From 75b5c3f2f36d527216920d6d437bc1eef3237cd0 Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Sat, 28 Mar 2015 04:28:46 -0400
Subject: problem 18

---
 src/aes.rs   | 30 ++++++++++++++++++++++++++++++
 src/lib.rs   |  1 +
 tests/lib.rs | 13 +++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/src/aes.rs b/src/aes.rs
index 77cbf7a..82b000c 100644
--- a/src/aes.rs
+++ b/src/aes.rs
@@ -1,4 +1,5 @@
 use openssl;
+use std;
 
 use primitives::{fixed_xor, pad_pkcs7, unpad_pkcs7};
 
@@ -53,6 +54,35 @@ pub fn encrypt_aes_128_cbc (bytes: &[u8], key: &[u8], iv: &[u8]) -> Vec<u8> {
     return ciphertext;
 }
 
+pub fn aes_128_ctr (bytes: &[u8], key: &[u8], nonce: u64) -> Vec<u8> {
+    let nonce_array: [u8; 8] = unsafe {
+        std::mem::transmute(nonce.to_le())
+    };
+    let mut counter = 0u64;
+    let mut ret = vec![];
+    for block in bytes.chunks(16) {
+        let counter_array: [u8; 8] = unsafe {
+            std::mem::transmute(counter.to_le())
+        };
+        let keystream = encrypt_aes_128_ecb(
+            &pad_pkcs7(
+                &nonce_array
+                    .iter()
+                    .chain(counter_array.iter())
+                    .map(|x| *x)
+                    .collect::<Vec<u8>>()[..],
+                16
+            )[..],
+            key
+        );
+        for c in fixed_xor(block, &keystream[..]) {
+            ret.push(c);
+        }
+        counter += 1;
+    }
+    return ret;
+}
+
 #[test]
 fn test_encrypt_decrypt () {
     let plaintext = b"Summertime and the wind is blowing outside in lower \
diff --git a/src/lib.rs b/src/lib.rs
index 875544b..c1f8cf8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,6 +12,7 @@ pub use aes::decrypt_aes_128_ecb;
 pub use aes::decrypt_aes_128_cbc;
 pub use aes::encrypt_aes_128_ecb;
 pub use aes::encrypt_aes_128_cbc;
+pub use aes::aes_128_ctr;
 pub use base64::to_base64;
 pub use http::parse_query_string;
 pub use http::create_query_string;
diff --git a/tests/lib.rs b/tests/lib.rs
index 5fb8261..f0ead77 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -392,3 +392,16 @@ fn problem_17 () {
         assert_eq!(&plaintext, expected);
     }
 }
+
+#[test]
+fn problem_18 () {
+    let ciphertext = b"L77na/nrFsKvynd6HzOoG7GHTLXsTVu9qvY/2syL\
+                       XzhPweyyMTJULu/6/kXX0KSvoOLSFQ==".from_base64().unwrap();
+    let plaintext = &b"Yo, VIP Let's kick it Ice, Ice, baby Ice, Ice, baby "[..];
+    let got = matasano::aes_128_ctr(
+        &ciphertext[..],
+        b"YELLOW SUBMARINE",
+        0
+    );
+    assert_eq!(got, plaintext);
+}
-- 
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