RFC 4398
Storing Certificates in the Domain Name System (DNS)
Okay bestie, gather round because this is RFC 4398 🎀✨ It's called Storing Certificates in the Domain Name System (DNS), it was written by S. Josefsson in March 2006, and it's in the Standards Track category. It obsoletes RFC 2538, so if you've seen 2538 floating around, this is the glow-up 💅
Status of This Memo 📜
This document specifies an Internet standards track protocol for the Internet community, and it's asking everyone for discussion and suggestions for improvements 🫶 For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited ✨
Copyright Notice ©️
Copyright (C) The Internet Society (2006) 🌈
Abstract 🌸
Cryptographic public keys get published all the time, and their authenticity is shown through certificates 🔐 So this doc defines a CERT resource record (RR) that lets those certificates, plus related certificate revocation lists, be stored right in the Domain Name System (DNS). Iconic storage behavior 💖
This document obsoletes RFC 2538.
Table of Contents 🗂️
1. Introduction ....................................................3
2. The CERT Resource Record ........................................3
2.1. Certificate Type Values ....................................4
2.2. Text Representation of CERT RRs ............................6
2.3. X.509 OIDs .................................................6
3. Appropriate Owner Names for CERT RRs ............................7
3.1. Content-Based X.509 CERT RR Names ..........................8
3.2. Purpose-Based X.509 CERT RR Names ..........................9
3.3. Content-Based OpenPGP CERT RR Names ........................9
3.4. Purpose-Based OpenPGP CERT RR Names .......................10
3.5. Owner Names for IPKIX, ISPKI, IPGP, and IACPKIX ...........10
4. Performance Considerations .....................................11
5. Contributors ...................................................11
6. Acknowledgements ...............................................11
7. Security Considerations ........................................12
8. IANA Considerations ............................................12
9. Changes since RFC 2538 .........................................13
10. References ....................................................14
10.1. Normative References .....................................14
10.2. Informative References ...................................15
Appendix A. Copying Conditions ...................................161. Introduction ✨
Public keys are frequently published as certificates, and their authenticity is commonly shown through certificates and related certificate revocation lists (CRLs) 🔑 A certificate is a binding, made with a cryptographic digital signature, of a public key, a validity interval and/or conditions, and identity, authorization, or other information. A certificate revocation list is a list of certificates that have been revoked, plus some incidental information, all signed by the signer (issuer) of the revoked certificates. Examples are X.509 certificates/CRLs in the X.500 directory system, or OpenPGP certificates/revocations used by OpenPGP software 🧚
Section 2 specifies a CERT resource record (RR) for storing certificates in the Domain Name System [1] [2] 💅
Section 3 talks about appropriate owner names for CERT RRs 🍓
Sections 4, 7, and 8 cover performance, security, and IANA considerations, respectively 🔥
Section 9 explains the changes in this document compared to RFC 2538 💜
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 [3] 🫶
2. The CERT Resource Record 🎀
The CERT resource record (RR) has the structure shown below, and its RR type code is 37 🦋
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| type | key tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| algorithm | /
+---------------+ certificate or CRL /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|The type field is the certificate type, as defined in Section 2.1 below 🌸
The key tag field is a 16-bit value computed for the key embedded in the certificate, using the RRSIG Key Tag algorithm described in Appendix B of [12]. It's an efficiency measure for picking which CERT RRs might apply to a particular key 👀 You can calculate the key tag for the key in question, and then only CERT RRs with that same key tag need to be examined. Note that two different keys can have the same key tag, so it's not a perfect ID 🙈 However, the key MUST be transformed to the format it would have as the public key portion of a DNSKEY RR before the key tag is computed. That's only possible if the key is applicable to an algorithm and complies with limits (such as key size) defined for DNS security. If it isn't, the algorithm field MUST be zero, and the tag field is meaningless and SHOULD be zero 💀
