int pack_message_add_noise(char* msgbuf, uint msglen) {
  ushort control = *(ushort *) (msgbuf + 8);
  int rval = 0;

  msglen = parse_packet_get_expected_payload_len(0x1FFCu, msgbuf);

  if (msglen >= 16 && msglen <= 8188 && msglen == (int) r && HIBYTE(control) >= 0 ) {
      *(ushort *)(msgbuf + 8) = control | 0x8000;
      /* populate the keys */
      call_fill_pseudorandom_bytes(msgbuf, 8);

      *(int *)(msgbuf + msglen) = compute_checksum(msgbuf, msglen);
      rval = msglen + 4;
      encrypt_decrypt_message(rval - 8, msgbuf + 8, *(int *)msgbuf, *(int *)
                             (msgbuf + 4));
      int noise_len = (8192 - rval) & 0x1FF;

      /* compute_random_noise length */
      for (i=0; i < 4; i++ ) {
      noise_len = critical_generate_random() % (unsigned int)(noise_len + 1);
      }
      /* append random noise */
      if ( noise_len ) {
      call_fill_pseudorandom_bytes(msgbuf + rval, noise_len);
      rval += noise_len;
      }
    }

  return rval;
}

int encrypt_decrypt_message(int buflen, char* buf, int key1, int key2) {
  int remlen;
  int64 key64;
  int keyrot;
  uchar carry;

  for (remlen=buflen; remlen > 0; remlen--, buf++) {
      *((int *)&key64 + 1) = key2;
      *(int *)&key64 = key1;
      key64 << 1;
      keyrot = 2 * key1 | (key2 >> 31);
      *buf = *buf ^ (uchar) keyrot;
      /* generate carry flag for addition */
      carry = __MKCADD__((uchar) keyrot, keyrot);
      key1 = (uchar) keyrot + keyrot;
      key2 = carry + *((int *)&key64 + 1);
  }
  return (uchar) keyrot;
}





 

 

Acknowledements

  This material is based upon work supported through the U.S. Army Research Office under the Cyber-TA Research Grant No. W911NF-06-1- 0316 and by the National Science Foundation, Grant No. CNS-07-16 612. The views expressed in this document are those of the authors and do not necessarily represent the official position of the sponsors.