draft-ietf-dnsext-rfc2538bis-02.txt   draft-ietf-dnsext-rfc2538bis-03.txt 
Network Working Group S. Josefsson Network Working Group S. Josefsson
Expires: November 26, 2005 Expires: December 12, 2005
Storing Certificates in the Domain Name System (DNS) Storing Certificates in the Domain Name System (DNS)
draft-ietf-dnsext-rfc2538bis-02 draft-ietf-dnsext-rfc2538bis-03
Status of this Memo Status of this Memo
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This Internet-Draft will expire on November 26, 2005. This Internet-Draft will expire on December 12, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
Cryptographic public key are frequently published and their Cryptographic public key are frequently published and their
authenticity demonstrated by certificates. A CERT resource record authenticity demonstrated by certificates. A CERT resource record
(RR) is defined so that such certificates and related certificate (RR) is defined so that such certificates and related certificate
revocation lists can be stored in the Domain Name System (DNS). revocation lists can be stored in the Domain Name System (DNS).
See <http://josefsson.org/rfc2538bis/> for more information. This document obsolete RFC 2538.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The CERT Resource Record . . . . . . . . . . . . . . . . . . 3 2. The CERT Resource Record . . . . . . . . . . . . . . . . . . 3
2.1 Certificate Type Values . . . . . . . . . . . . . . . . . 4 2.1 Certificate Type Values . . . . . . . . . . . . . . . . . 4
2.2 Text Representation of CERT RRs . . . . . . . . . . . . . 5 2.2 Text Representation of CERT RRs . . . . . . . . . . . . . 5
2.3 X.509 OIDs . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 X.509 OIDs . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Appropriate Owner Names for CERT RRs . . . . . . . . . . . . 6 3. Appropriate Owner Names for CERT RRs . . . . . . . . . . . . 6
3.1 Content-based X.509 CERT RR Names . . . . . . . . . . . . 7 3.1 Content-based X.509 CERT RR Names . . . . . . . . . . . . 7
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Section 2 below specifies a CERT resource record (RR) for the storage Section 2 below specifies a CERT resource record (RR) for the storage
of certificates in the Domain Name System. of certificates in the Domain Name System.
Section 3 discusses appropriate owner names for CERT RRs. Section 3 discusses appropriate owner names for CERT RRs.
Sections 4, 5, and 6 below cover performance, IANA, and security Sections 4, 5, and 6 below cover performance, IANA, and security
considerations, respectively. considerations, respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [10]. document are to be interpreted as described in [3].
2. The CERT Resource Record 2. The CERT Resource Record
The CERT resource record (RR) has the structure given below. Its RR The CERT resource record (RR) has the structure given below. Its RR
type code is 37. 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 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 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 | | type | key tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| algorithm | / | algorithm | /
+---------------+ certificate or CRL / +---------------+ certificate or CRL /
/ / / /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
The type field is the certificate type as define in section 2.1 The type field is the certificate type as define in section 2.1
below. below.
The algorithm field has the same meaning as the algorithm field in The algorithm field has the same meaning as the algorithm field in
DNSKEY and RRSIG RRs [9] except that a zero algorithm field indicates DNSKEY and RRSIG RRs [10] except that a zero algorithm field
the algorithm is unknown to a secure DNS, which may simply be the indicates the algorithm is unknown to a secure DNS, which may simply
result of the algorithm not having been standardized for DNSSEC. be the result of the algorithm not having been standardized for
DNSSEC.