The algorithm field has the same meaning as the algorithm field in DNSKEY and RRSIG RRs [12], with one twist: a zero algorithm field means the algorithm is unknown to a secure DNS. That may simply be because the algorithm hasn't been standardized for DNSSEC [11] 🧠
2.1. Certificate Type Values 🦄
The following values are defined or reserved:
Value Mnemonic Certificate Type
----- -------- ----------------
0 Reserved
1 PKIX X.509 as per PKIX
2 SPKI SPKI certificate
3 PGP OpenPGP packet
4 IPKIX The URL of an X.509 data object
5 ISPKI The URL of an SPKI certificate
6 IPGP The fingerprint and URL of an OpenPGP packet
7 ACPKIX Attribute Certificate
8 IACPKIX The URL of an Attribute Certificate
9-252 Available for IANA assignment
253 URI URI private
254 OID OID private
255 Reserved
256-65279 Available for IANA assignment
65280-65534 Experimental
65535 ReservedThese values are the initial content of the IANA registry, so see Section 8 for the details 📋
The PKIX type is reserved to indicate an X.509 certificate that conforms to the profile defined by the IETF PKIX working group [8] 🔐 The certificate section starts with a one-octet unsigned OID length, followed by an X.500 OID that says what the rest of the certificate section is (see Section 2.3, below). (NOTE: X.509 certificates do not include their X.500 directory-type-designating OID as a prefix 🙃)
The SPKI and ISPKI types are reserved to indicate the SPKI certificate format [15], for when the SPKI documents move out of experimental status. The format for these two CERT RR types will need to be specified later 🚧
The PGP type indicates an OpenPGP packet as described in [5] and its extensions and successors. It's used to transfer public key material and revocation signatures 🗝️ The data is binary and MUST NOT be encoded into an ASCII armor. An implementation SHOULD process transferable public keys as described in Section 10.1 of [5], but it MAY handle additional OpenPGP packets too ✨
The ACPKIX type indicates an Attribute Certificate format [9] 🏷️
The IPKIX and IACPKIX types indicate a URL that will serve the content that would have been in the "certificate, CRL, or URL" field of the matching type (PKIX or ACPKIX, respectively) 🌐
The IPGP type holds both an OpenPGP fingerprint for the key in question and a URL. The certificate portion of an IPGP CERT RR is a one-octet fingerprint length, followed by the OpenPGP fingerprint, followed by the URL. The OpenPGP fingerprint is calculated as defined in RFC 2440 [5]. A zero-length fingerprint or a zero-length URL is legal, and they mean URL-only IPGP data or fingerprint-only IPGP data, respectively. A zero-length fingerprint and a zero-length URL is meaningless and invalid 🙅♀️
The IPKIX, ISPKI, IPGP, and IACPKIX types are known as "indirect". These types MUST be used when the content is too large to fit in the CERT RR, and they MAY be used at the implementer's discretion. They SHOULD NOT be used where the DNS message is 512 octets or smaller and could therefore be expected to fit in a UDP packet 📦
The URI private type indicates a certificate format defined by an absolute URI 🌈 The certificate portion of the CERT RR MUST begin with a null-terminated URI [10], and the data after the null is the private format certificate itself. The URI SHOULD be such that retrieving it leads to documentation on the format of the certificate. Recognition of private certificate types doesn't need to be based on URI equality, and it can use various forms of pattern matching, so that, for example, subtype or version information can also be encoded into the URI 🧩
The OID private type indicates a private format certificate specified by an ISO OID prefix. The certificate section starts with a one-octet unsigned OID length, followed by a BER-encoded OID that indicates what the rest of the certificate section is. That can be an X.509 certificate format or some other format. X.509 certificates that conform to the IETF PKIX profile SHOULD be indicated by the PKIX type, not the OID private type. Recognition of private certificate types doesn't need to be based on OID equality, and it can use pattern matching such as OID prefix 🎯
2.2. Text Representation of CERT RRs 📝
