draft-ietf-dnsext-rfc2538bis-04.txt   draft-ietf-dnsext-rfc2538bis-05.txt 
Network Working Group S. Josefsson Network Working Group S. Josefsson
Expires: March 3, 2006 Expires: March 12, 2006
Storing Certificates in the Domain Name System (DNS) Storing Certificates in the Domain Name System (DNS)
draft-ietf-dnsext-rfc2538bis-04 draft-ietf-dnsext-rfc2538bis-05
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
Cryptographic public keys are frequently published and their Cryptographic public keys 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
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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
3.2. Purpose-based X.509 CERT RR Names . . . . . . . . . . . . 8 3.2. Purpose-based X.509 CERT RR Names . . . . . . . . . . . . 8
3.3. Content-based OpenPGP CERT RR Names . . . . . . . . . . . 9 3.3. Content-based OpenPGP CERT RR Names . . . . . . . . . . . 9
3.4. Purpose-based OpenPGP CERT RR Names . . . . . . . . . . . 9 3.4. Purpose-based OpenPGP CERT RR Names . . . . . . . . . . . 9
3.5. Owner names for IPKIX, ISPKI, and IPGP . . . . . . . . . . 9 3.5. Owner names for IPKIX, ISPKI, and IPGP . . . . . . . . . . 10
4. Performance Considerations . . . . . . . . . . . . . . . . . . 10 4. Performance Considerations . . . . . . . . . . . . . . . . . . 10
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Changes since RFC 2538 . . . . . . . . . . . . . . . . . . . . 11 9. Changes since RFC 2538 . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Copying conditions . . . . . . . . . . . . . . . . . 12 Appendix A. Copying conditions . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . . 12 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . . 13 10.2. Informative References . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 16
1. Introduction 1. Introduction
Public keys are frequently published in the form of a certificate and Public keys are frequently published in the form of a certificate and
their authenticity is commonly demonstrated by certificates and their authenticity is commonly demonstrated by certificates and
related certificate revocation lists (CRLs). A certificate is a related certificate revocation lists (CRLs). A certificate is a
binding, through a cryptographic digital signature, of a public key, binding, through a cryptographic digital signature, of a public key,
a validity interval and/or conditions, and identity, authorization, a validity interval and/or conditions, and identity, authorization,
or other information. A certificate revocation list is a list of or other information. A certificate revocation list is a list of
certificates that are revoked, and incidental information, all signed certificates that are revoked, and incidental information, all signed
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| algorithm | / | algorithm | /
+---------------+ certificate or CRL / +---------------+ certificate or CRL /
/ / / /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
The type field is the certificate type as defined in section 2.1 The type field is the certificate type as defined in section 2.1
below. below.
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 [10]. This field is used as an efficiency measure to Appendix B of [11]. 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. Note that two different keys
be transformed to the format it would have as the public key portion may have the same key tag. However, the key must always be
of a DNSKEY RR before the key tag is computed. This is only possible transformed to the format it would have as the public key portion of
if the key is applicable to an algorithm (and limits such as key size a DNSKEY RR before the key tag is computed. This is only possible if
limits) defined for DNS security. If it is not, the algorithm field the key is applicable to an algorithm and complies to limits (such as
MUST BE zero and the tag field is meaningless and SHOULD BE zero. key size) defined for DNS security. If it is not, 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 The algorithm field has the same meaning as the algorithm field in
DNSKEY and RRSIG RRs [10], except that a zero algorithm field DNSKEY and RRSIG RRs [11], except that a zero algorithm field
indicates the algorithm is unknown to a secure DNS, which may simply indicates the algorithm is unknown to a secure DNS, which may simply
be the result of the algorithm not having been standardized for be the result of the algorithm not having been standardized for
DNSSEC. DNSSEC [10].
2.1. Certificate Type Values 2.1. Certificate Type Values
The following values are defined or reserved: The following values are defined or reserved:
Value Mnemonic Certificate Type Value Mnemonic Certificate Type
----- -------- ---------------- ----- -------- ----------------
0 reserved 0 reserved
1 PKIX X.509 as per PKIX 1 PKIX X.509 as per PKIX
2 SPKI SPKI certificate 2 SPKI SPKI certificate
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4 IPKIX The URL of an X.509 data object 4 IPKIX The URL of an X.509 data object
5 ISPKI The URL of an SPKI certificate 5 ISPKI The URL of an SPKI certificate
6 IPGP The URL of an OpenPGP packet 6 IPGP The URL of an OpenPGP packet
7-252 available for IANA assignment 7-252 available for IANA assignment
253 URI URI private 253 URI URI private
254 OID OID private 254 OID OID private
255-65534 available for IANA assignment 255-65534 available for IANA assignment
65535 reserved 65535 reserved
The PKIX type is reserved to indicate an X.509 certificate conforming The PKIX type is reserved to indicate an X.509 certificate conforming
to the profile being defined by the IETF PKIX working group. The to the profile defined by the IETF PKIX working group [9]. 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 [14], for use when the SPKI documents are moved from experimental
status. status.
