[feat] changes index of split on odd length, odd round messages

haha!!!!! my theory was right !!

src/cipher.rs

@@ -68,16 +68,23 @@ fn round_fn(right: Vec<u32>, subkey: u32) -> Vec<u32> {
 
 pub fn feistel_decrypt(ciphertext: Vec<u32>, key: u32, rounds: u8) -> String {
     let mut right: Vec<u32> = ciphertext.clone();
-    let mut left: Vec<u32> = right.split_off(ciphertext.len() / 2);
+    let split_index;
+    if (ciphertext.len() % 2 == 1) && (rounds % 2 == 1) {
+        // cipher text is odd, change index of split
+        split_index = (ciphertext.len() / 2) + 1;
+    } else {
+        split_index = ciphertext.len() / 2;
+    }
+    let mut left: Vec<u32> = right.split_off(split_index);
     let mut subkey: u32;
     let mut salty: u32;
     let mut updated_left: Vec<u32>;
     let mut updated_right: Vec<u32>;
     // because encryption went from [0, rounds) decryption should
     // generate subkeys for (rounds, 0]
-    for x in 1..rounds + 1 {
+    for x in 0..rounds {
         // only difference in encryption & decryption is order of subkeys
-        salty = key.count_ones() + (rounds - x) as u32;
+        salty = key.count_ones() + (rounds - 1 - x) as u32;
         subkey = key.wrapping_mul(salty);
         // l[i] = R[i - 1]
         updated_left = right.clone();

src/lib.rs

@@ -43,9 +43,9 @@ fn max_key_rounds() {
         "The quick blue fox", 4294967295, 255);
     let even_plaintext = feistel_decrypt(
         even_ciphertext, 4294967295, 255);
-    assert_eq!("The quick brown fox", even_plaintext);
+    assert_eq!("The quick blue fox", even_plaintext);
 
-    let odd_ciphertext = feistel_encrypt("The quick blue fox", 4294967295, 255);
+    let odd_ciphertext = feistel_encrypt("The quick brown fox", 4294967295, 255);
     let odd_plaintext = feistel_decrypt(odd_ciphertext, 4294967295, 255);
     assert_eq!("The quick brown fox", odd_plaintext);
 }