between the super stable atomic time (Temps Atomique International - TAI) and solar time, which comes from the irregular Earth rotation (it's related to the Greenwich mean sidereal time (GMST) by a conventional relationship). it's a whole balancing act 🤹♀️ (see annex A for more details).
UTC(k): a time scale realized by the laboratory "k" and kept in close agreement with UTC, with the goal of reaching plus or minus 100 ns. (see ITU-R Recommendation TF.536-1 [TF.536-1]) ⏱️
NOTE: a list of UTC(k) laboratories is given in section 1 of Circular T, which BIPM disseminates and makes available from the BIPM website (http://www.bipm.org/) 🗂️
3.2. Abbreviations
for the purposes of this doc, these abbreviations apply, so you're gonna see them a lot 💕
TSA Time-Stamping Authority
TSU Time-Stamping Unit
TST Time-Stamp Token
UTC Coordinated Universal Time4. General Concepts
4.1. Time-Stamping Services
so the provision of time-stamping services gets broken down into these component services, so the requirements are easier to sort into buckets 🪣
- Time-stamping provision: this service component generates time-stamp tokens 🎀
- Time-stamping management: the service component that monitors and controls how the time-stamping services run, so the service is provided the way the TSA specified. it's also responsible for installing and de-installing the time-stamping provision service. for example, time-stamping management makes sure the clock used for time-stamping is correctly synchronized with UTC ⏰
this subdivision is only there to clarify the requirements in this doc. it doesn't put any restrictions on how anyone subdivides an implementation of time-stamping services 🧁
4.2. Time-Stamping Authority
the authority that issues time-stamp tokens, and that the users of time-stamping services trust (so subscribers and relying parties), is called the Time-Stamping Authority (TSA) 👑. the TSA has overall responsibility for the time-stamping services identified in clause 4.1. the TSA is responsible for running one or more TSUs, which create and sign on behalf of the TSA 🖊️. the TSA that's responsible for issuing a time-stamp token is identifiable (see 7.3.1 h) 🪪
the TSA may use other parties to provide parts of the Time-Stamping Services. but the TSA always keeps overall responsibility and makes sure the policy requirements in this doc are met 🫡. for example, a TSA may subcontract all of the component services, including the services that generate time-stamp tokens using the TSU's keys. even so, the private key or keys used to generate the time-stamp tokens belong to the TSA, which keeps overall responsibility for meeting the requirements in this document 🔐
a TSA may operate several identifiable time-stamping units. each unit has a different key. see Annex B for possible implementations 🧩
a TSA is a certification-service-provider, as defined in the EU Directive on Electronic Signatures (see article 2(11)), which issues time-stamp tokens 🇪🇺
4.3. Subscriber
the subscriber can be an organization made up of several end-users, or an individual end-user 🏢
when the subscriber is an organization, some of the obligations that apply to that organization will also have to apply to the end-users. either way, the organization gets held responsible if the end-users' obligations aren't correctly fulfilled, so the organization is expected to properly inform its end users 📣
when the subscriber is an end-user, that end-user gets held directly responsible if its obligations aren't correctly fulfilled 🙈
4.4. Time-Stamp Policy and TSA Practice Statement
this section explains how the time-stamp policy and the TSA practice statement relate to each other. it doesn't restrict the form that a time-stamp policy or practice statement takes 🌈
4.4.1. Purpose
basically, the time-stamp policy says "what is to be adhered to," and a TSA practice statement says "how it is adhered to". so, the processes the TSA uses to create time-stamps and to keep its clock accurate 🕰️. the relationship is kind of like business policies, which state what the business needs, while operational units work out the practices and procedures for carrying those policies out 💼
this doc specifies a time-stamp policy to meet general requirements for trusted time-stamping services. TSAs say, in their TSA practice statements, how those requirements get met 💖
4.4.2. Level of Specificity
the TSA practice statement is more specific than a time-stamp policy. it's a more detailed description of the terms and conditions, plus the business and operational practices a TSA uses when it issues and otherwise manages time-stamping services 🔍. the TSA practice statement enforces the rules the time-stamp policy sets up. it also defines how a specific TSA meets the technical, organizational and procedural requirements in a time-stamp policy 📋
NOTE: a TSA might even need lower-level internal documentation that details the specific procedures it takes to complete the practices in its TSA practice statement 🗒️
4.4.3. Approach
the approach of a time-stamp policy is really different from a TSA practice statement. a time-stamp policy is defined independently of the specific details of a TSA's operating environment, whereas a TSA practice statement is tailored to the TSA's organizational structure, operating procedures, facilities, and computing environment 🏗️. a time-stamp policy may be defined by the user of times-stamp services, but the TSA practice statement is always defined by the provider 🫶
5. Time-Stamp Policies
5.1. Overview
a time-stamp policy is a "named set of rules that indicates the applicability of a time-stamp token to a particular community and/or class of application with common security requirements" (see clauses 3.1 and 4.4) 📖
this doc defines requirements for a baseline time-stamp policy for TSAs issuing time-stamp tokens, supported by public key certificates, with an accuracy of 1 second or better ⏳
NOTE 1: without additional measures, the relying party might not be able to make sure a time-stamp token is valid past the end of the validity period of the supporting certificate. see Annex C on verifying the validity of a time-stamp token beyond the validity period of the TSU's certificate 🧐
a TSA may define its own policy that enhances the policy defined in this doc. such a policy shall incorporate or further constrain the requirements identified in this doc 🛠️
if a TSA provides an accuracy of better than 1 second, and all the TSUs have that same characteristic, then the accuracy shall be indicated in the TSA's disclosure statement (see section 7.1.2) saying that each time-stamp token is issued with an accuracy of better than 1 second 🎯
NOTE 2: it is required that a time-stamp token includes an identifier for the applicable policy (see section 7.3.1) 🪪
5.2. Identification
the object-identifier [X.208] of the baseline time-stamp policy is the following 🔢
itu-t(0) identified-organization(4) etsi(0) time-stamp-policy(2023)
policy-identifiers(1) baseline-ts-policy (1)in the TSA disclosure statement that's made available to subscribers and relying parties, a TSA shall also include the identifier for the time-stamp policy, to show its conformance ✅
5.3. User Community and Applicability
this policy is aimed at meeting the requirements of time-stamping qualified electronic signatures (see European Directive on Electronic Signatures) for long term validity (e.g., as defined in TS 101 733 [TS 101733]). but it's generally applicable to any requirement for an equivalent quality 💜
this policy may be used for public time-stamping services, or for time-stamping services used within a closed community 🌸
5.4. Conformance
the TSA shall use the identifier for the time-stamp policy in time-stamp tokens, as given in section 5.2. or it can define its own time-stamp policy that incorporates or further constrains the requirements in this doc, if either of these is true 📝
a) the TSA claims conformance to the identified time-stamp policy and makes the evidence that supports that claim available to subscribers and relying parties on request; or
b) the TSA has been assessed to conform to the identified time-stamp policy by an independent party.
a conformant TSA must demonstrate that:
a) it meets its obligations as defined in section 6.1;
b) it has implemented controls which meet the requirements specified in section 7.
