diff --git a/src/main.rs b/src/main.rs
index 5fb88ed..2979b3d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -9,7 +9,7 @@ mod set2;
 mod set3;
 
 fn main() {
-    const RUN_ALL: bool = true;
+    const RUN_ALL: bool = false;
     if RUN_ALL {
         set1::challenge1();
         set1::challenge2();
@@ -32,6 +32,6 @@ fn main() {
         set3::challenge19();
         set3::challenge20();
     } else {
-        set3::challenge20();
+        set3::challenge19();
     }
 }
diff --git a/src/set3.rs b/src/set3.rs
index e00ce94..d8260b3 100644
--- a/src/set3.rs
+++ b/src/set3.rs
@@ -3,6 +3,9 @@ use crate::bytes_base64::BytesBase64;
 use crate::cbc;
 use crate::ctr;
 use rand::Rng;
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::collections::HashSet;
 use std::fs;
 use std::io::{BufRead, BufReader};
 
@@ -133,6 +136,33 @@ pub fn challenge19() {
         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 {
+            h.insert(i, RefCell::new(HashSet::new()));
+        }
+        for c1 in letters {
+            for c2 in letters {
+                let xored = c1 ^ c2;
+                if let Some(h) = h.get(&xored) {
+                    let mut h_mut = h.borrow_mut();
+                    h_mut.insert(*c1);
+                    h_mut.insert(*c2);
+                };
+            }
+        }
+        h
+    }
+
+    fn _attack(_ciphers: Vec<Bytes>) -> Vec<Vec<u8>> {
+        vec![vec![]]
+    }
+
+    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);
+
     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.");
 }