VIPR J. Rosenberg
Internet-Draft jdrosen.net
Intended status: Standards Track C. Jennings
Expires: January 12, 2012 Cisco
M. Petit-Huguenin
Stonyfish
July 11, 2011
Session Initiation Protocol (SIP) Extensions for Blocking VoIP Spam
Using PSTN Validation
draft-petithuguenin-vipr-sip-antispam-02
Abstract
Verification Involving PSTN Reachability (ViPR) is a new technique
for inter-domain federation of SIP calls. ViPR makes use of the PSTN
as an introduction mechanism to verify the correctness of mappings
from phone numbers to domains. The PSTN introduction mechanism can
also be used as a technique for blocking spam - a SIP caller is only
authorized when its calling domain has previously called that same
number over the PSTN. This document describes an extension to SIP
which enables authorization of SIP calls based on a prior PSTN
introduction.
Legal
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on January 12, 2012.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Terminating Side Procedures . . . . . . . . . . . . . . . . . . 5
4. Originating Side Procedures . . . . . . . . . . . . . . . . . . 6
5. Tickets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7.1. IANA Registration of ViPR-Ticket Header Field . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Release notes . . . . . . . . . . . . . . . . . . . . 9
A.1. Modifications between vipr-02 and vipr-01 . . . . . . . . . 9
A.2. Modifications between vipr-01 and vipr-00 . . . . . . . . . 9
A.3. Modifications between vipr-00 and dispatch-03 . . . . . . . 9
A.4. Modifications between dispatch-03 and dispatch-02 . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
The anti-spam tickets described in this specification are the key
security mechanism in ViPR for mitigation of SPAM. The domain
originating a call inserts a ticket in the SIP INVITE sent to the
other domain. The Border Element in the domain receiving the call
(see Figure 1) can check the ticket to ensure that this originating
domain has been authorized by the terminating domain. This document
relies heavily on the concepts and terminology defined in
[VIPR-OVERVIEW] and will not make sense if you have not read that
document first.
+-+ +-+
| | | | +------+
| | +-----| |---|Enroll|
| | | | | +------+
|I| | |I|
|n| +-----+ |n|
VAP |t| | ViPR| |t|
+----------|r|---|Srvr |--|e|-----------------
| |a| | | |r| P2P-Validation
| |n| +-----+ |n|
| |e| |e|
| |t| |t|
+-----+ SIP | | +-----+ | |
| CA |-------|F|---| |--|F| ---------------
+-----+ |i| | | |i| SIP/TLS
. |r| | . | |r|
SIP/ . |e| | | |e|
MGCP/ . |w| | BE | |w|
TDM . |a| | | |a|
. |l| | | |l|
+-----+ |l| | | |l|
| UA |-------| |---| |--| |-----------------
+-----+ | | +-----+ | | SRTP
| | | |
+-+ +-+
| |
+--------------------+-----------------+
|
Single administrative domain
Figure 1: Architecture
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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].
3. Terminating Side Procedures
The Border Element will receive the TLS ClientHello which begins the
TLS handshake. The Border Element will present its own configured
cert. Once TLS handshaking is complete, the Border Element notes the
domain from the SubjectAltName on the other side of the TLS
connection, and associates it with that connection.
Next, the Border Element will receive an INVITE. This INVITE will
contain a ticket in the ViPR-Ticket header field value. The Border
Element extracts this header field. This call flow assumes it is
present. The Border Element parses it, and obtains the epoch value
encoded in the ticket. This is matched against the current epoch
value for the configured password. If they match, processing
continues. The Border Element verifies the signature is correct.
Next, it examines the start and stop time of the validity. If the
current time is between the start and stop times, the check is
passed. Next, the Border Element checks the granted-to domain in the
ticket. It compares that domain against the domain name in the
SubjectAltName of the peer on the other side of the TLS connection,
as noted above. Next, it takes the Request-URI of the SIP INVITE.
That will be of the form sip:+number@domain. If it is not in that
form, and if the number does not begin with a plus, the request is
dropped. The value, including the plus, is then compared to the
number in the ticket. If it is equal, the check has passed. The
Border Element leaves the header field in the request, but forwards
to the Call Agent.
In addition, the Border Element will typically be configured to apply
its SIP message validation logic, and enforce restrictions on the
sizes of various SIP header fields. This provides an additional
layer of security in case malicious SIP messages are sent.
The Border Element will also apply port forwarding in the case of
NAT, so that the incoming request is forwarded to the appropriate
Call Agent node.
The Call Agent will receive incoming SIP INVITEs. The Request-URI of
the INVITE will contain an E.164 number as indicated by a leading
plus. If the Request-URI is not an E.164, the request must be
rejected with a 403. Only E.164 numbers can be accepted on a ViPR
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trunk.
4. Originating Side Procedures
The routes stored to other domains in the Call Agent will each store
a ticket to utilize with calls to that route. The Call Agent learns
about these routes and the information needed to construct the ticket
from the VAP protocol [VIPR-VAP]. When sending a SIP request to one
of these domains, the Call Agent MUST include the ticket in any
dialog forming request or request that is not in an existing dialog.
5. Tickets
This ticket is a sequence of characters. These MUST be placed into a
ViPR-Ticket SIP header field value. Consequently the format for this
header field is:
Ticket = "ViPR-Ticket" HCOLON ticket-val
ticket-val = 1*(alphanum / "-" / "_" / ".")