6. Obligations and Liability
6.1. TSA Obligations
6.1.1. General
the TSA shall ensure that all requirements on the TSA, as detailed in section 7, are implemented as applicable to the selected trusted time-stamp policy 🦋
the TSA shall ensure conformance with the procedures prescribed in this policy, even when the TSA functionality is undertaken by sub-contractors 🤝
the TSA shall also ensure adherence to any additional obligations indicated in the time-stamp, either directly or incorporated by reference 🎀
the TSA shall provide all of its time-stamping services consistent with its practice statement 💅
6.1.2. TSA Obligations Towards Subscribers
okay so the TSA shall meet every claim it makes in its terms and conditions, including how available and how accurate its service is 🎀✨. no sneaky promises, bestie!
6.2. Subscriber Obligations
the current document doesn't put any specific obligations on the subscriber 💅 beyond whatever TSA-specific requirements are written in the TSA's terms and conditions 📜.
NOTE: It is advisable that, when obtaining a time-stamp token, the subscriber verifies that the time-stamp token has been correctly signed and that the private key used to sign the time-stamp token has not been compromised. 🙈🫶
6.3. Relying Party Obligations
the terms and conditions given to relying parties (see section 7.1.2) shall include an obligation on the relying party 🦋. when a relying party is relying on a time-stamp token, it shall:
- a) verify that the time-stamp token has been correctly signed, and that the private key used to sign the time-stamp has not been compromised until the time of the verification 🔐;
NOTE: During the TSU's certificate validity period, the validity of the signing key can be checked using current revocation status for the TSU's certificate. If the time of verification exceeds the end of the validity period of the corresponding certificate, see annex C for guidance. 🧚
- b) take into account any limitations on the usage of the time-stamp indicated by the time-stamp policy 📌;
- c) take into account any other precautions prescribed in agreements or elsewhere 💜.
6.4. Liability
this document doesn't specify any requirement on liability 🙃. the important bit is that a TSA may disclaim or limit any liability, unless the applicable law says otherwise ⚖️. it should be noticed, bestie 👀.
7. Requirements on TSA Practices
the TSA shall implement the controls that meet the following requirements 🔥.
these policy requirements are not meant to imply any restrictions on charging for TSA services 💸.
the requirements are written in terms of security objectives, followed by more specific requirements for controls to meet those objectives wherever it's needed to give confidence that those objectives will be met 🌸.
NOTE: The details of controls required to meet an objective is a balance between achieving the necessary confidence whilst minimizing the restrictions on the techniques that a TSA may employ in issuing time-stamp tokens. In the case of section 7.4 (TSA management and operation), a reference is made to a source of more detailed control requirements. Due to these factors the specificity of the requirements given under a given topic may vary. 🧠
providing a time-stamp token in response to a request is at the discretion of the TSA, depending on any service level agreements with the subscriber 🎀.
7.1. Practice and Disclosure Statements
7.1.1. TSA Practice Statement
the TSA shall ensure that it demonstrates the reliability necessary for providing time-stamping services ✨.
in particular:
- a) The TSA shall have a risk assessment carried out in order to evaluate business assets and threats to those assets, so it can determine the necessary security controls and operational procedures 🛡️.
- b) The TSA shall have a statement of the practices and procedures used to address all the requirements identified in this time-stamp policy 📝.
NOTE 1: This policy makes no requirement as to the structure of the TSA practice statement. 🌈
- c) The TSA's practice statement shall identify the obligations of all external organizations supporting the TSA services, including the applicable policies and practices 🤝.
- d) The TSA shall make available to subscribers and relying parties its practice statement, and other relevant documentation as necessary, to assess conformance to the time-stamp policy 👀.
NOTE 2: The TSA is not generally required to make all the details of its practices public. 🙈
- e) The TSA shall disclose to all subscribers and potential relying parties the terms and conditions regarding use of its time-stamping services, as specified in section 7.1.2 💌.
- f) The TSA shall have a high level management body with final authority for approving the TSA practice statement 👑.
- g) The senior management of the TSA shall ensure that the practices are properly implemented 💼.
- h) The TSA shall define a review process for the practices, including responsibilities for maintaining the TSA practice statement 🔁.
- i) The TSA shall give due notice of changes it intends to make in its practice statement and, following approval as in (f) above, shall make the revised TSA practice statement immediately available as required under (d) above 📣.
7.1.2. TSA Disclosure Statement
the TSA shall disclose to all subscribers and potential relying parties the terms and conditions regarding use of its time-stamping services 🫶. this statement shall at least specify, for each time-stamp policy supported by the TSA:
- a) The TSA contact information 📞.
- b) The time-stamp policy being applied 📜.
- c) At least one hashing algorithm which may be used to represent the datum being time-stamped. (No hash algorithm is mandated.) 🍓
- d) The expected life-time of the signature used to sign the time-stamp token. (This depends on the hashing algorithm being used, the signature algorithm being used and the private key length.) ⏳
- e) The accuracy of the time in the time-stamp tokens with respect to UTC 🕐.
- f) Any limitations on the use of the time-stamping service 🚧.
- g) The subscriber's obligations as defined in section 6.2, if any 🧾.
- h) The relying party's obligations as defined in section 6.3 🧾.
- i) Information on how to verify the time-stamp token, such that the relying party is considered to "reasonably rely" on the time-stamp token (see section 6.3), and any possible limitations on the validity period 🔍.
- j) The period of time during which TSA event logs (see section 7.4.10) are retained 🗂️.
- k) The applicable legal system, including any claim to meet the requirements on time-stamping services under national law 🏛️.
- l) Limitations of liability 🙃.
- m) Procedures for complaints and dispute settlement 🤝.
- n) If the TSA has been assessed to be conformant with the identified time-stamp policy, and if so, by which independent body 🏅.
NOTE 1: It is also recommended that the TSA includes in its time-stamping disclosure statement the availability of its service, for example the expected mean time between failure of the time-stamping service, the mean time to recovery following a failure, and provisions made for disaster recovery, including back-up services. 🛟
This information shall be available through a durable means of communication. This information shall be available in a readily understandable language. It may be transmitted electronically 💖.
NOTE 2: A model TSA disclosure statement which may be used as the basis of such a communication is given in annex D. Alternatively, this may be provided as part of a subscriber / relying party agreement. These TSA disclosure statements may be included in a TSA practice statement provided that they are conspicuous to the reader. 🦋
7.2. Key Management Life Cycle
7.2.1. TSA Key Generation
the TSA shall ensure that any cryptographic keys are generated under controlled circumstances 🔐✨.
in particular:
- a) The generation of the TSU's signing key(s) shall be undertaken in a physically secured environment (see section 7.4.4) by personnel in trusted roles (see section 7.4.3) under, at least, dual control. The personnel authorized to carry out this function shall be limited to those requiring to do so under the TSA's practices 👯♀️.
