draft-ietf-stir-rfc4474bis-03.txt   draft-ietf-stir-rfc4474bis-04.txt 
Network Working Group J. Peterson Network Working Group J. Peterson
Internet-Draft NeuStar Internet-Draft NeuStar
Intended status: Standards Track C. Jennings Intended status: Standards Track C. Jennings
Expires: September 9, 2015 Cisco Expires: January 7, 2016 Cisco
E. Rescorla E. Rescorla
RTFM, Inc. RTFM, Inc.
March 8, 2015 July 6, 2015
Authenticated Identity Management in the Session Initiation Protocol Authenticated Identity Management in the Session Initiation Protocol
(SIP) (SIP)
draft-ietf-stir-rfc4474bis-03.txt draft-ietf-stir-rfc4474bis-04.txt
Abstract Abstract
The baseline security mechanisms in the Session Initiation Protocol The baseline security mechanisms in the Session Initiation Protocol
(SIP) are inadequate for cryptographically assuring the identity of (SIP) are inadequate for cryptographically assuring the identity of
the end users that originate SIP requests, especially in an the end users that originate SIP requests, especially in an
interdomain context. This document defines a mechanism for securely interdomain context. This document defines a mechanism for securely
identifying originators of SIP requests. It does so by defining new identifying originators of SIP requests. It does so by defining new
SIP header fields for conveying a signature used for validating the SIP header fields for conveying a signature used for validating the
identity, and for conveying a reference to the credentials of the identity, and for conveying a reference to the credentials of the
skipping to change at page 1, line 41 skipping to change at page 1, line 41
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 9, 2015. This Internet-Draft will expire on January 7, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 20 skipping to change at page 2, line 20
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of Operations . . . . . . . . . . . . . . . . . . . 5 3. Overview of Operations . . . . . . . . . . . . . . . . . . . 5
4. Signature Generation and Validation . . . . . . . . . . . . . 6 4. Signature Generation and Validation . . . . . . . . . . . . . 6
4.1. Authentication Service Behavior . . . . . . . . . . . . . 6 4.1. Authentication Service Behavior . . . . . . . . . . . . . 6
4.2. Verifier Behavior . . . . . . . . . . . . . . . . . . . . 9 4.2. Verifier Behavior . . . . . . . . . . . . . . . . . . . . 9
5. Credentials . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Credentials . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Credential Use by the Authentication Service . . . . . . 10 5.1. Credential Use by the Authentication Service . . . . . . 11
5.2. Credential Use by the Verification Service . . . . . . . 12 5.2. Credential Use by the Verification Service . . . . . . . 12
5.3. Handling Identity-Info URIs . . . . . . . . . . . . . . . 12 5.3. Handling Identity-Info URIs . . . . . . . . . . . . . . . 13
5.4. Credential Systems . . . . . . . . . . . . . . . . . . . 13 5.4. Credential Systems . . . . . . . . . . . . . . . . . . . 13
6. Identity Types . . . . . . . . . . . . . . . . . . . . . . . 14 6. Identity Types . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Telephone Numbers . . . . . . . . . . . . . . . . . . . . 14 6.1. Telephone Numbers . . . . . . . . . . . . . . . . . . . . 14
6.1.1. Canonicalization Procedures . . . . . . . . . . . . . 15 6.1.1. Canonicalization Procedures . . . . . . . . . . . . . 15
6.2. Domain Names . . . . . . . . . . . . . . . . . . . . . . 16 6.2. Domain Names . . . . . . . . . . . . . . . . . . . . . . 17
7. Header Syntax . . . . . . . . . . . . . . . . . . . . . . . . 17 7. Header Syntax . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20 8. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 22
9.1. Handling of digest-string Elements . . . . . . . . . . . 21 10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9.1.1. Protection of the To Header and Retargeting . . . . . 24 10.1. Handling of digest-string Elements . . . . . . . . . . . 23
9.2. Securing the Connection to the Authentication Service . . 25 10.1.1. Protection of the To Header and Retargeting . . . . 26
9.3. Authorization and Transitional Strategies . . . . . . . . 26 10.2. Securing the Connection to the Authentication Service . 27
9.4. Display-Names and Identity . . . . . . . . . . . . . . . 27 10.3. Authorization and Transitional Strategies . . . . . . . 28
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 10.4. Display-Names and Identity . . . . . . . . . . . . . . . 29
10.1. Header Field Names . . . . . . . . . . . . . . . . . . . 27 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10.2. Identity-Info Parameters . . . . . . . . . . . . . . . . 28 11.1. Header Field Names . . . . . . . . . . . . . . . . . . . 29
10.3. Identity-Info Algorithm Parameter Values . . . . . . . . 28 11.2. Identity-Info Parameters . . . . . . . . . . . . . . . . 30
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 11.3. Identity-Info Algorithm Parameter Values . . . . . . . . 30
12. Changes from RFC4474 . . . . . . . . . . . . . . . . . . . . 28 11.4. Identity-Extension Names . . . . . . . . . . . . . . . . 30
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
13.1. Normative References . . . . . . . . . . . . . . . . . . 29 13. Changes from RFC4474 . . . . . . . . . . . . . . . . . . . . 31
13.2. Informative References . . . . . . . . . . . . . . . . . 29 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 14.1. Normative References . . . . . . . . . . . . . . . . . . 31
14.2. Informative References . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction 1. Introduction
This document provides enhancements to the existing mechanisms for This document provides enhancements to the existing mechanisms for
authenticated identity management in the Session Initiation Protocol authenticated identity management in the Session Initiation Protocol
(SIP, [RFC3261]). An identity, for the purposes of this document, is (SIP, [RFC3261]). An identity, for the purposes of this document, is
defined as either a SIP URI, commonly a canonical address-of-record defined as either a SIP URI, commonly a canonical address-of-record
(AoR) employed to reach a user (such as (AoR) employed to reach a user (such as
'sip:alice@atlanta.example.com'), or a telephone number, which can be 'sip:alice@atlanta.example.com'), or a telephone number, which can be
represented as either a TEL URI [RFC3966] or as the user portion of a represented as either a TEL URI [RFC3966] or as the user portion of a
skipping to change at page 8, line 24 skipping to change at page 8, line 24
name portion of the From header field (e.g., 'Alice Atlanta'). name portion of the From header field (e.g., 'Alice Atlanta').
