tamper proofing audio

Rasmus Kaj kaj at kth.se
Tue Jun 28 10:42:18 GMT 2005

>>>>> "TA" == Tim Aslat <tim at spyderweb.com.au> writes:

 TA> Hi All,


 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 at kaj.se --+-- http://www.stacken.kth.se/~kaj/
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