From a16eee14a18d4c345d6485593d3543e342c86af3 Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Tue, 7 Apr 2015 01:18:04 -0400
Subject: problem 26

---
 src/crack.rs  | 12 ++++++++++++
 src/lib.rs    |  1 +
 tests/set4.rs | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/src/crack.rs b/src/crack.rs
index abfd84a..b5ff9ff 100644
--- a/src/crack.rs
+++ b/src/crack.rs
@@ -435,6 +435,18 @@ pub fn crack_aes_128_ctr_random_access<F> (ciphertext: &[u8], edit: F) -> Vec<u8
     return fixed_xor(&keystream[..], ciphertext);
 }
 
+pub fn crack_ctr_bitflipping<F> (f: &F) -> Vec<u8> where F: Fn(&str) -> Vec<u8> {
+    let ciphertext = f("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00");
+    let replacement = fixed_xor(&ciphertext[32..44], b";admin=true;");
+    return ciphertext[..32]
+        .iter()
+        .chain(replacement.iter())
+        .chain(ciphertext[44..].iter())
+        .map(|x| *x)
+        .collect();
+}
+
+
 fn crack_single_byte_xor_with_confidence (input: &[u8]) -> (u8, f64) {
     let mut min_diff = 100.0;
     let mut best_key = 0;
diff --git a/src/lib.rs b/src/lib.rs
index 6cfb2d3..4209c0d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -43,3 +43,4 @@ pub use crack::clone_mersenne_twister_from_output;
 pub use crack::recover_16_bit_mt19937_key;
 pub use crack::recover_mt19937_key_from_time;
 pub use crack::crack_aes_128_ctr_random_access;
+pub use crack::crack_ctr_bitflipping;
diff --git a/tests/set4.rs b/tests/set4.rs
index 3967f85..35c3edf 100644
--- a/tests/set4.rs
+++ b/tests/set4.rs
@@ -48,3 +48,41 @@ fn problem_25 () {
     let got = matasano::crack_aes_128_ctr_random_access(&ciphertext[..], edit);
     assert_eq!(&got[..], &plaintext[..]);
 }
+
+#[test]
+fn problem_26 () {
+    let key = util::random_aes_128_key();
+    let nonce = rand::thread_rng().gen();
+    let prefix = "comment1=cooking%20MCs;userdata=";
+    let suffix = ";comment2=%20like%20a%20pound%20of%20bacon";
+    let admin = ";admin=true;";
+
+    let escape = |input: &str| {
+        input.replace("%", "%25").replace(";", "%3B").replace("=", "%3D")
+    };
+
+    let encode = |input: &str| -> Vec<u8> {
+        let plaintext: Vec<u8> = prefix
+            .as_bytes()
+            .iter()
+            .chain(escape(input).as_bytes().iter())
+            .chain(suffix.as_bytes().iter())
+            .map(|x| *x)
+            .collect();
+        return matasano::aes_128_ctr(&plaintext[..], &key[..], nonce);
+    };
+
+    let verify = |ciphertext: &[u8]| -> bool {
+        let plaintext = matasano::aes_128_ctr(ciphertext, &key[..], nonce);
+        return (0..(plaintext.len() - admin.len())).any(|i| {
+            plaintext
+                .iter()
+                .skip(i)
+                .zip(admin.as_bytes().iter())
+                .all(|(&c1, &c2)| c1 == c2)
+        });
+    };
+
+    let ciphertext = matasano::crack_ctr_bitflipping(&encode);
+    assert!(verify(&ciphertext[..]));
+}
-- 
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