Authentication services MAY check and validate the display-name as Authentication services MAY check and validate the display-name as
well, and compare it to a list of acceptable display-names that may well, and compare it to a list of acceptable display-names that may
be used by the sender; if the display-name does not meet policy be used by the sender; if the display-name does not meet policy
constraints, the authentication service could return a 403 response constraints, the authentication service could return a 403 response
code. In this case, the reason phrase should indicate the nature of code. In this case, the reason phrase should indicate the nature of
the problem; for example, "Inappropriate Display Name". However, the the problem; for example, "Inappropriate Display Name". However, the
display-name is not always present, and in many environments the display-name is not always present, and in many environments the
requisite operational procedures for display-name validation may not requisite operational procedures for display-name validation may not
exist, so no normative guidance is given here. For more information, exist, so no normative guidance is given here. For more information,
see Section 9.4. see Section 10.4.
Step 3: Step 3:
An authentication service MUST add a Date header field to SIP An authentication service MUST add a Date header field to SIP
requests if one is not already present. The authentication service requests if one is not already present. The authentication service
MUST ensure that any preexisting Date header in the request is MUST ensure that any preexisting Date header in the request is
accurate. Local policy can dictate precisely how accurate the Date accurate. Local policy can dictate precisely how accurate the Date
must be; a RECOMMENDED maximum discrepancy of sixty seconds will must be; a RECOMMENDED maximum discrepancy of sixty seconds will
ensure that the request is unlikely to upset any verifiers. If the ensure that the request is unlikely to upset any verifiers. If the
Date header contains a time different by more than one minute from Date header contains a time different by more than one minute from
skipping to change at page 9, line 15 skipping to change at page 9, line 15
environments where body security of INVITE transactions is necessary. environments where body security of INVITE transactions is necessary.
Details on the generation of this header are provided in Section 7. Details on the generation of this header are provided in Section 7.
If the authentication service is adding an Identity-Reliance header, If the authentication service is adding an Identity-Reliance header,
it MUST also add a Content-Length header field to SIP requests if one it MUST also add a Content-Length header field to SIP requests if one
is not already present; this can help verifiers to double-check that is not already present; this can help verifiers to double-check that
they are hashing exactly as many bytes of message-body as the they are hashing exactly as many bytes of message-body as the
authentication service when they verify the message. authentication service when they verify the message.
Step 5: Step 5:
The authentication service MAY an identity-extension signature and
add an Identity-Extension header to the request containing this
signature. The Identity-Extension header is created by this
specification, but the header field value is left undefined. Only
implementations that extend this base mechanism MAY popular this
header field and add this signature. See Section 8.
Step 6:
The authentication service MUST form the identity signature and add The authentication service MUST form the identity signature and add
an Identity header to the request containing this signature. After an Identity header to the request containing this signature. After
the Identity header has been added to the request, the authentication the Identity header has been added to the request, the authentication
service MUST also add an Identity-Info header. The Identity-Info service MUST also add an Identity-Info header. The Identity-Info
header contains a URI from which the authentication service's header contains a URI from which the authentication service's
credential can be acquired; see Section 5.3 for more on credential credential can be acquired; see Section 5.3 for more on credential
acquisition. Details on the syntax of both of these headers are acquisition. Details on the syntax of both of these headers are
provided in Section 7. provided in Section 7.
Finally, the authentication service MUST forward the message Finally, the authentication service MUST forward the message
skipping to change at page 10, line 38 skipping to change at page 10, line 47
following the procedures for generating the hashed reliance-digest- following the procedures for generating the hashed reliance-digest-
string described in Section 7. The Identity-Reliance header provides string described in Section 7. The Identity-Reliance header provides
important protections for non-INVITE transactions (such as MESSAGE or important protections for non-INVITE transactions (such as MESSAGE or
NOTIFY), but verifiers MAY elect not to verify Identity-Reliance when NOTIFY), but verifiers MAY elect not to verify Identity-Reliance when
it protects SDP. If a verifier determines that the signature on the it protects SDP. If a verifier determines that the signature on the
message does not correspond to the reconstructed digest-string, then message does not correspond to the reconstructed digest-string, then
a 438 'Invalid Identity Header' response SHOULD be returned. a 438 'Invalid Identity Header' response SHOULD be returned.
