From be04722ce7193922635ddcf61aeb592c059a1562 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Thu, 5 Apr 2018 06:42:44 -0700
Subject: [PATCH] XOR is still a work in progress, but it builds now, and I
 think the single_byte_xor does actually work...

---
 src/xor.rs | 136 +++++++++++++++++++++++++++++++++--------------------
 1 file changed, 84 insertions(+), 52 deletions(-)

diff --git a/src/xor.rs b/src/xor.rs
index a3bc413..79b4403 100644
--- a/src/xor.rs
+++ b/src/xor.rs
@@ -1,62 +1,94 @@
-use std::iter::{Iterator, Map, Zip};
+use std::iter;
 
-//#[derive(Debug)]
-//pub enum FixedXORError {
-//    Bad,
-//}
+pub type FixedXOR<T, U> = iter::Map<iter::Zip<T, U>, fn((u8, u8)) -> u8>;
+pub type SingleByteXOR<T> = FixedXOR<T, iter::Repeat<u8>>;
 
-pub trait FixedXORable<T> {
-    fn fixed_xor(self, other: T) -> Map<Zip<T, T>, fn((u8, u8)) -> u8>;
+pub trait FixedXORable<T, U> {
+    fn fixed_xor(self, other: U) -> FixedXOR<T, U>;
 }
 
-impl<'a, T> FixedXORable<T> for T
-    where T: Iterator<Item=u8> + 'a,
+impl<'a, 'b, T, U> FixedXORable<T, U> for T
+    where T: iter::Iterator<Item=u8> + 'a,
+          U: iter::Iterator<Item=u8> + 'b
 {
-    fn fixed_xor(self, other: T) -> Map<Zip<T, T>, fn((u8, u8)) -> u8> {
+    fn fixed_xor(self, other: U) -> FixedXOR<T, U> {
         fn xor(tup: (u8, u8)) -> u8 { tup.0 ^ tup.1 }
         self.zip(other).map(xor)
     }
 }
 
-//pub fn fixed(a: &str, b: &str) -> Result<String, FixedXORError> {
-//    let a_decoded = a.hex_bytes().valid();
-//    let b_decoded = b.hex_bytes().valid();
-//    let xor: Vec<u8> = a_decoded.zip(b_decoded).map(|(x, y)| x ^ y).collect();
-//    Ok(xor.hex_digest())
-//}
-//
-//#[cfg(test)]
-//mod tests {
-//    use hex::AsHexBytes;
-//    use std::char;
-//    use super::fixed;
-//
-//    #[test]
-//    fn cryptopals() {
-//        let a = "1c0111001f010100061a024b53535009181c";
-//        let b = "686974207468652062756c6c277320657965";
-//        let ex_output = "746865206b696420646f6e277420706c6179";
-//        let output = fixed(a, b);
-//        assert_eq!(output.unwrap(), ex_output);
-//    }
-//
-//    static ENGLISH_LETTER_FREQ: &'static str = "EARIOTNSLCUDPMHGBFYWKVXZJQ";
-//
-//    fn letter_freq_score(input: &str) -> f32 {
-//        let mut score: f32 = 0.0;
-//        score
-//    }
-//
-//    #[test]
-//    fn cryptopals13() {
-//        let input = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736";
-//        for key in 32u32..127 {
-//            let possible_output = input.hex_bytes().valid()
-//                .map(|c| char::from_u32(c as u32 ^ key))
-//                .take_while(|c| c.is_some())
-//                .map(|c| c.unwrap())
-//                .collect::<String>();
-//            println!("{}: {}", key, possible_output);
-//        }
-//    }
-//}
+pub trait SingleByteXORable<T> {
+    fn single_byte_xor(self, byte: u8) -> SingleByteXOR<T>;
+}
+
+impl<'a, T> SingleByteXORable<T> for T
+    where T: FixedXORable<T, iter::Repeat<u8>>
+{
+    fn single_byte_xor(self, byte: u8) -> SingleByteXOR<T> {
+        self.fixed_xor(iter::repeat(byte))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use hex::{HexDecodable, HexEncodable};
+
+    #[test]
+    fn cryptopals() {
+        println!();
+        let a = "1c0111001f010100061a024b53535009181c";
+        let b = "686974207468652062756c6c277320657965";
+        let ex_output = "746865206b696420646f6e277420706c6179";
+        let output: String = a.chars().hex_decoded()
+            .fixed_xor(b.chars().hex_decoded())
+            .hex_encoded().collect();
+        assert_eq!(output, ex_output);
+    }
+
+    static ENGLISH_LETTER_FREQS: &'static [f32] = &[
+        0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, // A-G
+        0.06094, 0.06996, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749, // H-N
+        0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09056, 0.02758, // O-U
+        0.00978, 0.02360, 0.00150, 0.01974, 0.00074                    // V-Z
+    ];
+
+    fn letter_freq_score(input: &str) -> f32 {
+        let mut freqs: Vec<f32> = iter::repeat(0.0f32).take(26).collect();
+        let mut num_alphabetic_chars = 0f32;
+        for c in input.chars() {
+            num_alphabetic_chars += 1f32;
+            if !c.is_alphabetic() { continue; }
+            let c = c.to_ascii_uppercase();
+            freqs[c as usize - 'A' as usize] += 1f32;
+        }
+        let freqs = freqs.into_iter().map(|sc| sc / num_alphabetic_chars);
+        // Calculate chi-squared for this string, comparing actual frequencies vs. English letter
+        // frequencies.
+        let score = freqs.zip(ENGLISH_LETTER_FREQS.iter())
+                         .fold(0f32, |acc, (obs, exp)| acc + (obs - exp).powf(2.0) / exp);
+        score
+    }
+
+    #[test]
+    fn cryptopals13() {
+        let input = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736";
+        let mut best_key = 0u8;
+        let mut best_score = -1f32;
+        let mut best_output: Option<String> = None;
+        for key in 32u8..127 {
+            let possible_output = input.chars().hex_decoded()
+                .single_byte_xor(key)
+                .map(|x| char::from(x))
+                .collect::<String>();
+            let score = letter_freq_score(&possible_output);
+            if score > best_score {
+                best_score = score;
+                best_output = Some(possible_output);
+                best_key = key;
+            }
+        }
+        let best_output = best_output.expect("expected output");
+        println!("{}: {} -> {}", best_key, best_output, best_score);
+    }
+}