Finish challenge 14.

src/bytes.rs

@@ -6,6 +6,10 @@ use std::fmt::Write; // need to import this trait
 pub struct Bytes(pub Vec<u8>);
 
 impl Bytes {
+    pub fn empty() -> Bytes {
+        Bytes(vec![])
+    }
+
     pub fn from_utf8(s: &str) -> Bytes {
         Bytes(s.as_bytes().iter().map(|c| c.clone()).collect())
     }
@@ -16,6 +20,10 @@ impl Bytes {
         String::from(std::str::from_utf8(&v).unwrap())
     }
 
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
     pub fn get_block(&self, block_index: usize, block_size: usize) -> Bytes {
         Bytes(self.0[(block_index * block_size)..(block_index + 1) * block_size].to_vec())
     }

src/main.rs

@@ -7,18 +7,18 @@ mod set1;
 mod set2;
 
 fn main() {
-    // set1::challenge1();
-    // set1::challenge2();
-    // set1::challenge3();
-    // set1::challenge4();
-    // set1::challenge5();
-    // set1::challenge6();
-    // set1::challenge7();
-    // set1::challenge8();
-    // set2::challenge9();
-    // set2::challenge10();
-    // set2::challenge11();
-    // set2::challenge12();
-    // set2::challenge13();
+    set1::challenge1();
+    set1::challenge2();
+    set1::challenge3();
+    set1::challenge4();
+    set1::challenge5();
+    set1::challenge6();
+    set1::challenge7();
+    set1::challenge8();
+    set2::challenge9();
+    set2::challenge10();
+    set2::challenge11();
+    set2::challenge12();
+    set2::challenge13();
     set2::challenge14();
 }

src/set2.rs

@@ -183,17 +183,17 @@ pub fn challenge12() {
     let key = Bytes::random(16); // consistent but unknown key
     assert_eq!(get_block_size(&key), 16); // 1. discover block size
     assert_eq!(is_encryption_ecb(&key), true); // 2. confirm oracle uses ecb
-    let rountrip_text = decode(&key); // 3.-6.
+    let roundtrip_text = decode(&key); // 3.-6.
     let clear_text = read("data/12.txt");
 
     // 138 (instead of 139); I think we get one additional byte because we guess
     // the first padding byte. The right approach would be to remove the last
     // byte, encrypt it, and then compare it to the result of the encryption
     // oracle, but this approach is fine too.
-    assert_eq!(rountrip_text.0[..138], clear_text.0);
+    assert_eq!(roundtrip_text.0[..138], clear_text.0);
     println!(
         "[okay] Challenge 12: {}",
-        rountrip_text.to_utf8()[..17].to_string()
+        roundtrip_text.to_utf8()[..17].to_string()
     );
 }
 
@@ -284,27 +284,109 @@ pub fn challenge14() {
 
         for i in 1..10 {
             let block_size = i * 16;
-            let chunks: Vec<&[u8]> = cipher.0.chunks(block_size).collect();
-            for i in 0..chunks.len() {
-                for j in (i + 1)..chunks.len() {
-                    if chunks[i] == chunks[j] {
+            match get_duplicated_block_indices(&cipher, block_size) {
+                Some((_, _)) => {
                     return block_size;
                 }
-                }
+                _ => (),
             }
         }
         0
     }
 