Step 5: Step 5:
If the request contains an Identity-Extension header, then if
verifier supports the extension specified in the Identity-Extension
header field, it SHOULD verify any associated following the
procedures specified in that extension. See Section 8. If a
verifier determines that such a signature in the message does not
correspond to the reconstructed digest-string, then a 438 'Invalid
Identity Header' response SHOULD be returned. If the verifier does
not support the extension, then the contents of the Identity-
Extension header may be ignored.
Step 6:
The verifier MUST must furthermore ensure that the value of the Date The verifier MUST must furthermore ensure that the value of the Date
header meets local policy for freshness (usually, within sixty header meets local policy for freshness (usually, within sixty
seconds) and that it falls within the validity period of the seconds) and that it falls within the validity period of the
credential used to sign the Identity header. For more on the attacks credential used to sign the Identity header. For more on the attacks
this prevents, see Section 9.1. this prevents, see Section 10.1.
5. Credentials 5. Credentials
5.1. Credential Use by the Authentication Service 5.1. Credential Use by the Authentication Service
In order to act as an authentication service, a SIP entity must have In order to act as an authentication service, a SIP entity must have
access to the private keying material of one or more credentials that access to the private keying material of one or more credentials that
cover domain names or telephone numbers. These credentials may cover domain names or telephone numbers. These credentials may
represent authority over an entire domain (such as example.com) or represent authority over an entire domain (such as example.com) or
potentially a set of domains enumerated by the credential. potentially a set of domains enumerated by the credential.
skipping to change at page 16, line 10 skipping to change at page 16, line 31
national or international dialing prefixes or performing similar national or international dialing prefixes or performing similar
procedures. It is only in the case that an implementation cannot procedures. It is only in the case that an implementation cannot
determine how to convert the number to a globally-routable format determine how to convert the number to a globally-routable format
that this step may be skipped. that this step may be skipped.
In some cases, further transformations MAY be made in accordance In some cases, further transformations MAY be made in accordance
with specific policies used within the local domain. For example, with specific policies used within the local domain. For example,
one domain may only use local number formatting and need to one domain may only use local number formatting and need to
convert all To/From user portions to E.164 by prepending country- convert all To/From user portions to E.164 by prepending country-
code and region code digits; another domain might prefix usernames code and region code digits; another domain might prefix usernames
with trunk-routing codes and need to remove the prefix. with trunk-routing codes and need to remove the prefix. Also, in
some networks, the P-Asserted-Identity header field value is used
in lieu of the From header field to convey the telephone number of
the sender of a request; while it is not envisioned that most of
those networks would or should make use of the Identity mechanism
described in this specification, where they do, local policy might
therefore dictate that the canonical string derive from the P-
Asserted-Identity header field rather than the From. In any case
where local policy canonicalizes the number into a form different
from how it appears in the From header field, the use of the
"canon" parameter by authentication services is RECOMMENDED, but
because "canon" itself could then divulge information about users
or networks, implementers should be mindful of the guidelines in
Section 9.
The resulting canonical number string will be used as input to the The resulting canonical number string will be used as input to the
hash calculation during signing and verifying processes. hash calculation during signing and verifying processes.
The ABNF of this number string is: The ABNF of this number string is:
tn-spec = [ "#" / "*" ] 1*DIGIT tn-spec = [ "#" / "*" ] 1*DIGIT
If the result of this procedure forms a complete telephone number, If the result of this procedure forms a complete telephone number,
that number is used for the purpose of creating and signing the that number is used for the purpose of creating and signing the
skipping to change at page 17, line 37 skipping to change at page 18, line 22
identity and the signing credential by following the procedures identity and the signing credential by following the procedures
defined in RFC 2818 [RFC2818], Section 3.1. While RFC 2818 [RFC2818] defined in RFC 2818 [RFC2818], Section 3.1. While RFC 2818 [RFC2818]
deals with the use of HTTP in TLS and is specific to certificates, deals with the use of HTTP in TLS and is specific to certificates,
the procedures described are applicable to verifying identity if one the procedures described are applicable to verifying identity if one
substitutes the "hostname of the server" in HTTP for the domain substitutes the "hostname of the server" in HTTP for the domain
portion of the user's identity in the From header field of a SIP portion of the user's identity in the From header field of a SIP
request with an Identity header. request with an Identity header.
