Finish challenge 20 statistical CTR.

data/20.txt

@@ -0,0 +1,60 @@
+SSdtIHJhdGVkICJSIi4uLnRoaXMgaXMgYSB3YXJuaW5nLCB5YSBiZXR0ZXIgdm9pZCAvIFBvZXRzIGFyZSBwYXJhbm9pZCwgREoncyBELXN0cm95ZWQ=
+Q3V6IEkgY2FtZSBiYWNrIHRvIGF0dGFjayBvdGhlcnMgaW4gc3BpdGUtIC8gU3RyaWtlIGxpa2UgbGlnaHRuaW4nLCBJdCdzIHF1aXRlIGZyaWdodGVuaW4nIQ==
+QnV0IGRvbid0IGJlIGFmcmFpZCBpbiB0aGUgZGFyaywgaW4gYSBwYXJrIC8gTm90IGEgc2NyZWFtIG9yIGEgY3J5LCBvciBhIGJhcmssIG1vcmUgbGlrZSBhIHNwYXJrOw==
+WWEgdHJlbWJsZSBsaWtlIGEgYWxjb2hvbGljLCBtdXNjbGVzIHRpZ2h0ZW4gdXAgLyBXaGF0J3MgdGhhdCwgbGlnaHRlbiB1cCEgWW91IHNlZSBhIHNpZ2h0IGJ1dA==
+U3VkZGVubHkgeW91IGZlZWwgbGlrZSB5b3VyIGluIGEgaG9ycm9yIGZsaWNrIC8gWW91IGdyYWIgeW91ciBoZWFydCB0aGVuIHdpc2ggZm9yIHRvbW9ycm93IHF1aWNrIQ==
+TXVzaWMncyB0aGUgY2x1ZSwgd2hlbiBJIGNvbWUgeW91ciB3YXJuZWQgLyBBcG9jYWx5cHNlIE5vdywgd2hlbiBJJ20gZG9uZSwgeWEgZ29uZSE=
+SGF2ZW4ndCB5b3UgZXZlciBoZWFyZCBvZiBhIE1DLW11cmRlcmVyPyAvIFRoaXMgaXMgdGhlIGRlYXRoIHBlbmFsdHksYW5kIEknbSBzZXJ2aW4nIGE=
+RGVhdGggd2lzaCwgc28gY29tZSBvbiwgc3RlcCB0byB0aGlzIC8gSHlzdGVyaWNhbCBpZGVhIGZvciBhIGx5cmljYWwgcHJvZmVzc2lvbmlzdCE=
+RnJpZGF5IHRoZSB0aGlydGVlbnRoLCB3YWxraW5nIGRvd24gRWxtIFN0cmVldCAvIFlvdSBjb21lIGluIG15IHJlYWxtIHlhIGdldCBiZWF0IQ==
+VGhpcyBpcyBvZmYgbGltaXRzLCBzbyB5b3VyIHZpc2lvbnMgYXJlIGJsdXJyeSAvIEFsbCB5YSBzZWUgaXMgdGhlIG1ldGVycyBhdCBhIHZvbHVtZQ==
+VGVycm9yIGluIHRoZSBzdHlsZXMsIG5ldmVyIGVycm9yLWZpbGVzIC8gSW5kZWVkIEknbSBrbm93bi15b3VyIGV4aWxlZCE=
+Rm9yIHRob3NlIHRoYXQgb3Bwb3NlIHRvIGJlIGxldmVsIG9yIG5leHQgdG8gdGhpcyAvIEkgYWluJ3QgYSBkZXZpbCBhbmQgdGhpcyBhaW4ndCB0aGUgRXhvcmNpc3Qh
+V29yc2UgdGhhbiBhIG5pZ2h0bWFyZSwgeW91IGRvbid0IGhhdmUgdG8gc2xlZXAgYSB3aW5rIC8gVGhlIHBhaW4ncyBhIG1pZ3JhaW5lIGV2ZXJ5IHRpbWUgeWEgdGhpbms=
+Rmxhc2hiYWNrcyBpbnRlcmZlcmUsIHlhIHN0YXJ0IHRvIGhlYXI6IC8gVGhlIFItQS1LLUktTSBpbiB5b3VyIGVhcjs=
+VGhlbiB0aGUgYmVhdCBpcyBoeXN0ZXJpY2FsIC8gVGhhdCBtYWtlcyBFcmljIGdvIGdldCBhIGF4IGFuZCBjaG9wcyB0aGUgd2Fjaw==
