Home > Cryptography > Cost of Brute-force

Cost of Brute-force

Over at crypto.se someone asked a question about the cost in dollars of brute-forcing a 256 bit key. In my answer, I estimated it to be about 8 octodecillion dollar ($8 * 10^57). And that is for the electricity only! Some of the answers were pretty interesting and I learned a few things. For example, I never knew exactly how a quantum computer would affect symmetric-key cryptography. It turns out that it would halve the key space, which is optimal (i.e., you cannot do better). If one could do better with a quantum computer, then that would prove that the key could be brute forced in less than 2^n time. I won’t pretend to understand exactly why that is, but it is a pretty interesting result that I had wondered about for some time.

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