Subject: [Sip] Errata report on errata 2602 and 2120 on RFC 5479, "Requirements and Analysis of Media Security Management Protocols"

From: "Worley, Dale R (Dale)" <[email-masked]>
Date: Mon, 13 Dec 2010 17:09:48 -0500

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RFC5479, "Requirements and Analysis of Media Security Management Protocols"
Source of RFC: sip (rai)

Errata ID: 2602

Status: Reported
Type: Technical

Reported By: Fabio Pietrosanti
Date Reported: 2010-11-04

Section A.5.2 says:

      SDP Security Descriptions with SIPS
         Not applicable; SDP Security Descriptions does not have a long-
         term secret.

It should say:

      SDP Security Descriptions with SIPS
         The PFS feature of SDP Security Description with SIPS rely on
         TLS and the availability or not of PFS for SRTP calls depends
         on the negotiated TLS key negotiation algorithm.

         If the selected TLS key negotiation algorithm of SIPS provide
         PFS feature, then the underlying SRTP encryption will support
         PFS.  For example TLS_DHE_RSA_WITH_AES_256_CBC_SHA provde PFS
         feature as described in RFC5246.  If the selected TLS key
         negotiation algorithm of SIPS does not provide PFS feature,
         then the underlying SRTP encryption will not support PFS.
         For example TLS_RSA_WITH_AES_256_CBC_SHA does not provide PFS
         feature as described in RFC5246.

Notes:

It's not true that SDP Security Descriptions with SIPS have PFS "Not
applicable" because the SDES rely on TLS that is part of the security
scheme.

Practically if the long terms keys (the x509v3 RSA key of SIPS server)
is compromised, the TLS sessions can be decrypted, the SDES key
extracted and SRTP calls deciphered.

TLS support key exchange methods that provide PFS trough the use of
Ephemeral Diffie Hellman keys.

When SIPS use TLS with DHE key negotiation, then SDES acquire PFS
feature because even in case of long-term key compromise (the server
x509v3 RSA key), the short term keys (the SDES keys exchanged) will be
safe.
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Recommended status:  (correct) Verified (publish)
Should be reviewed by a security expert.

It seems that the entry for "SDP Security Descriptions with S/MIME" is
also incorrect, as revelation of the private keys of the participants
will render the SDES readable.  I think better phrasing of the revised
wording is:

      SDP Security Descriptions with SIPS
         PFS if the selected TLS cipher suites for the SIPS hops provide PFS.

      SDP Security Descriptions with S/MIME
         No PFS.

This needs to be reviewed by a security expert.
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RFC5479, "Requirements and Analysis of Media Security Management Protocols"
Source of RFC: sip (rai)

Errata ID: 2120

Status: Reported
Type: Editorial

Reported By: Alfred Hoenes
Date Reported: 2010-04-05

Section 4.4,3rd para says:

|  A typical case of using media security where two entities are having
   a Voice over IP (VoIP) conversation over IP-capable networks.
   [...]

It should say:

|  A typical case of using media security is where two entities are
   having a Voice over IP (VoIP) conversation over IP-capable networks.
   [...]

Notes:

Rationale: missing verb.
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Recommended status:  (correct) Hold for document update
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Dale