Network Working Group D. Wing
Internet-Draft Cisco
Intended status: Standards Track February 5, 2008
Expires: August 8, 2008
SIP E.164 Return Routability Check (RRC)
draft-wing-sip-e164-rrc-00
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Copyright (C) The IETF Trust (2008).
Abstract
SIP lacks a mechanism to determine which domain can claim ownership
of a certain telephone number. Due to this, it is impossible to
establish meaningful identity or to authenticate endpoints that use
telephone number URIs and domain names in their From address. This
document proposes a solution to this problem using a return
routability test.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Verifier Operation . . . . . . . . . . . . . . . . . . . . 4
3.2. Authentication Service or Calling Endpoint Operation . . . 5
4. Performance Considerations . . . . . . . . . . . . . . . . . . 5
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.1. Reverse-Route Event Package . . . . . . . . . . . . . . . 9
8.2. The "application/return-routability-nonce" Media Type . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . . 10
9.2. Informational References . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
SIP [RFC3261] allows using both email-style addresses (user@domain)
and telephone-style addresses (1234@domain). The latter is most
often used with E.164 [ITU.E164.1991] numbers, especially between
different administrative domains.
SIP's use of E.164 numbers poses several problems. This draft
provides a solution to one of the problems: determining if a domain
name rightfully 'owns' an E.164 phone number. In order to do this, a
new SIP request is routed towards that E.164 and, if it is received
by the same domain, that domain is deemed to 'own' that E.164 number.
This is termed a 'return routability check' (RRC).
The return routability check relies on SIP routing to ascertain which
domain 'owns' a certain E.164 number.
2. Notational Conventions
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].
3. Operation
In order to check if a domain actually 'owns' the E.164 number it
claims to own, a new SIP request is sent towards that E.164. Upon
receipt of a SIP request conaining an E.164 number in the From
address, the verifying agent in the receiving domain sends a new,
out-of-dialog request (a SUBSCRIBE) towards that E.164 using the
verifiering domain's normal routing rules. This SUBSCRIBE contains a
body (with a nonce) that the verifying domains wants the owner of the
E.164 to sign. That SIP SUBSCRIBE request is routed to the 'owner'
of that E.164. Upon receipt of the SUBSCRIBE, the owner of that
E.164 number generates a NOTIFY request. This is signed, using
RFC4474, and sent to the verifying domain. The verifing domain
verifies the signature on the NOTIFY. If it verified, and if the
same public key was used in the original SIP request and in this
NOTIFY, the verifying domain has now verified the remote domain
'owns' that E.164 number. If a different public key was used in the
original SIP request and in this NOTIFY, the verifying domain has no
verified the remote domain does not own that E.164 number.
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3.1. Verifier Operation
Upon receipt of an INVITE where the From: address contains a SIP URI
with an E.164, a Verifier (as defined in [RFC4474]) needs to verify
if the signer is authorized to sign for that domain. To do this, the
Verifier has an additional task: it sends an out of dialog SIP
SUBSCRIBE request containing a random nonce to that E.164, using the
Verifier's default SIP routing rules for routing an E.164 address.
The domain that owns the E.164 will sign the nonce and send a NOTIFY
request back.
The steps the Verifier uses to perform this operation are:
1. Strip the domain name of the From: of the incoming INVITE. This
results in a TEL URI. For example,
"sip:+14085551234@example.com" is rewritten to
"tel:+14085551212"s
2. Rewrite the TEL URI to a SIP URI, following the Verifier's
default routing rules. For example, "tel:+14085551212" is
rewritten to "sip:+14085551212@example.net", the service provider
used by the verifying domain).
3. Generate a random nonce.
4. Using the SIP URI constructed in step (2), construct a SIP
SUBSCRIBE message with Request-URI and To headers that use that
SIP URI, and an "Expires" header of 0. The SUBSCRIBE contains
the random nonce in its body as Content-Type application/
return-routability-nonce.
5. Send the SUBSCRIBE message. This will cause the calling party to
send a NOTIFY.
Upon receipt of the NOTIFY message, the Verifier performs the
following steps:
1. Validate the [RFC4474] signature of the NOTIFY.
2. Extract the application/return-routability-nonce from the NOTIFY,
and compare it to the nonce that was sent in the SUBSCRIBE.
3. Compare the certificate used to sign the NOTIFY is the same
certificate used to sign the original SIP request that it is
attempting to validate with this procedure.
A. If they match, the E.164 return routability test has
succeeded.
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B. If they do not match, the E.164 return routability test has
failed.
3.2. Authentication Service or Calling Endpoint Operation
The steps described in this section can be performed by the
authentication service or by the calling endpoint.
The authentication service or the calling endpoint, upon receiving a
SUBSCRIBE for the return-routability event package, performs the
following steps:
1. The SUBSCRIBE should be immediately acknowledged with a 200 Ok
message.
2. A NOTIFY should be immediately created, containing the same
application/return-routability-nonce copied from the SUBSCRIBE.
This NOTIFY contains a To and Request-URI which match the From of
the SUBSCRIBE.
3. This NOTIFY is sent.
4. The RFC4474 authentication service, operating at the domain, will
create a signature over the NOTIFY. This is used by the remote
domain's verification service (see Section 3.1).
4. Performance Considerations
To reduce SUBSCRIBE/NOTIFY traffic, a verifier SHOULD cache
successful and failed return routability checks. Successful checks
will only become unsuccessful if SIP E.164 routing is changed to a
different terminating domain. This only occurs when a domain
relinquishes an E.164, so it is RECOMMENDED that the result of
ssuccessful tests be cached for 24 hours. However, unsuccessful
tests could be a result of misconfiguration and it is useful to re-
verify such failures in the event the misconfiguration is fixed.
