draft-ietf-sip-eku-01.txt   draft-ietf-sip-eku-02.txt 
SIP WG S. Lawrence SIP WG S. Lawrence
Internet-Draft Bluesocket Inc. Internet-Draft Bluesocket Inc.
Updates: 3261 (if approved) V. Gurbani Updates: 3261 (if approved) V. Gurbani
Intended status: Standards Track Bell Laboratories, Alcatel-Lucent Intended status: Standards Track Bell Laboratories, Alcatel-Lucent
Expires: August 21, 2008 February 18, 2008 Expires: January 12, 2009 July 11, 2008
Using Extended Key Usage (EKU) for Session Initiation Protocol (SIP) Using Extended Key Usage (EKU) for Session Initiation Protocol (SIP)
X.509 Certificates X.509 Certificates
draft-ietf-sip-eku-01 draft-ietf-sip-eku-02
Status of this Memo Status of this Memo
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This Internet-Draft will expire on August 21, 2008. This Internet-Draft will expire on January 12, 2009.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
Abstract Abstract
This memo documents an extended key usage (EKU) X.509 certificate This memo documents an extended key usage (EKU) X.509 certificate
extension for identifying the holder of a certificate as extension for identifying the holder of a certificate as
authoritative for a Session Initiation Protocol (SIP) service in the authoritative for a Session Initiation Protocol (SIP) service in the
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1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Abstract syntax notation . . . . . . . . . . . . . . . . . 3 1.2. Abstract syntax notation . . . . . . . . . . . . . . . . . 3
2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Restricting usage to SIP . . . . . . . . . . . . . . . . . . . 4 3. Restricting usage to SIP . . . . . . . . . . . . . . . . . . . 4
3.1. Extended Key Usage values for SIP domains . . . . . . . . 4 3.1. Extended Key Usage values for SIP domains . . . . . . . . 4
4. Using the SIP EKU in a certificate . . . . . . . . . . . . . . 5 4. Using the SIP EKU in a certificate . . . . . . . . . . . . . . 5
5. Guidelines for a Certification Authority . . . . . . . . . . . 6 5. Guidelines for a Certification Authority . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 8 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10 Intellectual Property and Copyright Statements . . . . . . . . . . 10
1. Terminology 1. Terminology
1.1. Key Words 1.1. Key Words
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 RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [1].
1.2. Abstract syntax notation 1.2. Abstract syntax notation
All X.509 certificate X.509 [4] extensions are defined using ASN.1 All X.509 certificate X.509 [4] extensions are defined using ASN.1
X.680 [5],X.690 [6]. X.680 [5],X.690 [6].
2. Problem statement 2. Problem statement
Consider the SIP [2] trapezoid shown in Figure 1. Consider the SIP [2] trapezoid shown in Figure 1.
proxyA.example.com ------------ proxyB.example.net Proxy-A.example.com Proxy-B.example.net
+-------+ +-------+
| Proxy |--------------------| Proxy |
+----+--+ +---+---+
| | | |
| | | |
| | | |
| +---+ | +---+
0---0 | | 0---0 | |
/-\ |___| /-\ |___|
+---+ / / +---+ / /
+----+ +----+
alice@example.com bob@example.net alice@example.com bob@example.net
Figure 1: SIP Trapezoid Figure 1: SIP Trapezoid
Assume that alice@example.com creates an INVITE for bob@example.net; An user, alice@example.com, invites bob@example.net for a multimedia
her user agent routes the request to some proxy in her domain, communication session. Her user agent routes the request to a proxy,
example.com. Suppose also that example.com is a large organization in her domain. Assume also that example.com is a large organization
that maintains several SIP proxies, and normal resolution rules cause that maintains several SIP proxies, and normal request forwarding
her INVITE to be sent to an outbound proxy proxyA.example.com, which rules cause her invitation to be sent to an outbound proxy, Proxy-
then uses RFC 3263 [7] resolution and finds that proxyB.example.net A.example.com. This proxy uses RFC 3263 [7] resolution to discover
is a valid proxy for example.net that uses TLS. proxyA.example.com that Proxy-B.example.net offers TLS support and can accept the
requests a TLS connection to proxyB.example.net, and each presents a request on behalf of the example.net domain. Proxy-A establishes a
certificate to authenticate that connection. This is the basic TLS connection to Proxy-B, each proxy presents a X.509 certificate to
mutual authentication model explored in depth in [8]. authenticate and protect the confidentiality of the connection. This
is the basic mututal authentication model explored in depth in [8].
However, there arise certain cases where one SIP proxy needs to know However, there arise certain cases where one SIP proxy needs to know
whether it has reached an authoritative proxy in target SIP domain. whether it has reached an authoritative proxy in target SIP domain.
