solve Challenge 6 of Set 1

Cargo.lock

@@ -17,9 +17,22 @@ version = "2.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "327762f6e5a765692301e5bb513e0d9fef63be86bbc14528052b1cd3e6f03e07"
 
+[[package]]
+name = "break_repeating_xor"
+version = "0.1.0"
+dependencies = [
+ "common",
+ "env_logger",
+ "log",
+ "rustc-serialize",
+]
+
 [[package]]
 name = "common"
 version = "0.1.0"
+dependencies = [
+ "log",
+]
 
 [[package]]
 name = "detect_xor"

Cargo.toml

@@ -7,5 +7,6 @@ members = [
   "set1/challenge3_xor_cipher",
   "set1/challenge4_detect_xor",
   "set1/challenge5_repeating_xor",
+  "set1/challenge6_break_repeating_xor",
 ]
 resolver = "2"

common/Cargo.toml

@@ -5,3 +5,4 @@ edition = "2021"
 authors = ["Thomas Lindner <tom@dl6tom.de>"]
 
 [dependencies]
+log = "0.4"

common/src/lib.rs

@@ -1,6 +1,12 @@
+use log::{debug, trace};
+use std::ascii::escape_default;
 use std::iter::repeat;
 
-pub fn score(plaintext: &Vec<u8>) -> u32 {
+pub fn escape(text: &[u8]) -> String {
+    String::from_utf8(text.iter().map(|ch| escape_default(ch.clone())).flatten().collect()).unwrap()
+}
+
+pub fn score(plaintext: &[u8]) -> u32 {
     let ranking = [24, 7, 15, 17, 26, 11, 10, 19, 22, 4, 5, 16, 13,
                    21, 23, 8, 2, 18, 20, 25, 14, 6, 12, 3, 9, 1];
     let mut score = 0;
@@ -8,7 +14,9 @@ pub fn score(plaintext: &Vec<u8>) -> u32 {
     for ch in plaintext.iter() {
         if ch >= &0x20 && ch <= &0x7e {
             score += 1;
-            if ch >= &('a' as u8) && ch <= &('z' as u8) {
+            if ch == &(' ' as u8) {
+                score += 27;
+            } else if ch >= &('a' as u8) && ch <= &('z' as u8) {
                 score += ranking[(ch - 'a' as u8) as usize];
             } else if ch >= &('A' as u8) && ch <= &('Z' as u8) {
                 score += ranking[(ch - 'A' as u8) as usize];
@@ -18,6 +26,26 @@ pub fn score(plaintext: &Vec<u8>) -> u32 {
     score
 }
 
+pub fn hamming(v1: &[u8], v2: &[u8]) -> u32 {
+    v1.iter().zip(v2.iter()).map(|(a, b)| a ^ b)
+        .map(|x| ((x & 0xaa) >> 1) + (x & 0x55))
+        .map(|x| ((x & 0xcc) >> 2) + (x & 0x33))
+        .map(|x| ((x & 0xf0) >> 4) + (x & 0x0f))
+        .map(|x| x as u32).sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn challenge6_hamming() {
+        let v1 = "this is a test";
+        let v2 = "wokka wokka!!!";
+        assert_eq!(hamming(v1.as_bytes(), v2.as_bytes()), 37);
+    }
+}
+
 pub fn generic_xor_cipher(text: &[u8], keyiter: &mut dyn Iterator<Item = &u8>) -> Vec<u8> {
     text.iter().zip(keyiter).map(|(c, k)| c ^ k).collect()
 }
@@ -35,16 +63,58 @@ pub fn break_xor_cipher(ciphertext: &[u8]) -> (Vec<u8>, u32) {
     let mut decrypted: Vec<u8> = vec![];
 
     for key in 0..0xff {
-        let plaintext: Vec<u8> = xor_cipher(&ciphertext, key);
-        let s = score(&plaintext);
+        let plaintext = xor_cipher(ciphertext, key);
+        let s = score(plaintext.as_slice());
+        trace!("score:{} \"{}\"", s, escape(plaintext.as_slice()));
         if s > maxscore {
             maxscore = s;
             decrypted = plaintext;
         }
     }
+    debug!("score:{} \"{}\"", maxscore, escape(decrypted.as_slice()));
     (decrypted, maxscore)
 }
 
 pub fn repeating_xor_cipher(text: &[u8], key: &[u8]) -> Vec<u8> {
     generic_xor_cipher(text, &mut key.iter().cycle())
 }
+
+pub fn break_repeating_xor_cipher(ciphertext: &[u8]) -> Vec<u8> {
+    let mut mindistance = u32::MAX;
+    let mut keylength = 0;
+    for length in 1..40 {
+        let mut distance = 0;
+        let maxoffset = ciphertext.len() / length - 1;
+        for offset in 0..maxoffset {
+            distance += hamming(&ciphertext[offset * length .. (offset + 1) * length],
+                                &ciphertext[(offset + 1) * length .. (offset + 2) * length]);
+        }
+        // scale and normalize
+        distance *= 1024;
+        distance /= (maxoffset * length) as u32;
+        trace!("distance:{} keylength:{}", distance, length);
+        if distance < mindistance {
+            mindistance = distance;
+            keylength = length;
+        }
+    }
+    debug!("estimated keylength: {}", keylength);
+
+    let mut decryptedcolumns: Vec<Vec<u8>> = vec![];
+    for offset in 0..keylength {
+        let ciphercolumn: Vec<u8> = ciphertext[offset..].iter().step_by(keylength).cloned().collect();
+        let (decrypted, _) = break_xor_cipher(ciphercolumn.as_slice());
+        decryptedcolumns.push(decrypted);
+    }
+
+    let mut decrypted: Vec<u8> = vec![];
+    for i in 0..decryptedcolumns[0].len() {
+        for column in decryptedcolumns.iter() {
+            if column.len() <= i {
+                break;
+            }
+            decrypted.push(column[i]);
+        }
+    }
+    decrypted
+}

set1/challenge6_break_repeating_xor/6.txt

@@ -0,0 +1,64 @@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set1/challenge6_break_repeating_xor/6_plaintext.txt

