Date: Mon, 17 May 1999 23:09:09 +0930 (CST) From: Kris Kennaway <kkennawa@physics.adelaide.edu.au> To: Adam Shostack <adam@homeport.org> Cc: Adam Shostack <adam@breakwater.homeport.org>, nr1@ihug.co.nz, freebsd-security@FreeBSD.ORG Subject: Re: secure backup Message-ID: <Pine.OSF.4.10.9905172252050.22357-100000@bragg> In-Reply-To: <19990517093143.B2322@weathership.homeport.org>
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On Mon, 17 May 1999, Adam Shostack wrote: > 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. Yes, but the question is whether tapes do this at all. The normal use of a backup tape (preserving a perfect copy of everything you send to it) is ruined if tapes are dropping bits - I don't think you'd see this unless your hardware was bad, in which case any relatively lightweight encoding method is likely to be in trouble too. The best you could do to guard against this would be to either run your encrypted data stream through an error-correcting code filter (I don't know of any tools which can do this, but it's not hard to write), or break up your input into blocks and encrypt them separately (or use the DES ECB mode). > | 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. I was talking about authentication for access to the tape server process itself (preventing other people from writing onto your tape). You're correct about PGP - it's probably better to use PGP instead of bdes (or equivalent symmetric encryption filter) for this reason - verification that your data stream was read back intact (and assuming perfect retrieval, was stored intact) when you restore. Kris ----- "That suit's sharper than a page of Oscar Wilde witticisms that's been rolled up into a point, sprinkled with lemon juice and jabbed into someone's eye" "Wow, that's sharp!" - Ace Rimmer and the Cat, _Red Dwarf_ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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