lab1_rust/src/oracle_machine.rs

   1 use std::io;
   2 use std::io::TcpStream;
   3 use std::iter::range_inclusive;
   4 use std::slice::bytes::copy_memory;
   5 use packet;
   6 use packet::Packet;
   7 use packet::PacketType::Error;
   8 use end_point::EndPoint;
   9
  10 /// Tries to decipher a ciphered data block by using the previous XOR operand and an oracle on the provided address and port.
  11 /// May print some messages on stdout.
  12 pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8; 16], cipher_block: &[u8; 16], variant: packet::Variant) -> Option<Vec<u8>> {
  13    let mut end_point = EndPoint::new(
  14       match TcpStream::connect((address, port)) {
  15          Ok(s) => s,
  16          _ => {
  17             println!("Unable to connect to the oracle on [{}]:{}", address, port);
  18             return None
  19          }
  20       },
  21       variant,
  22    );
  23
  24    // Sees 'packet::Packet' documentation for a complete description about the binary packet structure.
  25    let mut final_packet = [0u8; 2 + 1 + 8 + 32 + 10];
  26    final_packet[1] = (final_packet.len() as u8) - 2; // Data length.
  27    copy_memory(final_packet.slice_mut(2 + 1 + 8 + 16, 2 + 1 + 8 + 32), cipher_block);
  28
  29    let mut decipher_block = [0u8; 16]; // The result.
  30    let mut x_prime_block = [0u8; 16]; // The cipher block ('cipher_block') after AES and before XOR.
  31    let mut current_timestamp = 0u64;
  32    let mut first_byte = 0u8; // Used to save the first byte for the first iteration.
  33
  34    #[inline(always)]
  35    fn forged_xor_operand(packet: &mut [u8]) -> &mut [u8] { packet.slice_mut(2 + 1 + 8, 2 + 1 + 8 + 16) }
  36
  37    // For each bytes.
  38    let mut byte = 15;
  39    'main_loop: loop {
  40       let mut get_mac_mismatch_error = false; // For the first byte we need to insure there is only one AUTH error (one valid padding).
  41
  42       for v in range_inclusive(0u8, 255) { // For each values of the current byte.
  43
  44          // Computes and writes timestamp.
  45          current_timestamp += 2;
  46          {
  47             let mut timestamp_writer = io::BufWriter::new(final_packet.slice_mut(2 + 1, 2 + 1 + 8));
  48             let _ = timestamp_writer.write_be_u64(current_timestamp - 1);
  49          }
  50
  51          forged_xor_operand(&mut final_packet)[byte] = v;
  52
  53          match end_point.send_raw_with_result(&final_packet) {
  54             Ok(Ok(p @ Packet { t: Error(packet::ErrorType::Auth), .. })) => {
  55                println!("We received a MAC Error: {}", p);
  56
  57                // If we already got a MAC mismatch for the first byte then
  58                // the second byte is incremented and the main loop is replayed for the first byte.
  59                if byte == 15 && get_mac_mismatch_error {
  60                   forged_xor_operand(&mut final_packet)[14] += 1;
  61                   continue 'main_loop;
  62                }
  63
  64                get_mac_mismatch_error = true;
  65
  66                let padding_value = 16 - byte;
  67                x_prime_block[byte] = v ^ (padding_value as u8);
  68                decipher_block[byte] = x_prime_block[byte] ^ original_xor_operand[byte];
  69
  70                // We set the processed bytes of the forged XOR operand to have the next padding value (2, 3, 4, etc..).
  71                for i in range(16 - padding_value, 16) {
  72                   forged_xor_operand(&mut final_packet)[i] = x_prime_block[i] ^ ((padding_value as u8) + 1);
  73                }
  74
  75                // Special case for the first byte: we have to test all the values to avoid a valid padding
  76                // which is not [.., 0x01], for instance [.., 0x02, 0x02]. It's a very rare case but not impossible.
  77                if byte == 15 {
  78                   first_byte = forged_xor_operand(&mut final_packet)[15];
  79                } else {
  80                   break;
  81                }
  82             },
  83             Ok(Ok(Packet { t: Error(packet::ErrorType::Crypt), .. })) => (), // Ignored case: the padding is wrong.
  84             other => {
  85                println!("Unexcepted response, aborting. {}", other);
  86                return None
  87             }
  88          }
  89       }
  90
  91       if byte == 15 {
  92          forged_xor_operand(&mut final_packet)[15] = first_byte;
  93       }
  94
  95       // It was the last byte.
  96       if byte == 0 { break; }
  97
  98       byte -= 1;
  99    }
 100
 101    Some(decipher_block.to_vec())
 102 }