Subject: [AVT] SRTP Redundancy Support

From: Elad Roichman <[email-masked]>
Date: Mon, 26 Apr 2010 13:55:23 +0300

Hello,

My name is Elad Roichman and I work as a DSP engineer in AudioCodes Ltd.
I have a question regarding SRTP: Does SRTP support redundant RTP packets (Using RFC 2198, for example)? Is SRTP defined for RFC 2198 RTP packets?
I wonder if I should be able to encrypt / decrypt RFC 2198 RTP packets.

I'm looking forward to your response.

Thanks in advance,

Elad Roichman.

________________________________
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---

From: Jonathan Lennox <[email-masked]>
Date: Mon, 26 Apr 2010 11:46:00 -0400

As far as SRTP is concerned, RFC 2198 is just another RTP payload.  Thus, it's supported, but there's no "special" support for it in the protocol - you aggregate the redundant packets, then encrypt the entire resulting payload.

It should be possible, on decryption, to decrypt only the payload header and then those data blocks you actually need, as (I believe) all the currently-defined SRTP encryption transforms use counter modes and thus could support random-access decryption within a payload.  (I doubt many existing SRTP implementations are designed to support this optimization, however.)

Authentication tags, however, still need to be verified over the entire (compound) RTP packet.

--
Jonathan Lennox
Vidyo, Inc
[email-masked]

From: Elad Roichman [mailto:[email-masked]]
Sent: Monday, April 26, 2010 6:55 AM
To: [email-masked]
Subject: [AVT] SRTP Redundancy Support

Hello,

Thanks in advance,

Elad Roichman.

---

From: Elad Roichman <[email-masked]>
Date: Tue, 27 Apr 2010 10:11:18 +0300

First of all, thanks for the quick response.
Secondly, I would like to clarify an issue concerning the encryption / decryption of RFC 2198 packets: if RFC 2198 packet should be able to be secured using SRTP, what part of the packet is encrypted?
According to RFC 3711 (SRTP), section 3.1, Figure 1., only the payload of the packet is encrypted. What should be considered as payload in RFC 2198 packet? Are the additional redundancy headers (indicating the PT, timestamp offset and block length) considered as part of the RTP header (which means that they're not encrypted / decrypted) or as part of the payload (which means that they're encrypted / decrypted)?

Thanks in advance,

Elad.

From: Jonathan Lennox [mailto:[email-masked]]
Sent: Monday, April 26, 2010 18:46
To: Elad Roichman; [email-masked]
Subject: RE: SRTP Redundancy Support

--
Jonathan Lennox
Vidyo, Inc
[email-masked]

Hello,

Thanks in advance,

Elad Roichman.

---

From: Roni Even <[email-masked]>
Date: Tue, 27 Apr 2010 11:06:29 +0300

Hi,

The redundancy header are part of the payload and not part of the RTP
header. They are not specified as RTP  header extensions so they are part of
the payload that need to be encrypted. I think that this is also what
Jonathan is saying

Roni Even

As individual

From: [email-masked] [mailto:[email-masked]] On Behalf Of Elad
Roichman
Sent: Tuesday, April 27, 2010 10:11 AM
To: Jonathan Lennox; [email-masked]
Subject: Re: [AVT] SRTP Redundancy Support

Secondly, I would like to clarify an issue concerning the encryption /
decryption of RFC 2198 packets: if RFC 2198 packet should be able to be
secured using SRTP, what part of the packet is encrypted?

According to RFC 3711 (SRTP), section 3.1, Figure 1., only the payload of
the packet is encrypted. What should be considered as payload in RFC 2198
packet? Are the additional redundancy headers (indicating the PT, timestamp
offset and block length) considered as part of the RTP header (which means
that they're not encrypted / decrypted) or as part of the payload (which
means that they're encrypted / decrypted)?

Thanks in advance,

Elad.

As far as SRTP is concerned, RFC 2198 is just another RTP payload.  Thus,
it's supported, but there's no "special" support for it in the protocol -
you aggregate the redundant packets, then encrypt the entire resulting
payload.

It should be possible, on decryption, to decrypt only the payload header and
then those data blocks you actually need, as (I believe) all the
currently-defined SRTP encryption transforms use counter modes and thus
could support random-access decryption within a payload.  (I doubt many
existing SRTP implementations are designed to support this optimization,
however.)

Authentication tags, however, still need to be verified over the entire
(compound) RTP packet.

-- 

Jonathan Lennox

Vidyo, Inc

[email-masked]

Hello,

I have a question regarding SRTP: Does SRTP support redundant RTP packets
(Using RFC 2198, for example)? Is SRTP defined for RFC 2198 RTP packets?

Thanks in advance,

Elad Roichman. 

  _____  

This email and any files transmitted with it are confidential material. They
are intended solely for the use of the designated individual or entity to
whom they are addressed. If the reader of this message is not the intended
recipient, you are hereby notified that any dissemination, use, distribution
or copying of this communication is strictly prohibited and may be unlawful.

If you have received this email in error please immediately notify the
sender and delete or destroy any copy of this message

  _____  

This email and any files transmitted with it are confidential material. They
are intended solely for the use of the designated individual or entity to
whom they are addressed. If the reader of this message is not the intended
recipient, you are hereby notified that any dissemination, use, distribution
or copying of this communication is strictly prohibited and may be unlawful.

If you have received this email in error please immediately notify the
sender and delete or destroy any copy of this message

---

From: Elad Roichman <[email-masked]>
Date: Tue, 27 Apr 2010 11:16:01 +0300

Hi Jonathan & Roni,

Thank you for helping to clarify this issue.

Regards,

Elad Roichman.

From: Roni Even [mailto:[email-masked]]
Sent: Tuesday, April 27, 2010 11:06
To: Elad Roichman; 'Jonathan Lennox'; [email-masked]
Subject: RE: [AVT] SRTP Redundancy Support

Hi,
The redundancy header are part of the payload and not part of the RTP header. They are not specified as RTP  header extensions so they are part of the payload that need to be encrypted. I think that this is also what Jonathan is saying

Roni Even
As individual

From: [email-masked] [mailto:[email-masked]] On Behalf Of Elad Roichman
Sent: Tuesday, April 27, 2010 10:11 AM
To: Jonathan Lennox; [email-masked]
Subject: Re: [AVT] SRTP Redundancy Support

Thanks in advance,

Elad.

--
Jonathan Lennox
Vidyo, Inc
[email-masked]

Hello,

Thanks in advance,

Elad Roichman.