Network Working Group D. Wing
Internet-Draft Cisco Systems
Intended status: Standards Track July 1, 2007
Expires: January 2, 2008
SIP Identity using Media Path
draft-wing-sip-identity-media-00
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Copyright (C) The IETF Trust (2007).
Abstract
The existing SIP identity mechanism (RFC4474) creates a signature
over the SIP body, including the entire SDP. As part of their normal
operation, Session Border Controllers (SBCs) and SIP Back-to-Back
User Agents (B2BUAs) modify various fields in the SDP, breaking the
signature.
This document defines a new mechanism to securely identify the
originator of a SIP message while also allowing modification of the
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SDP by SBCs and B2BUAs. This new mechanism creates a signature over
certain SIP headers and certain SDP lines. Proof of identity over
the media path using DTLS, TLS, HIP, and an extension to ICE are
described.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Media Fingerprint Signature . . . . . . . . . . . . . . . 7
4.2. Authentication Service . . . . . . . . . . . . . . . . . . 9
4.3. Validation . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Proof of Identity Techniques . . . . . . . . . . . . . . . . . 9
5.1. TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. DTLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3. ICE . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.3.1. ICE Public Key SDP Attribute . . . . . . . . . . . . . 11
5.3.2. New STUN attributes . . . . . . . . . . . . . . . . . 11
5.4. HIP . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Device Disclosure . . . . . . . . . . . . . . . . . . . . 12
8. Operational Differences from RFC4474 . . . . . . . . . . . . . 13
9. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 13
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. DTLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.2. ICE . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
13. Normative References . . . . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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1. Introduction
SIP Identity [RFC4474] defines a mechanism to provide cryptographic
identity for SIP requests. It provides this protection by signing
certain SIP header fields (Contact, Date, Call-ID, CSeq, To, and
From) and the body of the message. RFC4474 also signs the SIP body,
which typically contains the SDP, with this explanation:
This mechanism also provides a signature over the bodies of SIP
requests. The most important reason for doing so is to protect
Session Description Protocol (SDP) bodies carried in SIP requests.
There is little purpose in establishing the identity of the user
that originated a SIP request if this assurance is not coupled
with a comparable assurance over the media descriptors.
A weakness of RFC4474's approach is that SBCs and B2BUAs typically
modify the media transport address and thus destroy the RFC4474
signature. Furthermore, even if such modification were not typical,
the transport address by itself does not ensure media communication
with the expected endpoint when NATs, Session Border Controllers, and
media relays (e.g., TURN [I-D.ietf-behave-turn]) are considered as
part of the end-to-end architecture. This is because the transport
address could be reused by a malicious party within the replay
window.
The mechanism described in this document provides cryptographic
assurance of the endpoint's identity by signing certain SIP headers,
much like RFC4474. However, unlike RFC4474 which signs the entire
SDP, the mechanism described in this document signs only certain SDP
attributes. The remote endpoint is expected to validate the
signature over the SIP headers and to initiate a proof of possession
test over the media path, which proves the session has been
established with the "From:" party in the SIP header. Mechanisms to
perform this proof of possession are shown using DTLS and using a
small extension ICE.
Readers of this document are expected to be familiar with RFC4474,
"Enhancements for Authenticated Identity Management in the Session
Initiation Protocol (SIP)", which defines the Identity and Identity-
Info header fields. A future version of this document will have less
reliance on RFC4474.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Background
SIP signaling has been evolving from direct UA-to-UA signaling to
always signaling through proxies. This has been driven primarily by
technical reasons, such as NATs or firewalls that prevent direct UA-
to-UA signaling. While quite controversial in the IETF, Session
Border Controllers are an aspect of SIP's evolution, and are driven
by both technical reasons and market reasons. The primary technical
driver for SBCs is to police media traffic into a network so that
only media that was appropriately signaled via SIP is permitted into
the network, ensuring IP packets are sent only to/from the SBC which
eases ACL configuration (among other things). The primary market
driver for SBCs is to hide business relationships -- this is, removal
of Via headers and exposing only the IP address of the SBC to
customers.
The following diagram shows two service providers (SP1 and SP2), and
each has an SBC at the edge of their respective networks. Each of
these SBCs would need to rewrite the IP addresses in the SDP.
