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/* $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 <stdlib.h>
#include <stdint.h>
#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;
}
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