Start work on challenge 14.

src/main.rs

@@ -15,9 +15,10 @@ fn main() {
     // set1::challenge6();
     // set1::challenge7();
     // set1::challenge8();
-    set2::challenge9();
-    set2::challenge10();
-    set2::challenge11();
-    set2::challenge12();
-    set2::challenge13();
+    // set2::challenge9();
+    // set2::challenge10();
+    // set2::challenge11();
+    // set2::challenge12();
+    // set2::challenge13();
+    set2::challenge14();
 }

src/set2.rs

@@ -221,7 +221,7 @@ pub fn challenge13() {
         // "valid" ciphertexts) and the ciphertexts themselves, make a
         // role=admin profile.
         // (FelixM) I assume ECB and block_size = 16; we could figure
-        // it out easily my adding enough 'a' to the email
+        // it out easily by adding enough 'a' to the email
         let mut r = vec![];
 
         //             ________________________________
@@ -250,9 +250,61 @@ pub fn challenge13() {
     let dict = decrypt(&key, &profile);
     let role = dict.get("role").unwrap();
     assert_eq!(role, "admin");
-    println!("[done] Challenge 13: role={}", role);
+    println!("[okay] Challenge 13: role={}", role);
 }
 
 pub fn challenge14() {
-    println!("[xxxx] Challenge 14:");
+    fn read(path: &str) -> Bytes {
+        let s = std::fs::read_to_string(path).unwrap();
+        BytesBase64::from_base64(&s).to_bytes()
+    }
+
+    fn encryption_oracle(
+        Bytes(random_prefix): &Bytes,
+        random_key: &Bytes,
+        Bytes(attacker_controlled): &Bytes,
+    ) -> Bytes {
+        // AES-128-ECB(random-prefix || attacker-controlled || target-bytes, random-key)
+        // Thoughts: If I generate a random prefix for every encryption, then I don't
+        // know how to decode it because I cannot really run experiments. If I generate
+        // a single random prefix it becomes rather trivial. I just have to find out how
+        // long it is and then adjust the decoding routine.
+        let mut plaintext = random_prefix.to_vec();
+        plaintext.append(&mut attacker_controlled.to_vec());
+        let mut target_bytes = read("data/12.txt").0;
+        plaintext.append(&mut target_bytes);
+        let cipher = ecb::encrypt(&random_key, &Bytes(plaintext));
+        cipher
+    }
+
+    fn get_block_size(prefix: &Bytes, key: &Bytes) -> usize {
+        // Detect cipher block size this approach also confirms that it is ECB
+        let v = vec![b'a'; 256];
+        let cipher = encryption_oracle(prefix, key, &Bytes(v));
+
+        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] {
+                        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");
+
+    // AES-128-ECB(random-prefix || attacker-controlled || target-bytes, random-key)
+    // rrrrrrrrrrrrrrrrrrraaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaathe 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
+
+    println!("[xxxx] Challenge 14: {}", get_block_size(&prefix, &key));
 }