17 Dec
2003
17 Dec
'03
11:17 p.m.
Antonomasia <ant@notatla.demon.co.uk> wrote:
My attack takes a long chunk of known text and looks for repetition.
ppppppppppppppp.11.pppppppppppppppppppppp ccccccccccccccc.22.cccccccccccccccccccccc
When a two neighbouring p-c pairs are the same you can test whether they have the same value of a and b. (That is a_n == a_n+1 and b_n == b+n+1, a != b usually.)
This involves 16 inputs to each byte - very cheap. What I really want next is to know "a".
Wouldn't this only happen (on average) in one out of every 65536 p-c pairs? Since the state array is changed entirely with every 128 bytes encrypted, 1 out of 2^16 doesn't seem to help much.