Subject: Question with Using AES CCM Mode With IPsec ESP

From: Jimmy Hsieh (謝侑村) <[email-masked]>
Date: Mon, 8 Mar 2004 14:02:53 +0800

Hi Mr. Housley:
	After reading "Using AES CCM Mode With IPsec ESP
<draft-ietf-ipsec-ciph-aes-ccm-05.txt>," I have two questions about constructing AAD.
	1.	Is the "64-bit Extended Sequence Number" transmitted? Or only "Low
		32-bit of Extended Sequence Number" is transmitted.
	2.	In "IP Encapsulating Security Payload (ESP)
		<draft-ietf-ipsec-esp-v3-08.txt>," it is mentioned that the high 32-bit of
		Extended Sequence Number is placed after the "Next Header" field. The
		Location for high 32-bit of Extended Sequence Number is differently
		defined in <draft-ietf-ipsec-esp-v3-08.txt> and
		<draft-ietf-ipsec-ciph-aes-ccm-05.txt>. Could you comment on this?

Thank you very much.

Jimmy Hsieh

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From: Russ Housley <[email-masked]>
Date: Tue, 23 Mar 2004 10:31:45 -0500

Jimmy:

I do not find any problems between the CCM cipher specification and the 
latest ESP draft.  By the way, the CCM specification is in the RFC Editor's 
queue.

1. Only the low order bits are transmitted.  The AAD is constructed by the 
sender and the receiver from other information.  A combined mode 
specification could specify that the high order bits are transmitted and 
that would still be consistent with the ESP specification, but the CCM 
cipher specification does not do so.

2. The CCM cipher specification defines the structure for the AAD.  With 
regard to combined mode algorithms, the ESP draft says:

         The Sequence Number (or Extended Sequence Number, as
         appropriate) and the SPI are inputs to the algorithm, as
         they must be included in the integrity check computation.
         The means by which these values are included in this
         computation are a function of the combined mode algorithm
         employed and thus not specified in this standard.

Again, I see no problem.

Russ