Re: draft-ietf-ipsec-ciph-aes-ctr-00.txt

[Stephen Kent <kent@bbn.com>]

At 4:56 PM -0400 8/27/02, Housley, Russ wrote:
>Steve:
>
>I disagree.  AES-CTR only uses the AES encrypt operation for both 
>packet encryption and decryption.  Since AES encrypt and AES decrypt 
>are quite different, unlike DES where they were nearly identical, 
>there can be a considerable savings in code size and development 
>time for AES-CTR since AES-CBC used both AES encrypt and decrypt 
>operations.
>
>Russ
>

Russ,

Yes, that point has been made and I concur that, relative to CBC, a 
CTR or an OFB mode implementation is simpler because only the encrypt 
operation needs be created. I doubt that this will be an issue in the 
IPsec context, unless we mandate ONLY CTR, since modes like CBC do 
require both encrypt and decrypt codebooks, but your point is correct.

Steve