Solve challenge 6.

src/set1.rs

@@ -31,8 +31,8 @@ pub fn challenge3() {
     let a = Bytes::from_hex("1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736");
     let mut h: Vec<Bytes> = (0..=255).map(|i| Bytes::xor_byte(&a, i)).collect();
     h.sort_by(|a, b| a.ascii_score().partial_cmp(&b.ascii_score()).unwrap());
-    let h: Vec<Bytes> = h.into_iter().filter(|b| b.is_ascii()).collect();
+    // let h: Vec<Bytes> = h.into_iter().filter(|b| b.is_ascii()).collect();
-    let r = h[h.len() - 1].to_utf8();
+    let r = h.last().unwrap().to_utf8();
     println!("[okay] Challenge 3: {}", r);
 }
 
@@ -125,8 +125,34 @@ pub fn challenge6() {
         lowest_size
     }
 
+    fn transpose(Bytes(v): &Bytes, size: usize) -> Vec<Bytes> {
+        let mut result = vec![];
+        for i in 0..size {
+            let mut column = vec![];
+            for j in (i..v.len()).step_by(size) {
+                column.push(v[j]);
+            }
+            result.push(Bytes(column));
+        }
+        result
+    }
+
+    fn guess_key(bytes: &Bytes) -> u8 {
+        let mut h: Vec<(Bytes, u8)> = (0..=255).map(|i| (Bytes::xor_byte(bytes, i), i)).collect();
+        h.sort_by(|a, b| a.0.ascii_score().partial_cmp(&b.0.ascii_score()).unwrap());
+        h.last().unwrap().1
+    }
+
     _test_roundtrip();
     let bytes = read("data/6.txt");
     let key_size = guess_key_size(&bytes);
-    println!("[open] Challenge 6: guessed_key_size={}", key_size);
+    let bytes_tranposed = transpose(&bytes, key_size);
+    let key = Bytes(bytes_tranposed.iter().map(|b| guess_key(&b)).collect());
+    let msg = Bytes::xor_cycle(&bytes, &key);
+
+    let partial_msg = Bytes(msg.0[..20].to_vec()).to_utf8();
+    println!(
+        "[okay] Challenge 6: size={} msg={}...",
+        key_size, partial_msg
+    );
 }