The PGP type indicates an OpenPGP packet as described in [6] 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 [6], but it transferable public keys as described in section 10.1 of [6], 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
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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 [10]. a mnemonic symbol as listed in [11].
The certificate / CRL portion is represented in base 64 [14] and may The certificate / CRL portion is represented in base 64 [15] 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
the certificate / CRL proper. But only a single logical base 64 the certificate / CRL proper. But only a single logical base 64
string will appear in the text representation. string will appear in the text representation.
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3. Appropriate Owner Names for CERT RRs 3. Appropriate Owner Names for CERT RRs
It is recommended that certificate CERT RRs be stored under a domain It is recommended that certificate CERT RRs be stored under a domain
name related to their subject, i.e., the name of the entity intended name related to their subject, i.e., the name of the entity intended
to control the private key corresponding to the public key being to control the private key corresponding to the public key being
certified. It is recommended that certificate revocation list CERT certified. It is recommended that certificate revocation list CERT
RRs be stored under a domain name related to their issuer. RRs be stored under a domain name related to their issuer.
Following some of the guidelines below may result in the use in DNS Following some of the guidelines below may result in the use in DNS
names of characters that require DNS quoting which is to use a names with characters that require DNS quoting as per section 5.1 of
backslash followed by the octal representation of the ASCII code for RFC 1035 [2].
the character (e.g., \000 for NULL).
The choice of name under which CERT RRs are stored is important to The choice of name under which CERT RRs are stored is important to
clients that perform CERT queries. In some situations, the clients clients that perform CERT queries. In some situations, the clients
may not know all information about the CERT RR object it wishes to may not know all information about the CERT RR object it wishes to
retrieve. For example, a client may not know the subject name of an retrieve. For example, a client may not know the subject name of an
X.509 certificate, or the e-mail address of the owner of an OpenPGP X.509 certificate, or the e-mail address of the owner of an OpenPGP
key. Further, the client might only know the hostname of a service key. Further, the client might only know the hostname of a service
that uses X.509 certificates or the Key ID of an OpenPGP key. that uses X.509 certificates or the Key ID of an OpenPGP key.
Therefore, two owner name guidelines are defined: content-based owner Therefore, two owner name guidelines are defined: content-based owner
names and purpose-based owner names. A content-based owner name is names and purpose-based owner names. A content-based owner name is
derived from the content of the CERT RR data; for example, the derived from the content of the CERT RR data; for example, the
Subject field in an X.509 certificate or the User ID field in OpenPGP Subject field in an X.509 certificate or the User ID field in OpenPGP
keys. A purpose-based owner name is a name that a client retrieving keys. A purpose-based owner name is a name that a client retrieving
CERT RRs MUST already know; for example, the host name of an X.509 CERT RRs ought to already know; for example, the host name of an
protected service or the Key ID of an OpenPGP key. The content-based X.509 protected service or the Key ID of an OpenPGP key. The
and purpose-based owner name MAY be the same; for example, when a content-based and purpose-based owner name may be the same; for
client looks up a key based on the From: address of an incoming example, when a client looks up a key based on the From: address of
e-mail. an incoming e-mail.