For instance, billing transactions may be triggered when an For instance, billing transactions may be triggered when an
authoritative SIP proxy in one domain sends messages to its authoritative SIP proxy in one domain sends messages to its
equivalent in another domain. In Figure 1, proxyA.example.com equivalent in another domain. In Figure 1, Proxy-A.example.com
performs certain DNS queries to arrive at proxyB.example.net. performs certain DNS queries to arrive at Proxy-B.example.net.
Because of the answers to the DNS queries, proxyA has a certain Because of the answers to the DNS queries, Proxy-A has a certain
expectation that proxyB is a valid proxy in the example.net domain expectation that Proxy-B is a valid proxy in the example.net domain
and is authorized to receive inbound requests targeted to that and is authorized to receive inbound requests targeted to that
domain. domain.
However, the problem for proxyB is different; it is presented with a The problem for Proxy-B is different: it accepts a connection from a
connection from a specific host, but what it needs to determine is specific host (Proxy-A.example.com) but what it needs to determine is
whether or not that connection can be treated as coming from a whether or not that connection can be treated as coming
particular SIP domain. If it receives a certificate that contains authoritatively from a particular SIP domain. If Proxy-B receives a
only the name proxyA.example.com, then it cannot determine that certificate tha only contains the identity "sip:Proxy-A.example.com",
proxyA is authorized to act as a SIP outbound proxy for example.com, it is unable to make a determination that Proxy-A is authorized to
because example.com may use different systems for inbound messages so act as a SIP outbound proxy for the example.com domain (note that
SIP DNS resolution of example.com may not lead to proxyA.example.com example.com domain may use different inbound proxies, so SIP DNS
(if this is the case, proxyB should not reuse this connection if it resolution of "sip:example.com" may not lead to "Proxy-
needs to send a request to example.com). The certificate usage in A.example.com".) Certificate usage in SIP cannot require that every
SIP should not require that every outbound proxy for a domain must outbound proxy for a domain also serve as its inbound proxy. Thus,
also be an inbound proxy for that domain, but should provide for there is a need for an extra attribute that allows an inbound proxy
certificate based binding of the SIP domain name to a particular to know that its peer is an authorized proxy for that domain. This
connection. document discusses such an attribute as part of the X.509 certificate
Thus, there is a need for an extra attribute that allows a proxy to
know that its peer is an authorized proxy for that domain. This memo
discusses such an attribute as part of the X.509 certificate
exchanged by the proxies when a TLS connection is first established. exchanged by the proxies when a TLS connection is first established.
3. Restricting usage to SIP 3. Restricting usage to SIP
This memo defines a certificate profile for binding a SIP domain name This memo defines a certificate profile for binding a SIP domain name
to an entity. A SIP domain name is frequently textually identical to to an entity. A SIP domain name is frequently textually identical to
the same DNS name used for other purposes. For example, the DNS name the same DNS name used for other purposes. For example, the DNS name
example.com may serve as a SIP domain name, an email domain name, and example.com may serve as a SIP domain name, an email domain name, and
web service name. Since these different services within a single web service name. Since these different services within a single
organization might be administered independently and hosted organization might be administered independently and hosted
separately, it should be possible to create a certificate that binds separately, it should be possible to create a certificate that binds
the DNS name to its usage as a SIP domain name without creating the the DNS name to its usage as a SIP domain name without creating the
implication that the usage is also valid for some other purpose. RFC implication that the usage is also valid for some other purpose.
3280 [3] section 4.2.1.13 defines a mechanism for this purpose: an RFC5280 [3] section 4.2.1.12 defines a mechanism for this purpose:
"Extended Key Usage" attribute. Certificates whose purpose is to an "Extended Key Usage" attribute. Certificates whose purpose is to
bind a SIP domain identity without binding other non-SIP identities bind a SIP domain identity without binding other non-SIP identities
MUST include an id-kp-SIPdomain attribute. MUST include an id-kp-SIPdomain attribute.
3.1. Extended Key Usage values for SIP domains 3.1. Extended Key Usage values for SIP domains
RFC 3280 [3] specifies the EKU X.509 certificate Extension for use in RFC 5280 [3] specifies the EKU X.509 certificate Extension for use in
the Internet. The extension indicates one or more purposes for which the Internet. The extension indicates one or more purposes for which
the certified public key may be used. The EKU extension can be used the certified public key may be used. The EKU extension can be used
in conjunction with the key usage extension, which indicates how the in conjunction with the key usage extension, which indicates how the
public key in the certificate may be used, in a more basic public key in the certificate may be used, in a more basic
cryptographic way. cryptographic way.
