1 #ifndef SPX_HASH_STATE_H 2 #define SPX_HASH_STATE_H 3 4 /** 5 * Defines the type of the hash function state. 6 * 7 * Don't be fooled into thinking this instance of SPHINCS+ isn't stateless! 8 * 9 * From Section 7.2.2 from the SPHINCS+ round-2 specification: 10 * 11 * Each of the instances of the tweakable hash function take PK.seed as its 12 * first input, which is constant for a given key pair – and, thus, across 13 * a single signature. This leads to a lot of redundant computation. To remedy 14 * this, we pad PK.seed to the length of a full 64-byte SHA-256 input block. 15 * Because of the Merkle-Damgård construction that underlies SHA-256, this 16 * allows for reuse of the intermediate SHA-256 state after the initial call to 17 * the compression function which improves performance. 18 * 19 * We pass this hash state around in functions, because otherwise we need to 20 * have a global variable. 21 */ 22 23 #include "sha2.h" 24 #define hash_state sha256ctx 25 26 #endif 27