The key tag field is the 16 bit value computed for the key embedded The key tag field is the 16 bit value computed for the key embedded
in the certificate, using the RRSIG Key Tag Algorithm described in in the certificate, using the RRSIG Key Tag algorithm described in
Appendix B of [9]. This field is used as an efficiency measure to Appendix B of [10]. This field is used as an efficiency measure to
pick which CERT RRs may be applicable to a particular key. The key pick which CERT RRs may be applicable to a particular key. The key
tag can be calculated for the key in question and then only CERT RRs tag can be calculated for the key in question and then only CERT RRs
with the same key tag need be examined. However, the key must always with the same key tag need be examined. However, the key must always
be transformed to the format it would have as the public key portion be transformed to the format it would have as the public key portion
of a DNSKEY RR before the key tag is computed. This is only possible of a DNSKEY RR before the key tag is computed. This is only possible
if the key is applicable to an algorithm (and limits such as key size if the key is applicable to an algorithm (and limits such as key size
limits) defined for DNS security. If it is not, the algorithm field limits) defined for DNS security. If it is not, the algorithm field
MUST BE zero and the tag field is meaningless and SHOULD BE zero. MUST BE zero and the tag field is meaningless and SHOULD BE zero.
2.1 Certificate Type Values 2.1 Certificate Type Values
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to the profile being defined by the IETF PKIX working group. The to the profile being defined by the IETF PKIX working group. The
certificate section will start with a one byte unsigned OID length certificate section will start with a one byte unsigned OID length
and then an X.500 OID indicating the nature of the remainder of the and then an X.500 OID indicating the nature of the remainder of the
certificate section (see 2.3 below). (NOTE: X.509 certificates do certificate section (see 2.3 below). (NOTE: X.509 certificates do
not include their X.500 directory type designating OID as a prefix.) not include their X.500 directory type designating OID as a prefix.)
The SPKI type is reserved to indicate the SPKI certificate format The SPKI type is reserved to indicate the SPKI certificate format
[13], for use when the SPKI documents are moved from experimental [13], for use when the SPKI documents are moved from experimental
status. status.
The PGP type indicates an OpenPGP packet as described in [5] and its The PGP type indicates an OpenPGP packet as described in [6] and its
extensions and successors. Two uses are to transfer public key extensions and successors. Two uses are to transfer public key
material and revocation signatures. The data is binary, and MUST NOT material and revocation signatures. The data is binary, and MUST NOT
be encoded into an ASCII armor. An implementation SHOULD process be encoded into an ASCII armor. An implementation SHOULD process
transferable public keys as described in section 10.1 of [5], but it transferable public keys as described in section 10.1 of [5], but it
MAY handle additional OpenPGP packets. MAY handle additional OpenPGP packets.
The IPKIX, ISPKI and IPGP types indicate a URL which will serve the The IPKIX, ISPKI and IPGP types indicate a URL which will serve the
content that would have been in the "certificate, CRL or URL" field content that would have been in the "certificate, CRL or URL" field
of the corresponding (PKIX, SPKI or PGP) packet types. These types of the corresponding (PKIX, SPKI or PGP) packet types. These types
are known as "indirect". These packet types MUST be used when the are known as "indirect". These packet types MUST be used when the
content is too large to fit in the CERT RR, and MAY be used at the content is too large to fit in the CERT RR, and MAY be used at the
implementations discretion. They SHOULD NOT be used where the entire implementations discretion. They SHOULD NOT be used where the entire
UDP packet would have fit in 512 bytes. UDP packet would have fit in 512 bytes.
The URI private type indicates a certificate format defined by an The URI private type indicates a certificate format defined by an
absolute URI. The certificate portion of the CERT RR MUST begin with absolute URI. The certificate portion of the CERT RR MUST begin with
a null terminated URI [4] and the data after the null is the private a null terminated URI [5] and the data after the null is the private
format certificate itself. The URI SHOULD be such that a retrieval format certificate itself. The URI SHOULD be such that a retrieval
from it will lead to documentation on the format of the certificate. from it will lead to documentation on the format of the certificate.
Recognition of private certificate types need not be based on URI Recognition of private certificate types need not be based on URI
equality but can use various forms of pattern matching so that, for equality but can use various forms of pattern matching so that, for
example, subtype or version information can also be encoded into the example, subtype or version information can also be encoded into the
URI. URI.