- b) The generation of the TSU's signing key(s) shall be carried out within a cryptographic module(s) which either:
- meets the requirements identified in FIPS 140-1 [FIPS 140-1] level 3 or higher, or
- meets the requirements identified in CEN Workshop Agreement 14167-2 [CWA 14167-2], or
- is a trustworthy system which is assured to EAL 4 or higher in accordance to ISO 15408 [ISO 15408], or equivalent security criteria. This shall be to a security target or protection profile which meets the requirements of the current document, based on a risk analysis and taking into account physical and other non-technical security measures. 🛡️
- c) The TSU key generation algorithm, the resulting signing key length, and the signature algorithm used for signing time-stamp tokens key shall be recognized by any national supervisory body, or in accordance with existing current state of the art, as being fit for the purposes of time-stamp tokens as issued by the TSA 🏅.
7.2.2. TSU Private Key Protection
the TSA shall ensure that TSU private keys remain confidential and maintain their integrity 🤫💜.
in particular:
- a) The TSU private signing key shall be held and used within a cryptographic module which:
- meets the requirements identified in FIPS 140-1 [FIPS 140-1] level 3 or higher; or
- meets the requirements identified in CEN Workshop Agreement 14167-2 [CWA 14167-2]; or
- is a trustworthy system which is assured to EAL 4 or higher in accordance to ISO 15408 [ISO 15408], or equivalent security criteria. This shall be a security target or protection profile which meets the requirements of the current document, based on a risk analysis and taking into account physical and other non-technical security measures.
NOTE: Backup of TSU private keys is deprecated in order to minimize risk of key compromise. 🚨
- b) If TSU private keys are backed up, they shall be copied, stored, and recovered only by personnel in trusted roles, using, at least, dual control, in a physically secured environment (see section 7.4.4). The personnel authorized to carry out this function shall be limited to those requiring to do so under the TSA's practices 🗝️.
- c) Any backup copies of the TSU private signing keys shall be protected to ensure their confidentiality by the cryptographic module before being stored outside that device 🔒.
7.2.3. TSU Public Key Distribution
the TSA shall ensure that the integrity and authenticity of the TSU signature verification (public) keys and any associated parameters are maintained during their distribution to relying parties 📬🌈.
in particular:
- a) TSU signature verification (public) keys shall be made available to relying parties in a public key certificate 📄.
NOTE: For example, TSU's certificates may be issued by a certification authority operated by the same organization as the TSA, or issued by another authority. 🧚
- b) The TSU's signature verification (public) key certificate shall be issued by a certification authority operating under a certificate policy which provides a level of security equivalent to, or higher than, this time-stamping policy 🦋👑.
7.2.4. Rekeying TSU's Key ✨
okay bestie, this one's about how long a TSU's certificate is allowed to live 🎀 The life-time of the TSU's certificate shall be no longer than the period of time that the chosen algorithm and key length is recognized as being fit for purpose (see section 7.2.1c)) 💅
NOTE 1: The following additional considerations apply when limiting that lifetime:
- Section 7.4.10 requires that records concerning time-stamping services shall be held for a period of time, as appropriate, for at least 1 year after the expiration of the validity of the TSU's signing keys. The longer the validity period of the TSU certificates will be, the longer the size of the records to be kept will be. 📚
- Should a TSU private key be compromised, then the longer the life-time, the more affected time-stamp tokens there will be. 😭
NOTE 2: TSU key compromise does not only depend on the characteristics of the cryptographic module being used but also on the procedures being used at system initialization and key export (when that function is supported). 🔐
7.2.5. End of TSU Key Life Cycle 🕰️
the TSA shall ensure that TSU private signing keys are not used beyond the end of their life cycle. no cap, this is a hard line 🙅♀️
in particular:
- a) Operational or technical procedures shall be in place to ensure that a new key is put in place when a TSU's key expires. 🔄
- b) The TSU private signing keys, or any key part, including any copies shall be destroyed such that the private keys cannot be retrieved. 💀
- c) The TST generation system SHALL reject any attempt to issue TSTs if the signing private key has expired. 🚫
7.2.6. Life Cycle Management of the Cryptographic Module used to Sign Time-Stamps 🔧
the TSA shall ensure the security of cryptographic hardware throughout its lifecycle. it's giving "protect the hardware from start to finish" 🧚
in particular the TSA shall ensure that:
- a) Time-stamp token signing cryptographic hardware is not tampered with during shipment; 📦
- b) Time-stamp token signing cryptographic hardware is not tampered with while stored; 🗄️
- c) Installation, activation and duplication of TSU's signing keys in cryptographic hardware shall be done only by personnel in trusted roles using, at least, dual control in a physically secured environment. (see section 7.4.4); 👯
- d) Time-stamp token signing cryptographic hardware is functioning correctly; and ✅
- e) TSU private signing keys stored on TSU cryptographic module are erased upon device retirement. 🗑️
7.3. Time-Stamping ⏰
7.3.1. Time-Stamp Token 🎫
the TSA shall ensure that time-stamp tokens are issued securely and include the correct time. this is the core vibe of the whole thing 👑
in particular:
- a) The time-stamp token shall include an identifier for the time-stamp policy; 🏷️
- b) Each time-stamp token shall have a unique identifier; 🆔
- c) The time values the TSU uses in the time-stamp token shall be traceable to at least one of the real time values distributed by a UTC(k) laboratory.
NOTE 1: The Bureau International des Poids et Mesures (BIPM) computes UTC on the basis of its local representations UTC(k) from a large ensemble of atomic clocks in national metrology institutes and national astronomical observatories round the world. The BIPM disseminates UTC through its monthly Circular T [list 1]. This is available on the BIPM website (www.bipm.org) and it officially identifies all those institutes having recognized UTC(k) time scales. 🌍
- d) The time included in the time-stamp token shall be synchronized with UTC within the accuracy defined in this policy and, if present, within the accuracy defined in the time-stamp token itself; ⌚
- e) If the time-stamp provider's clock is detected (see section 7.3.2c)) as being out of the stated accuracy (see section 7.1.2e)) then time-stamp tokens shall not be issued. 🙅♀️
- f) The time-stamp token shall include a representation (e.g., hash value) of the datum being time-stamped as provided by the requestor; 🔏
- g) The time-stamp token shall be signed using a key generated exclusively for this purpose.
NOTE 2: A protocol for a time-stamp token is defined in RFC 3631 and profiled in TS 101 861 [TS 101861].
NOTE 3: In the case of a number of requests at approximately the same time, the ordering of the time within the accuracy of the TSU clock is not mandated. 🤷♀️
- h) The time-stamp token shall include:
- where applicable, an identifier for the country in which the TSA is established; 🌏
- an identifier for the TSA; 🏢
- an identifier for the unit which issues the time-stamps. 🧾
7.3.2. Clock Synchronization with UTC 🕐
the TSA shall ensure that its clock is synchronized with UTC within the declared accuracy. keeping the clock honest is everything 🫶
in particular:
- a) The calibration of the TSU clocks shall be maintained such that the clocks shall not be expected to drift outside the declared accuracy. 🎯
- b) The TSU clocks shall be protected against threats which could result in an undetected change to the clock that takes it outside its calibration.