+----[SP1-SBC1]-[SP1-SBC1]---[SP2-SBC1]-[SP2-SBC2]----+
| |
[Enterprise-A] [Enterprise-B]
Figure 1: Two Service Providers with SBCs Between Two Enterprises
Enterprise-A can populate the "From:" address in its SIP requests
using E.164 telephone number URLs (e.g.,
'sip:+17005551008@example.com;user=phone') or using a mailto URL
(e.g., 'sip:john.doe@example.com'). The characteristics of each
choice, as the message traverses the SBCs operated by another
administrative domain (service providers) are described below:
E.164 telephone numbers:
SP1 would validate the RFC4474 signature and modify the SDP. This
breaks the RFC4474 signature created by the enterprise. So that a
new RFC4474 signature can be created using its own public/private
key pair, SP1 needs to modify the From: field. SP1 would
substitute its own domain on the right-hand side, and signs the
message with its own private key. SP2 would receive the SIP
request from SP1, validate the signature, and perform a similar
SDP modification, substitution, and resigning operation.
Enterprise-B would receive the SIP request from SP2, validate its
signature, and process the SIP request.
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mailto URLs:
SP1 would validate the RFC4474 signature modify the SDP. This
breaks the RFC4474 signature created by the enterprise. So that a
new RFC4474 signature can be created using its own public/private
key pair, SP1 needs to modify the From: field. Unlike with E.164
numbers which are globally unique, the SP1 isn't able to
substitute its domain name for the enterprise's domain name due to
name collisions (that is, dwing@cisco.com cannot simply be
rewritten as dwing@pacbell.net). One unappealing technique is to
resurrect the percent hack from email: SP1 would rewrite the
address to be 'sip:john.doe%example.com@sp1.net', sign it, and
send it to SP2. SP2 would validate the signature, modify the SDP,
and rewrite the address to be 'sip:john.doe%example.com@sp2.net',
sign it, and send it to Enterprise-B. Enterprise-B would receive
the SIP request from SP2, validate its signature, and process the
SIP request.
Both of these approaches share several weaknesses:
1. They create a natural incentive for the service providers to use
transitive trust between themselves, rather than RFC4474, due to
the computational expense of the per-call public key operations
on each SIP request. For similar reasons, there is a natural
incentive for the service providers to not even validate an
enterprise's RFC4474 signature but rather to rely on a contract
or rely on TLS to ensure the SIP signaling originated from the
enterprise.
2. Because the original signature is destroyed by the first SBC, no
other network (SP2 nor Enterprise-B) can validate the original
signature. This means all downstream entities (in the example
above, SP2 and Enterprise-B) are relying wholly on SP1 to
validate the signature. This creates transitive trust which is
undesirable - a single bad actor or compromised system anywhere
along the path can compromise the entire identity system.
3. If an enterprise is connected to different service providers, one
call from the same identity at Enterprise-A might appear to be
from +14085551212@sp2.net and the next call from the same
identity, routed through a different service provider, would
appear to come from +14085551212@sp3.net. The terminating system
would need to treat both From: addresses as identical for
purposes of call routing, whitelists, reputation systems, and so
on. This adds further complexity to system administration.
Thus, we need a mechanism that allows Enterprise-B to
cryptographically validate the identity of the remote party at
Enterprise-A, even though intermediate SBCs have rewritten the media
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transport address and forced the media to pass through their
networks.
4. Operation
The operation is very similar to RFC4474 and uses authentication
service proxies exactly like RFC4474. Rather than reproducing the
text of RFC4474, this section describes only the differences from
RFC4474. The differences are:
o A new header is created containing certain SDP attributes
o This new header is signed in addition to the same set of SIP
headers signed by RFC4474 (detailed in )
o Unlike RFC4474, the body of the SIP message (containing the SDP)
is not signed
The following figure shows how the Authentication Service and the
media validation is performed. The figure assumes the endpoints
themselves perform the media validation. In practice, if the
: Service :
Enterprise-A : Provider(s): Enterprise-B
: :
Auth. : B2BUA or : Auth.
