Subject: FYI: Brief decription of [email-masked] cipher

From: Henrick Hellström <[email-masked]>
Date: Thu, 28 Apr 2005 16:28:31 +0200

Description:
Helix with a 256 bit key, a 128 bit block size and a 3*128 bit IV.

The IV is parsed as nonce(128)||key(256) and is used for setting up
a second instance of Helix. The second instance is used as a continuous
PRNG for generating the per packet nonces for the main instance.
The PRNG instance is set up normally, as for encryption, with the key
and nonce from the SSH NEWKEYS IV, without processing any unencrypted
header data before the first nonce for the main instance is generated.
Each nonce for the main instance is the next 4*32 bits of keystream
generated by the PRNG instance. The PRNG instance is never generating
any MAC and never changes the nonce. If the SSH transport layer rekeys,
a new NEWKEYS IV is generated and a new PRNG instance will be keyed by it.

This cipher provides integrated data integrity. When used, the 
negotiated SSH integrity algorithm is simply ignored

-- 
Henrick Hellström
www.streamsec.com