From: Anonymous <nobody@REPLAY.COM>
Date: Sun, 21 Dec 1997 06:44:15 +0800
To: cypherpunks@Algebra.COM
Subject: ECB, CBC, CFB, OFB
Message-ID: <199712202235.XAA24669@basement.replay.com>
MIME-Version: 1.0
Content-Type: text/plain



Can somebody more experienced than I am explain the strengths and weaknesses
of these encryption modes as applied to CAST, IDEA, DES, and Blowfish?

>       -m mode
>              Set the transfer mode.
>
>              Valid ENCRYPTION modes are:
>
>              ecb    Electronic codebook mode
>                     c[i] = f1(K, p[i])
>                     p[i] = f2(K, c[i])
>
>              cbc    Ciphertext block chaining mode
>                     c[i] = f1(K, p[i] ^ c[i-1])
>                     p[i] = f2(K, c[i]) ^ c[i-1]
>
>              cfb    Ciphertext feeback mode
>                     c[i] = f1(K, c[i-1]) ^ p[i]
>                     p[i] = f2(K, c[i-1]) ^ c[i]
>
>              ofb    Output feeback mode
>                     h[i] = f1(K, h[i-1])
>                     c[i] = p[i] ^ h[i]
>                     p[i] = c[i] ^ h[i]