All the blocks in the Bitcoin block chain have a short string of meaningless data—called a nonce—attached to them. The mining computers are required to search for the right meaningless string such that the block as a whole satisfies a certain arbitrary condition. Specifically, it is required that the SHA-256 hash of the block have a certain number of leading zeros.2 Hashes are one-way functions, so there is no easy way to find the right nonce or otherwise to engineer a block to be correct. The only known way to find a good nonce is to simply to try randomly until one turns out to work.