7. Header Syntax 7. Header Syntax
This document specifies three SIP headers: Identity, Identity- This document specifies four SIP headers: Identity, Identity-
Reliance and Identity- Info. Each of these headers can appear only Reliance, Identity- Info, and Identity-Extension. Each of these
once in a SIP request; Identity-Reliance is OPTIONAL, while Identity headers can appear only once in a SIP request; Identity-Reliance are
and Identity-Info are REQUIRED for securing requests with this Identity-Extension are OPTIONAL, while Identity and Identity-Info are
specification. The grammar for these three headers is (following the REQUIRED for securing requests with this specification. The grammar
ABNF [RFC4234] in RFC 3261 [RFC3261]): for the first three headers is (following the ABNF [RFC4234] in RFC
3261 [RFC3261]):
Identity = "Identity" HCOLON signed-identity-digest Identity = "Identity" HCOLON signed-identity-digest
signed-identity-digest = LDQUOT 32LHEX RDQUOT signed-identity-digest = LDQUOT *base64-char RDQUOT
Identity-Reliance = "Identity-Reliance" HCOLON signed-identity-reliance-digest Identity-Reliance = "Identity-Reliance" HCOLON signed-identity-reliance-digest
signed-identity-reliance-digest = LDQUOT 32LHEX RDQUOT signed-identity-reliance-digest = LDQUOT *base64-char RDQUOT
Identity-Info = "Identity-Info" HCOLON ident-info Identity-Info = "Identity-Info" HCOLON ident-info
*( SEMI ident-info-params ) *( SEMI ident-info-params )
ident-info = LAQUOT absoluteURI RAQUOT ident-info = LAQUOT absoluteURI RAQUOT
ident-info-params = ident-info-alg / canonical-str / ident-info-extension ident-info-params = ident-info-alg / canonical-str / ident-info-extension
ident-info-alg = "alg" EQUAL token ident-info-alg = "alg" EQUAL token
canonical-str = "canon" EQUAL tn-spec canonical-str = "canon" EQUAL tn-spec
ident-info-extension = generic-param ident-info-extension = generic-param
base64-char = ALPHA / DIGIT / "/" / "+"
The grammar for the Identity-Extension header field is given in
Section 8.
The signed-identity-reliance-digest is a signed hash of a canonical The signed-identity-reliance-digest is a signed hash of a canonical
string generated from certain components of a SIP request. Creating string generated from certain components of a SIP request. Creating
this hash and the Identity-Reliance header field to contain it is this hash and the Identity-Reliance header field to contain it is
OPTIONAL, and its usage is a matter of local policy for OPTIONAL, and its usage is a matter of local policy for
authentication services. To create the contents of the signed- authentication services. To create the contents of the signed-
identity-reliance-digest, the following element of a SIP message MUST identity-reliance-digest, the following element of a SIP message MUST
be placed in a bit-exact string: be placed in a bit-exact string:
The body content of the message with the bits exactly as they are The body content of the message with the bits exactly as they are
in the message (in the ABNF for SIP, the message-body). This in the message (in the ABNF for SIP, the message-body). This
skipping to change at page 19, line 35 skipping to change at page 20, line 19
including the algorithm description and hexadecimal key including the algorithm description and hexadecimal key
representation, any whitespace, carriage returns, and "/" line representation, any whitespace, carriage returns, and "/" line
break indicators. If multiple non-identical "a=fingerprint" break indicators. If multiple non-identical "a=fingerprint"
attributes appear in an SDP body, then all non-identical attributes appear in an SDP body, then all non-identical
attributes values MUST be concatenated, with no separating attributes values MUST be concatenated, with no separating
character, after sorting the values in alphanumeric order. If the character, after sorting the values in alphanumeric order. If the
SDP body contains no "a=fingerprint" attribute, the fifth element SDP body contains no "a=fingerprint" attribute, the fifth element
MUST be empty, containing no whitespace, resulting in a "||" in MUST be empty, containing no whitespace, resulting in a "||" in
the signed-identity-digest. the signed-identity-digest.
Sixth, the Identity-Reliance header field value, if there is an Sixth, the Identity-Extension header field value, if there is an
Identity-Reliance field in the request. If the message has no Identity-Extension header field in the request. If the message
body, or no Identity-Reliance header, then the fifth slot will be has no Identity-Extension header, then the sixth slot MUST be
empty, and the final "|" will not be followed by any additional empty, containing no whitespace, resulting in a "||" in the
characters. signed-identity-digest. characters.
Seventh, the Identity-Reliance header field value, if there is an
Identity-Reliance header field in the request. If the message has
no body, or no Identity-Reliance header, then the seventh slot
MUST be empty, and the final "|" will not be followed by any
additional characters.
For more information on the security properties of these headers, and For more information on the security properties of these headers, and
why their inclusion mitigates replay attacks, see Section 9 and why their inclusion mitigates replay attacks, see Section 10 and
[RFC3893]. The precise formulation of this digest-string is, [RFC3893]. The precise formulation of this digest-string is,
therefore (following the ABNF[RFC4234] in RFC 3261 [RFC3261]): therefore (following the ABNF[RFC4234] in RFC 3261 [RFC3261]):
digest-string = ( addr-spec / tn-spec ) "|" ( addr-spec / tn-spec ) "|" digest-string = ( addr-spec / tn-spec ) "|" ( addr-spec / tn-spec ) "|"
Method "|" SIP-date "|" [ sdp-fingerprint ] "|" Method "|" SIP-date "|" [ sdp-fingerprint ] "|"
[ signed-identity-extension-digest ] "|"
[ signed-identity-reliance-digest ] [ signed-identity-reliance-digest ]
sdp-fingerprint = byte-string sdp-fingerprint = byte-string
For the definition of 'tn-spec' see Section 6.1.1. For the definition of 'tn-spec' see Section 6.1.1.