The EKU extension syntax is repeated here for convenience: The EKU extension syntax is repeated here for convenience:
ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
KeyPurposeId ::= OBJECT IDENTIFIER KeyPurposeId ::= OBJECT IDENTIFIER
This specification defines the KeyPurposeId id-kp-sipDomain. This specification defines the KeyPurposeId id-kp-sipDomain.
Inclusion of this KeyPurposeId in a certificate indicates that any
DNS Subject names in the certificate are intended to identify the
holder as authoritative for a SIP service in the domain named by the
subjectAltName values. Whether or not to include this restriction is
up to the certificate issuer, but if it is included, it MUST be
marked as critical so that implementations that do not understand it
will not accept the certificate for any other purpose.
id-kp OBJECT IDENTIFIER ::= id-kp OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) 3 } security(5) mechanisms(5) pkix(7) 3 }
id-kp-sipDomain OBJECT IDENTIFIER ::= { id-kp VALUE-TBD } id-kp-sipDomain OBJECT IDENTIFIER ::= { id-kp VALUE-TBD }
Inclusion of this KeyPurposeId in a certificate indicates that any
DNS subject names in the certificate are intended to identify the
holder as authoritative for a SIP service in the domain named by the
subjectAltName values. Whether or not to include this restriction is
up to the certificate issuer, but if it is included, it SHOULD be
marked as critical.
This is so that implementations that understand this extension
will honor it while those that do not are not impeded by its
presence.
See Section 4 for how the presence of an id-kp-sipDomain value See Section 4 for how the presence of an id-kp-sipDomain value
affects the interpretation of the certificate. affects the interpretation of the certificate.
4. Using the SIP EKU in a certificate 4. Using the SIP EKU in a certificate
Section 7.1 of [8] contains two steps for finding an identity (or a Section 7.1 of [8] contains two steps for finding an identity (or a
set of identities) in an X.509 certificate. In order to determine set of identities) in an X.509 certificate. In order to determine
whether a SIP proxy is authoritative for its domain, implementations whether the SIP entity presenting the certificate is authoritative
MUST perform the step given below first, and then proceed with the for its domain, implementations MUST perform the step given below
steps in Section 7.1 of [8]. first, and then proceed with the steps in Section 7.1 of [8].
The Extended Key Usage value(s), if any, MUST be examined to The Extended Key Usage value(s), if any, MUST be examined to
determine whether or not the certificate is valid for use in SIP: determine whether or not the certificate is valid for use in SIP
(note that in the steps below, we assume that the certificate is
otherwise valid following the checks in RFC5280 [3]):
o If the certificate does not contain any EKU values (the Extended o If the certificate does not contain any EKU values (the Extended
Key Usage extension does not exist), it is a matter of local Key Usage extension does not exist), it is a matter of local
policy whether or not to accept the certificate for use as a SIP policy whether or not to accept the certificate for use as a SIP
certificate. certificate.
o If the certificate contains the id-kp-sipDomain EKU extension, o If the certificate contains the id-kp-sipDomain EKU extension,
then the certificate MUST be accepted as valid for use as a SIP then the certificate MUST be acceptable as valid for use as a SIP
certificate. certificate.
o If the certificate does not contain the id-kp-sipDomain EKU value, o If the certificate does not contain the id-kp-sipDomain EKU value,
but does contain the id-kp-anyExtendedKeyUsage EKU value, it is a but does contain the id-kp-anyExtendedKeyUsage EKU value, it is a
matter of local policy whether or not to accept it for use as a matter of local policy whether or not to accept it for use as a
SIP certificate. SIP certificate.
o If the certificate does not contain the id-kp-sipDomain EKU value, o If the certificate does not contain the id-kp-sipDomain EKU value,
but does contain either the id-kp-serverAuth or id-kp-clientAuth but does contain either the id-kp-serverAuth or id-kp-clientAuth
EKU values, it is a matter of local policy whether or not to EKU values, it is a matter of local policy whether or not to
accept it for use as a SIP certificate. accept it for use as a SIP certificate.
id-kp-serverAuth and id-kp-clientAuth EKU values are defined in
Section 4.2.1.12 of RFC 5280 [3].
o If EKU extension exists but does not contain any of the id-kp- o If EKU extension exists but does not contain any of the id-kp-
sipDomain, id-kp-anyExtendedKeyUsage, id-kp-serverAuth, or id-kp- sipDomain, id-kp-anyExtendedKeyUsage, id-kp-serverAuth, or id-kp-
clientAuth EKU values, then the certificate MUST NOT be accepted clientAuth EKU values, then the certificate MUST NOT be considered
as valid for use as a SIP certificate. acceptable as being authoritative for the domain portion of the
SIP domain identities contained in the certificate.
The term "SIP domain identity" is defined in RFC XXXX [8].
