Solve challenge 7 using openssl.

src/main.rs

@@ -9,4 +9,5 @@ fn main() {
     set1::challenge4();
     set1::challenge5();
     set1::challenge6();
+    set1::challenge7();
 }

src/set1.rs

@@ -1,6 +1,7 @@
 #![allow(dead_code)]
 use crate::bytes::Bytes;
 use crate::bytes_base64::BytesBase64;
+use openssl::symm::{decrypt, Cipher};
 use std::io::{BufRead, BufReader, Write};
 use std::str;
 
@@ -148,11 +149,25 @@ pub fn challenge6() {
     let key_size = guess_key_size(&bytes);
     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 msg = Bytes::xor_cycle(&bytes, &key).to_utf8();
 
-    let partial_msg = Bytes(msg.0[..20].to_vec()).to_utf8();
-    println!(
-        "[okay] Challenge 6: size={} msg={}...",
-        key_size, partial_msg
-    );
+    let partial_msg = msg[..20].to_string();
+    println!("[okay] Challenge 6: {}...", partial_msg);
+}
+
+pub fn challenge7() {
+    fn read(path: &str) -> Bytes {
+        let s = std::fs::read_to_string(path).unwrap();
+        BytesBase64::from_base64(&s).to_bytes()
+    }
+    let ciphertext = &read("data/7.txt").0;
+    let key = b"YELLOW SUBMARINE";
+    let cipher = Cipher::aes_128_ecb();
+    let data = decrypt(cipher, key, None, ciphertext);
+    let result = match data {
+        Ok(data) => Bytes(data).to_utf8(),
+        Err(err) => err.to_string(),
+    };
+    let partial_msg = result[..20].to_string();
+    println!("[okay] Challenge 7: {}...", partial_msg);
 }