After the digest-string or reliance-digest-string is formed, each After the digest-string or reliance-digest-string is formed, each
MUST be hashed and signed with the certificate of authority over the MUST be hashed and signed with the certificate of authority over the
identity. The hashing and signing algorithm is specified by the identity. The hashing and signing algorithm is specified by the
'alg' parameter of the Identity-Info header (see below for more 'alg' parameter of the Identity-Info header (see below for more
information on Identity-Info header parameters). This document information on Identity-Info header parameters). This document
defines only one value for the 'alg' parameter: 'rsa-sha256'; further defines only one value for the 'alg' parameter: 'rsa-sha256'; further
values MUST be defined in a Standards Track RFC, see Section 10.3 for values MUST be defined in a Standards Track RFC, see Section 11.3 for
more information. All implementations of this specification MUST more information. All implementations of this specification MUST
support 'rsa-sha256'. When the 'rsa-sha256' algorithm is specified support 'rsa-sha256'. When the 'rsa-sha256' algorithm is specified
in the 'alg' parameter of Identity-Info, the hash and signature MUST in the 'alg' parameter of Identity-Info, the hash and signature MUST
be generated as follows: compute the results of signing this string be generated as follows: compute the results of signing this string
with sha1WithRSAEncryption as described in RFC 3370 [RFC3370] and with sha1WithRSAEncryption as described in RFC 3370 [RFC3370] and
base64 encode the results as specified in RFC 3548 [RFC3548]. A base64 encode the results as specified in RFC 3548 [RFC3548]. A
2048-bit or longer RSA key MUST be used. The result of the digest- 2048-bit or longer RSA key MUST be used. The result of the digest-
string hash is placed in the Identity header field; the optional string hash is placed in the Identity header field; the optional
reliance-digest-string hash goes in the Identity-Reliance header. reliance-digest-string hash goes in the Identity-Reliance header.
The 'absoluteURI' portion of the Identity-Info header MUST contain a The 'absoluteURI' portion of the Identity-Info header MUST contain a
URI; see Section 5.3 for more on choosing how to advertise URI; see Section 5.3 for more on choosing how to advertise
credentials through Identity-Info. credentials through Identity-Info.
8. Privacy Considerations 8. Extensibility
As future requirements may warrant increasing the scope of the
Identity mechanism, this specification defines an optional Identity-
Extension header. Each extension header field value MUST consist of
a right hand side identifying the extension, an equals sign, and then
a left hand side consisting of a signature over an element in a SIP
request.
Future specifications that define extensions to the Identity
mechanism must explicitly designate which elements of a SIP request
are to be signed, how a canonical string of those elements is
generated by both the authentication service and the verifier, and
the mechanism and algorithms used to generate the signature (it is
RECOMMENDED that these follow the algorithm choice of this
specification). Note that per verifier behavior in Section 4.2,
verifying an extension is always optional. An authentication service
cannot assume that verifiers will understand any given extension.
Verifiers that do support an extension may then trigger appropriate
application-level behavior in the presence of a signature over
additional part of the SIP request; authors of Identity extensions
should provide appropriate extension-specific guidance to application
developers on this point.
Identity-Extension = "Identity-Extension" HCOLON identity-extension-string
identity-extension-string = identity-extension-name EQUAL *base64-char
identity-extension-name = token
signed-identity-extension-digest = LDQUOT *base64-char RDQUOT
Defining a new Identity-Extension requires a Standards Action; see
Section 11.4.
No provision is made in this specification for multiple extensions to
appear in a single SIP request.
9. Privacy Considerations
The purpose of this mechanism is to provide a strong identification The purpose of this mechanism is to provide a strong identification
of the originator of a SIP request, specifically a cryptographic of the originator of a SIP request, specifically a cryptographic
assurance that the URI given in the From header field value can assurance that the URI given in the From header field value can
legitimately be claimed by the originator. This URI may contain a legitimately be claimed by the originator. This URI may contain a
variety of personally identifying information, including the name of variety of personally identifying information, including the name of
a human being, their place of work or service provider, and possibly a human being, their place of work or service provider, and possibly
further details. The intrinsic privacy risks associated with that further details. The intrinsic privacy risks associated with that
URI are, however, no different from those of baseline SIP. Per the URI are, however, no different from those of baseline SIP. Per the
guidance in [RFC6973], implementors should make users aware of the guidance in [RFC6973], implementors should make users aware of the
skipping to change at page 21, line 31 skipping to change at page 23, line 7
the sender of a message that may go beyond what appears in the From the sender of a message that may go beyond what appears in the From
header field; P-Asserted-Identity holds a definitive identity for the header field; P-Asserted-Identity holds a definitive identity for the
sender that is somehow known to a closed network of intermediaries sender that is somehow known to a closed network of intermediaries
that presumably the network will use this identity for billing or that presumably the network will use this identity for billing or
security purposes. The danger of this network-specific information security purposes. The danger of this network-specific information
leaking outside of the closed network motivated the "id" priv-value leaking outside of the closed network motivated the "id" priv-value
token. The "id" priv-value token has no implications for the token. The "id" priv-value token has no implications for the
Identity header, and privacy services MUST NOT remove the Identity Identity header, and privacy services MUST NOT remove the Identity
header when a priv-value of "id" appears in a Privacy header. header when a priv-value of "id" appears in a Privacy header.