Endpoint-A Service : SBC : Service Endpoint-B
| | : | : | |
1. |--Invite->| : | : | |
2. | sign : | : | |
3. | |-Invite-->|-Invite-->| |
4. | | : | : validate |
5. | | : | : |-------->|
6. |<=========tls, dtls, ice, or hip=========>|
7. | | : | : | validated
8. | | : | : | ring phone
| | : | : | |
: :
Figure 2: Message Flow
Step 1: Originating endpoint prepares to send an Invite and chooses
the identity-challenge technique it supports, and indicates
that in the SDP it generates. Described in this document
are identity challenges for TLS, DTLS, ICE, and HIP. It
then sends the Invite to its local SIP proxy.
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Step 2: Originating endpoint's authentication service creates a new
header, Identity-Fingerprints, containing certain lines of
the SDP (e.g., a=fingerprint, a=ice-pub-key). The
authentication service then creates a signature over certain
SIP headers (e.g., From, To, Call-Id) and this new Identity-
Fingerprints header. The resulting signature is inserted
into the new Identity-Media header. The invite is forwarded
to the next administrative domain.
Step 3: The next administrative domain has an SBC (or B2BUA). The
SBC modifies or rewrites certain SDP fields. Most typically
an SBC will modify the "m" and "c" lines. These
modifications do not break the signature.
Step 4: The terminating endpoint's authentication service receives
the Invite. It validates the Identity-Media signature is
valid and was validates it was generated by the originating
domain in step 2.
Step 5: If the validation was successful, the terminating endpoint's
authentication service forwards the Invite to the endpoint.
Step 6: The terminating endpoint chooses a compatible identity-
challenge technique from the Invite, and performs that
challenge. Described in this document are identity
challenges for TLS, DTLS, ICE, and HIP.
Step 7: TLS, DTLS, and HIP cause the exchange of a certificate or
public key. The terminating endpoint validates the
certificate or public key has a fingerprint matching the
Identity-Fingerprint header (originally created in step 2).
If it does, the terminating endpoint completes the identity
challenge exchange. After completion, the originating
endpoint has proven (to the terminating endpoint) that it
knows the private key associated with the certificate (or
public key) signed in step 2. The terminating endpoint has
now validated the identity of the originating endpoint.
Step 8: You can reliably and honestly indicate calling party
information ("caller-id") to the terminating endpoint, and
ring their phone.
4.1. Media Fingerprint Signature
In RFC4474, a signature is formed over some SIP headers and over the
entire body (which most typically contains SDP). In this
specification, some SIP headers are signed but only specific SDP
attributes that provide cryptographic identity are signed (e.g.,
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"fingerprint"). The specific SDP attribute that are signed depends
on which cryptographic identity technique(s) is used; see section
Section 5.
The SIP headers that are signed are signed the same as done by
RFC4474, with the additional signing of the Media-Identity header;
the body is not signed. They signed headers are:
o The AoR of the UA sending the message, or addr-spec of the From
header field (referred to occasionally here as the 'identity
field').
o The addr-spec component of the To header field, which is the AoR
to which the request is being sent.
o The callid from Call-Id header field.
o The digit (1*DIGIT) and method (method) portions from CSeq header
field, separated by a single space (ABNF SP, or %x20). Note that
the CSeq header field allows linear whitespace (LWS) rather than
SP to separate the digit and method portions, and thus the CSeq
header field may need to be transformed in order to be
canonicalized. The authentication service MUST strip leading
zeros from the 'digit' portion of the Cseq before generating the
digest-string.
o The Date header field, with exactly one space each for each SP and
the weekday and month items case set as shown in BNF in RFC 3261.
RFC 3261 specifies that the BNF for weekday and month is a choice
amongst a set of tokens. The RFC 2234 rules for the BNF specify
that tokens are case sensitive. However, when used to construct
the canonical string defined here, the first letter of each week
and month MUST be capitalized, and the remaining two letters must
be lowercase. This matches the capitalization provided in the
definition of each token. All requests that use the Identity
mechanism MUST contain a Date header.
o The addr-spec component of the Contact header field value. If the
request does not contain a Contact header, this field MUST be
empty (i.e., there will be no whitespace between the fourth and
fifth "|" characters in the canonical string).
o The fingerprints component of the Identity-Media header field
value.
In this specification, the Identity-Media header is signed instead of
the message body. The Identity-Media contains only certain SDP lines
from the SDP body.
