[MeganC]

One-time cipher pads are still pretty safe so long as you just use them once.

[Jack Hydrazine]

http://en.wikipedia.org/wiki/One-time_pad

[JoeFromSidney]

One-time cipher pads are still pretty safe so long as you just use them once.

The problem is getting genuinely random numbers for the key. Computers produce only pseudorandom numbers, and even if the keys are genuinely random, keeping the "code book" secure is difficult.