The RDATA portion of a CERT RR has the type field as an unsigned decimal integer, or as a mnemonic symbol listed in Section 2.1 above 🔢
The key tag field is represented as an unsigned decimal integer 💖
The algorithm field is represented as an unsigned decimal integer or a mnemonic symbol, as listed in [12] ✨
The certificate/CRL portion is represented in base 64 [16]. It may be divided into any number of white-space-separated substrings, all the way down to single base-64 digits, and those get concatenated to get the full signature. These substrings can span lines using the standard parenthesis 🧁
Note that the certificate/CRL portion may have internal sub-fields, but those don't show up in the master file representation. For example, with type 254, there will be an OID size, an OID, and then the certificate/CRL proper. However, only a single logical base-64 string will appear in the text representation 🫧
2.3. X.509 OIDs ✨
OIDs got defined for the X.500 directory covering user certificates, certification authority certificates, revocations of certification authority, and revocations of user certificates 🔐. Here's the table with each OID, its BER encoding, and its length-prefixed hex format, ready for CERT RRs 💖
id-at-userCertificate
= { joint-iso-ccitt(2) ds(5) at(4) 36 }
== 0x 03 55 04 24
id-at-cACertificate
= { joint-iso-ccitt(2) ds(5) at(4) 37 }
== 0x 03 55 04 25
id-at-authorityRevocationList
= { joint-iso-ccitt(2) ds(5) at(4) 38 }
== 0x 03 55 04 26
id-at-certificateRevocationList
= { joint-iso-ccitt(2) ds(5) at(4) 39 }
== 0x 03 55 04 273. Appropriate Owner Names for CERT RRs 🏷️
Okay so this part is about where you store your CERT RRs. It is recommended that certificate CERT RRs get stored under a domain name related to their subject, meaning the entity that's supposed to control the private key for the public key being certified 🔑. It is recommended that certificate revocation list CERT RRs get stored under a domain name related to their issuer 📜.
Heads up, following some of these guidelines might give you DNS names with characters that need DNS quoting, as described in Section 5.1 of RFC 1035 [2] 🙈.
The name you pick for your CERT RRs matters a lot for clients doing CERT queries 🎯. Sometimes a client doesn't know everything about the CERT RR it wants. Like, it might not know the subject name of an X.509 certificate, or the email address of the owner of an OpenPGP key 🥺. It might only know the hostname of a service using X.509 certificates, or the Key ID of an OpenPGP key.
So there are two owner name guidelines: content-based owner names and purpose-based owner names 💜. A content-based owner name is derived from the content of the CERT RR data, like the Subject field in an X.509 certificate or the User ID field in OpenPGP keys. A purpose-based owner name is one a client retrieving CERT RRs ought to already know, like the host name of an X.509 protected service or the Key ID of an OpenPGP key 🧚. The two can be the same, for example when a client looks up a key based on the From: address of an incoming email 💌.
Implementations SHOULD use the purpose-based owner name guidelines described in this document and MAY use CNAME RRs at content-based owner names (or other names), pointing to the purpose-based owner name 🎀.
Note that this section describes an application-based mapping from the name space used in a certificate to the name space used by DNS. The DNS does not infer any relationship amongst CERT resource records based on similarities or differences of the DNS owner name(s) of CERT resource records. For example, if multiple labels are used when mapping from a CERT identifier to a domain name, then care must be taken in understanding wildcard record synthesis 🌸.
3.1. Content-Based X.509 CERT RR Names 🪪
Some X.509 versions, such as the PKIX profile of X.509 [8], let you associate multiple names with subjects and issuers under "Subject Alternative Name" and "Issuer Alternative Name" 🦋. The PKIX profile has these Alternate Names defined with this ASN.1 specification:
GeneralName ::= CHOICE {
otherName [0] OtherName,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER }The recommended CERT storage locations go in this priority order 👑:
- If a domain name is included in the identification in the certificate or CRL, that ought to be used.
- If a domain name is not included but an IP address is included, then the translation of that IP address into the appropriate inverse domain name ought to be used.
