public void changeSendCipher(BlockCipher bc, MAC mac) {
if ((bc instanceof NullCipher) == false) {
/* Only use zero byte padding for the first few packets */
useRandomPadding = true;
/* Once we start encrypting, there is no way back */
}
cos.changeCipher(bc);
send_mac = mac;
send_mac_buffer = (mac != null) ? new byte[mac.size()] : null;
send_padd_blocksize = bc.getBlockSize();
if (send_padd_blocksize < 8) send_padd_blocksize = 8;
}
public void sendMessage(byte[] message, int off, int len, int padd) throws IOException {
if (padd < 4) padd = 4;
else if (padd > 64) padd = 64;
int packet_len = 5 + len + padd; /* Minimum allowed padding is 4 */
int slack = packet_len % send_padd_blocksize;
if (slack != 0) {
packet_len += (send_padd_blocksize - slack);
}
if (packet_len < 16) packet_len = 16;
int padd_len = packet_len - (5 + len);
if (useRandomPadding) {
for (int i = 0; i < padd_len; i = i + 4) {
/*
* don't waste calls to rnd.nextInt() (by using only 8bit of the
* output). just believe me: even though we may write here up to 3
* bytes which won't be used, there is no "buffer overflow" (i.e.,
* arrayindexoutofbounds). the padding buffer is big enough =) (256
* bytes, and that is bigger than any current cipher block size + 64).
*/
int r = rnd.nextInt();
send_padding_buffer[i] = (byte) r;
send_padding_buffer[i + 1] = (byte) (r >> 8);
send_padding_buffer[i + 2] = (byte) (r >> 16);
send_padding_buffer[i + 3] = (byte) (r >> 24);
}
} else {
/* use zero padding for unencrypted traffic */
for (int i = 0; i < padd_len; i++) send_padding_buffer[i] = 0;
/* Actually this code is paranoid: we never filled any
* bytes into the padding buffer so far, therefore it should
* consist of zeros only.
*/
}
send_packet_header_buffer[0] = (byte) ((packet_len - 4) >> 24);
send_packet_header_buffer[1] = (byte) ((packet_len - 4) >> 16);
send_packet_header_buffer[2] = (byte) ((packet_len - 4) >> 8);
send_packet_header_buffer[3] = (byte) ((packet_len - 4));
send_packet_header_buffer[4] = (byte) padd_len;
cos.write(send_packet_header_buffer, 0, 5);
cos.write(message, off, len);
cos.write(send_padding_buffer, 0, padd_len);
if (send_mac != null) {
send_mac.initMac(send_seq_number);
send_mac.update(send_packet_header_buffer, 0, 5);
send_mac.update(message, off, len);
send_mac.update(send_padding_buffer, 0, padd_len);
send_mac.getMac(send_mac_buffer, 0);
cos.writePlain(send_mac_buffer, 0, send_mac_buffer.length);
}
cos.flush();
if (log.isEnabled()) {
log.log(
90, "Sent " + Packets.getMessageName(message[off] & 0xff) + " " + len + " bytes payload");
}
send_seq_number++;
}