/* $OpenBSD: xmss_wots.c,v 1.3 2018/04/10 00:10:49 djm Exp $ */ /* wots.c version 20160722 Andreas Hülsing Joost Rijneveld Public domain. */ #include "includes.h" #ifdef WITH_XMSS #include <stdlib.h> #ifdef HAVE_STDINT_H # include <stdint.h> #endif #include <limits.h> #include "xmss_commons.h" #include "xmss_hash.h" #include "xmss_wots.h" #include "xmss_hash_address.h" /* libm-free version of log2() for wots */ static inline int wots_log2(uint32_t v) { int b; for (b = sizeof (v) * CHAR_BIT - 1; b >= 0; b--) { if ((1U << b) & v) { return b; } } return 0; } void wots_set_params(wots_params *params, int n, int w) { params->n = n; params->w = w; params->log_w = wots_log2(params->w); params->len_1 = (CHAR_BIT * n) / params->log_w; params->len_2 = (wots_log2(params->len_1 * (w - 1)) / params->log_w) + 1; params->len = params->len_1 + params->len_2; params->keysize = params->len * params->n; } /** * Helper method for pseudorandom key generation * Expands an n-byte array into a len*n byte array * this is done using PRF */ static void expand_seed(unsigned char *outseeds, const unsigned char *inseed, const wots_params *params) { uint32_t i = 0; unsigned char ctr[32]; for(i = 0; i < params->len; i++){ to_byte(ctr, i, 32); prf((outseeds + (i*params->n)), ctr, inseed, params->n); } } /** * Computes the chaining function. * out and in have to be n-byte arrays * * interprets in as start-th value of the chain * addr has to contain the address of the chain */ static void gen_chain(unsigned char *out, const unsigned char *in, unsigned int start, unsigned int steps, const wots_params *params, const unsigned char *pub_seed, uint32_t addr[8]) { uint32_t i, j; for (j = 0; j < params->n; j++) out[j] = in[j]; for (i = start; i < (start+steps) && i < params->w; i++) { setHashADRS(addr, i); hash_f(out, out, pub_seed, addr, params->n); } } /** * base_w algorithm as described in draft. * * */ static void base_w(int *output, const int out_len, const unsigned char *input, const wots_params *params) { int in = 0; int out = 0; uint32_t total = 0; int bits = 0; int consumed = 0; for (consumed = 0; consumed < out_len; consumed++) { if (bits == 0) { total = input[in]; in++; bits += 8; } bits -= params->log_w; output[out] = (total >> bits) & (params->w - 1); out++; } } void wots_pkgen(unsigned char *pk, const unsigned char *sk, const wots_params *params, const unsigned char *pub_seed, uint32_t addr[8]) { uint32_t i; expand_seed(pk, sk, params); for (i=0; i < params->len; i++) { setChainADRS(addr, i); gen_chain(pk+i*params->n, pk+i*params->n, 0, params->w-1, params, pub_seed, addr); } } int wots_sign(unsigned char *sig, const unsigned char *msg, const unsigned char *sk, const wots_params *params, const unsigned char *pub_seed, uint32_t addr[8]) { //int basew[params->len]; int csum = 0; uint32_t i = 0; int *basew = calloc(params->len, sizeof(int)); if (basew == NULL) return -1; base_w(basew, params->len_1, msg, params); for (i=0; i < params->len_1; i++) { csum += params->w - 1 - basew[i]; } csum = csum << (8 - ((params->len_2 * params->log_w) % 8)); int len_2_bytes = ((params->len_2 * params->log_w) + 7) / 8; unsigned char csum_bytes[len_2_bytes]; to_byte(csum_bytes, csum, len_2_bytes); int csum_basew[params->len_2]; base_w(csum_basew, params->len_2, csum_bytes, params); for (i = 0; i < params->len_2; i++) { basew[params->len_1 + i] = csum_basew[i]; } expand_seed(sig, sk, params); for (i = 0; i < params->len; i++) { setChainADRS(addr, i); gen_chain(sig+i*params->n, sig+i*params->n, 0, basew[i], params, pub_seed, addr); } free(basew); return 0; } int wots_pkFromSig(unsigned char *pk, const unsigned char *sig, const unsigned char *msg, const wots_params *params, const unsigned char *pub_seed, uint32_t addr[8]) { int csum = 0; uint32_t i = 0; int *basew = calloc(params->len, sizeof(int)); if (basew == NULL) return -1; base_w(basew, params->len_1, msg, params); for (i=0; i < params->len_1; i++) { csum += params->w - 1 - basew[i]; } csum = csum << (8 - ((params->len_2 * params->log_w) % 8)); int len_2_bytes = ((params->len_2 * params->log_w) + 7) / 8; unsigned char csum_bytes[len_2_bytes]; to_byte(csum_bytes, csum, len_2_bytes); int csum_basew[params->len_2]; base_w(csum_basew, params->len_2, csum_bytes, params); for (i = 0; i < params->len_2; i++) { basew[params->len_1 + i] = csum_basew[i]; } for (i=0; i < params->len; i++) { setChainADRS(addr, i); gen_chain(pk+i*params->n, sig+i*params->n, basew[i], params->w-1-basew[i], params, pub_seed, addr); } free(basew); return 0; } #endif /* WITH_XMSS */