The optional "canon" parameter of the Identity-Info header specified
in this document provides a canonicalized form of the telephone
number of the originator of a call. In some contexts, local policy
may be used to populate a "canon" that may differ substantially from
the original From header field. Depending on those policies,
potentially the "canon" parameter might divulge information about the
originating network or user that might not appear elsewhere in the
SIP request. Were it to be used to reflect the contents of the P-
Asserted-Identity header field, for example, then "canon" would need
to be removed when the P-Asserted-Identity header is removed to avoid
any such leakage outside of a trust domain. Since, in those
contexts, the canonical form of the sender's identity could not be
reassembled by a verifier, and thus the Identity signature validation
process would fail, using P-Asserted-Identity with the Identity
"canon" parameter in this fashion is NOT RECOMMENDED outside of
environments where SIP requests will never leave the trust domain.
Finally, note that unlike [RFC3325], the mechanism described in this Finally, note that unlike [RFC3325], the mechanism described in this
specification adds no information to SIP requests that has privacy specification adds no information to SIP requests that has privacy
implications. implications.
9. Security Considerations 10. Security Considerations
9.1. Handling of digest-string Elements 10.1. Handling of digest-string Elements
This document describes a mechanism that provides a signature over This document describes a mechanism that provides a signature over
the Date header field, and either the whole or part of the To and the Date header field, and either the whole or part of the To and
From header fields of SIP requests, as well as optional protections From header fields of SIP requests, as well as optional protections
for the message body. While a signature over the From header field for the message body. While a signature over the From header field
would be sufficient to secure a URI alone, the additional headers would be sufficient to secure a URI alone, the additional headers
provide replay protection and reference integrity necessary to make provide replay protection and reference integrity necessary to make
sure that the Identity header will not be replayed in cut-and-paste sure that the Identity header will not be replayed in cut-and-paste
attacks. In general, the considerations related to the security of attacks. In general, the considerations related to the security of
these headers are the same as those given in [RFC3261] for including these headers are the same as those given in [RFC3261] for including
skipping to change at page 24, line 31 skipping to change at page 26, line 26
important to note that preventing men-in-the-middle is not the important to note that preventing men-in-the-middle is not the
primary impetus for this mechanism. Moreover, changing the 'alg' primary impetus for this mechanism. Moreover, changing the 'alg'
would at worst result in some sort of bid-down attack, and at best would at worst result in some sort of bid-down attack, and at best
cause a failure in the verifier. Note that only one valid 'alg' cause a failure in the verifier. Note that only one valid 'alg'
parameter is defined in this document and that thus there is parameter is defined in this document and that thus there is
currently no weaker algorithm to which the mechanism can be bid down. currently no weaker algorithm to which the mechanism can be bid down.
'alg' has been incorporated into this mechanism for forward- 'alg' has been incorporated into this mechanism for forward-
compatibility reasons in case the current algorithm exhibits compatibility reasons in case the current algorithm exhibits
weaknesses, and requires swift replacement, in the future. weaknesses, and requires swift replacement, in the future.
9.1.1. Protection of the To Header and Retargeting 10.1.1. Protection of the To Header and Retargeting
The mechanism in this document provides a signature over the identity The mechanism in this document provides a signature over the identity
information in the To header field value of requests. This provides information in the To header field value of requests. This provides
a means for verifiers to detect replay attacks where a signed request a means for verifiers to detect replay attacks where a signed request
originally sent to one target is modified and then forwarded by an originally sent to one target is modified and then forwarded by an
attacker to another, unrelated target. Armed with the original value attacker to another, unrelated target. Armed with the original value
of the To header field, the recipient of a request may compare it to of the To header field, the recipient of a request may compare it to
their own identity in order to determine whether or not the identity their own identity in order to determine whether or not the identity
information in this call might have been replayed. However, any information in this call might have been replayed. However, any
request may be legitimately retargeted as well, and as a result request may be legitimately retargeted as well, and as a result
skipping to change at page 25, line 19 skipping to change at page 27, line 13
guidance is given for implementers here regarding the 'connected guidance is given for implementers here regarding the 'connected
party' problem (see [RFC4916]); authentication service behavior is party' problem (see [RFC4916]); authentication service behavior is
unchanged if retargeting has occurred for a dialog-forming request. unchanged if retargeting has occurred for a dialog-forming request.
Ultimately, the authentication service provides an Identity header Ultimately, the authentication service provides an Identity header
for requests in the backwards dialog when the user is authorized to for requests in the backwards dialog when the user is authorized to
assert the identity given in the From header field, and if they are assert the identity given in the From header field, and if they are
not, an Identity header is not provided. And per the threat model of not, an Identity header is not provided. And per the threat model of
[RFC7375], resolving problems with 'connected' identity has little [RFC7375], resolving problems with 'connected' identity has little
bearing on detecting robocalling or related impersonation attacks. bearing on detecting robocalling or related impersonation attacks.