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4.2. Authentication Service
The authentication service examines the SIP message body for the
application/sdp Content-Type. For all such content-types found, the
authentication service retrieves the cryptographic attributes
described in Section 5, concatenates them together, and inserts a new
SIP header field called Media-Fingerprints containing a comma-
separated list of those signed attributes.
This new header, along with all the headers and portions of headers
signed by RFC4474 (From, Call-ID, etc.), are all signed by the
authentication service. The resulting signature is placed on the new
Identity-Fingerprints header.
4.3. Validation
The validation service can be performed by the remote endpoint itself
or by an SBC acting on behalf of the endpoint. The validation
service first checks the Identity-Fingerprints signature. If this is
valid, the endpoint (or its validation service operating on its
behalf) then initiates a DTLS, TLS, ICE, or HIP identity proof
(Section 5). This causes the originating endpoint to prove
possession of its private key that corresponds to the certificate (or
public key) that was signed by the remote domain's authentication
service.
5. Proof of Identity Techniques
Four techniques are described below, TLS, DTLS, ICE, and HIP. Each
provides a means to cryptographically prove the identity signed by
the authentication service in SIP is the same as the identity on the
media path.
Each of these techniques work similarly -- a fingerprint of the
certificate (or, with ICE, the public key itself) is included in the
SDP. The authentication service creates a new Identity-Fingerprints
header and places into that header those certificate fingerprints
(or, with ICE, the fingerprint of the public key). The
authentication service then creates a signature over specific SIP
headers (see Section 4.1), and places that signature into the new
Identity-Media header. The SIP request is then sent outside of the
originating domain.
The receiving domain validates the Identity-Media signature. If
successful, the SIP request is forwarded to the end system (or an SBC
operating on its behalf). The end system initiates a TLS, DTLS, ICE,
or HIP session and validates the certificate fingerprint presented in
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SIP signaling matches the certificate presented in the TLS, DTLS,
ICE, or HIP exchange. If they match, and the TLS, DTLS, ICE, or HIP
exchange completes successfully, the local endpoint has validated the
identity of the remote endpoint.
Note: Due to SIP forking, the calling party may receive many
identity challenges, each incurring a public key operation to prove
identity. Mechanisms to deal with this are for future study.
5.1. TLS
TLS uses the "fingerprint" attribute to provide a hash of the
certificate in the SDP. The fingerprint attribute is defined by
[RFC4572] for TLS.
5.2. DTLS
DTLS uses the same "fingerprint" attribute originally described for
TLS. The syntax is described in [I-D.fischl-sipping-media-dtls].
Note: DTLS is only necessary to prove identity with DTLS; SRTP
[RFC3711] does not need to be used afterwards. Obviously, using
SRTP provides significant benefits over continuing to use RTP,
because an attacker can inject bogus RTP after a successful
validation of identity which is quite undesirable. The SDP for
doing RTP after a DTLS exchange might be signaled in SDP by using
"RTP/AVP" rather than "RTP/SAVP" (lines folded for readability):
v=0
o=- 25678 753849 IN IP4 192.0.2.1
s=
c=IN IP4 192.0.2.1
t=0 0
m=audio 3456 RTP/AVP 0 18
a=fingerprint
SHA-1 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=setup:passive
a=connection:new
Of course, it would be desirable to more clearly indicate this
somehow in SDP, as there are existing "best-effort" media
encryption mechanisms which overload the meaning of a=crypto and
a=key-mgmt to mean RTP/SAVP, and other implementations may also
overload a=fingerprint in a similar, undesirable, way.
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5.3. ICE
ICE doesn't have inherent support for public/private keys. If public
keys were sent with other ICE attributes, there can be a real risk of
an ICE connectivity check exceeding the MTU. ICE lacks a mechanism
to fragment such large messages. It is also bandwidth inefficient to
send multiple ICE connectivity checks containing public keys, either
as retransmissions or with multiple candidates. Thus, for ICE, the
public key is sent in SDP and the public key's fingerprint is
exchanged on the media path -- opposite of TLS, DTLS, and HIP.
5.3.1. ICE Public Key SDP Attribute
The offerer includes its public key, which it will use for the
subsequent PK-CHALLANGE and PK-RESPONSE, in its SDP. The syntax is a
BASE64-encoded version of the endpoint's public key.
The new attribute is called "ice-pub-key", which may appear on the
session level, media level, or both.