This header field MUST be utilized in all dialog forming requests and
all out-of-dialog requests. It is not utilized in responses. The
ticket-value is a modified base64 encoded version of an object that
is composed of a series of TLVs. Each TLV is a 16 bit type, a 16 bit
length, and a variable length value. The length field refers to the
length of the value portion of the TLV, measured in bytes. The
following TLV types are defined:
1. Ticket Unique ID: This TLV has a type of 0x0001. It contains a
128 bit ID that has a unique identifier for this ticket. The
value MUST contain a 128 bit UUID defined by [RFC4122]. This TLV
MUST be present. However at this time it is used for diagnostic
purposes only.
2. Salt: This TLV has a type of 0x0002. It contains a value which
MUST be at least 32 bits, and contains a random number. Its
presence ensures that each ticket contains sufficient randomness.
This TLV MUST be present.
3. Validity: This TLV has a type of 0x0003. It contains two 64 bit
NTP times. The first is the start of the validity of the ticket,
the next is the end time for the validity of the ticket. This
TLV MUST be present.
4. Number: This TLV has a type of 0x0004. It contains a string
which has an E.164 number, included the "+", which may be called
using this ticket. The TLV has variable length. This TLV MUST
be present.
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5. Granting Node: This TLV has a type of 0x0005. It contains a 128
bit value which is the Node-ID of the node which granted the
ticket. This TLV MUST be present.
6. Granting Domain: This TLV has a type of 0x0006. The domain
which granted the ticket. A string, up to 256 characters, each
of which must be a valid domain name character. The TLV has
variable length. This TLV MUST be present.
7. Granted-To Domain: This TLV has a type of 0x0007. The domain to
which the ticket is granted. A string, up to 256 characters,
each of which must be a valid domain name character. The TLV has
a variable length. This TLV MUST be present.
8. Epoch: This TLV has a type of 0x0008. It contains a 32 bit
epoch value. It is used to select a key. This TLV MUST be
present.
9. Integrity: This TLV has a type of 0x0009. It contains a 160 bit
integrity value, computed using HMAC-SHA1. This TLV MUST be
present and MUST be the last TLV in the object.
The base64 encoding uses the base64url encoding from RFC4648
[RFC4648], with the exception of the pad character, which is a "."
instead of an "=". This ensures that the output is a valid SIP
token.
To compute the MAC, the following is done. First, the key is
obtained. The key is actually a 128 bit key, configured into the
system. The key, P, is then used to compute Km:
Km = HMAC-SHA1(P, S | Epoch)
Based on PBKDF2 from PKCS #5 [RFC2898] with HMAC-SHA1 as PRF and
iteration count of 1. Where S is the 32 bit salt and Epoch is the 32
bit Epoch, from the ticket. This produces a 160 bit Km. The MAC is
then computed as another HMAC-SHA1, over the entire ticket up to but
not including the Integrity itself, using Km as the key. This
produces the 160 bit MAC.
6. Security Considerations
TBD
7. IANA Considerations
7.1. IANA Registration of ViPR-Ticket Header Field
This document defines a new SIP header field: ViPR-Ticket. Its
syntax is defined in Section 5. This header field must be registered
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by IANA in the SIP Parameters registry under the Header Fields
subregistry with the following information:
Header Name: ViPR-Ticket
Compact Form: none
8. Acknowledgements
Thanks to Patrice Bruno for his comments, suggestions and questions
that helped to improve this document.
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.
[RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography
Specification Version 2.0", RFC 2898, September 2000.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[VIPR-OVERVIEW]
Jennings, C., Rosenberg, J., and M. Petit-Huguenin,
"Verification Involving PSTN Reachability: Requirements
and Architecture Overview",
draft-jennings-vipr-overview-01 (work in progress),
July 2011.
9.2. Informative References
[VIPR-VAP]
Jennings, C., Rosenberg, J., and M. Petit-Huguenin,
"Verification Involving PSTN Reachability: The ViPR Access
Protocol (VAP)", draft-jennings-vipr-vap-01 (work in
progress), July 2011.
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Appendix A. Release notes
This section must be removed before publication as an RFC.
A.1. Modifications between vipr-02 and vipr-01
o Renamed Ticket to ViPR-Ticket to synchronize with -overview.
A.2. Modifications between vipr-01 and vipr-00
o Renamed X-Cisco-ViPR-Ticket to Ticket and filled the IANA section.
A.3. Modifications between vipr-00 and dispatch-03
o Moved to new Working Group.
A.4. Modifications between dispatch-03 and dispatch-02
o Added terminology section.
o Nits
o Shorter I-Ds references.
o Changed issued-to to granted-to.
o Fixed the ABNF.
o The tickets is used in all dialog forming requests, not only
INVITE.
o The Number TLV has a variable length.
o The Integrity TLV MUST be the last in the object.
o Fixed a discrepancy in the epoch length.
Authors' Addresses
Jonathan Rosenberg
jdrosen.net
Monmouth, NJ
US
Email: jdrosen@jdrosen.net
URI: http://www.jdrosen.net
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Cullen Jennings
Cisco
170 West Tasman Drive
MS: SJC-21/2
San Jose, CA 95134
USA
Phone: +1 408 421-9990
Email: fluffy@cisco.com
Marc Petit-Huguenin
Stonyfish
Email: marc@stonyfish.com
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