- If neither of the above is used, but a URI containing a domain name is present, that domain name ought to be used.
- If none of the above is included but a character string name is included, then it ought to be treated as described below for OpenPGP names.
- If none of the above apply, then the distinguished name (DN) ought to be mapped into a domain name as specified in [4].
Example 1: An X.509v3 certificate is issued to /CN=John Doe /DC=Doe/ DC=com/DC=xy/O=Doe Inc/C=XY/ with Subject Alternative Names of (a) string "John (the Man) Doe", (b) domain name john-doe.com, and (c) URI <https://www.secure.john-doe.com:8080/>. The storage locations recommended, in priority order, would be 1. john-doe.com, 2. www.secure.john-doe.com, and 3. Doe.com.xy. 🫶
Example 2: An X.509v3 certificate is issued to /CN=James Hacker/ L=Basingstoke/O=Widget Inc/C=GB/ with Subject Alternate names of (a) domain name widget.foo.example, (b) IPv4 address 10.251.13.201, and (c) string "James Hacker <hacker@mail.widget.foo.example>". The storage locations recommended, in priority order, would be:
- widget.foo.example,
- 201.13.251.10.in-addr.arpa, and
- hacker.mail.widget.foo.example.
3.2. Purpose-Based X.509 CERT RR Names 🎯
Clients that don't already have a certificate can't easily rebuild the content-based owner name, so purpose-based owner names are recommended in this section 🥹. The recommendations vary per scenario. This table sums up the purpose-based X.509 CERT RR owner name guidelines for use with S/MIME [17], SSL/TLS [13], and IPsec [14] 📋:
Scenario Owner name
------------------ ----------------------------------------------
S/MIME Certificate Standard translation of an RFC 2822 email
address. Example: An S/MIME certificate for
"postmaster@example.org" will use a standard
hostname translation of the owner name,
"postmaster.example.org".
TLS Certificate Hostname of the TLS server.
IPsec Certificate Hostname of the IPsec machine and/or, for IPv4
or IPv6 addresses, the fully qualified domain
name in the appropriate reverse domain.An alternate approach for IPsec is to store raw public keys [18] 🌈.
3.3. Content-Based OpenPGP CERT RR Names 💌
OpenPGP signed keys (certificates) use a general character string User ID [5]. However, OpenPGP itself recommends that these names include the RFC 2822 [7] email address of the party, as in "Leslie Example <Leslie@host.example>" 💅. If that format is used, the CERT ought to live under the standard translation of the email address into a domain name, which would be leslie.host.example in this case. If no RFC 2822 name can be extracted from the string name, no specific domain name is recommended 🤷♀️.
If a user has more than one email address, the CNAME type can cut down on the amount of data stored in the DNS. For example:
$ORIGIN example.org.
smith IN CERT PGP 0 0 <OpenPGP binary>
john.smith IN CNAME smith
js IN CNAME smith3.4. Purpose-Based OpenPGP CERT RR Names 🔑
Applications that get an OpenPGP packet with encrypted or signed data, but don't know the sender's email address, have trouble building the right owner name 😩. They can't use the content-based guidelines either. Still, these clients usually know the key fingerprint or the Key ID. The Key ID shows up in OpenPGP packets, and the key fingerprint is often in auxiliary data that might be around 🧩. So in this case, using an owner name identical to the key fingerprint, and the key ID expressed in hexadecimal [16], is recommended. For example:
$ORIGIN example.org.
0424D4EE81A0E3D119C6F835EDA21E94B565716F IN CERT PGP ...
F835EDA21E94B565716F IN CERT PGP ...
B565716F IN CERT PGP ...If the same key material gets stored under several owner names, CNAME can help avoid duplicating data. Just note that CNAME isn't always applicable, because it maps one owner name to the other for all purposes. That can be sub-optimal when two keys with the same Key ID are stored 👀.
