Re: Listening to Crypto

From: Bob Deblier (bob_at_nospam.com)
Date: 09/29/04 

Date: Wed, 29 Sep 2004 07:10:43 GMT

On Tue, 28 Sep 2004 18:44:56 -0700, flip wrote:

> Hi All,
>
> I am giving a talk that includes some discussion on crypto.
>
> Instead of showing a typical figure of plaintext versus ciphertext, I was
> wondering if one could "listen" to encrypted music.
>
> For example, take B's Sonata (an mp3) and AES encrypt it.
>
> Play the plaintext version and then play the encrypted version.
>
> One could also look at the graphic equalizer and should see quite a
> difference in the output.
>
> My only problem is this, I am not sure this is a sound comparison, but was
> having a tough time convincing myself why not.
>
> Shouldn't an encrypted file take music which has beautiful melodic
> properties and turn that into mush?
>
> The equalizer may be a stretch, but again it seems that for a demo this
> shouldn't be so far fetched.
>
> Has anyone ever done this (all of the special characters from the songs
> encrypt may blow it!)?
>
> Any thoughts?
>
> P.S. Can someone take a classical piece, AES encrypt it and send me the
> files? I'd appreciate that.

I'm not an audio engineer, but I did work professionally on CD-i disks, so
I do know a bit about the theory and practical application.

If you were to start with CD-quality audio in raw 16-bit samples (padding
with zero samples), encrypt them with any modern block cipher (like AES),
and master these as a new audio track, you would end up with what is
called "white noise" (see http://en.wikipedia.org/wiki/White_noise).

In other words, your encrypted sound will be indistinguishable from
random noise. If you do decide to listen to white noise, keep the volume
low, to prevent damage to your eardrums and equipment.

Sincerely,

Bob Deblier

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