Subject: [AVTCORE] comments on draft-ietf-avtcore-srtp-ekt-02

From: Yi Cheng <[email-masked]>
Date: Tue, 8 Apr 2014 15:13:59 +0000

Hi,

Here are some comments on draft-ietf-avtcore-srtp-ekt-02:

2.2.1. last paragraph
"Implementation note: Because of the format of the Full EKT Field, a
packet containing the Full EKT Field MUST be sent when the ROC changes (i.e., every 2^32 packets)."
The ROC changes every 2^16 packets, not every 2^32 packets

2.5. the 3rd paragraph
"The Full EKT Field is appended to the SRTP or SRTCP payload and is
42, 50, or 58 octets long for AES-128, AES-192, or AES-192,
respectively..."
Should be "...42, 50, or 58 octets long for AES-128, AES-192, or AES-256 respectively..."

2.6. the 1st paragraph
"A system using EKT has the SRTP keys distributed with EKT, rather
   than with call signaling.  This means a receiver can immediately
   decrypt an SRTP (or SRTCP packet) using that new key, provided the
   SRTP packet (or SRTCP packet) also contains the EKT key."

The SRTP or SRTCP packet does not contain the EKT key which is a key encrypting key (as stated in section 2), rather the encrypted SRTP master key. The same goes for the 4th paragraph "...Inclusion of that Full EKT Field can be
   stopped early if the sender determines all receivers have received
   the new EKT key...".

Best regards,
Yi Cheng
Ericsson Research