Re: Proposal for keying encrypted filesystem

[Edward Shushkin <edward@namesys.com>]

Pierre Abbat wrote:
> 
> On Saturday 29 March 2003 11:46, Edward Shushkin wrote:
> > Never trust 4-byte ID. The first collision that provides any assigned 4
> > bytes in SHA1 output can be found very easy..
> 
> How many bytes of key ID would you use? A 4-byte key ID would mean that if
> about 92682 different keys were in use, there would be half a chance of a
> collision.
> 

Any collision can be used by attacker for access to remained decrypted data
in memory, so you should assign the *whole* output of any crypto-stable hash 
function (20 bytes for SHA1). If you use 19 bytes for ID, there is no any
guarantee that someone can not find a collision easy.
Edward.
 
> By the way, I am on the list.