Common use of Hash Functions Clause in Contracts

Hash Functions. ‌ Performance is dominated by the cost of a call to the chaining function in WOTS+ and the hash function in the binary trees. In essence, these functions consist of many applications of SHA-256 to small arrays of data (i.e. 32 to 128 bytes) and some xor operations. This is not a particularly common pattern of operations in traditional cryptography – a signature operation typically requires just one hash function call to digest the message, often negligible in the overall performance of the signing operation. Note also that there is significant cost associated with a single call to a hash function that is constant in the length of the input, likely representing the overhead of the function call, as shown in Table 1.