Fwd: Re: Quor's cypher

[Anonymous]

Antonomasia <ant at 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.