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Subject: RE: [AVT] SRTCP key derivation
Date: Thu, 21 Jul 2005 11:08:10 -0400
Message-ID: <183DD1B052A11A40B76125E42F1CBAAB04C3304A@zcarhxm1.corp.nortel.com>
Thread-Topic: [AVT] SRTCP key derivation
Thread-Index: AcV+FUV6HBMFW37sSWu/MwpHdvnY8APM2A7wACNnOJAAC5oe4A==
From: "Guoqiang Lu" <guoqian@nortel.com>
To: "Karl Norrman \(KI/EAB\)" <karl.norrman@ericsson.com>
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Cc: mcgrew@cisco.com, avt@ietf.org,
 =?iso-8859-1?Q?Mats_N=E4slund_=28KI/EAB=29?= <mats.naslund@ericsson.com>
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Errors-To: avt-bounces@ietf.org


>This means that, e.g., the labels will not be in the same octet =
position for SRTP and SRTCP.

This seems to contradict the reference implementation by David McGrew =
found in srtp.sourceforge.net: The SRTCP key was derived as:

 srtp_kdf_generate(&kdf, (uint64_t) label_rtcp_encryption,=20
		     tmp_key, cipher_get_key_length(srtp->rtcp_cipher));
While SRTCP key was derived as:

 srtp_kdf_generate(&kdf, (uint64_t) label_rtp_encryption,=20
		     tmp_key, cipher_get_key_length(srtp->rtp_cipher));

And within the srtp_kdf_generate() function, the label is always =
assigned to nonce.octet[7].

Thanks!

Guoqiang Lu
ESN: 39-36277
Phone: (613) 763-6277
guoqian@nortel.com
--------------------------
The contents of the this e-mail may be Nortel Confidential!=20


-----Original Message-----
From: Karl Norrman (KI/EAB) [mailto:karl.norrman@ericsson.com]=20
Sent: Thursday, July 21, 2005 5:47 AM
To: Lu, Guoqiang [CAR:9D40:EXCH]
Cc: mcgrew@cisco.com; Mats N=E4slund (KI/EAB); avt@ietf.org
Subject: RE: [AVT] SRTCP key derivation


Hello!

The SRTCP index should not be padded with zeros to be 48 bits long.  =
This means that, e.g., the labels will not be in the same octet position =
for SRTP and SRTCP.

Regards,
Karl

> -----Original Message-----
> From: avt-bounces@ietf.org [mailto:avt-bounces@ietf.org]On Behalf Of=20
> Guoqiang Lu
> Sent: den 20 juli 2005 18:40
> To: avt@ietf.org
> Cc: mcgrew@cisco.com; Mats N=E4slund (KI/EAB)
> Subject: [AVT] SRTCP key derivation
>=20
>=20
> Hi,
> In RFC3711, section 4.3.2. SRTCP Key Derivation, it says:
>=20
> "Replace the SRTP index by the 32-bit quantity: 0 || SRTCP index ..."
>=20
> My question is that SRTP index is a 48-bit quantity, should
> the SRTCP 32-bit quantity "0 || SRTCP index" be patched with=20
> 16 leading zeros?
>=20
> Thanks!
>=20
> Guoqiang Lu
> ESN: 39-36277
> Phone: (613) 763-6277
> guoqian@nortel.com
> --------------------------
> The contents of the this e-mail may be Nortel Confidential!
>=20
>=20
> _______________________________________________
> Audio/Video Transport Working Group
> avt@ietf.org
> https://www1.ietf.org/mailman/listinfo/avt
>=20


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