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RE: [Ipsec] a new draft



Hi.

As you state in section 3.5.2, there is a requirement for the IV to be
unique within the lifetime of the key.

Suppose we are using 3DES-CBC, and replacing the key after 1,000,000 IP
packets have been sent.  If you generate the full 64-bit IV randomly, the
chances of a collision (two IVs being identical) are 0.0000027%.  That's low
enough that most of us will accept the risk.
If we fix 16 bits of the IV, and generate only 48 random bits, then the
likelihood of a collision rises to 0.177%, which may very well be
unacceptable to many.

With AES-CBC, this is not a problem, as 112 bits of randomness are plenty.

________________________________

From: ipsec-bounces@ietf.org [mailto:ipsec-bounces@ietf.org] On Behalf Of
Souhwan Jung
Sent: Monday, July 19, 2004 11:44 PM
To: ipsec@ietf.org
Subject: [Ipsec] a new draft 


Dear all,
 
I apologize if you got this meessage twice.
 
We have submitted a draft related to multiple senders that shares a SA.
The main focus is to solve the problem of sequence number problem. 
Any comments on the draft will be appreciated. 
 
http://www.ietf.org/internet-drafts/draft-zhao-ipsec-multi-sender-sa-00.txt
 
Thanks.
 
 
Souhwan
============================================================
Souhwan Jung
Associate Professor                      email:souhwanj@ssu.ac.kr
School of Electronic Engineering     phone: +82-2-820-0714
Soongsil University                         fax: +82-2-821-7653
1-1 Sangdo-dong, Dongjak-ku, 
Seoul 156-743
============================================================


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