From mboxrd@z Thu Jan 1 00:00:00 1970 From: Edward Shushkin Subject: Re: Proposal for keying encrypted filesystem Date: Sat, 29 Mar 2003 21:17:28 +0300 Sender: edward Message-ID: <3E85E338.CEAA7DC7@namesys.com> References: <200303282026.23543.phma@webjockey.net> <3E85CDEF.7B6BD323@namesys.com> <200303291155.40419.phma@webjockey.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com List-Id: Content-Type: text/plain; charset="us-ascii" To: Pierre Abbat Cc: reiserfs-list@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.