-    let prefix = Bytes::random_range(0, 200);
-    let key = Bytes::random(16); // consistent but unknown key
-    assert_eq!(get_block_size(&prefix, &key), 16);
-    let _clear_text = read("data/12.txt");
+    fn get_duplicated_block_indices(cipher: &Bytes, block_size: usize) -> Option<(usize, usize)> {
+        let chunks: Vec<&[u8]> = cipher.0.chunks(block_size).collect();
+        for i in 0..chunks.len() {
+            for j in (i + 1)..chunks.len() {
+                if chunks[i] == chunks[j] {
+                    return Some((i, j));
+                }
+            }
+        }
+        None
+    }
+
+    fn get_prefix_size(prefix: &Bytes, key: &Bytes) -> usize {
+        let block_size = get_block_size(&prefix, &key);
+        let duplicated_text = Bytes::from_utf8("aaaabbbbccccddddaaaabbbbccccdddd").0;
+
+        for i in 0..block_size {
+            let mut padding = vec![b'a'; i];
+            padding.append(&mut duplicated_text.to_vec());
+            let cipher = encryption_oracle(prefix, key, &Bytes(padding));
+            match get_duplicated_block_indices(&cipher, block_size) {
+                Some((first_block, _)) => {
+                    return block_size * first_block - i;
+                }
+                _ => (),
+            }
+        }
+        0
+    }
+
+    fn decode(prefix: &Bytes, key: &Bytes) -> Bytes {
+        let block_size = get_block_size(prefix, key);
+        let prefix_size = get_prefix_size(prefix, key);
+        let prefix_padding_size = block_size - (prefix_size % block_size);
+        let prefix_padding = Bytes(vec![b'a'; prefix_padding_size]);
+        let block_count = encryption_oracle(&prefix, &key, &prefix_padding).len() / block_size;
+        let first_block_index = (prefix_size + prefix_padding_size) / block_size;
+        let mut clear_text = vec![];
 
         // AES-128-ECB(random-prefix || attacker-controlled || target-bytes, random-key)
-    // rrrrrrrrrrrrrrrrrrraaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaathe real text
+        // rrrrrrrrrrrrrrrrrrrpppppppppppppaaaaaaaaaaaaaaathe real text
         // 0..34..78..bc..f0..34..78..bc..f0..34..78..bc..f0..34..78..bc..f0..34..78..bc..f
-    // 0               1               2               4               5
+        // 0               1  ^            2               4               5
+        //                    |            ^ first_block_index
+        //                    \ prefix_padding
+        for block_index in first_block_index..block_count {
+            let mut clear_text_block = vec![];
+            for padding_length in (0..block_size).rev() {
+                let full_padding_text = vec![b'-'; prefix_padding_size + padding_length];
+                let expected = encryption_oracle(prefix, key, &Bytes(full_padding_text.to_vec()));
+                let expected_block = expected.get_block(block_index, block_size);
 
-    println!("[xxxx] Challenge 14: {}", get_block_size(&prefix, &key));
+                let mut known_text = if block_index == first_block_index {
+                    full_padding_text.to_vec()
+                } else {
+                    let mut prefix_padding = vec![b'-'; prefix_padding_size];
+                    let clear_text_offset = ((block_index - first_block_index - 1) * block_size)
+                        + (block_size - padding_length);
+                    prefix_padding.append(
+                        &mut clear_text[clear_text_offset..(clear_text_offset + padding_length)]
+                            .to_vec(),
+                    );
+                    prefix_padding
+                };
+                known_text.append(&mut clear_text_block.to_vec());
+
+                for i in 0..255 {
+                    let mut guess_text = known_text.to_vec();
+                    guess_text.push(i);
+                    let cipher_block = encryption_oracle(prefix, key, &Bytes(guess_text))
+                        .get_block(first_block_index, block_size);
+                    if cipher_block.0 == expected_block.0 {
+                        clear_text_block.push(i);
+                        break;
+                    }
+                }
+            }
+            clear_text.append(&mut clear_text_block);
+        }
+        // We get last byte from cbs padding so remove it.
+        Bytes(clear_text[0..(clear_text.len() - 1)].to_vec())
+    }
+
+    let prefix = Bytes::random_range(0, 200);
+    let key = Bytes::random(16);
+    assert_eq!(get_block_size(&prefix, &key), 16);
+    let prefix_len = get_prefix_size(&prefix, &key);
+    assert_eq!(prefix.len(), prefix_len);
+    let roundtrip_text = decode(&prefix, &key);
+    let clear_text = read("data/12.txt");
+    assert_eq!(roundtrip_text, clear_text);
+    println!(
+        "[okay] Challenge 14: {}",
+        roundtrip_text.to_utf8()[..17].to_string()
+    );
 }