From owner-freebsd-security Mon May 17 6:18:26 1999 Delivered-To: freebsd-security@freebsd.org Received: from weathership.homeport.org (breakwater.homeport.org [216.67.13.2]) by hub.freebsd.org (Postfix) with ESMTP id D73E814CCD for ; Mon, 17 May 1999 06:18:22 -0700 (PDT) (envelope-from adam@weathership.homeport.org) Received: (from adam@localhost) by weathership.homeport.org (8.8.8/8.8.5) id JAA02339; Mon, 17 May 1999 09:31:43 -0400 (EDT) Date: Mon, 17 May 1999 09:31:43 -0400 From: Adam Shostack To: Kris Kennaway Cc: Adam Shostack , nr1@ihug.co.nz, freebsd-security@FreeBSD.ORG Subject: Re: secure backup Message-ID: <19990517093143.B2322@weathership.homeport.org> References: <19990516223322.B1851@weathership.homeport.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.95.3i In-Reply-To: ; from Kris Kennaway on Mon, May 17, 1999 at 12:45:09PM +0930 Sender: owner-freebsd-security@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Mon, May 17, 1999 at 12:45:09PM +0930, Kris Kennaway wrote: | On Sun, 16 May 1999, Adam Shostack wrote: | | > You're worried about errors on the tape, I presume? You could | > pipe the output of pgp through something that does redundant encoding, | > such that errors on the tape are recoverable outside the tape. There | > are some direct tradeoffs that you can find between bloat and | > recoverability; as you add bits, your odds of being able to | > reconstruct increase. | | Pipe the output of dump or tar or whatever you're using through bdes(1). You | don't need the overhead of PGP unless you want a trusted third party to read | the backup without knowing the encryption key. Pass the data through three | rounds of bdes doing an encrypt, decrypt, followed by encrypt (with different | keys, of course) and you've got yourself 3DES, which bdes doesn't seem to do | natively. Make the keys random, and stick those in a PGP file if you like. | | Hmm, there seems to be a void of any general-purpose tools which provide | error-correcting data encoding - but in this case do you really need it? | It'll only multiply the size of your backup, and if you're using a reliable | transport protocol between client and server (i.e. TCP) then this shouldn't be | an issue. If your tape is dropping bits, then it would be a big problem if you | were using it in the normal way (attached to local computer). I suppose the | untrusted server could cause your data stream to be corrupted, but they could | also cause it to never make the tape in the first place. If the tape is unreliable, and you lose a few bits of a plaintext file, you've lost a few bits. If its a few bits of an encrypted and compressed file, you may lose the whole file. | ther server and modify it to nullify ANY authentication measures (easy if this | is a shell script) - so you can't really be sure that no-one else is writing | data onto the tape, only that the data you do write which ends up on the tape | is secure from decryption. No, if you use pgp, you can sign the data on your local (trusted) machine, and only be vulnerable to a DOS attack, not authentication attacks. | In summary, there's only so much you can do if you don't trust the server - | you still have to trust them to provide basic functions like actually writing | your data to the tape. This is correct. Adam -- "It is seldom that liberty of any kind is lost all at once." -Hume To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message