Implement challenge 19 in Rust so that I can move on with good conscience.

src/main.rs

@@ -9,7 +9,7 @@ mod set2;
 mod set3;
 
 fn main() {
-    const RUN_ALL: bool = false;
+    const RUN_ALL: bool = true;
     if RUN_ALL {
         set1::challenge1();
         set1::challenge2();
@@ -32,6 +32,6 @@ fn main() {
         set3::challenge19();
         set3::challenge20();
     } else {
-        set3::challenge19();
+        set3::challenge20();
     }
 }

src/set3.rs

@@ -6,7 +6,6 @@ use rand::Rng;
 use std::cell::RefCell;
 use std::collections::HashMap;
 use std::collections::HashSet;
-use std::fs;
 use std::io::{BufRead, BufReader};
 
 pub fn challenge17() {
@@ -124,18 +123,6 @@ pub fn challenge19() {
             .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");
-    }
-
     fn xor_to_char_set(letters: &Vec<u8>) -> HashMap<u8, RefCell<HashSet<u8>>> {
         let mut h = HashMap::new();
         for i in 0..255_u8 {
@@ -154,17 +141,130 @@ pub fn challenge19() {
         h
     }
 
-    fn _attack(_ciphers: Vec<Bytes>) -> Vec<Vec<u8>> {
-        vec![vec![]]
+    fn u8_lower(s: u8) -> u8 {
+        if s >= b'A' && s <= b'Z' {
+            return s + 32;
+        }
+        s
     }
 
-    let mut letters: Vec<u8> = (0..255_u8).filter(u8::is_ascii_alphabetic).collect();
-    letters.append(&mut vec![b'_', b'-', b'.']);
-    let lookup = xor_to_char_set(&letters);
-    println!("{:?}", lookup);
+    fn ascii_letters(additional: &str) -> Vec<u8> {
+        let mut letters: Vec<u8> = (0..255_u8).filter(u8::is_ascii_alphabetic).collect();
+        for b in additional.as_bytes() {
+            letters.push(*b);
+        }
+        letters
+    }
 
-    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.");
+    fn attack(ciphers: Vec<Bytes>) -> Vec<RefCell<Vec<u8>>> {
+        let ciphers_len = ciphers.len();
+        let deciphered = vec![RefCell::new(vec![]); ciphers_len];
+        let max_cipher_len = ciphers.iter().map(|c| c.len()).max().unwrap_or(0);
+
+        for byte_index in 0..max_cipher_len {
+            let letters = match byte_index {
+                // chars that work for 10 and 20 found via trial and error
+                10 => ascii_letters(" _-.,;:'"),
+                20 => ascii_letters(" _-.,;:?"),
+                _ => ascii_letters(" _-.,;:"),
+            };
+            let lookup = xor_to_char_set(&letters);
+
+            let target_bytes: Vec<Option<u8>> = ciphers
+                .iter()
+                .map(|c| {
+                    if c.len() > byte_index {
+                        Some(c.0[byte_index])
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+            let mut possible_chars: Vec<HashSet<u8>> = ciphers
+                .iter()
+                .map(|_| HashSet::from_iter(letters.iter().cloned()))
+                .collect();
+
+            for i in 0..ciphers_len {
+                for j in i..ciphers_len {
+                    if target_bytes[i] == None || target_bytes[j] == None {
+                        continue;
+                    }
+                    let xored = target_bytes[i].unwrap() ^ target_bytes[j].unwrap();
+                    let chars = lookup.get(&xored).unwrap().borrow();
+                    possible_chars[i] = possible_chars[i].intersection(&chars).cloned().collect();
+                    possible_chars[j] = possible_chars[j].intersection(&chars).cloned().collect();
+                }
+            }
+
+            for cipher_index in 0..ciphers_len {
+                if ciphers[cipher_index].len() <= byte_index {
+                    continue;
+                }
+                let chars: Vec<u8> = possible_chars[cipher_index].iter().cloned().collect();
+                match chars.len() {
+                    0 => {
+                        // println!("No chars for {cipher_index} {byte_index}");
+                        deciphered[cipher_index].borrow_mut().push(b'?');
+                    }
+                    1 => {
+                        deciphered[cipher_index]
+                            .borrow_mut()
+                            .push(u8_lower(chars[0]));
+                    }
+                    2 => {
+                        if u8_lower(chars[0]) == u8_lower(chars[1]) {
+                            deciphered[cipher_index]
+                                .borrow_mut()
+                                .push(u8_lower(chars[0]));
+                        } else {
+                            // println!("Two {chars:?} {cipher_index} {byte_index}");
+                            deciphered[cipher_index].borrow_mut().push(b'^');
+                        }
+                    }
+                    _ => {
+                        // println!("Two {chars:?} {cipher_index} {byte_index}");
+                        deciphered[cipher_index].borrow_mut().push(b'^');
+                    }
+                }
+            }
+        }
+
+        deciphered
+    }
+
+    fn manual(decrypts: &Vec<RefCell<Vec<u8>>>) {
+        // Add manually guessed letters
+        decrypts[0].borrow_mut()[30] = b'y';
+        decrypts[2].borrow_mut()[30] = b'y';
+        let mut d4 = decrypts[4].borrow_mut();
+        d4[30] = b'e';
+        d4[32] = b'h';
+        d4[33] = b'e';
+        d4[34] = b'a';
+        d4[35] = b'd';
+        decrypts[6].borrow_mut()[30] = b'i';
+        decrypts[13].borrow_mut()[30] = b' ';
+        decrypts[20].borrow_mut()[30] = b' ';
+        decrypts[25].borrow_mut()[30] = b'n';
+        decrypts[28].borrow_mut()[30] = b' ';
+        decrypts[29].borrow_mut()[30] = b't';
+        decrypts[37].borrow_mut()[30] = b'i';
+    }
+
+    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 decrypts = attack(ciphers);
+    manual(&decrypts);
+    for row in decrypts {
+        println!(
+            "[okay] Challenge 19: {}",
+            Bytes(row.borrow().to_vec()).to_utf8()
+        );
+        break;
+    }
 }
 
 pub fn challenge20() {

src/set3c19.py

@@ -36,7 +36,6 @@ def attack(ciphers: List[bytes]) -> List[List[str]]:
         else:
             LETTERS = string.ascii_letters + " _-.,;:"
         lookup = xor_lookup_set(LETTERS)
-        ciphers_len = len(ciphers)
         target_bytes = [cipher[byte_index]
                         if len(cipher) > byte_index
                         else None