FW: FW: Last Call: The AES Cipher Algorithm in the SNMP's User-based Security Model to Proposed Standard

["Wijnen, Bert (Bert)" <bwijnen@lucent.com>]

FYI, another comment (and answer) on the IETF Last Call

Thanks,
Bert 

-----Original Message-----
From: Uri Blumenthal [mailto:uri@bell-labs.com]
Sent: maandag 28 april 2003 21:52
To: Daniel Chuang
Cc: Bert Wijnen; Snmpv3-wg (E-mail)
Subject: Re: FW: Last Call: The AES Cipher Algorithm in the SNMP's
User-based Security Model to Proposed Standard


Daniel Chuang wrote:
> I have one simple question on this draft, why the aes cfb mode is chosen
> instead of cbc mode ?

Because of its properties, of course.

1. Preserves the size of the plaintext (CBC would increase it).
2. Has error propagation within one block (like CBC).
3. Has chaining dependency (reordering ciphertext blocks affects
    decryption, like CBC).
4. Uses AES crypto engine in Encryption mode only (no need to
    implement AES_decrypt).