5.3.2. New STUN attributes
Two new STUN attributes are defined to carry the plaintext challenge
and the encrypted response.
5.3.2.1. PK-CHALLANGE
This is sent in a STUN Binding Request, and contains the bits to be
encrypted by the private key. Up to 256 bits can be included in the
challenge. When a STUN Binding Request is received containing this
attribute, the contents of the PK-CHALLENGE are encrypted using the
private key, and the result is included in the PK-RESPONSE attribute
of the Binding Response.
The PK-CHALLENGE MUST be the same for each candidate address that is
being tested for connectivity. If this requirement is not followed,
the peer will incur a public key operation for every ICE connectivity
check, which is not reasonable or necessary.
5.3.2.2. PK-RESPONSE
This is sent in a STUN Binding Response from the offerer to the
answerer, and contains the encrypted result of the PK-CHALLENGE.
5.4. HIP
In [I-D.tschofenig-hiprg-host-identities], a new attribute "key-
mgmt:host-identity-tag" is defined which contains the hash of the
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public key used in the subsequent HIP exchange. This can be utilized
and signed exactly like the "fingerprint" attribute for TLS or DTLS.
6. ABNF
The following figure shows the syntax of the new SIP header fields
using ABNF [RFC4234]
media-fingerprint = "Identity-Fingerprints" HCOLON
fingerprints
fingerprints = fingerprint *(COMMA fingerprint)
fingerprint = 2UHEX *(":" 2UHEX)
; Each byte in upper-case hex, separated
; by colons.
UHEX = DIGIT / %x41-46 ; A-F uppercase
identity-media = "Identity-Media" HCOLON signature
signature = LDQUOT 32LHEX RDQUOT
Figure 4: ABNF for new SIP headers
The following figure shows the syntax of the new SDP attribute
containing the ICE public key:
ice-pub-key = token ; BASE64 encoded public key
Figure 5: ABNF for new SDP attribute
7. Security Considerations
[[some of RFC4474's security considerations also apply.]]
7.1. Device Disclosure
Although the mechanism described in this paper allows SBCs to be used
with a cryptographic identity scheme, it does expose the identity of
the user's certificate. If a unique certificate is installed on each
user's device, the remote party will be able to discern which device
is terminating the call. This problem is more pronounced when SIP
retargeting occurs in conjunction with Connected Identity [RFC4916].
If this isn't desired, there are two solutions:
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o all devices under the control of the user will need to have the
same certificate (and associated private key) installed on them,
or
o the device to manufacture a new self-signed certificate (or public
key) for each call, and populate the a=fingerprint or a=ice-pub-
key attributes, as appropriate. This is possible because the
identity service described in this paper does not require the same
certificate or public key to be used on every call.
8. Operational Differences from RFC4474
RFC4474 imposes one public key operation for the authentication
service and one for validation. In addition to that, the mechanism
described in this paper also requires an additional public key
operation for the authentication service and an additional public key
operation for validation. If Connected Identity [RFC4916] is used,
only one additional public key operation is necessary for the header
signature validation; the expense of the DTLS, TLS, or ICE public key
operation has already been incurred by both parties and is not
repeated.
The mechanism described in this document has the following advantages
over RFC4474:
o Only the edge network needs to create signatures on SIP requests
-- not every intervening SBC,
o The original cryptographically-provable identity is preserved
across any number of SBCs.
9. Limitations
For the identity procedure described in this document to function,
every device -- including Session Border Controllers -- on the path
MUST permit DTLS, TLS, ICE, or HIP messages to be exchanged in the
media path. Further, those devices MUST NOT interfere with the SDP
attributes or two new SIP headers necessary for Identity Media to
operate.
10. Examples
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10.1. DTLS
This example shows how two a=fingerprint lines in SDP would populate
a the Media-Fingerprints SIP header field. The following is an
example of an Invite created by the endpoint.
(lines folded for readability)
INVITE sip:bob@biloxi.example.org SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@biloxi.example.org>
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Max-Forwards: 70
Date: Thu, 21 Feb 2002 13:02:03 GMT
Contact: <sip:alice@pc33.atlanta.example.com>
Content-Type: application/sdp
Content-Length: 147
v=0
o=- 6418913922105372816 2105372818 IN IP4 192.0.2.1
s=example2
c=IN IP4 192.0.2.1
t=0 0
m=audio 54113 RTP/SAVP 0
a=setup:active
a=connection:new
a=fingerprint:SHA-1
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Figure 6: Example with DTLS
The SIP proxy performing the Media Identity authentication service
would then insert the following two SIP headers into the message.
