mgf1.c

/*
 * @seed: 20 bytes
 * @result: 120 bytes (but use first 107 bytes only)
 */

int mgf1(char *seed, BYTE *result)
{
   int hlen = 20;
   int length = 127 - hlen;
   int i, d = 0;

   for(i = 0; i <= length; i += hlen)
   {
      unsigned char C[4];
      SHA1_CTX ctx;

      format_int(C, i, 4, MP_BIG_ENDIAN);

      sha1_init(&ctx);
      sha1_update(&ctx, seed, 20);
      sha1_update(&ctx, C, 4);
      sha1_final(&ctx, &result[d * 20]);
      d++;
   }
}