Date: 28 Jun 2005 12:42:13 +0200 From: Rasmus Kaj <kaj@kth.se> To: Tim Aslat <tim@spyderweb.com.au> Cc: freebsd-multimedia@freebsd.org Subject: Re: tamper proofing audio Message-ID: <rqcvf3yzrsq.fsf@kashyyyk.ite.kth.se> In-Reply-To: <20050622141220.2cabee63@bofh.spyderweb.com.au> References: <20050622141220.2cabee63@bofh.spyderweb.com.au>
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>>>>> "TA" == Tim Aslat <tim@spyderweb.com.au> writes: TA> Hi All, Hi! TA> can anyone tell me if it's possible to tamper-proof an audio recording TA> in such a way that it can still be played on a normal audio CD player? TA> I'm not worried about the recording being copied, but I am worried TA> about it being modified and want to guard against it. [...] Checksums and digital signatures comes to mind. Store the signed sound file in a filsystem on the cd, then it can be verified by anyone with access to the public key that the sound file is identic to what someone with access to the private key. A normal audio CD player won't be able to verify the authenticy of the recording, but it can still play the audio copy (there can be audio and data tracks on the same cd). If you need to store as much audio as possible, with the signature, on a single cd, you can stora a signed checksum of the audio track instead of a signed copy, then the data track can be much smaller. But in that case you need to create the checksum in such a way that the errors that do happen on an audio cd can be excused but still exclude the possiblilty of tampering. That might be a research area in its own right. It would no doubt be much simpler to store a signed copy of the audio (possibly compressed). The authenticy can then be established by first validating the signature and then listening to the signed audio file. -- Rasmus Kaj --+-- rasmus@kaj.se --+-- http://www.stacken.kth.se/~kaj/ Lottery: A tax on people who are bad at math
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