NOTE 1: Threats may include tampering by unauthorized personnel, radio or electrical shocks. ⚡
- c) The TSA shall ensure that, if the time that would be indicated in a time-stamp token drifts or jumps out of synchronization with UTC, this will be detected (see also 7.3.1e)).
NOTE 2: Relying parties are required to be informed of such events (see section 7.4.8). 📣
- d) The TSA shall ensure that clock synchronization is maintained when a leap second occurs as notified by the appropriate body. The change to take account of the leap second shall occur during the last minute of the day when the leap second is scheduled to occur. A record shall be maintained of the exact time (within the declared accuracy) when this change occurred. See annex A for more details. 🕛
NOTE 3: A leap second is an adjustment to UTC by skipping or adding an extra second on the last second of a UTC month. First preference is given to the end of December and June, and second preference is given to the end of March and September. 🌙
7.4. TSA Management and Operation 🏛️
7.4.1. Security Management 🔐
the TSA shall ensure that the administrative and management procedures applied are adequate and correspond to recognized best practice. main character energy for the whole org 💅
in particular:
TSA General
- a) The TSA shall retain responsibility for all aspects of the provision of time-stamping services within the scope of this time-stamp policy, whether or not functions are outsourced to subcontractors. Responsibilities of third parties shall be clearly defined by the TSA and appropriate arrangements made to ensure that third parties are bound to implement any controls required by the TSA. The TSA shall retain responsibility for the disclosure of relevant practices of all parties. 🤝
- b) The TSA management shall provide direction on information security through a suitable high level steering forum that is responsible for defining the TSA's information security policy. The TSA shall ensure publication and communication of this policy to all employees who are impacted by it. 📢
- c) The information security infrastructure necessary to manage the security within the TSA shall be maintained at all times. Any changes that will impact on the level of security provided shall be approved by the TSA management forum.
NOTE 1: See ISO/IEC 17799 [ISO 17799] for guidance on information security management including information security infrastructure, management information security forum and information security policies. 📖
- d) The security controls and operating procedures for TSA facilities, systems and information assets providing the time-stamping services shall be documented, implemented and maintained.
NOTE 2: The present documentation (commonly called a system security policy or manual) should identify all relevant targets, objects and potential threats related to the services provided and the safeguards required to avoid or limit the effects of those threats, consistent with the Risk Assessment required under section 7.1.1a). It should describe the rules, directives and procedures regarding how the specified services and the associated security assurance are granted in addition to stating policy on incidents and disasters. 🗂️
- e) TSA shall ensure that the security of information is maintained when the responsibility for TSA functions has been outsourced to another organization or entity. 🧳
7.4.2. Asset Classification and Management 🗃️
the TSA shall ensure that its information and other assets receive an appropriate level of protection. every asset gets a label, period 🏷️
in particular:
- The TSA shall maintain an inventory of all assets and shall assign a classification for the protection requirements to those assets consistent with the risk analysis. 📋
7.4.3. Personnel Security ✨
Okay so, this is the part where the TSA gets its people in order, bestie 💅 The whole point is that personnel and hiring practices should enhance and support the trustworthiness of the TSA's operations. No cap, the people are the trust 🫶
In particular (TSA general):
a) The TSA MUST employ personnel who have the expert knowledge, experience and qualifications needed for the services offered and for their job function. Literally the bare minimum, but make it count 🧚
NOTE 1: TSA personnel can meet the "expert knowledge, experience and qualifications" bar through formal training and credentials, real hands-on experience, or a mix of both 🎀
NOTE 2: Personnel employed by a TSA include individuals who are contractually engaged to perform functions supporting the TSA's time-stamping services. Anyone who helps monitor the TSA services doesn't have to be TSA personnel though 🦋
b) Security roles and responsibilities, as laid out in the TSA's security policy, MUST be written down in job descriptions. Trusted roles, the ones the TSA's security depends on, MUST be clearly identified 🔥
c) TSA personnel (temporary and permanent alike) MUST have job descriptions defined from the view point of separation of duties and least privilege. Position sensitivity is determined by duties and access levels, plus background screening and employee training and awareness 🌸 Where it makes sense, these SHOULD differentiate between general functions and TSA-specific functions. These SHOULD also include skills and experience requirements 💜
d) Personnel MUST carry out administrative and management procedures and processes that line up with the TSA's information security management procedures (see section 7.4.1) 🍓
NOTE 3: See ISO/IEC 17799 [ISO 17799] for guidance.
The following additional controls MUST be applied to time-stamping management:
e) Managerial personnel MUST be employed who possess:
- knowledge of time-stamping technology; and
- knowledge of digital signature technology; and
- knowledge of mechanisms for calibration or synchronization of the TSU clocks with UTC; and
- familiarity with security procedures for personnel with security responsibilities; and
- experience with information security and risk assessment.
f) All TSA personnel in trusted roles MUST be free from any conflict of interest that might prejudice the impartiality of the TSA operations 🫧
g) Trusted roles include roles with the following responsibilities:
- Security Officers: Overall responsibility for administering the implementation of the security practices. 👑
- System Administrators: Authorized to install, configure and maintain the TSA trustworthy systems for time-stamping management. 🛠️
- System Operators: Responsible for operating the TSA trustworthy systems on a day-to-day basis. Authorized to perform system backup and recovery. 🌈
- System Auditors: Authorized to view archives and audit logs of the TSA trustworthy systems. 🔍
h) TSA personnel MUST be formally appointed to trusted roles by senior management responsible for security. Official appointment energy 🎀
i) The TSA MUST NOT appoint to trusted roles or management any person who is known to have a conviction for a serious crime or other offense that affects their suitability for the position. Personnel MUST NOT have access to the trusted functions until any necessary checks are completed. Background checks first, access second, always 🙅♀️
NOTE 4: In some countries it may not be possible for the TSA to get information on past convictions without the collaboration of the candidate employee. So that's a real-world wrinkle 🌍
7.4.4. Physical and Environmental Security 🏰
The TSA MUST make sure physical access to critical services is controlled and that physical risks to its assets are minimized. Locks, walls, and no random visitors 🔐
In particular (general):
a) For both the time-stamping provision and the time-stamping management:
- physical access to facilities concerned with time-stamping services MUST be limited to properly authorized individuals;
- controls MUST be implemented to avoid loss, damage or compromise of assets and interruption to business activities; and
- controls MUST be implemented to avoid compromise or theft of information and information processing facilities.
b) Access controls MUST be applied to the cryptographic module to meet the requirements of security of cryptographic modules as identified in clauses 7.2.1 and 7.2.2 🔑
c) The following additional controls MUST be applied to time-stamping management:
- The time-stamping management facilities MUST be operated in an environment which physically protects the services from compromise through unauthorized access to systems or data. 🛡️
- Physical protection MUST be achieved through the creation of clearly defined security perimeters (i.e., physical barriers) around the time-stamping management. Any parts of the premises shared with other organizations MUST be outside this perimeter. 🧱
- Physical and environmental security controls MUST be implemented to protect the facility that houses system resources, the system resources themselves, and the facilities used to support their operation. The TSA's physical and environmental security policy for systems concerned with time-stamping management MUST address, as a minimum, physical access control, natural disaster protection, fire safety factors, failure of supporting utilities (e.g., power, telecommunications), structure collapse, plumbing leaks, protection against theft, breaking and entering, and disaster recovery. ⚡🔥💧
- Controls MUST be implemented to protect against equipment, information, media and software relating to the time-stamping services being taken off-site without authorization. 📦
NOTE 1: See ISO/IEC 17799 [ISO 17799] for guidance on physical and environmental security.
