The University of SydneyPage 24Constructing a block–Difficulty target & Nonce–Mining is the process of hashing the block header repeatedly changing one parameter (nonce), until the resulting hash is less than a threshold.–This threshold is the difficulty target.–F(block,nonce) àSHA256(SHA256(nonce, block)) < difficulty target–Hash result cannot be determined in advance, nor can find a pattern.–The only way to find a matching hash result is to try again and again, randomly modifying the input.–The resulting Nonce is the proof-of-work[DN93]:–finding the nonce takes time, but –validating that the nonce is correct is easy.[DN93] C. Dworkand M. Naor. Pricing via processing or combatting junk mail. In Proceedings of the 12th Annual International Cryptology Conference on Advances in Cryptology, CRYPTO '92, pages 139-147, 1993.