The Media-Fingerprints header contains all of the fingerprint lines
and the Identity-Signature header contains the signature of all of
the relevant SIP headers and of the Media-Fingerprints header. Lines
are folded for readability:
Identity-Fingerprints:
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Identity-Media:
"ZYNBbHC00VMZr2kZt6VmCvPonWJMGvQTBDqghoWeLxJfzB2a1pxAr3VgrB0SsSAa
ifsRdiOPoQZYOy2wrVghuhcsMbHWUSFxI6p6q5TOQXHMmz6uEo3svJsSH49thyGn
FVcnyaZ++yRlBYYQTLqWzJ+KVhPKbfU/pryhVn9Yc6U="
Figure 7: SIP Headers Inserted by Authentication Service
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10.2. ICE
With ICE, the public key is exchanged in the signaling path (in SDP)
rather than in the media path (as is done with TLS, DTLS, and HIP).
The Media-Fingerprints header only needs to contain the fingerprint
of the ICE public key that is in the SDP.
This is the INVITE as it left the SIP user agent (lines folded for
readability):
INVITE sip:bob@biloxi.example.org SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@biloxi.example.org>
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Max-Forwards: 70
Date: Thu, 21 Feb 2002 13:02:03 GMT
Contact: <sip:alice@pc33.atlanta.example.com>
Content-Type: application/sdp
Content-Length: 147
v=0
o=- 6418913922105372816 2105372818 IN IP4 192.0.2.1
s=example2
c=IN IP4 192.0.2.1
t=0 0
a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
a=pub-key:ejfiwj289ceucuezeceEJFjefkcjeiquiefekureickejfeefe
uirujejfecejejejkfeJJCEIUQQIEFJCQUCJCEQUURIE09dnjkeefjek
m=audio 54113 RTP/AVP 0
a=candidate:1 1 UDP 2130706431 192.0.2.1 54113 typ host
Figure 8: Example with ICE
The SIP proxy performing the Media Identity authentication service
would then insert the following two SIP headers into the message.
The Media-Fingerprints header contains the fingerprint of the ICE
public key (A3:EA:B3:...), and the Identity-Signature header contains
the signature of all of the relevant SIP headers and of the Media-
Fingerprints header (lines are folded for readability):
Identity-Fingerprints:
A3:EA:B3:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB:08
Identity-Identity:
"jjsRdiOPoQZYOy2wrVghuhcsMbHWUSFxI+p6q5TOQXHMmz6uEo3svJsSH49th8qc
efQBbHC00VMZr2k+t6VmCvPonWJMGvQTBDqghoWeLxJfzB2a1pxAr3VgrB0Ssjcd
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VcunyaZucyRlBYYQTLqWzJ+KVhPKbfU/pryhVn9Jcqe="
Figure 9: Headers Inserted by Authentication Service
11. Acknowledgements
The mechanism described in this paper is derived from Jon Peterson
and Cullen Jennings' [RFC4474], which was formerly a document of the
SIP working group.
12. IANA Considerations
This document will add new IANA registrations for new STUN
attributes.
[[This section will be completed in a later version of this
document.]]
13. Normative References
[I-D.ietf-behave-turn]
Rosenberg, J., "Obtaining Relay Addresses from Simple
Traversal Underneath NAT (STUN)",
draft-ietf-behave-turn-03 (work in progress), March 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[I-D.fischl-sipping-media-dtls]
Fischl, J., "Datagram Transport Layer Security (DTLS)
Protocol for Protection of Media Traffic Established with
the Session Initiation Protocol",
draft-fischl-sipping-media-dtls-02 (work in progress),
March 2007.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
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Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[RFC4916] Elwell, J., "Connected Identity in the Session Initiation
Protocol (SIP)", RFC 4916, June 2007.
[I-D.tschofenig-hiprg-host-identities]
Tschofenig, H., "Interaction between SIP and HIP",
draft-tschofenig-hiprg-host-identities-05 (work in
progress), June 2007.
Author's Address
Dan Wing
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: dwing@cisco.com
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