5. Guidelines for a Certification Authority 5. Guidelines for a Certification Authority
The procedures and practices employed by the certification authority The procedures and practices employed by the certification authority
MUST ensure that the correct values for the EKU extension and MUST ensure that the correct values for the EKU extension and
subjectAltName are inserted in each certificate that is issued. For subjectAltName are inserted in each certificate that is issued. For
certificates that indicate authority over a SIP domain, but not over certificates that indicate authority over a SIP domain, but not over
services other than SIP, certificate authorities MUST include the id- services other than SIP, certificate authorities SHOULD include the
kp-sipDomain EKU extension. id-kp-sipDomain EKU extension.
6. Security Considerations 6. Security Considerations
This memo defines an EKU X.509 certificate extension that enables the This memo defines an EKU X.509 certificate extension that enables the
holder of a certificate to be authoritative for a SIP service holder of a certificate to be authoritative for a SIP service
belonging to an autonomous domain. Relying parties may execute belonging to an autonomous domain. Relying parties may execute
applicable policies (such as those related to billing) on receiving a applicable policies (such as those related to billing) on receiving a
certificate with the id-kp-sipDomain EKU value. An id-kp-sipDomain certificate with the id-kp-sipDomain EKU value. An id-kp-sipDomain
EKU value does not introduce any new security or privacy concerns. EKU value does not introduce any new security or privacy concerns.
At the very most, it simply allows the relying party to know that the At the very most, it simply allows the relying party to know that the
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9.1. Normative References 9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997. Levels", RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[3] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 [3] Cooper, D., Santesson, S., Farrell, S., Boyen, S., Housley, R.,
Public Key Infrastructure Certificate and Certificate Revocation and W. Polk, "Internet X.509 Public Key Infrastructure
List (CRL) Profile", RFC 3280, April 2002. Certificate and Certificate Revocation List (CRL) Profile",
RFC 5280, May 2008.
[4] International International Telephone and Telegraph Consultative [4] International International Telephone and Telegraph Consultative
Committee, "Information Technology - Open Systems Committee, "Information Technology - Open Systems
Interconnection - The Directory: Authentication Framework", Interconnection - The Directory: Authentication Framework",
CCITT Recommendation X.509, November 1988. CCITT Recommendation X.509, November 1988.
[5] International International Telephone and Telegraph Consultative [5] International International Telephone and Telegraph Consultative
Committee, "Specification of Abstract Syntax Notation One Committee, "Specification of Abstract Syntax Notation One
(ASN.1): Specification of Basic Notation", CCITT Recommendation (ASN.1): Specification of Basic Notation", CCITT Recommendation
X.680, July 1994. X.680, July 1994.
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(BER), Canonical Encoding Rules (CER) and Distinguished Encoding (BER), Canonical Encoding Rules (CER) and Distinguished Encoding
Rules (DER)", ITU-T Recommendation X.690, 1994. Rules (DER)", ITU-T Recommendation X.690, 1994.
[7] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol [7] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Location SIP Servers", RFC 3263, June 2002. (SIP): Location SIP Servers", RFC 3263, June 2002.
9.2. Informative References 9.2. Informative References
[8] Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain Certificates [8] Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain Certificates
in the Session Initiation Protocol (SIP)", in the Session Initiation Protocol (SIP)",
draft-ietf-sip-domain-certs-00.txt (work in progress), draft-ietf-sip-domain-certs-01.txt (work in progress),
November 2007. July 2008.
Appendix A. ASN.1 Module Appendix A. ASN.1 Module
SIPDomainCertExtn SIPDomainCertExtn
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-sip-domain-extns2007(VALUE-TBD) } id-mod-sip-domain-extns2007(VALUE-TBD) }
DEFINITIONS IMPLICIT TAGS ::= DEFINITIONS IMPLICIT TAGS ::=
BEGIN BEGIN
skipping to change at page 8, line 38 skipping to change at page 8, line 49
id-kp OBJECT IDENTIFIER ::= id-kp OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) 3 } security(5) mechanisms(5) pkix(7) 3 }
id-aca OBJECT IDENTIFIER ::= id-aca OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) 10 } security(5) mechanisms(5) pkix(7) 10 }
-- Extended Key Usage Values -- Extended Key Usage Values
id-kp-sipDomain OBJECT IDENTIFIER ::= { id-kp VALUE-TBD } id-kp-sipDomain OBJECT IDENTIFIER ::= { id-kp 20 }
END END
Authors' Addresses Authors' Addresses
Scott Lawrence Scott Lawrence
Bluesocket Inc. Bluesocket Inc.
10 North Ave. 10 North Ave.
Burlington, MA 01803 Burlington, MA 01803
USA USA
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