The bitcoin mining process
The computational complexity of the SHA-256 algorithm relates directly to the feasibility of bitcoin mining as a profitable endeavor. The only way to determine the SHA-256 hash of a particular data block is to perform all the steps of the SHA-256 algorithm over all the bits in the block.
A key feature of the bitcoin mining process is that it is intentionally very difficult to find a valid nonce that produces a block hash below the current target network hash target. In fact, it is likely to take an enormous number of guesses of different nonce values before a target-satisfying value is found. Due to the lack of any predictable relationship between the block data content and the SHA-256 hash of that block, there is no more efficient method to determine a suitable nonce value than simply hashing the data block repeatedly with varying nonces until a hash turns up that satisfies the target criteria.
The process of identifying a nonce value that satisfies...