Implementations SHOULD use the purpose-based owner name guidelines Implementations SHOULD use the purpose-based owner name guidelines
described in this document, and MAY use CNAMEs of content-based owner described in this document, and MAY use CNAME RRs at content-based
names (or other names), pointing to the purpose-based owner name. 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 3.1. Content-based X.509 CERT RR Names
Some X.509 versions permit multiple names to be associated with Some X.509 versions, such as the PKIX profile of X.509 [9], permit
subjects and issuers under "Subject Alternate Name" and "Issuer multiple names to be associated with subjects and issuers under
Alternate Name". For example, X.509v3 has such Alternate Names with "Subject Alternative Name" and "Issuer Alternative Name". For
an ASN.1 specification as follows: example, the PKIX profile has such Alternate Names with an ASN.1
specification as follows:
GeneralName ::= CHOICE { GeneralName ::= CHOICE {
otherName [0] INSTANCE OF OTHER-NAME, otherName [0] OtherName,
rfc822Name [1] IA5String, rfc822Name [1] IA5String,
dNSName [2] IA5String, dNSName [2] IA5String,
x400Address [3] EXPLICIT OR-ADDRESS.&Type, x400Address [3] ORAddress,
directoryName [4] EXPLICIT Name, directoryName [4] Name,
ediPartyName [5] EDIPartyName, ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String, uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING, iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER registeredID [8] OBJECT IDENTIFIER }
}
The recommended locations of CERT storage are as follows, in priority The recommended locations of CERT storage are as follows, in priority
order: order:
1. If a domain name is included in the identification in the 1. If a domain name is included in the identification in the
certificate or CRL, that should be used. certificate or CRL, that ought 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 ought to be used.
3. If neither of the above is used, but a URI containing a domain 3. If neither of the above is used, but a URI containing a domain
name is present, that domain name should be used. name is present, that domain name ought to 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 ought to 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 [4]. 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/ 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) 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) string "John (the Man) Doe", (b) domain name john-doe.com, and (c)
uri <https://www.secure.john-doe.com:8080/>. The storage locations URI <https://www.secure.john-doe.com:8080/>. The storage locations
recommended, in priority order, would be 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.
Example 2: An X.509v3 certificate is issued to /CN=James Hacker/ 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) 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 domain name widget.foo.example, (b) IPv4 address 10.251.13.201, and
(c) string "James Hacker <hacker@mail.widget.foo.example>". The (c) string "James Hacker <hacker@mail.widget.foo.example>". The
storage locations recommended, in priority order, would be storage locations recommended, in priority order, would be
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2. 201.13.251.10.in-addr.arpa, and 2. 201.13.251.10.in-addr.arpa, and
3. hacker.mail.widget.foo.example. 3. hacker.mail.widget.foo.example.
3.2. Purpose-based X.509 CERT RR Names 3.2. Purpose-based X.509 CERT RR Names
Due to the difficulty for clients that do not already possess a Due to the difficulty for clients that do not already possess a
certificate to reconstruct the content-based owner name, purpose- certificate to reconstruct the content-based owner name, purpose-
based owner names are recommended in this section. Recommendations based owner names are recommended in this section. Recommendations
for purpose-based owner names vary per scenario. The following table for purpose-based owner names vary per scenario. The following table
summarizes the purpose-based X.509 CERT RR owner name guidelines for summarizes the purpose-based X.509 CERT RR owner name guidelines for
use with S/MIME [16], SSL/TLS [11], and IPSEC [12]: use with S/MIME [16], SSL/TLS [12], and IPSEC [13]:
Scenario Owner name Scenario Owner name
------------------ ---------------------------------------------- ------------------ ----------------------------------------------
S/MIME Certificate Standard translation of an RFC 2822 email S/MIME Certificate Standard translation of an RFC 2822 email
address. Example: An S/MIME certificate for address. Example: An 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,
"postmaster.example.org". "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, for IPv4 IPSEC Certificate Hostname of the IPSEC machine and/or, for IPv4
or IPv6 addresses, the fully qualified domain or IPv6 addresses, the fully qualified domain
name in the appropriate reverse domain. name in the appropriate reverse domain.
An alternate approach for IPSEC is to store raw public keys [15]. An alternate approach for IPSEC is to store raw public keys [17].
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 [6]. 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 [8] 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 ought to be under the standard translation of the email address into
domain name, which would be leslie.host.example in this case. If no a domain name, which would be leslie.host.example in this case. If
RFC 2822 name can be extracted from the string name, no specific no 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. Example: to reduce the amount of data stored in the DNS. Example:
$ORIGIN example.org. $ORIGIN example.org.
