Add Rail Fence Encryption (TheAlgorithms#476)

Author: yosefahab

src/ciphers/mod.rs

@@ -8,6 +8,7 @@ mod hashing_traits;
 mod kerninghan;
 mod morse_code;
 mod polybius;
+mod rail_fence;
 mod rot13;
 mod salsa;
 mod sha256;
@@ -17,7 +18,6 @@ mod theoretical_rot13;
 mod transposition;
 mod vigenere;
 mod xor;
-
 pub use self::aes::{aes_decrypt, aes_encrypt, AesKey};
 pub use self::another_rot13::another_rot13;
 pub use self::base64::{base64_decode, base64_encode};
@@ -29,6 +29,7 @@ pub use self::hashing_traits::HMAC;
 pub use self::kerninghan::kerninghan;
 pub use self::morse_code::{decode, encode};
 pub use self::polybius::{decode_ascii, encode_ascii};
+pub use self::rail_fence::{rail_fence_decrypt, rail_fence_encrypt};
 pub use self::rot13::rot13;
 pub use self::salsa::salsa20;
 pub use self::sha256::SHA256;

src/ciphers/rail_fence.rs

@@ -0,0 +1,41 @@
+// wiki: https://en.wikipedia.org/wiki/Rail_fence_cipher
+pub fn rail_fence_encrypt(plain_text: &str, key: usize) -> String {
+    let mut cipher = vec![Vec::new(); key];
+
+    for (c, i) in plain_text.chars().zip(zigzag(key)) {
+        cipher[i].push(c);
+    }
+
+    return cipher.iter().flatten().collect::<String>();
+}
+
+pub fn rail_fence_decrypt(cipher: &str, key: usize) -> String {
+    let mut indices: Vec<_> = zigzag(key).zip(1..).take(cipher.len()).collect();
+    indices.sort();
+
+    let mut cipher_text: Vec<_> = cipher
+        .chars()
+        .zip(indices)
+        .map(|(c, (_, i))| (i, c))
+        .collect();
+
+    cipher_text.sort();
+    return cipher_text.iter().map(|(_, c)| c).collect();
+}
+
+fn zigzag(n: usize) -> impl Iterator<Item = usize> {
+    (0..n - 1).chain((1..n).rev()).cycle()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn rails_basic() {
+        assert_eq!(rail_fence_encrypt("attack at once", 2), "atc toctaka ne");
+        assert_eq!(rail_fence_decrypt("atc toctaka ne", 2), "attack at once");
+
+        assert_eq!(rail_fence_encrypt("rust is cool", 3), "r cuti olsso");
+        assert_eq!(rail_fence_decrypt("r cuti olsso", 3), "rust is cool");
+    }
+}