Solve challenge 19 in Python because my Rust still sucks.

src/set3.rs

@@ -3,6 +3,7 @@ use crate::bytes_base64::BytesBase64;
 use crate::cbc;
 use crate::ctr;
 use rand::Rng;
+use std::fs;
 use std::io::{BufRead, BufReader};
 
 pub fn challenge17() {
@@ -100,7 +101,7 @@ pub fn challenge18() {
 
     let cleartext = Bytes::from_utf8("Let's see if we can get the party started hard my friends.");
     let cipher = ctr::encrypt(&key, 42351234, &cleartext);
-    let roundtrip = ctr::encrypt(&key, 42351234, &cipher);
+    let roundtrip = ctr::decrypt(&key, 42351234, &cipher);
     assert_eq!(cleartext, roundtrip);
 
     let cipher = BytesBase64::from_base64(
@@ -112,5 +113,30 @@ pub fn challenge18() {
 }
 
 pub fn challenge19() {
-    println!("[xxxx] Challenge 19: TBD");
+    fn read(path: &str) -> Vec<Bytes> {
+        let file = std::fs::File::open(path).unwrap();
+        let br = BufReader::new(file);
+        br.lines()
+            .map(|line| BytesBase64::from_base64(&line.unwrap()).to_bytes())
+            .collect()
+    }
+
+    let plaintexts = read("data/19.txt");
+    let key = Bytes::from_utf8("YELLOW SUBMARINE");
+    let encrypt = |plaintext: &Bytes| -> Bytes { ctr::encrypt(&key, 0, plaintext) };
+    let ciphers: Vec<Bytes> = plaintexts.iter().map(|ct| encrypt(&ct)).collect();
+    let mut data = String::new();
+    for cipher in ciphers.iter() {
+        let copy_cipher = Bytes(cipher.0.to_vec());
+        let cipher_base64 = BytesBase64::from_bytes(copy_cipher);
+        data.push_str(&cipher_base64.to_string());
+        data.push_str("\n");
+    }
+
+    fs::write("data/19_enc.txt", data).expect("Unable to write file");
+    println!("[okay] Challenge 19: encrypted to data/19_enc.txt, attack in set3c19.py.");
+}
+
+pub fn challenge20() {
+    println!("[xxxx] Challenge 20: TBD");
 }