Thus, it is RECOMMENDED that the result of unsuccessful tests be
cached for 1 hour.
5. Deployment Considerations
Intermediate SIP elements (proxies, SBCs, B2BUAs) MUST all forward
the application/return-routability-nonce Content-Type.
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6. Security Considerations
An attacker could cause a domain to perform public key operations by
sending a bunch of bogus SUBSCRIBE messages. This can be thwarted by
only responding with NOTIFYs if there is an active INVITE dialog.
However, that could disclose information about active calls, and also
restricts the usefulness of this feature to INVITEs. More evaluation
of countermeasures against such an attack is needed.
[[This section will be completed in a later version of this
document.]]
7. Examples
Example message flow for a successful return routability check.
Calling Auth. Called
UA Service proxies Verifier UA
------- ------- -------- -------- ------ --------
| | | | | ^
| INVITE | | | | |
|--------->| | | | |
| | | | | |
| (signs request) | | | |
| | | | | |
|100 | INVITE | | | | steps which
|<---------|--------->| | | | are part of
| | | | | | normal RFC4474
| |100 | INVITE | | |
| |<---------|--------->| | |
| | | | | |
| | |100 | | |
| | |<---------| | |
| | | | | |
| | | (validates | |
| | | signature) | V
| | | | | ----------
| | |SUBSCRIBE | |
| | |(containing nonce) |
| |SUBSCRIBE |<---------| |
| |<---------| | |
| | | | |
| |200 Ok | | |
| |--------->|200 Ok | |
| | |--------->| |
| NOTIFY | | | |
| (containing nonce) | | |
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| +----| | | |
| | | | | |
| +--->| | | |
| | | | |
| (signs NOTIFY) | | |
| | | | |
| |NOTIFY | | |
| |--------->|NOTIFY | |
| | |--------->| |
| | | | |
| | |200 Ok | |
| |200 Ok |<---------| |
| |<---------| | |
| | | | |
| | | (validates NOTIFY |
| | | signature, and |
| | | checks that same |
| | | cert. signed both |
| | | the INVITE and |
| | | the NOTIFY) |
| | | | |
| | | | INVITE |
| | | |--------->|
| | | | |
| | | | |display e.164
| | | | |------------>
| | | | |
Figure 1: Message Flow -- Return Routability Check Success
Example message flow for an unsuccessful return routability check,
where the NOTIFY is signed by a different RFC4474 authentication
service:
Calling E.164
User's Owner's
Calling Auth. Auth. Called
UA Service Service proxies Verifier UA
------- ------- ------- ------- -------- ------
| | | | | |
| INVITE | | | | |
|--------->| | | | |
| | | | | |
| (signs request) | | | |
| | | | | |
|100 | INVITE | | | |
|<---------|-------------------->| | |
| | | | | |
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| |100 | | INVITE | |
| |<--------------------|--------->| |
| | | | | |
| | | |100 | |
| | | |<---------| |
| | | | | |
| | | | (validates |
| | | | signature) |
| | | | | |
| | | |SUBSCRIBE | |
| | |SUBSCRIBE |(containing nonce) |
| | |<---------| | |
| | |200 Ok | | |
| | |--------->|200 Ok | |
| | NOTIFY | |--------->| |
| | (containing nonce) | | |
| | +----| | | |
| | | | | | |
| | +--->| | | |
| | | | | |
| | (signs NOTIFY) | | |
| | | | | |
| | |NOTIFY | | |
| | |--------->|NOTIFY | |
| | | |--------->| |
| | | | | |
| | | |200 Ok | |
| | |200 Ok |<---------| |
| | |<---------| | |
| | | | | |
| | | | (NOTIFY validates; |
| | | | however, different |
| | | | cert. was used for |
| | | | INVITE) |
| | | | | |
| | | | | |
| | | | | INVITE |
| | | | |--------->|
| | | | | |
| | | | | |display
| | | | | |e.164
| | | | | |------>
| | | | | |
Figure 2: Message Flow -- Return Routability Check Failure
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8. IANA Considerations
IANA is requested to register the following new event package and one
new media type.
8.1. Reverse-Route Event Package
This specification registers an event package, based on the
registration procedures defined in [RFC3265]. The following is the
information required for such a registration:
Package Name: reverse-route
Package or Package-Template: This is a package.
Published Specification: <this document>.
Person to Contact: Dan Wing, <dwing@cisco.com>
8.2. The "application/return-routability-nonce" Media Type
Type name: application
Subtype name: return-routability-nonce
Required parameters: None.
Optional parameters: None.
Encoding considerations: The nonce is primarily binary content.
Security considerations: See Section 6 of <this document>.
Interoperability considerations: See <this document>.
Published specification: <this document>
Applications which use this media type: SIP.
Additional information:
Magic number(s): None.
File extension(s): None.
Macintosh File Type Code(s): none.
Person & email address to contact for further information: Dan Wing
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<dwing@cisco.com>
Intended Usage: COMMON
Author/Change Controller: Dan Wing <dwing@cisco.com>
9. References
9.1. Normative References
[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.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
9.2. Informational References
[ITU.E164.1991]
International Telecommunications Union, "The International
Public Telecommunication Numbering Plan", ITU-
T Recommendation E.164, 1991.
Author's Address
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Email: dwing@cisco.com
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