9.2. Securing the Connection to the Authentication Service 10.2. Securing the Connection to the Authentication Service
In the absence of user agent-based authentication services, the In the absence of user agent-based authentication services, the
assurance provided by this mechanism is strongest when a user agent assurance provided by this mechanism is strongest when a user agent
forms a direct connection, preferably one secured by TLS, to an forms a direct connection, preferably one secured by TLS, to an
intermediary-based authentication service. The reasons for this are intermediary-based authentication service. The reasons for this are
twofold: twofold:
If a user does not receive a certificate from the authentication If a user does not receive a certificate from the authentication
service over the TLS connection that corresponds to the expected service over the TLS connection that corresponds to the expected
domain (especially when the user receives a challenge via a domain (especially when the user receives a challenge via a
skipping to change at page 26, line 18 skipping to change at page 28, line 11
constrain UAC behavior, and moreover there will be some deployment constrain UAC behavior, and moreover there will be some deployment
architectures where a direct connection is simply infeasible and the architectures where a direct connection is simply infeasible and the
UAC cannot act as an authentication service itself. Accordingly, UAC cannot act as an authentication service itself. Accordingly,
when a direct connection and TLS are not possible, a UAC should use when a direct connection and TLS are not possible, a UAC should use
the SIPS mechanism, Digest 'auth-int' for body integrity, or both the SIPS mechanism, Digest 'auth-int' for body integrity, or both
when it can. The ultimate decision to add an Identity header to a when it can. The ultimate decision to add an Identity header to a
request lies with the authentication service, of course; domain request lies with the authentication service, of course; domain
policy must identify those cases where the UAC's security association policy must identify those cases where the UAC's security association
with the authentication service is too weak. with the authentication service is too weak.
9.3. Authorization and Transitional Strategies 10.3. Authorization and Transitional Strategies
Ultimately, the worth of an assurance provided by an Identity header Ultimately, the worth of an assurance provided by an Identity header
is limited by the security practices of the authentication service is limited by the security practices of the authentication service
that issues the assurance. Relying on an Identity header generated that issues the assurance. Relying on an Identity header generated
by a remote administrative domain assumes that the issuing domain by a remote administrative domain assumes that the issuing domain
uses recommended administrative practices to authenticate its users. uses recommended administrative practices to authenticate its users.
However, it is possible that some authentication services will However, it is possible that some authentication services will
implement policies that effectively make users unaccountable (e.g., implement policies that effectively make users unaccountable (e.g.,
ones that accept unauthenticated registrations from arbitrary users). ones that accept unauthenticated registrations from arbitrary users).
The value of an Identity header from such authentication services is The value of an Identity header from such authentication services is
skipping to change at page 27, line 21 skipping to change at page 29, line 14
Finally, it is worth noting that the presence or absence of the Finally, it is worth noting that the presence or absence of the
Identity headers cannot be the sole factor in making an authorization Identity headers cannot be the sole factor in making an authorization
decision. Permissions might be granted to a message on the basis of decision. Permissions might be granted to a message on the basis of
the specific verified Identity or really on any other aspect of a SIP the specific verified Identity or really on any other aspect of a SIP
request. Authorization policies are outside the scope of this request. Authorization policies are outside the scope of this
specification, but this specification advises any future specification, but this specification advises any future
authorization work not to assume that messages with valid Identity authorization work not to assume that messages with valid Identity
headers are always good. headers are always good.
9.4. Display-Names and Identity 10.4. Display-Names and Identity
As a matter of interface design, SIP user agents might render the As a matter of interface design, SIP user agents might render the
display-name portion of the From header field of a caller as the display-name portion of the From header field of a caller as the
identity of the caller; there is a significant precedent in email identity of the caller; there is a significant precedent in email
user interfaces for this practice. Securing the display-name user interfaces for this practice. Securing the display-name
component of the From header field value is outside the scope of this component of the From header field value is outside the scope of this
document, but may be the subject of future work. document, but may be the subject of future work.
10. IANA Considerations 11. IANA Considerations
This document relies on the headers and response codes defined in RFC This document relies on the headers and response codes defined in RFC
4474. It also retains the requirements for the specification of new 4474. It also retains the requirements for the specification of new
algorithms or headers related to the mechanisms described in that algorithms or headers related to the mechanisms described in that
document. document.
10.1. Header Field Names 11.1. Header Field Names
This document specifies one new SIP header called Identity-Reliance. This document specifies a new SIP header called Identity-Reliance.
Its syntax is given in Section 7. This header is defined by the Its syntax is given in Section 7. This header is defined by the
following information, which has been added to the header sub- following information, which has been added to the header sub-
registry under http://www.iana.org/assignments/sip-parameters registry under http://www.iana.org/assignments/sip-parameters
Header Name: Identity-Reliance Header Name: Identity-Reliance
Compact Form: N/A Compact Form: N/A
10.2. Identity-Info Parameters This document also specifies a new SIP header called Identity-
Extension. Its syntax is given in Section 8. A registry for
Identity-Extension names is defined in Section 11.4.
Header Name: Identity-Extension
Compact Form: N/A
11.2. Identity-Info Parameters
The IANA has already created a registry for Identity-Info header The IANA has already created a registry for Identity-Info header
parameters. This specification defines a new value called "canon" as parameters. This specification defines a new value called "canon" as
defined in Section 5.3. defined in Section 5.3.