smith IN CERT PGP 0 0 <OpenPGP binary> smith IN CERT PGP 0 0 <OpenPGP binary>
john.smith IN CNAME smith john.smith IN CNAME smith
js IN CNAME smith js IN CNAME smith
3.4. Purpose-based OpenPGP CERT RR Names 3.4. Purpose-based OpenPGP CERT RR Names
Applications that receive an OpenPGP packet containing encrypted or Applications that receive an OpenPGP packet containing encrypted or
signed data but do not know the email address of the sender will have signed data but do not know the email address of the sender will have
difficulties constructing the correct owner name and cannot use the difficulties constructing the correct owner name and cannot use the
content-based owner name guidelines. However, these clients commonly content-based owner name guidelines. However, these clients commonly
know the key fingerprint or the Key ID. The key ID is found in know the key fingerprint or the Key ID. The key ID is found in
OpenPGP packets, and the key fingerprint is commonly found in OpenPGP packets, and the key fingerprint is commonly found in
auxilliary data that may be available. In this case, use of an owner auxiliary data that may be available. In this case, use of an owner
name identical to the key fingerprint and the key ID expressed in name identical to the key fingerprint and the key ID expressed in
hexadecimal [14] is recommended. Example: hexadecimal [15] is recommended. Example:
$ORIGIN example.org. $ORIGIN example.org.
0424D4EE81A0E3D119C6F835EDA21E94B565716F IN CERT PGP ... 0424D4EE81A0E3D119C6F835EDA21E94B565716F IN CERT PGP ...
F835EDA21E94B565716F IN CERT PGP ... F835EDA21E94B565716F IN CERT PGP ...
B565716F IN CERT PGP ... B565716F IN CERT PGP ...
If the same key material is stored for several owner names, the use If the same key material is stored for several owner names, the use
of CNAME may be used to avoid data duplication. Note that CNAME is of CNAME may be used to avoid data duplication. Note that CNAME is
not always applicable, because it maps one owner name to the other not always applicable, because it maps one owner name to the other
for all purposes, which may be sub-optimal when two keys with the for all purposes, which may be sub-optimal when two keys with the
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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, Olaf M. Kolkman, Ben Laurie, Edward Lewis, Jason Dubuisson, Peter Koch, Olaf M. Kolkman, Ben Laurie, Edward Lewis,
Sloderbeck, Samuel Weiler, and Florian Weimer. No doubt the list is Marcos Sanz, Jason Sloderbeck, Samuel Weiler, and Florian Weimer. No
incomplete. We apologize to anyone we left out. 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- signature. Thus, it is reasonable to store certificates in non-
secure DNS zones or to retrieve certificates from DNS with DNS secure DNS zones or to retrieve certificates from DNS with DNS
security checking not implemented or deferred for efficiency. The security checking not implemented or deferred for efficiency. The
results MAY be trusted if the certificate chain is verified back to a results may be trusted if the certificate chain is verified back to a
known trusted key and this conforms with the user's security policy. known trusted key and this conforms with the user's security policy.
Alternatively, if certificates are retrieved from a secure DNS zone Alternatively, if certificates are retrieved from a secure DNS zone
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.
If an organization chooses to issue certificates for it's employees, If an organization chooses to issue certificates for its employees,
placing CERT RR's in the DNS by owner name, and if DNSSEC (with NSEC) placing CERT RR's in the DNS by owner name, and if DNSSEC (with NSEC)
is in use, it is possible for someone to enumerate all employees of is in use, it is possible for someone to enumerate all employees of
the organization. This is usually not considered desirable, for the the organization. This is usually not considered desirable, for the
same reason enterprise phone listings are not often publicly same reason enterprise phone listings are not often publicly
published and are even mark confidential. published and are even mark confidential.
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 [9], so there are no security
considerations related to CERT RRs and securing the DNS itself.
If DNSSEC 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 [7]. 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 [7] types 0x0100 through 0xFEFF are assigned through IETF Consensus [7]
skipping to change at page 13, line 20 skipping to change at page 13, line 33
[6] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, [6] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer,
"OpenPGP Message Format", RFC 2440, November 1998. "OpenPGP Message Format", RFC 2440, November 1998.
[7] 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, Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998. October 1998.
[8] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [8] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[9] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [9] 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.
[10] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033, "DNS Security Introduction and Requirements", RFC 4033,
March 2005. March 2005.
[10] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [11] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Resource Records for the DNS Security Extensions", RFC 4034, "Resource Records for the DNS Security Extensions", RFC 4034,
March 2005. March 2005.
10.2. Informative References 10.2. Informative References
[11] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", [12] 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 [13] 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., [14] 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", [15] 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
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.
[17] Richardson, M., "A Method for Storing IPsec Keying Material in
DNS", RFC 4025, March 2005.
Author's Address Author's Address
Simon Josefsson Simon Josefsson
Email: simon@josefsson.org Email: simon@josefsson.org
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
 End of changes. 

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