3.5. Owner Names for IPKIX, ISPKI, IPGP, and IACPKIX 🌷
These types get stored under the same owner names, both purpose- and content-based, as the PKIX, SPKI, PGP, and ACPKIX types 💫.
4. Performance Considerations 🚀
The Domain Name System (DNS) protocol was designed for small transfers, typically below 512 octets 🐣. Larger transfers still work correctly, and work is underway to make them more efficient. Even so, it is still advisable right now that every reasonable effort be made to minimize the size of certificates stored within the DNS 🧳. Some things you can do include using the fewest possible optional or extension fields and using short field values for necessary variable-length fields ✂️.
The RDATA field in the DNS protocol can only hold data of size 65535 octets (64kb) or less. This means each CERT RR MUST NOT contain more than 64kb of payload, even if the corresponding certificate or certificate revocation list is larger 🚫. This document deals with that by defining "indirect" data types for each normal type ✨.
Deploying CERT RRs to support digitally signed email changes the access patterns of DNS lookups from per-domain to per-user 📈. If digitally signed email and a key/certificate lookup based on CERT RRs get deployed on a wide scale, this may lead to increased DNS load, with potential performance and cache effectiveness consequences 😬. Whether or not this load increase will be noticeable is not known 🤔.
5. Contributors 🎀
The majority of this document is copied verbatim from RFC 2538, by Donald Eastlake 3rd and Olafur Gudmundsson 🫡.
6. Acknowledgements 💜
Thanks to David Shaw and Michael Graff for their contributions to earlier works that motivated, and served as inspiration for, this document 🥰.
This document was improved by suggestions and comments from Olivier Dubuisson, Scott Hollenbeck, Russ Housley, Peter Koch, Olaf M. Kolkman, Ben Laurie, Edward Lewis, John Loughney, Allison Mankin, Douglas Otis, Marcos Sanz, Pekka Savola, Jason Sloderbeck, Samuel Weiler, and Florian Weimer. No doubt the list is incomplete. We apologize to anyone we left out 🙏✨.
7. Security Considerations 🔐✨
Okay bestie, certificates literally come with their own authenticating signatures built in 🫶. So it's totally reasonable to stash them in non-secure DNS zones, or to pull them from DNS while DNS security checking isn't implemented yet or is deferred for efficiency 💅. The results can be trusted if the certificate chain gets verified all the way back to a known trusted key, and only if that lines up with the user's security policy 🎀.
Alternatively, if you grab certs from a secure DNS zone with DNS security checking enabled and they get verified by DNS security, the key inside the retrieved certificate can be trusted without verifying the chain, as long as it matches the user's security policy ✨.
Now, if an organization decides to issue certs for its employees and places CERT RRs in the DNS by owner name, AND DNSSEC (with NSEC) is in use, someone can enumerate every single employee 😭💀. This is usually not considered desirable, for the same reason enterprise phone listings aren't often published publicly and are even marked confidential 🙈.
Using the URI type adds another level of indirection, and that may open a new vulnerability 🚨. One way to lock that indirection down is to include a hash of the certificate in the URI itself 🔒.
If DNSSEC is used, then the non-existence of a CERT RR (and so, certificates or revocation lists) can be securely asserted 👑. Without DNSSEC, that's not possible 💔.
8. IANA Considerations 🦋
IANA made a brand new registry for CERT RR certificate types 🧚. Here's what's in it at the start:
Decimal Type Meaning Reference
------- ---- ------- ---------
0 Reserved RFC 4398
1 PKIX X.509 as per PKIX RFC 4398
2 SPKI SPKI certificate RFC 4398
3 PGP OpenPGP packet RFC 4398
4 IPKIX The URL of an X.509 data object RFC 4398
5 ISPKI The URL of an SPKI certificate RFC 4398
6 IPGP The fingerprint and URL RFC 4398
of an OpenPGP packet
7 ACPKIX Attribute Certificate RFC 4398
8 IACPKIX The URL of an Attribute RFC 4398
Certificate
9-252 Available for IANA assignment
by IETF Standards action
253 URI URI private RFC 4398
254 OID OID private RFC 4398
255 Reserved RFC 4398
256-65279 Available for IANA assignment
by IETF Consensus
65280-65534 Experimental RFC 4398
65535 Reserved RFC 4398Certificate types 0x0000 through 0x00FF and 0xFF00 through 0xFFFF can only be assigned by an IETF standards action [6] 🔥. This document assigns 0x0001 through 0x0008, plus 0x00FD and 0x00FE 🎀. Certificate types 0x0100 through 0xFEFF are assigned through IETF Consensus [6], based on RFC documentation of the certificate type 📚. The private types under 0x00FD and 0x00FE ought to satisfy most requirements for proprietary or private types, so that's the vibe 💜.
