Work on challenge 17.

src/bytes.rs

@@ -101,7 +101,7 @@ impl Bytes {
         }
     }
 
-    pub fn has_valid_pkcs7(&mut self, block_size: usize) -> bool {
+    pub fn has_valid_pkcs7(&self, block_size: usize) -> bool {
         if self.len() > 0 && self.len() % block_size != 0 {
             return false;
         }

src/main.rs

@@ -8,21 +8,21 @@ mod set2;
 mod set3;
 
 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();
-    set2::challenge14();
-    set2::challenge15();
-    set2::challenge16();
+    // 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();
+    // set2::challenge15();
+    // set2::challenge16();
     set3::challenge17();
 }

src/set3.rs

@@ -13,10 +13,11 @@ pub fn challenge17() {
             .collect()
     }
 
-    fn encrypt(ten_strings: &Vec<Bytes>, key: &Bytes) -> (Bytes, Bytes) {
+    fn encrypt(key: &Bytes) -> (Bytes, Bytes) {
         // The first function should select at random one of the ten strings
-        let index: usize = rand::thread_rng().gen_range(0..ten_strings.len());
-        let mut cleartext = Bytes(ten_strings[index].0.to_vec());
+        let cleartexts = read("data/17.txt");
+        let index: usize = rand::thread_rng().gen_range(0..cleartexts.len());
+        let mut cleartext = Bytes(cleartexts[index].0.to_vec());
 
         // pad the string out to the 16-byte AES block size and
         cleartext.pad_pkcs7(16);
@@ -26,11 +27,33 @@ pub fn challenge17() {
         let iv = Bytes::random(16);
         (cbc::encrypt(&key, &iv, &cleartext), iv)
     }
-    let cleartexts = read("data/17.txt");
 
     // generate a random AES key (which it should save for all future encryptions)
     let key = Bytes::random(16);
-    let (cipher, _iv) = encrypt(&cleartexts, &key);
+    let (cipher, _iv) = encrypt(&key);
+    let decryption_oracle = |iv: &Bytes, cipher: &Bytes| -> bool {
+        // The second function should consume the ciphertext produced by the
+        // first function, decrypt it, check its padding, and return true or
+        // false depending on whether the padding is valid.
+        let roundtrip = cbc::decrypt(&key, iv, cipher);
+        roundtrip.has_valid_pkcs7(16)
+    };
 
-    println!("[xxxx] Challenge 17: {}", cipher.len());
+    let attack_block = |cipher_block: &Bytes| -> Bytes {
+        let block_size = cipher_block.len();
+        let mut iv = Bytes::random(block_size);
+
+        for i in 0..=255 {
+            iv.0[15] = i;
+
+            if decryption_oracle(&iv, cipher_block) {
+                println!("{i:#016b}");
+            }
+        }
+        Bytes(vec![])
+    };
+
+    let _block_count = cipher.len() / 16;
+    let first_block = attack_block(&cipher.get_block(0, 16));
+    println!("[xxxx] Challenge 17: {:?}", first_block);
 }