10.3. Identity-Info Algorithm Parameter Values 11.3. Identity-Info Algorithm Parameter Values
The IANA has already created a registry for Identity-Info 'alg' The IANA has already created a registry for Identity-Info 'alg'
parameter values. This registry is to be prepopulated with a single parameter values. This registry is to be prepopulated with a single
entry for a value called 'rsa-sha256', which describes the algorithm entry for a value called 'rsa-sha256', which describes the algorithm
used to create the signature that appears in the Identity header. used to create the signature that appears in the Identity header.
Registry entries must contain the name of the 'alg' parameter value Registry entries must contain the name of the 'alg' parameter value
and the specification in which the value is described. New values and the specification in which the value is described. New values
for the 'alg' parameter may be defined only in Standards Track RFCs. for the 'alg' parameter may be defined only in Standards Track RFCs.
RFC4474 defined the 'rsa-sha1' value for this registry. That value RFC4474 defined the 'rsa-sha1' value for this registry. That value
is hereby deprecated, and should be treated as such. It is not is hereby deprecated, and should be treated as such. It is not
believed that any implementations are making use of this value. believed that any implementations are making use of this value.
Future specifications may consider elliptical curves for smaller key Future specifications may consider elliptical curves for smaller key
sizes. sizes.
11. Acknowledgments 11.4. Identity-Extension Names
This specification requests that the IANA create a new registry for
Identity-Extension names. The registry will consist solely of a list
of names mapped to the Standards Track RFCs in which those extensions
are defined.
The syntax of Identity-Extension names is given in Section 8.
Registering a new Identity-Extension name requires a Standards
Action.
This specification does not provide any initial values for Identity-
Extension names.
12. Acknowledgments
The authors would like to thank Stephen Kent, Brian Rosen, Alex The authors would like to thank Stephen Kent, Brian Rosen, Alex
Bobotek, Paul Kyzviat, Jonathan Lennox, Richard Shockey, Martin Bobotek, Paul Kyzviat, Jonathan Lennox, Richard Shockey, Martin
Dolly, Andrew Allen, Hadriel Kaplan, Sanjay Mishra, Anton Baskov, Dolly, Andrew Allen, Hadriel Kaplan, Sanjay Mishra, Anton Baskov,
Pierce Gorman, David Schwartz, Philippe Fouquart, Michael Hamer, Pierce Gorman, David Schwartz, Philippe Fouquart, Michael Hamer,
Henning Schulzrinne, and Richard Barnes for their comments. Henning Schulzrinne, and Richard Barnes for their comments.
12. Changes from RFC4474 13. Changes from RFC4474
The following are salient changes from the original RFC 4474: The following are salient changes from the original RFC 4474:
Generalized the credential mechanism; credential enrollment and Generalized the credential mechanism; credential enrollment and
acquisition is now outside the scope of this document acquisition is now outside the scope of this document
Reduced the scope of the Identity signature to remove CSeq, Call- Reduced the scope of the Identity signature to remove CSeq, Call-
ID, Contact, and the message body ID, Contact, and the message body
Added any DTLS-SRTP fingerprint in SDP as a mandatory element of Added any DTLS-SRTP fingerprint in SDP as a mandatory element of
the digest-string the digest-string
Added the Identity-Reliance header Added the Identity-Reliance header
Added the Identity-Extension header and extensibility mechanism
Deprecated 'rsa-sha1' in favor of new baseline signing algorithm Deprecated 'rsa-sha1' in favor of new baseline signing algorithm
13. References 14. References
13.1. Normative References 14.1. Normative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263, June Protocol (SIP): Locating SIP Servers", RFC 3263, June
skipping to change at page 29, line 36 skipping to change at page 32, line 10
Algorithms", RFC 3370, August 2002. Algorithms", RFC 3370, August 2002.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC
3966, December 2004. 3966, December 2004.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008. (CRL) Profile", RFC 5280, May 2008.
13.2. Informative References 14.2. Informative References
[I-D.ietf-stir-certificates] [I-D.ietf-stir-certificates]
Peterson, J., "Secure Telephone Identity Credentials: Peterson, J., "Secure Telephone Identity Credentials:
Certificates", draft-ietf-stir-certificates-00 (work in Certificates", draft-ietf-stir-certificates-01 (work in
progress), October 2014. progress), March 2015.
[I-D.kaplan-stir-cider] [I-D.kaplan-stir-cider]
Kaplan, H., "A proposal for Caller Identity in a DNS-based Kaplan, H., "A proposal for Caller Identity in a DNS-based
Entrusted Registry (CIDER)", draft-kaplan-stir-cider-00 Entrusted Registry (CIDER)", draft-kaplan-stir-cider-00
(work in progress), July 2013. (work in progress), July 2013.
[I-D.peterson-sipping-retarget] [I-D.peterson-sipping-retarget]
Peterson, J., "Retargeting and Security in SIP: A Peterson, J., "Retargeting and Security in SIP: A
Framework and Requirements", draft-peterson-sipping- Framework and Requirements", draft-peterson-sipping-
retarget-00 (work in progress), February 2005. retarget-00 (work in progress), February 2005.
 End of changes. 41 change blocks. 
63 lines changed or deleted 188 lines changed or added

This html diff was produced by rfcdiff 1.42. The latest version is available from http://tools.ietf.org/tools/rfcdiff/