The OID private type indicates a private format certificate specified The OID private type indicates a private format certificate specified
by a an ISO OID prefix. The certificate section will start with a by a an ISO OID prefix. The certificate section will start with a
one byte unsigned OID length and then a BER encoded OID indicating one byte unsigned OID length and then a BER encoded OID indicating
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2.2 Text Representation of CERT RRs 2.2 Text Representation of CERT RRs
The RDATA portion of a CERT RR has the type field as an unsigned The RDATA portion of a CERT RR has the type field as an unsigned
decimal integer or as a mnemonic symbol as listed in section 2.1 decimal integer or as a mnemonic symbol as listed in section 2.1
above. above.
The key tag field is represented as an unsigned decimal integer. The key tag field is represented as an unsigned decimal integer.
The algorithm field is represented as an unsigned decimal integer or The algorithm field is represented as an unsigned decimal integer or
a mnemonic symbol as listed in [9]. a mnemonic symbol as listed in [10].
The certificate / CRL portion is represented in base 64 [14] and may The certificate / CRL portion is represented in base 64 [14] and may
be divided up into any number of white space separated substrings, be divided up into any number of white space separated substrings,
down to single base 64 digits, which are concatenated to obtain the down to single base 64 digits, which are concatenated to obtain the
full signature. These substrings can span lines using the standard full signature. These substrings can span lines using the standard
parenthesis. parenthesis.
Note that the certificate / CRL portion may have internal sub-fields Note that the certificate / CRL portion may have internal sub-fields
but these do not appear in the master file representation. For but these do not appear in the master file representation. For
example, with type 254, there will be an OID size, an OID, and then example, with type 254, there will be an OID size, an OID, and then
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certificate or CRL, that should be used. certificate or CRL, that should be used.
2. If a domain name is not included but an IP address is included, 2. If a domain name is not included but an IP address is included,
then the translation of that IP address into the appropriate then the translation of that IP address into the appropriate
inverse domain name should be used. inverse domain name should be used.
3. If neither of the above it used but a URI containing a domain 3. If neither of the above it used but a URI containing a domain
name is present, that domain name should be used. name is present, that domain name should be used.
4. If none of the above is included but a character string name is 4. If none of the above is included but a character string name is
included, then it should be treated as described for OpenPGP included, then it should be treated as described for OpenPGP
names below. names below.
5. If none of the above apply, then the distinguished name (DN) 5. If none of the above apply, then the distinguished name (DN)
should be mapped into a domain name as specified in [3]. should be mapped into a domain name as specified in [4].
Example 1: Assume that an X.509v3 certificate is issued to /CN=John Example 1: Assume that an X.509v3 certificate is issued to /CN=John
Doe/DC=Doe/DC=com/DC=xy/O=Doe Inc/C=XY/ with Subject Alternative 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- names of (a) string "John (the Man) Doe", (b) domain name john-
doe.com, and (c) uri <https://www.secure.john-doe.com:8080/>. Then doe.com, and (c) uri <https://www.secure.john-doe.com:8080/>. Then
the storage locations recommended, in priority order, would be the storage locations recommended, in priority order, would be
1. john-doe.com, 1. john-doe.com,
2. www.secure.john-doe.com, and 2. www.secure.john-doe.com, and
3. Doe.com.xy. 3. Doe.com.xy.
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Scenario Owner name Scenario Owner name
------------------------------------------------------------------- -------------------------------------------------------------------
S/MIME Certificate Standard translation of RFC 822 email address. S/MIME Certificate Standard translation of RFC 822 email address.
Example: A S/MIME certificate for Example: A S/MIME certificate for
"postmaster@example.org" will use a standard "postmaster@example.org" will use a standard
hostname translation of the owner name, hostname translation of the owner name,
i.e. "postmaster.example.org". i.e. "postmaster.example.org".
TLS Certificate Hostname of the TLS server. TLS Certificate Hostname of the TLS server.
