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What would be the max number of bits that hashing hardware specifically designed for bitcoin mining would ever need to hash per operation? For example:
block header = 80 bytes = 640 bits
after first hash = 256 bits
To find merkle root: 256(per txn) x 2 = 512 bits
So is 640 bits the max input message size the hashing hardware needs to handle?
2Note that 1. finding the Merkle root only needs to be done once per 4 billion hash attempts. 2. Most of the time just one branch needs to be calclated. 3. The main loop in SHA-256 calculation always works on a 2048-bit message schedule, so the initial message size might not have a great significance on hardware design. – Meni Rosenfeld – 2014-06-25T07:03:05.757
SHA-256 operates on a 512 bit message block. So I believe the hashing hardware can compute the initial block header hash with just two blocks. – Joe M – 2014-06-25T19:51:48.603