NOTE 2: Other functions may be supported within the same secured area provided that the access is limited to authorized personnel. 🙌
7.4.5. Operations Management ⚙️
The TSA MUST make sure the TSA system components are secure and correctly operated, with minimal risk of failure:
In particular (general):
a) The integrity of TSA system components and information MUST be protected against viruses, malicious and unauthorized software. 🦠🚫
b) Incident reporting and response procedures MUST be employed in such a way that damage from security incidents and malfunctions is minimized. 🚨
c) Media used within the TSA trustworthy systems MUST be securely handled to protect media from damage, theft, unauthorized access and obsolescence. 💾
NOTE 1: Every member of personnel with management responsibilities is responsible for planning and effectively implementing the time-stamp policy and associated practices as documented in the TSA practice statement. Everyone with a management role owns this 💜
d) Procedures MUST be established and implemented for all trusted and administrative roles that impact the provision of time-stamping services. 📋
Media handling and security
e) All media MUST be handled securely in accordance with the requirements of the information classification scheme (see section 7.4.2). Media containing sensitive data MUST be securely disposed of when no longer required. 🗑️
System Planning
f) Capacity demands MUST be monitored, and projections of future capacity requirements MUST be made to ensure that adequate processing power and storage are available. 📈
Incident reporting and response
g) The TSA MUST act in a timely and coordinated manner in order to respond quickly to incidents and to limit the impact of breaches of security. All incidents MUST be reported as soon as possible after the incident. 🏃♀️💨
The following additional controls MUST be applied to time-stamping management:
Operations procedures and responsibilities
h) TSA security operations MUST be separated from other operations. 🧱
NOTE 2: TSA security operations' responsibilities include:
- operational procedures and responsibilities;
- secure systems planning and acceptance;
- protection from malicious software;
- housekeeping;
- network management;
- active monitoring of audit journals, event analysis and follow-up;
- media handling and security;
- data and software exchange.
These operations MUST be managed by TSA trusted personnel, but MAY actually be performed by non-specialist, operational personnel (under supervision), as defined within the appropriate security policy, and roles and responsibility documents. Supervised helpers can run the day-to-day stuff 🫶
7.4.6. System Access Management 🔐
The TSA MUST make sure TSA system access is limited to properly authorized individuals. Only the right people get the keys 🗝️
In particular (general):
a) Controls (e.g., firewalls) MUST be implemented to protect the TSA's internal network domains from unauthorized access, including access by subscribers and third parties. 🔥
NOTE 1: Firewalls SHOULD also be configured to prevent all protocols and accesses not required for the operation of the TSA. 🧱
b) The TSA MUST ensure effective administration of user access (this includes operators, administrators and auditors) to maintain system security, including user account management, auditing and timely modification or removal of access. 📝
c) The TSA MUST ensure that access to information and application system functions is restricted in accordance with the access control policy, and that the TSA system provides sufficient computer security controls for the separation of trusted roles identified in the TSA's practices, including the separation of security administrator and operation functions. In particular, use of system utility programs MUST be restricted and tightly controlled. 🎀
d) TSA personnel MUST be properly identified and authenticated before using critical applications related to time-stamping. 🪪
e) TSA personnel MUST be accountable for their activities, for example by retaining event logs (see section 7.4.10). 📒
The following additional controls MUST be applied to time-stamping management:
f) The TSA MUST ensure that local network components (e.g., routers) are kept in a physically secure environment and that their configurations are periodically audited for compliance with the requirements specified by the TSA. 🛣️
g) Continuous monitoring and alarm facilities MUST be provided to enable the TSA to detect, register and react in a timely manner upon any unauthorized and/or irregular attempts to access its resources. 🚨👀
NOTE 2: This may use, for example, an intrusion detection system, access control monitoring and alarm facilities. 🕵️♀️
7.4.7. Trustworthy Systems Deployment and Maintenance ✨
okay so the TSA shall use trustworthy systems and products that are protected against modification 🔒 no sneaky edits allowed, bestie 💅
NOTE: The risk analysis carried out on the TSA's services (see section 7.1.1) should identify its critical services requiring trustworthy systems and the levels of assurance required.
In particular:
- a) An analysis of security requirements shall be carried out at the design and requirements specification stage of any systems development project undertaken by the TSA or on behalf of the TSA to ensure that security is built into IT systems. 🧚
- b) Change control procedures shall be applied for releases, modifications and emergency software fixes of any operational software. 🎀
7.4.8. Compromise of TSA Services
the TSA shall make sure that if something happens that affects the security of its services 😭 like a compromise of a TSU's private signing keys or a detected loss of calibration, the relevant information gets made available to subscribers and relying parties. it's giving transparency 🫶
In particular:
- a) The TSA's disaster recovery plan shall address the compromise or suspected compromise of TSU's private signing keys or loss of calibration of a TSU clock, which may have affected time-stamp tokens which have been issued. 🚨
- b) In the case of a compromise, or suspected compromise or loss of calibration the TSA shall make available to all subscribers and relying parties a description of compromise that occurred. 📣
- c) In the case of compromise to a TSU's operation (e.g., TSU key compromise), suspected compromise or loss of calibration the TSU shall not issue time-stamp tokens until steps are taken to recover from the compromise 🛑
- d) In case of major compromise of the TSA's operation or loss of calibration, wherever possible, the TSA shall make available to all subscribers and relying parties information which may be used to identify the time-stamp tokens which may have been affected, unless this breaches the privacy of the TSAs users or the security of the TSA services. 🕵️♀️
NOTE: In case the private key does become compromised, an audit trail of all tokens generated by the TSA may provide a means to discriminate between genuine and false backdated tokens. Two time-stamp tokens from two different TSAs may be another way to address this issue. 🔍
7.4.9. TSA Termination
the TSA shall make sure that potential disruptions to subscribers and relying parties are minimized when it stops its time-stamping services 🌸 and especially that the info needed to verify the correctness of time-stamp tokens keeps getting maintained. no one left hanging 🫶
In particular:
- a) Before the TSA terminates its time-stamping services the following procedures shall be executed as a minimum:
- the TSA shall make available to all subscribers and relying parties information concerning its termination;
- TSA shall terminate authorization of all subcontractors to act on behalf of the TSA in carrying out any functions relating to the process of issuing time-stamp tokens;
- the TSA shall transfer obligations to a reliable party for maintaining event log and audit archives (see section 7.4.10) necessary to demonstrate the correct operation of the TSA for a reasonable period;
- the TSA shall maintain or transfer to a reliable party its obligations to make available its public key or its certificates to relying parties for a reasonable period;
- TSU private keys, including backup copies, shall be destroyed in a manner such that the private keys cannot be retrieved. 💀
- b) The TSA shall have an arrangement to cover the costs to fulfill these minimum requirements in case the TSA becomes bankrupt or for other reasons is unable to cover the costs by itself. 💸
- c) The TSA shall state in its practices the provisions made for termination of service. This shall include:
- notification of affected entities;
- transferring the TSA obligations to other parties.
