problem 5

2 files changed, 20 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
index cd5fda7..0371b54 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -45,6 +45,18 @@ pub fn fixed_xor (bytes1: &[u8], bytes2: &[u8]) -> Vec<u8> {
         .collect();
 }
 
+pub fn repeating_key_xor (plaintext: &[u8], key: &[u8]) -> Vec<u8> {
+    return fixed_xor(
+        plaintext,
+        &key
+            .iter()
+            .cycle()
+            .take(plaintext.len())
+            .map(|c| *c)
+            .collect::<Vec<u8>>()[..]
+    );
+}
+
 pub fn crack_single_byte_xor (input: &[u8]) -> Vec<u8> {
     let (decrypted, _) = crack_single_byte_xor_with_confidence(input);
     return decrypted;
diff --git a/tests/lib.rs b/tests/lib.rs
index 231be41..80342e3 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -37,3 +37,11 @@ fn problem_4 () {
         .collect::<Vec<Vec<u8>>>();
     assert_eq!(matasano::find_single_byte_xor_encrypted_string(&possibles[..]), b"nOW\0THAT\0THE\0PARTY\0IS\0JUMPING*");
 }
+
+#[test]
+fn problem_5 () {
+    let plaintext = b"Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal";
+    let key = b"ICE";
+    let ciphertext = "0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f".from_hex().unwrap();
+    assert_eq!(matasano::repeating_key_xor(plaintext, key), ciphertext);
+}