@@ -0,0 +1,79 @@
+I'm back and I'm ringin' the bell 
+A rockin' on the mike while the fly girls yell 
+In ecstasy in the back of me 
+Well that's my DJ Deshay cuttin' all them Z's 
+Hittin' hard and the girlies goin' crazy 
+Vanilla's on the mike, man I'm not lazy. 
+
+I'm lettin' my drug kick in 
+It controls my mouth and I begin 
+To just let it flow, let my concepts go 
+My posse's to the side yellin', Go Vanilla Go! 
+
+Smooth 'cause that's the way I will be 
+And if you don't give a damn, then 
+Why you starin' at me 
+So get off 'cause I control the stage 
+There's no dissin' allowed 
+I'm in my own phase 
+The girlies sa y they love me and that is ok 
+And I can dance better than any kid n' play 
+
+Stage 2 -- Yea the one ya' wanna listen to 
+It's off my head so let the beat play through 
+So I can funk it up and make it sound good 
+1-2-3 Yo -- Knock on some wood 
+For good luck, I like my rhymes atrocious 
+Supercalafragilisticexpialidocious 
+I'm an effect and that you can bet 
+I can take a fly girl and make her wet. 
+
+I'm like Samson -- Samson to Delilah 
+There's no denyin', You can try to hang 
+But you'll keep tryin' to get my style 
+Over and over, practice makes perfect 
+But not if you're a loafer. 
+
+You'll get nowhere, no place, no time, no girls 
+Soon -- Oh my God, homebody, you probably eat 
+Spaghetti with a spoon! Come on and say it! 
+
+VIP. Vanilla Ice yep, yep, I'm comin' hard like a rhino 
+Intoxicating so you stagger like a wino 
+So punks stop trying and girl stop cryin' 
+Vanilla Ice is sellin' and you people are buyin' 
+'Cause why the freaks are jockin' like Crazy Glue 
+Movin' and groovin' trying to sing along 
+All through the ghetto groovin' this here song 
+Now you're amazed by the VIP posse. 
+
+Steppin' so hard like a German Nazi 
+Startled by the bases hittin' ground 
+There's no trippin' on mine, I'm just gettin' down 
+Sparkamatic, I'm hangin' tight like a fanatic 
+You trapped me once and I thought that 
+You might have it 
+So step down and lend me your ear 
+'89 in my time! You, '90 is my year. 
+
+You're weakenin' fast, YO! and I can tell it 
+Your body's gettin' hot, so, so I can smell it 
+So don't be mad and don't be sad 
+'Cause the lyrics belong to ICE, You can call me Dad 
+You're pitchin' a fit, so step back and endure 
+Let the witch doctor, Ice, do the dance to cure 
+So come up close and don't be square 
+You wanna battle me -- Anytime, anywhere 
+
+You thought that I was weak, Boy, you're dead wrong 
+So come on, everybody and sing this song 
+
+Say -- Play that funky music Say, go white boy, go white boy go 
+play that funky music Go white boy, go white boy, go 
+Lay down and boogie and play that funky music till you die. 
+
+Play that funky music Come on, Come on, let me hear 
+Play that funky music white boy you say it, say it 
+Play that funky music A little louder now 
+Play that funky music, white boy Come on, Come on, Come on 
+Play that funky music 

set1/challenge6_break_repeating_xor/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "break_repeating_xor"
+version = "0.1.0"
+edition = "2021"
+authors = ["Thomas Lindner <tom@dl6tom.de>"]
+
+[dependencies]
+common = { path = "../../common" }
+log = "0.4"
+env_logger = "0.10"
+rustc-serialize = "0.3"

set1/challenge6_break_repeating_xor/src/main.rs

@@ -0,0 +1,37 @@
+use common::break_repeating_xor_cipher;
+use log::error;
+use rustc_serialize::base64::FromBase64;
+use std::error::Error;
+use std::io::{Read, read_to_string, stdin};
+
+fn break_xor(input: &mut dyn Read) -> Result<String, Box<dyn Error>> {
+    let ciphertext = read_to_string(input)?.from_base64()?;
+    let decrypted = break_repeating_xor_cipher(ciphertext.as_slice());
+    Ok(String::from_utf8(decrypted)?)
+}
+
+fn main() {
+    env_logger::init();
+
+    match break_xor(&mut stdin().lock()) {
+        Ok(s) => println!("{}", s),
+        Err(e) => error!("{}", e)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::fs::File;
+    use std::io::BufReader;
+    use std::path::Path;
+    use super::*;
+
+    #[test]
+    fn challenge6_break_repeating_xor() {
+        let cargo_manifest_dir = Path::new(env!("CARGO_MANIFEST_DIR"));
+        let testinput = File::open(cargo_manifest_dir.join("6.txt")).unwrap();
+        let decrypted = break_xor(&mut BufReader::new(testinput)).unwrap();
+        let plaintext = read_to_string(File::open(cargo_manifest_dir.join("6_plaintext.txt")).unwrap()).unwrap();
+        assert_eq!(decrypted, plaintext);
+    }
+}