- d) The TSA shall take steps to have the TSU's certificates revoked. 🙅♀️
7.4.10. Compliance with Legal Requirements
the TSA shall ensure compliance with legal requirements ⚖️ no shortcuts, periodt.
In particular:
- a) The TSA shall ensure that the requirements of the European data protection Directive [Dir 95/46/EC], as implemented through national legislation, are met. 🇪🇺
- b) Appropriate technical and organizational measures shall be taken against unauthorized or unlawful processing of personal data and against accidental loss or destruction of, or damage to, personal data. 🔐
- c) The information contributed by users to the TSA shall be completely protected from disclosure unless with their agreement or by court order or other legal requirement. 🤫
7.4.11. Recording of Information Concerning Operation of Time-Stamping Services
the TSA shall make sure all the relevant info about how the time-stamping services run gets recorded for a defined period of time 📝 especially as evidence for legal proceedings. receipts, bestie 🧾
In particular:
General
- a) The specific events and data to be logged shall be documented by the TSA. 📋
- b) The confidentiality and integrity of current and archived records concerning operation of time-stamping services shall be maintained. 🛡️
- c) Records concerning the operation of time-stamping services shall be completely and confidentially archived in accordance with disclosed business practices. 🗄️
- d) Records concerning the operation of time-stamping services shall be made available if required for the purposes of providing evidence of the correct operation of the time-stamping services for the purpose of legal proceedings. ⚖️
- e) The precise time of significant TSA environmental, key management and clock synchronization events shall be recorded. ⏰
- f) Records concerning time-stamping services shall be held for a period of time after the expiration of the validity of the TSU's signing keys as appropriate for providing necessary legal evidence and as notified in the TSA disclosure statement (see section 7.1.2). 📆
- g) The events shall be logged in a way that they cannot be easily deleted or destroyed (except if reliably transferred to long-term media) within the period of time that they are required to be held. 🔒
NOTE: This may be achieved, for example, through the use of write-only media, a record of each removable media used and the use of off-site backup.
- h) Any information recorded about subscribers shall be kept confidential except as where agreement is obtained from the subscriber for its wider publication. 🙈
TSU key management
- i) Records concerning all events relating to the life-cycle of TSU keys shall be logged. 🔑
- j) Records concerning all events relating to the life-cycle of TSU certificates (if appropriate) shall be logged. 📜
Clock Synchronization
- k) Records concerning all events relating to synchronization of a TSU's clock to UTC shall be logged. This shall include information concerning normal re-calibration or synchronization of clocks use in time-stamping. 🕰️
- l) Records concerning all events relating to detection of loss of synchronization shall be logged. 🚩
7.5. Organizational
the TSA shall make sure its organization is reliable 👑 it's giving stable, trustworthy queen energy.
In particular that:
- a) Policies and procedures under which the TSA operates shall be non-discriminatory. 🌈
- b) The TSA shall make its services accessible to all applicants whose activities fall within its declared field of operation and that agree to abide by their obligations as specified in the TSA disclosure statement. 🚪
- c) The TSA is a legal entity according to national law. 🏛️
- d) The TSA has a system or systems for quality and information security management appropriate for the time-stamping services it is providing. ✅
- e) The TSA has adequate arrangements to cover liabilities arising from its operations and/or activities. 🧯
- f) It has the financial stability and resources required to operate in conformity with this policy.
NOTE 1: This includes requirements for TSA termination identified in section 7.4.9.
- g) It employs a sufficient number of personnel having the necessary education, training, technical knowledge and experience relating to the type, range and volume of work necessary to provide time-stamping services.
NOTE 2: Personnel employed by a TSA include individual personnel contractually engaged in performing functions in support of the TSA's time-stamping services. Personnel who may be involved only in monitoring the TSA services need not be TSA personnel.
- h) It has policies and procedures for the resolution of complaints and disputes received from customers or other parties about the provisioning of the time-stamping services or any other related matters. 🗣️
- i) It has a properly documented agreement and contractual relationship in place where the provisioning of services involves subcontracting, outsourcing or other third party arrangements. 📑
8. Security Considerations 🔐
⚠️ Big security moment, bestie. Read this part carefully. ⚠️
When verifying time-stamp tokens it is necessary for the verifier to ensure that the TSU certificate is trusted and not revoked. This means that the security is dependent upon the security of the CA that has issued the TSU certificate for both issuing the certificate and providing accurate revocation status information for that certificate.
When a time-stamp is verified as valid at a given point of time, this does not mean that it will necessarily remain valid later on. Every time, a time-stamp token is verified during the validity period of the TSU certificate, it must be verified again against the current revocation status information, since in case of compromise of a TSU private key, all the time-stamp tokens generated by that TSU become invalid. Annex C provides guidance about the long term verification of time-stamp tokens. 🕰️
In applying time-stamping to applications, consideration also needs to be given to the security of the application. In particular, when applying time-stamps it is necessary to ensure that the integrity of data is maintained before the time-stamp is applied. The requester ought to really make sure that the hash value included in the time-stamp token matches with the hash of the data. 🧮
9. Acknowledgments 🌷
The development of this document was supported by ETSI and the European Commission. Special thanks are due to Franco Ruggieri for his valuable inputs. 🫶
10. References 📚
10.1. Normative References
- [RFC 2119] Bradner, S. "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
- [TF.460-5] ITU-R Recommendation TF.460-5 (1997): Standard-frequency and time-signal emissions.
- [TF.536-1] ITU-R Recommendation TF.536-1 (1998): Time-scale notations.
- [CWA 14167-2] CEN Workshop Agreement 14167-2: Cryptographic Module for CSP Signing Operations - Protection Profile (MCSO-PP).
- [FIPS 140-1] FIPS PUB 140-1 (1994): Security Requirements for Cryptographic Modules.
- [ISO 15408] ISO/IEC 15408 (1999) (parts 1 to 3): Information technology - Security techniques and Evaluation criteria for IT security.
