[Cryptography] cheap sources of entropy

[Ben Laurie]

On 27 January 2014 21:14, Jon Callas <jon at callas.org> wrote:
> Assume a frame F_i taken from the camera. If the attacker cannot guess the *exact* contents of that frame, even with filters, in-camera JPEG, etc. with an advantage over guessing flips of a fair coin, then it's got one bit of entropy.
>
> So take 512 frames and hash them. Poof you're done.
>
> Extrapolate from there to the case of a frame having N bits of entropy.

Where N, it should be noted, can be less than one. Which makes
extrapolation hard.