xmss-KAT-generator/wots.c

/*
wots.c version 20150811
Andreas Hülsing
Public domain.
*/

#include "math.h"
#include "stdio.h"
#include "xmss_commons.h"
//#include "params.h"
#include "prg.h"
#include "hash.h"
#include "wots.h"

/**
 * Macros used to manipulate the respective fields
 * in the 16byte hash address
 */
#define SET_HASH_ADDRESS(a, v) {\
  a[15] = (a[15] & 1) | ((v << 1) & 255);\
  a[14] = (a[14] & 254) | ((v >> 7) & 1);}
  
#define SET_CHAIN_ADDRESS(a, v) {\
  a[14] = (a[14] & 1) | ((v << 1) & 255);\
  a[13] = (v >> 7) & 255;\
  a[12] = (a[12] & 254) | ((v >> 15) & 1);}


void wots_set_params(wots_params *params, int m, int n, int w)
{
  params->m = m;
  params->n = n;
  params->w = w;
  params->log_w = (int) log2(w);
  params->len_1 = (int) ceil(((8*m) / params->log_w));
  params->len_2 = (int) floor(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 a 32 byte array into a len*n byte array 
 * this is done using chacha20 with nonce 0 and counter 0
 */
static void expand_seed(unsigned char *outseeds, const unsigned char *inseed, const wots_params *params)
{
  prg(outseeds, params->keysize, inseed, params->n);
}

/**
 * Computes the chaining function.
 * out and in have to be n-byte arrays
 * 
 * interpretes 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, int start, int steps, const wots_params *params, const unsigned char *pub_seed, unsigned char addr[16])
{
  unsigned int i,j;
  for(j=0;j<params->n;j++) 
    out[j] = in[j];

  for(i=start;i<(start+steps) && i<params->w;i++){
    SET_HASH_ADDRESS(addr,i);
//     printf("Hash %d:",i);
//     hexdump(addr,16);
//     printf("\n");
     hash_n_n(out,out, pub_seed, addr,params->n);
  }
}

/**
 * base_w algorithm as described in draft.
 * 
 * 
 */
static void base_w(int *output, const unsigned char *input, int in_len, const wots_params *params)
{
  int in = 0;
  int out = 0;
  int total = 0;
  int bits = 0;
  int consumed = 0;
  
  for(consumed = 0; consumed < 8 * in_len; consumed += params->log_w)
  {
    if(bits == 0){
      total = input[in_len - 1 - in];
      in++;
      bits += 8;
    }
    bits -= params->log_w;
    output[out] = (total >> bits) & (params->w - 1);
    out++;
  }
}

/**
 * Alternative base w algorithm for w = 16 to check...
 */
static void base_w_alternative(int *output, unsigned char *input, int in_len, const wots_params *params)
{
  unsigned int i = 0;
  for(i = 0; i < in_len; i += 2)
  {
    output[i] = input[in_len - 1 - (i / 2)] >> 4;
    output[i+1] = input[in_len - 1 - (i / 2)] & 0xf;
  }
}

void wots_pkgen(unsigned char *pk, const unsigned char *sk, const wots_params *params, const unsigned char *pub_seed, unsigned char addr[16])
{
  unsigned int i;
  expand_seed(pk, sk, params);
  for(i=0;i<params->len;i++){
    SET_CHAIN_ADDRESS(addr,i);
//     printf("Chain: %d\n",i);
//     hexdump(addr,16);
//     printf("\n");
     gen_chain(pk+i*params->n, pk+i*params->n, 0, params->w-1, params, pub_seed, addr);
  }
}


void wots_sign(unsigned char *sig, const unsigned char *msg, const unsigned char *sk, const wots_params *params, const unsigned char *pub_seed, unsigned char addr[16])
{
  int basew[params->len];
  int csum = 0;
  unsigned int i=0;

  base_w(basew, msg, params->m, 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[len_2_bytes / params->log_w];
  base_w(csum_basew, csum_bytes, len_2_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++){
    SET_CHAIN_ADDRESS(addr,i);
//     printf("Chain: %d\n",i);
//     hexdump(addr,16);
//     printf("\n");
     gen_chain(sig+i*params->n, sig+i*params->n, 0, basew[i], params, pub_seed, addr);
  }
}

void wots_pkFromSig(unsigned char *pk, const unsigned char *sig, const unsigned char *msg, const wots_params *params, const unsigned char *pub_seed, unsigned char addr[16])
{
  int basew[params->len];
  int csum = 0;
  unsigned int i=0;

  base_w(basew, msg, params->m, 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[len_2_bytes / params->log_w];
  base_w(csum_basew, csum_bytes, len_2_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++){
    SET_CHAIN_ADDRESS(addr,i);
//     printf("Chain: %d\n",i);
//     hexdump(addr,16);
//     printf("\n");
     gen_chain(pk+i*params->n, sig+i*params->n, basew[i], params->w-1-basew[i], params, pub_seed, addr);
  }
}