IPSEC Certificate Hostname of the IPSEC machine, and/or IPSEC Certificate Hostname of the IPSEC machine, and/or for
for the in-addr.arpa reverse lookup IP address. IPv4 or IPv6 addresses the fully qualified
domain name in the appropriate reverse domain.
An alternative approach for IPSEC is to store raw public keys [15]. An alternative approach for IPSEC is to store raw public keys [15].
3.3 Content-based OpenPGP CERT RR Names 3.3 Content-based OpenPGP CERT RR Names
OpenPGP signed keys (certificates) use a general character string OpenPGP signed keys (certificates) use a general character string
User ID [5]. However, it is recommended by OpenPGP that such names User ID [6]. However, it is recommended by OpenPGP that such names
include the RFC 2822 [7] email address of the party, as in "Leslie include the RFC 2822 [8] email address of the party, as in "Leslie
Example <Leslie@host.example>". If such a format is used, the CERT Example <Leslie@host.example>". If such a format is used, the CERT
should be under the standard translation of the email address into a should be under the standard translation of the email address into a
domain name, which would be leslie.host.example in this case. If no 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 RFC 2822 name can be extracted from the string name no specific
domain name is recommended. domain name is recommended.
If a user has more than one email address, the CNAME type can be used If a user has more than one email address, the CNAME type can be used
to reduce the amount of data stored in the DNS. For example: to reduce the amount of data stored in the DNS. For example:
$ORIGIN example.org. $ORIGIN example.org.
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The majority of this document is copied verbatim from RFC 2538, by The majority of this document is copied verbatim from RFC 2538, by
Donald Eastlake 3rd and Olafur Gudmundsson. Donald Eastlake 3rd and Olafur Gudmundsson.
6. Acknowledgements 6. Acknowledgements
Thanks to David Shaw and Michael Graff for their contributions to Thanks to David Shaw and Michael Graff for their contributions to
earlier works that motivated, and served as inspiration for, this earlier works that motivated, and served as inspiration for, this
document. document.
This document was improved by suggestions and comments from Olivier This document was improved by suggestions and comments from Olivier
Dubuisson, Ben Laurie, Samuel Weiler, and Florian Weimer. No doubt Dubuisson, Olaf M. Kolkman, Ben Laurie, Samuel Weiler, and Florian
the list is incomplete. We apologize to anyone we left out. Weimer. No doubt the list is incomplete. We apologize to anyone we
left out.
7. Security Considerations 7. Security Considerations
By definition, certificates contain their own authenticating By definition, certificates contain their own authenticating
signature. Thus it is reasonable to store certificates in non-secure signature. Thus it is reasonable to store certificates in non-secure
DNS zones or to retrieve certificates from DNS with DNS security DNS zones or to retrieve certificates from DNS with DNS security
checking not implemented or deferred for efficiency. The results MAY checking not implemented or deferred for efficiency. The results MAY
be trusted if the certificate chain is verified back to a known be trusted if the certificate chain is verified back to a known
trusted key and this conforms with the user's security policy. trusted key and this conforms with the user's security policy.
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with DNS security checking enabled and are verified by DNS security, with DNS security checking enabled and are verified by DNS security,
the key within the retrieved certificate MAY be trusted without the key within the retrieved certificate MAY be trusted without
verifying the certificate chain if this conforms with the user's verifying the certificate chain if this conforms with the user's
security policy. security policy.
When the URI type is used, it should be understood that it introduces When the URI type is used, it should be understood that it introduces
an additional indirection that may allow for a new attack vector. an additional indirection that may allow for a new attack vector.
One method to secure that indirection is to include a hash of the One method to secure that indirection is to include a hash of the
certificate in the URI itself. certificate in the URI itself.
CERT RRs are not used by DNSSEC [8] so there are no security CERT RRs are not used by DNSSEC [9] so there are no security
considerations related to CERT RRs and securing the DNS itself. considerations related to CERT RRs and securing the DNS itself.
