It'd also be trivial to devise a decryption algorithm, and key, which "decrypts" anyones hard drive to reveal illegal images even when none are really there...

It'd also be trivial to devise a decryption algorithm, and key, which "decrypts" anyones hard drive to reveal illegal images even when none are really there... Well the revealed images could not be significantly larger in size than then the "key material" you supplied plus the most concise description of the algorithm. http://en.wikipedia.org/wiki/Kolmogorov_complexity http://en.wikipedia.org/wiki/Kolmogorov_complexity