X-Git-Url: http://git.euphorik.ch/?a=blobdiff_plain;f=lab1_rust%2Fsrc%2Foracle_machine.rs;h=dd0430db9dc2632c9b6f75bf504847092b0d212b;hb=fe03a7f9df6b8f4cf03e2399aeb68a7dc2605a67;hp=a5be2d758b5c6a9003f4728332d8608358e4eba0;hpb=307b73948c18f26a4ff12fc29f9055397a999f44;p=crypto_lab1.git

diff --git a/lab1_rust/src/oracle_machine.rs b/lab1_rust/src/oracle_machine.rs
index a5be2d7..dd0430d 100644
--- a/lab1_rust/src/oracle_machine.rs
+++ b/lab1_rust/src/oracle_machine.rs
@@ -1,14 +1,14 @@
 use std::io;
-use std::io::{ TcpStream };
-use std::iter::{ range_inclusive };
+use std::io::TcpStream;
+use std::iter::range_inclusive;
 use std::slice::bytes::copy_memory;
 use packet;
 use packet::{ Packet, Error };
 use end_point::EndPoint;
 
-/// Try to decipher a ciphered data block by using the previous xor operand and an oracle on the provided address and port.
-/// May prints some message on the stdout.
-pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cipherblock: &[u8, ..16], variant: packet::Variant) -> Option<Vec<u8>> {
+/// Tries to decipher a ciphered data block by using the previous XOR operand and an oracle on the provided address and port.
+/// May print some messages on stdout.
+pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cipher_block: &[u8, ..16], variant: packet::Variant) -> Option<Vec<u8>> {
    let mut end_point = EndPoint::new(
       match TcpStream::connect(address, port) {
          Ok(s) => s,
@@ -20,12 +20,13 @@ pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cip
       variant,
    );
 
+   // Sees 'packet::Packet' documentation for a complete description about the binary packet structure.
    let mut final_packet = [0u8, ..2 + 1 + 8 + 32 + 10];
-   final_packet[1] = 1 + 8 + 32 + 10; // Data length.
-   copy_memory(final_packet.slice_mut(2 + 1 + 8 + 16, 2 + 1 + 8 + 32), cipherblock);
+   final_packet[1] = (final_packet.len() as u8) - 2; // Data length.
+   copy_memory(final_packet.slice_mut(2 + 1 + 8 + 16, 2 + 1 + 8 + 32), cipher_block);
 
    let mut decipher_block = [0u8, ..16]; // The result.
-   let mut x_prime_block = [0u8, ..16]; // The cipher block ('cipherblock') after AES and before XOR.
+   let mut x_prime_block = [0u8, ..16]; // The cipher block ('cipher_block') after AES and before XOR.
    let mut current_timestamp = 0u64;
    let mut first_byte = 0u8; // Used to save the first byte for the first iteration.
 
@@ -39,7 +40,7 @@ pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cip
 
       for v in range_inclusive(0u8, 255) { // For each values of the current byte.
 
-         // Compute and write timestamp.
+         // Computes and writes timestamp.
          current_timestamp += 2;
          {
             let mut timestamp_writer = io::BufWriter::new(final_packet.slice_mut(2 + 1, 2 + 1 + 8));
@@ -52,7 +53,8 @@ pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cip
             Ok(Ok(p @ Packet { t: Error(packet::AuthError), .. })) => {
                println!("We received a MAC Error: {}", p);
 
-               // If we already got a MAC mismatch for the first byte then the second byte is incremented and the loop is replayed.
+               // If we already got a MAC mismatch for the first byte then
+               // the second byte is incremented and the main loop is replayed for the first byte.
                if byte == 15 && get_mac_mismatch_error {
                   forged_xor_operand(&mut final_packet)[14] += 1;
                   continue 'main_loop;
@@ -64,12 +66,13 @@ pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cip
                x_prime_block[byte] = v ^ (padding_value as u8);
                decipher_block[byte] = x_prime_block[byte] ^ original_xor_operand[byte];
 
-               // We set the processed bytes of the forged XOR operand to have the next padding value.
+               // We set the processed bytes of the forged XOR operand to have the next padding value (2, 3, 4, etc..).
                for i in range(16 - padding_value, 16) {
                   forged_xor_operand(&mut final_packet)[i] = x_prime_block[i] ^ ((padding_value as u8) + 1);
                }
 
-               // Special case for the first byte: we have to test all the values.
+               // Special case for the first byte: we have to test all the values to avoid a valid padding
+               // which is not [.., 0x01], for instance [.., 0x02, 0x02]. It's a very rare case but not impossible.
                if byte == 15 {
                   first_byte = forged_xor_operand(&mut final_packet)[15];
                } else {