10.2. Informative References ✨
Okay, time for the bibliography bestie 📚 These are the extra reads that back up the spec. They're not required reading, but they're worth a look 💅
[CWA 14172] CEN Workshop Agreement 14172: EESSI Conformity
Assessment Guidance.
[Dir 95/46/EC] Directive 95/46/EC of the European Parliament and of
the Council of 24 October 1995 on the protection of
individuals with regard to the processing of personal
data and on the free movement of such data.
[Dir 99/93/EC] Directive 1999/93/EC of the European Parliament and of
the Council of 13 December 1999 on a Community
framework for electronic signatures.
[ISO 17799] ISO/IEC 17799: Information technology Code of practice
for information security management
[RFC 3126] Pinkas, D., Ross, J. and N. Pope, "Electronic
Signature Formats for long term electronic
signatures", RFC 3126, September 2001.
[RFC 3161] Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, August 2001.
[TS 101733] ETSI Technical Specification 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.
[TS 101861] ETSI Technical Specification TS 101 861 V1.2.1.
(2001-11). Time stamping profile. Note: copies of
ETSI TS 101 861 can be freely downloaded from the ETSI
web site www.etsi.org.
[TS 102023] ETSI Technical Specification TS 102 023. Policy
requirements for Time-Stamping Authorities. Note:
copies of ETSI TS 102 023 can be freely downloaded
from the ETSI web site www.etsi.org.
[X.208] CCITT Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.Annex A (informative): Coordinated Universal Time 🕰️
Okay so, Coordinated Universal Time (UTC) is the international time standard that kicked in on January 1, 1972 🌍 It replaced Greenwich Mean Time (GMT), but in practice they're never more than 1 second apart, so tons of people still say GMT when they're really using UTC 🙈 Iykyk.
Zero (0) hours UTC is midnight in Greenwich, England, which sits on the zero longitudinal meridian 🧚 Universal time runs on a 24 hour clock, so something like 4 pm UTC is written as 16:00 UTC (sixteen hours, zero minutes). Literally the most iconic format ✨
International Atomic Time (TAI) is calculated by the Bureau International des Poids et Mesures (BIPM) using readings from more than 200 atomic clocks spread across metrology institutes and observatories in more than 30 countries 🔥 The info gets published every month in the BIPM Circular T at ftp://62.161.69.5/pub/tai/publication. And the wild part is that TAI doesn't gain or lose against an imaginary perfect clock by more than about one tenth of a microsecond (0.0000001 second) per year 🤯
Here's the key vocab, bestie:
- Coordinated Universal Time (UTC) is a time scale based on the second. It's defined and recommended by the International Telecommunications Radio Committee (ITU-R) and maintained by the BIPM, with cooperation from national labs all over the world 🫶 The full definition lives in ITU-R Recommendation TF.460-4.
- Atomic Time uses the SI second as its unit, which is the duration of 9 192 631 770 cycles of radiation matching the transition between two hyperfine levels of the ground state of caesium 133 💜
- TAI is the International Atomic Time scale, a statistical timescale built from a large number of atomic clocks 🧚
- Universal Time (UT) counts from 0 hours at midnight, with the mean solar day as its unit, defined to be as uniform as possible even though the Earth's rotation keeps changing 🌸
Within UT, there are two versions you need to know about:
- UT0 is the rotational time at a particular place of observation. You observe it through the diurnal motion of stars or extraterrestrial radio sources ⭐
- UT1 is UT0 corrected for the effect of polar motion on the longitude of the observing site. It isn't perfectly uniform because the Earth's rotation is a little irregular 🌎 Those irregularities usually lead to a net decrease in the Earth's average rotational velocity, which causes UT1 to lag behind UTC over time 🐢
So UTC is the basis for international timekeeping, and it follows TAI exactly except for an integral number of seconds (32 in year 2001) 🎀 Those leap seconds get inserted on the advice of the International Earth Rotation Service (IERS) at http://hpiers.obspm.fr/. The point is to make sure that, after accounting for irregularities, the Sun is overhead within 0,9 seconds of 12:00:00 UTC on the Greenwich meridian. UTC is the modern successor of Greenwich Mean Time, which was used back when the unit of time was the mean solar day 🍓
Adjustments to the atomic (UTC) time scale are an occasional addition or deletion of one full second, called a leap second ⏱️ Twice a year, during the last minute of June 30 and December 31 (Universal Time), adjustments may be made so the accumulated difference between UTC and UT1 never goes over 0,9 s before the next scheduled adjustment. Historically, when they were needed, adjustments have usually meant adding an extra second to UTC so the Earth could "catch up" 🏃♀️ That means the last minute of the UTC time scale on an adjustment day has 61 seconds. Adjustment dates are usually announced several months ahead in IERS Bulletin C at ftp://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat.
Bottom line: UTC differs from TAI by an integral number of seconds, and it's kept within 0,9 s of UT1 by one-second steps called "leap seconds" 💖 So far, those steps have always been positive 👑
Tiny reminder: that 0,9 s figure uses a comma as the decimal separator in the original, and it stays that way here so nothing gets lost in translation 🙈
Annex B (informative): Possible for Implementation Architectures and Time-Stamping Services 🧚
B.1. Managed Time-Stamping Service
Some organizations might want to host one or more Time-Stamping Units 🏢 They get the perks of being close to the service and getting high quality timestamps, without having to install, operate, or manage those units themselves. Ta-da 💅
Here's how it works: the units get installed on the hosting organization's premises, and then a Time-Stamping Authority remotely manages them. That TSA takes overall responsibility for the quality of the service delivered to the hosting organization 🫶
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ +
+ Time-Stamping Authority +
+_____________ _____________ _____________+
|+ __________ | | | | __________ +|
|+| | | | Time - | | | |+|
|+| Time - |<-------------| Stamping |------------->| Time - |+|
|+| Stamping | | Install. | Management | Install. | | Stamping |+|
|+| Unit | | Management | | Management | | Unit |+|
|+|__________| | |_____________| | |__________|+|
|+ | | +|
|+ | | +|
|+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
| Hosting | | Hosting |
| Organization | | Organization |
|______________| |______________|
Figure B.1: Managed Time-stamping ServiceThe requirements for time-stamping services in this document cover both the time-stamping management and the operation of the unit that issues the time-stamp tokens 🎀 The TSA, as identified in the time-stamp token, is the one responsible for making sure those requirements are met (for example, through contractual obligations) 📜
Hosting organizations will generally want to keep an eye on how the service is used 👀 At the very least, they want to know whether the service is working, and they might even want to measure its performance, like the number of time-stamps generated over a certain period of time 📊 That kind of monitoring can be considered outside the TSA's time-stamping authority 🦋
So the description of management operations in the main body of the document isn't meant to be the only option 🌈 If monitoring is done directly on the unit, the Time-Stamping service provider may permit it.
