On Wed, 4 Aug 2004, Hal Finney wrote:
As you can see, breaking 128 bit keys is certainly not a task which is so impossible that it would fail even if every atom were a computer. If we really needed to do it, it's not outside the realm of possibility that it could be accomplished within 50 years, using nanotech and robotics to move and reassemble asteroids into the necessary disk.
There are easier targets than the symmetric cipher algorithm itself. You may aim at RSA, try to break through the factorization problem, or find another weakness in it. Same for other algorithms of this class. You may aim at the passphrase, as several other people suggested. You may use nanotech to compromise the hardware, and/or to intercept the data. This includes "eating and duplicating" chips, including key storage tokens; just go layer after layer and rebuild it (or create its "virtual" image) including the levels of electric charge in the memory cells. How to design a token that would be resistant to nanoprobes? (Perhaps by equipping it with an "immune system" of nanoprobes of its own?) Quantum computers may be the way to break factoring-related algorithms. Nanotechnology can bring many ways for physical compromising of the targets and their vicinity (the "fly on the wall" attack). The impracticability of breaking symmetric ciphers is only a comparatively small part of the overall problem.