Subject: I-D ACTION:draft-ietf-secsh-newmodes-03.txt

From: [email-masked]
Date: Wed, 23 Mar 2005 16:14:01 -0500

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Secure Shell Working Group of the IETF.

	Title		: SSH Transport Layer Encryption Modes
	Author(s)	: M. Bellare, et al.
	Filename	: draft-ietf-secsh-newmodes-03.txt
	Pages		: 12
	Date		: 2005-3-23
	
Researchers have recently discovered that the authenticated
encryption portion of the current SSH Transport Protocol is
vulnerable to several attacks.
This document describes new symmetric encryption methods for the SSH
Transport Protocol and gives specific recommendations on how
frequently SSH implementations should rekey.
Bellare, Kohno, and Namprempre [ACM CCS 2002] prove that if an SSH
application implements the modifications described in this document,
then the symmetric cryptographic portion of that application will
provably resist chosen-plaintext, chosen-ciphertext, reaction-based
privacy and integrity/authenticity attacks.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-secsh-newmodes-03.txt

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---

From: Bill Sommerfeld <[email-masked]>
Date: Wed, 23 Mar 2005 17:24:29 -0500

> 	Filename	: draft-ietf-secsh-newmodes-03.txt
	
I am starting an official WG Last Call on this document, for publication
as an Proposed Standard.  This last call period expires on April 6th,
2005.

This is an important draft; please read it carefully.

During this Last Call period, comments supporting publication are
encouraged as are comments pointing out problems or suggesting changes
to the spec. 

Reports of successful implementation of this draft are encouraged.  As a
reminder, tests of interoperability are *not* a prerequisite for
publication as Proposed Standard but any obstacles to implementation or
spec ambiguities should be corrected before publication..

Please send comments to the WG list as a whole.

						- Bill

---

From: Ben Harris <[email-masked]>
Date: Fri, 25 Mar 2005 17:22:05 +0000

>encouraged as are comments pointing out problems or suggesting changes

The semantics af the specification seem fine to me, but there are a few
nits:

The abstract and the introduction state that the security problems with CBC
modes were identified "recently".  I'd suggest dropping the word "recently"
in both cases since it's over two years ago now.

The abstract mentions [ACM CCS 2002], which doesn't appear in the
references.

In section 3, "Section 7" should read "Section 9".  In section 4, "Section
4.3" should read "Section 6.3", and "Section 5.2" should read "Section 7.2".

"vice versa" is mis-spelt as "visa-versa" in sections 3 and 6.1.

There should perhaps be an explicit note in section 4 that blowfish-ctr uses
a different key size from blowfish-cbc.

In the paragraph describing blowfish-ctr, "256 bit" should read "256-bit".

The reference for triple-DES in section 4 should be changed from [SCHNEIER]
to FIPS PUB 46-3.

The sentence "IDEA is patented by Ascom AG" shoud be removed.

The key size of cast128-ctr should be specified.

In section 6.2, the phrase "Although there may be networks savings for
padding to only 8-bytes" should read "Although there may be network savings
from padding to only 8 bytes".

The reference for [AES] should be to FIPS PUB 197 rather than to the
Rijndael submission.

References [BN] and [KRAWCZYK] are never used.

>Reports of successful implementation of this draft are encouraged.

I've written a client implementation of aes128-ctr, aes192-ctr, aes256-ctr,
3des-ctr, and blowfish-ctr for PuTTY, and tested the first three against
OpenSSH 3.9p1.  I haven't yet found a server implementation of 3des-ctr or
blowfish-ctr to test against (though I haven't looked hard).

-- 
Ben Harris