From owner-freebsd-security Mon May 3 2:22:13 1999 Delivered-To: freebsd-security@freebsd.org Received: from enst.enst.fr (enst.enst.fr [137.194.2.16]) by hub.freebsd.org (Postfix) with ESMTP id C37E31564C for ; Mon, 3 May 1999 02:22:10 -0700 (PDT) (envelope-from beyssac@enst.fr) Received: from bofh.enst.fr (bofh.enst.fr [137.194.32.191]) by enst.enst.fr (8.9.1a/8.9.1) with ESMTP id LAA19857; Mon, 3 May 1999 11:21:54 +0200 (MET DST) Received: by bofh.enst.fr (Postfix, from userid 12426) id 734EBD223; Mon, 3 May 1999 11:21:54 +0200 (CEST) Message-ID: <19990503112154.A20922@enst.fr> Date: Mon, 3 May 1999 11:21:54 +0200 From: Pierre Beyssac To: Allen Smith , Robert Watson , 0x1c Cc: freebsd-security@FreeBSD.ORG Subject: Re: Blowfish/Twofish References: <9905030205.ZM6442@beatrice.rutgers.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.93.2i In-Reply-To: <9905030205.ZM6442@beatrice.rutgers.edu>; from Allen Smith on Mon, May 03, 1999 at 02:05:30AM -0400 Sender: owner-freebsd-security@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Mon, May 03, 1999 at 02:05:30AM -0400, Allen Smith wrote: > One can use any cryptographically secure one-way hash function as a > (secret key) encryption method. The procedure is as follows: > > Sender and recipient have shared secret key K. They want to transmit > information I. Sender takes three-bit chunks (the most efficient size) > of information I, finds a random salt S of sufficient size for each There's a simpler way that doesn't requires you to compute several hashes for the same data: simply use your hash function as a pseudo-random generator using the key as a seed, then XOR the resulting stream with your data. However, it seems using this scheme is not recommended by experts in the field, on the assumption that hash functions are not designed to withstand the same kind of attacks as ciphers functions. -- Pierre Beyssac pb@enst.fr To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message