The CERT RR reuses the DNS Security Algorithm Numbers registry 🌸. In particular, the CERT RR requires that algorithm number 0 remain reserved, as described in Section 2. IANA will reference the CERT RR as a user of this registry, and value 0 in particular 👑.
9. Changes since RFC 2538 🍓
Here's the glow-up list of everything that changed since RFC 2538 💅:
- Editorial changes to match new document requirements ✍️. This includes splitting the reference section into two parts, updating the references to point at the latest versions, and adding some extra references.
- Better terminology 💖. For example, "PGP" got replaced with "OpenPGP" to align with RFC 2440.
- In Section 2.1, it's now clarified that OpenPGP public key data are binary, not the ASCII armored format 🦋. It also points to reference 10.1 in RFC 2440 for how to deal with OpenPGP keys, and acknowledges that implementations may handle additional packet types.
- It's now clarified that integers in the representation format are decimal 🔢.
- KEY/SIG got replaced with DNSKEY/RRSIG etc, to align with DNSSECbis terminology 🫶. The reference for Key Tag Algorithm calculations was also improved.
- Examples that suggest using CNAME to reduce bandwidth were added 📉.
- In Section 3, the last paragraphs that discuss "content-based" vs "purpose-based" owner names got appended ✨. Section 3.2 was added for purpose-based X.509 CERT owner names, and Section 3.4 for purpose-based OpenPGP CERT owner names.
- Size considerations were added 📏.
- The SPKI types got reserved, until RFC 2692/2693 moves off experimental status 🔒.
- Indirect types IPKIX, ISPKI, IPGP, and IACPKIX were added 🧚.
- An IANA registry of CERT type values was created 🎉.
10. References 📚
10.1. Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[4] Kille, S., Wahl, M., Grimstad, A., Huber, R., and S. Sataluri, "Using Domains in LDAP/X.500 Distinguished Names", RFC 2247, January 1998.
[5] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, "OpenPGP Message Format", RFC 2440, November 1998.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[7] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[8] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002.
[9] Farrell, S. and R. Housley, "An Internet Attribute Certificate Profile for Authorization", RFC 3281, April 2002.
[10] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.
[11] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005.
[12] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005.
10.2. Informative References
[13] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999.
[14] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005.
[15] Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas, B., and T. Ylonen, "SPKI Certificate Theory", RFC 2693, September 1999.
[16] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 3548, July 2003.
[17] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification", RFC 3851, July 2004.
[18] Richardson, M., "A Method for Storing IPsec Keying Material in DNS", RFC 4025, March 2005.
Appendix A. Copying Conditions 🎀
Regarding the portion of this document that was written by Simon Josefsson ("the author", for the remainder of this section), the author makes no guarantees and is not responsible for any damage resulting from its use. The author grants irrevocable permission to anyone to use, modify, and distribute it in any way that does not diminish the rights of anyone else to use, modify, and distribute it, provided that redistributed derivative works do not contain misleading author or version information. Derivative works need not be licensed under similar terms.
Author's Address ✉️
Simon Josefsson
EMail: simon@josefsson.org
Full Copyright Statement ©️
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property 💜
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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org.
Acknowledgement 🫶
Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). 🌈
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