If DNSSEC [8] is used then the non-existence of a CERT RR, and If DNSSEC is used then the non-existence of a CERT RR, and
consequently certificates or revocation lists, can be securely consequently certificates or revocation lists, can be securely
asserted. Without DNSSEC, this is not possible. asserted. Without DNSSEC, this is not possible.
8. IANA Considerations 8. IANA Considerations
Certificate types 0x0000 through 0x00FF and 0xFF00 through 0xFFFF can Certificate types 0x0000 through 0x00FF and 0xFF00 through 0xFFFF can
only be assigned by an IETF standards action [6]. This document only be assigned by an IETF standards action [7]. This document
assigns 0x0001 through 0x0006 and 0x00FD and 0x00FE. Certificate assigns 0x0001 through 0x0006 and 0x00FD and 0x00FE. Certificate
types 0x0100 through 0xFEFF are assigned through IETF Consensus [6] types 0x0100 through 0xFEFF are assigned through IETF Consensus [7]
based on RFC documentation of the certificate type. The availability based on RFC documentation of the certificate type. The availability
of private types under 0x00FD and 0x00FE should satisfy most of private types under 0x00FD and 0x00FE should satisfy most
requirements for proprietary or private types. requirements for proprietary or private types.
The CERT RR reuses the DNS Security Algorithm Numbers registry. In The CERT RR reuses the DNS Security Algorithm Numbers registry. In
particular, the CERT RR requires that algorithm number 0 remain particular, the CERT RR requires that algorithm number 0 remain
reserved, as described in Section 2. The IANA is directed to reserved, as described in Section 2. The IANA is directed to
reference the CERT RR as a user of this registry and value 0, in reference the CERT RR as a user of this registry and value 0, in
particular. particular.
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10. References 10. References
10.1 Normative References 10.1 Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", [1] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and [2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[3] Kille, S., Wahl, M., Grimstad, A., Huber, R., and S. Sataluri, [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, "Using Domains in LDAP/X.500 Distinguished Names", RFC 2247,
January 1998. January 1998.
[4] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [5] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998. August 1998.
[5] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, "OpenPGP [6] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer,
Message Format", RFC 2440, November 1998. "OpenPGP Message Format", RFC 2440, November 1998.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [7] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[7] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [8] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[8] Arends, R., Austein, R., Massey, D., Larson, M., and S. Rose, [9] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", "DNS Security Introduction and Requirements", RFC 4033,
draft-ietf-dnsext-dnssec-intro-13 (work in progress), March 2005.
October 2004.
[9] Arends, R., "Resource Records for the DNS Security Extensions", [10] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
draft-ietf-dnsext-dnssec-records-11 (work in progress), "Resource Records for the DNS Security Extensions", RFC 4034,
October 2004. March 2005.
10.2 Informative References 10.2 Informative References
[10] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[11] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", [11] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999. RFC 2246, January 1999.
[12] Kent, S. and R. Atkinson, "Security Architecture for the [12] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998. Internet Protocol", RFC 2401, November 1998.
[13] Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas, B., [13] Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas, B.,
and T. Ylonen, "SPKI Certificate Theory", RFC 2693, and T. Ylonen, "SPKI Certificate Theory", RFC 2693,
September 1999. September 1999.
[14] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", [14] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548, July 2003. RFC 3548, July 2003.
[15] Richardson, M., "A method for storing IPsec keying material in [15] Richardson, M., "A Method for Storing IPsec Keying Material in
DNS", draft-ietf-ipseckey-rr-11 (work in progress), July 2004. DNS", RFC 4025, March 2005.
[16] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions [16] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851, (S/MIME) Version 3.1 Message Specification", RFC 3851,
July 2004. July 2004.
Author's Address Author's Address
Simon Josefsson Simon Josefsson
Email: simon@josefsson.org Email: simon@josefsson.org
 End of changes. 

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