From owner-freebsd-questions Mon Aug 7 5:44:52 2000 Delivered-To: freebsd-questions@freebsd.org Received: from mail-in-02.piro.net (mail-out-01.piro.net [194.64.31.11]) by hub.freebsd.org (Postfix) with ESMTP id EC33D37B5A4 for ; Mon, 7 Aug 2000 05:44:48 -0700 (PDT) (envelope-from marc.vanwoerkom@science-factory.com) Received: from nil.science-factory.com (ScienceFactory-atm1-153.piro.net [195.135.137.205]) by mail-in-02.piro.net (8.9.3/8.9.3/PN-991208) with ESMTP id OAA12234; Mon, 7 Aug 2000 14:44:42 +0200 Received: by nil.science-factory.com (Postfix, from userid 501) id 1637B1EE7; Mon, 7 Aug 2000 14:39:25 +0200 (CEST) From: Marc van Woerkom To: zzhang@cs.binghamton.edu Cc: freebsd-questions@freebsd.org In-reply-to: (message from Zhihui Zhang on Thu, 3 Aug 2000 10:58:00 -0400 (EDT)) Subject: Re: How to use checksum.md5 References: Message-Id: <20000807123925.1637B1EE7@nil.science-factory.com> Date: Mon, 7 Aug 2000 14:39:25 +0200 (CEST) Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > I download the FreeBSD ISO image. I notice there is a checksum.md5 file > there. Can anyone tell me how to use it (which tools do I need)? Like you wrote MD5 is a checksum or hash. The idea is to compute the checksum of the (well known) algorithm yourself and compare it to the checksum listed. If they differ it is clear that something fishy is going on, either transmission errors or even tampering. That is because hash functions are choosen in a way that this equality is *very* hard to accomplish: hash(x) = hash(x + dx + comp) (meaning: manipulating input first x+dx and then compensating in a way +comp that one still gets the original hash number) On a FreeBSD system you have a 'md5' command that computes this checksum. There might be other programs that provide this calculation (a Perl built in?) Porting md5.c is easy as well, I once made it run with Cygwin under Win32 (just throw a bit unnecessary stuff away) > Do I absolutely need to do the check? Thanks. You need not - this is something for the cautious/paranoid who fear that they got some altered version of the file. I am not sure, if an ISO image per se has some checksum integrated, so that you would run into some warning at burning time. Otherwise running a checksum over a 650MB download seems not a bad idea. Regards, Marc To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message