B.2. Selective Alternative Quality
Some relying parties might want to take advantage of particular characteristics of a time-stamp token, like a specific signature algorithm and/or key length, or a specific accuracy for the time in the token 🔐 Those parameters can be seen as specifying a "quality" for the time stamp token 💜
Time stamp tokens with different qualities may be issued by different time-stamping units, operated by the same or different TSAs 🧚
A particular time-stamping unit only provides one combination of algorithm and key length, since a time-stamping unit is a set of hardware and software managed as one unit with a single time-stamp token signing key 🔑 So if you want different combinations of algorithm and key length, different time-stamping units shall be used 🙌
A particular time-stamping unit may provide a fixed accuracy for the time in the token, or a different accuracy if instructed to do so. That can happen either through a specific mode of access (e.g., e-mail or http) or through specific parameters in the request 🎯
Annex C (informative): Long Term Verification of Time-Stamp Tokens ⏳🦋
okay so bestie, this annex is literally about the question "how do we still trust a time-stamp token after the certificate has expired?" 😭 it's giving time-travel energy, and I'm obsessed.
Usually, a time-stamp token becomes unverifiable once the validity period of the TSU's certificate is over. Why? Because the CA that issued that certificate doesn't promise anymore that it will keep publishing revocation data, including data about revocations caused by key compromises. Major mood 💀
Verification might still happen after that certificate expiry, though, if at verification time you can know that:
- the TSU private key has not been compromised at any time up to the time that a relying part verifies a time-stamp token;
- the hash algorithms used in the time-stamp token exhibit no collisions at the time of verification;
- the signature algorithm and signature key size under which the time-stamp token has been signed are still beyond the reach of cryptographic attacks at the time of verification.
If these conditions cannot be met, then the validity MAY be maintained by applying an additional time-stamp to protect the integrity of the previous one. 🔐✨
The present document does not specify the details of how such protection may be obtained. For the time being, and until some enhancements are defined to support these features, the information MAY be obtained using out-of-band means or alternatively in the context of closed environments. As an example, should a CA guarantee to maintain the revocation status of TSU certificates after the end of its validity period, this would fulfill the first requirement. 🌸
NOTE 1: An alternative to Time-Stamping is for a Trusted Service Provider to record a representation of a datum bound to a particular time in an audit trail, thus establishing evidence that the datum existed before that time. This technique, which is called Time-Marking, can be a valuable alternative for checking the long term validity of signatures. 🍓
NOTE 2: The TSA or other trusted third party service provider MAY support the verification of time-stamp tokens. 🫶
Annex D (informative): Model TSA Disclosure Statement Structure 📜💜
okay so the TSA disclosure statement has a section for each defined statement type, and every section holds a descriptive statement that MAY include hyperlinks to the relevant certificate policy/certification practice statement sections. Let's go through the list, bestie! 🧚
D.1. STATEMENT TYPE: Entire agreement 🎀
STATEMENT DESCRIPTION: A statement indicating that the disclosure statement is not the entire agreement, but only a part of it.
D.2. STATEMENT TYPE: TSA contact info 📞
STATEMENT DESCRIPTION: The name, location and relevant contact information for the TSA.
D.3. STATEMENT TYPE: time-stamp token types and usage 🦋
STATEMENT DESCRIPTION: A description of each class/type of time-stamp tokens issued by the TSA (in accordance with each time-stamp policy) and any restrictions on time-stamp usage.
SPECIFIC REQUIREMENT: Indication of the policy being applied, including the contexts for which the time-stamp token can be used (e.g., only for use with electronic signatures), the hashing algorithms, the expected life time of the time-stamp token signature, any limitations on the use of the time-stamp token and information on how to verify the time-stamp token. 💅
D.4. STATEMENT TYPE: Reliance limits. ⭐
STATEMENT DESCRIPTION: reliance limits, if any.
SPECIFIC REQUIREMENT: Indication of the accuracy of the time in the time-stamp token, and the period of time for which TSA event logs (see section 7.4.10) are maintained (and hence are available to provide supporting evidence). 🔥
D.5. STATEMENT TYPE: Obligations of subscribers. 🌈
STATEMENT DESCRIPTION: The description of, or reference to, the critical subscriber obligations.
SPECIFIC REQUIREMENT: No specific requirements identified in the current document. Where applicable the TSA MAY specify additional obligations. 🙈
D.6. STATEMENT TYPE: TSU public key status checking obligations of relying parties. 🔍
STATEMENT DESCRIPTION: The extent to which relying parties are obligated to check the TSU public key status, and references to further explanation.
SPECIFIC REQUIREMENT: Information on how to validate the TSU public key status, including requirements to check the revocation status of TSU public key, such that the relying party is considered to "reasonably rely" on the time-stamp token (see section 6.3). 👑
D.7. STATEMENT TYPE: Limited warranty and disclaimer/Limitation of liability. ⚖️
STATEMENT DESCRIPTION: Summary of the warranty, disclaimers, limitations of liability and any applicable warranty or insurance programs.
SPECIFIC REQUIREMENT: Limitations of liability (see section 6.4). 🌸
D.8. STATEMENT TYPE: Applicable agreements and practice statement. 📚
STATEMENT DESCRIPTION: Identification and references to applicable agreements, practice statement, time-stamp policy and other relevant documents. 🧾
D.9. STATEMENT TYPE: Privacy policy. 🔒
STATEMENT DESCRIPTION: A description of and reference to the applicable privacy policy.
SPECIFIC REQUIREMENT: Note: TSA's under this policy are required to comply with the requirements of Data Protection Legislation. 🫶
D.10. STATEMENT TYPE: Refund policy 💸
STATEMENT DESCRIPTION: A description of and reference to the applicable refund policy.
D.11. STATEMENT TYPE: Applicable law, complaints and dispute resolution mechanisms. ⚖️
STATEMENT DESCRIPTION: Statement of the choice of law, complaints procedure and dispute resolution mechanisms.
SPECIFIC REQUIREMENT: The procedures for complaints and dispute settlements. The applicable legal system. 🌈
D.12. STATEMENT TYPE: TSA and repository licenses, trust marks, and audit. 🏅
STATEMENT DESCRIPTION: Summary of any governmental licenses, seal programs; and a description of the audit process and if applicable the audit firm.
SPECIFIC REQUIREMENT: If the TSA has been assessed to be conformant with the identified time-stamp policy, and if so through which independent party. ✨
Authors' Addresses 🌷
Denis Pinkas 💜 Bull Rue Jean Jaures, 78340 Les Clayes CEDEX FRANCE
EMail: Denis.Pinkas@bull.net
Nick Pope 💜 Security & Standards 192 Moulsham Street Chelmsford, Essex CM2 0LG United Kingdom
EMail: pope@secstan.com
John Ross 💜 Security & Standards 192 Moulsham Street Chelmsford, Essex CM2 0LG United Kingdom
EMail: ross@secstan.com
This Informational RFC has been produced in ETSI ESI. 🦋
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📦 where this page comes from
- ietf: rfc3628 2003-11
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