Update the report.

[crypto_lab1.git] / lab1_rust / src / oracle_machine.rs

diff --git a/lab1_rust/src/oracle_machine.rs b/lab1_rust/src/oracle_machine.rs
index a5be2d7..3d72ddf 100644 (file)
--- a/lab1_rust/src/oracle_machine.rs
+++ b/lab1_rust/src/oracle_machine.rs
@@ -1,13 +1,13 @@
 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.
+/// Try to decipher a ciphered data block by using the previous XOR operand and an oracle on the provided address and port.
+/// May print some message on stdout.
 pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cipherblock: &[u8, ..16], variant: packet::Variant) -> Option<Vec<u8>> {
    let mut end_point = EndPoint::new(
       match TcpStream::connect(address, port) {
@@ -20,8 +20,9 @@ pub fn decipher(address: &str, port: u16, original_xor_operand: &[u8, ..16], cip
       variant,
    );
 
+   // See '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.
+   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), cipherblock);
 
    let mut decipher_block = [0u8, ..16]; // The result.
@@ -64,12 +65,13 @@ 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 {