+U29vbiB0aGUgbHlyaWNhbCBmb3JtYXQgaXMgc3VwZXJpb3IgLyBGYWNlcyBvZiBkZWF0aCByZW1haW4=
+TUMncyBkZWNheWluZywgY3V6IHRoZXkgbmV2ZXIgc3RheWVkIC8gVGhlIHNjZW5lIG9mIGEgY3JpbWUgZXZlcnkgbmlnaHQgYXQgdGhlIHNob3c=
+VGhlIGZpZW5kIG9mIGEgcmh5bWUgb24gdGhlIG1pYyB0aGF0IHlvdSBrbm93IC8gSXQncyBvbmx5IG9uZSBjYXBhYmxlLCBicmVha3MtdGhlIHVuYnJlYWthYmxl
+TWVsb2RpZXMtdW5tYWthYmxlLCBwYXR0ZXJuLXVuZXNjYXBhYmxlIC8gQSBob3JuIGlmIHdhbnQgdGhlIHN0eWxlIEkgcG9zc2Vz
+SSBibGVzcyB0aGUgY2hpbGQsIHRoZSBlYXJ0aCwgdGhlIGdvZHMgYW5kIGJvbWIgdGhlIHJlc3QgLyBGb3IgdGhvc2UgdGhhdCBlbnZ5IGEgTUMgaXQgY2FuIGJl
+SGF6YXJkb3VzIHRvIHlvdXIgaGVhbHRoIHNvIGJlIGZyaWVuZGx5IC8gQSBtYXR0ZXIgb2YgbGlmZSBhbmQgZGVhdGgsIGp1c3QgbGlrZSBhIGV0Y2gtYS1za2V0Y2g=
+U2hha2UgJ3RpbGwgeW91ciBjbGVhciwgbWFrZSBpdCBkaXNhcHBlYXIsIG1ha2UgdGhlIG5leHQgLyBBZnRlciB0aGUgY2VyZW1vbnksIGxldCB0aGUgcmh5bWUgcmVzdCBpbiBwZWFjZQ==
+SWYgbm90LCBteSBzb3VsJ2xsIHJlbGVhc2UhIC8gVGhlIHNjZW5lIGlzIHJlY3JlYXRlZCwgcmVpbmNhcm5hdGVkLCB1cGRhdGVkLCBJJ20gZ2xhZCB5b3UgbWFkZSBpdA==
+Q3V6IHlvdXIgYWJvdXQgdG8gc2VlIGEgZGlzYXN0cm91cyBzaWdodCAvIEEgcGVyZm9ybWFuY2UgbmV2ZXIgYWdhaW4gcGVyZm9ybWVkIG9uIGEgbWljOg==
+THlyaWNzIG9mIGZ1cnkhIEEgZmVhcmlmaWVkIGZyZWVzdHlsZSEgLyBUaGUgIlIiIGlzIGluIHRoZSBob3VzZS10b28gbXVjaCB0ZW5zaW9uIQ==
+TWFrZSBzdXJlIHRoZSBzeXN0ZW0ncyBsb3VkIHdoZW4gSSBtZW50aW9uIC8gUGhyYXNlcyB0aGF0J3MgZmVhcnNvbWU=
+WW91IHdhbnQgdG8gaGVhciBzb21lIHNvdW5kcyB0aGF0IG5vdCBvbmx5IHBvdW5kcyBidXQgcGxlYXNlIHlvdXIgZWFyZHJ1bXM7IC8gSSBzaXQgYmFjayBhbmQgb2JzZXJ2ZSB0aGUgd2hvbGUgc2NlbmVyeQ==
+VGhlbiBub25jaGFsYW50bHkgdGVsbCB5b3Ugd2hhdCBpdCBtZWFuIHRvIG1lIC8gU3RyaWN0bHkgYnVzaW5lc3MgSSdtIHF1aWNrbHkgaW4gdGhpcyBtb29k
+QW5kIEkgZG9uJ3QgY2FyZSBpZiB0aGUgd2hvbGUgY3Jvd2QncyBhIHdpdG5lc3MhIC8gSSdtIGEgdGVhciB5b3UgYXBhcnQgYnV0IEknbSBhIHNwYXJlIHlvdSBhIGhlYXJ0
+UHJvZ3JhbSBpbnRvIHRoZSBzcGVlZCBvZiB0aGUgcmh5bWUsIHByZXBhcmUgdG8gc3RhcnQgLyBSaHl0aG0ncyBvdXQgb2YgdGhlIHJhZGl1cywgaW5zYW5lIGFzIHRoZSBjcmF6aWVzdA==
+TXVzaWNhbCBtYWRuZXNzIE1DIGV2ZXIgbWFkZSwgc2VlIGl0J3MgLyBOb3cgYW4gZW1lcmdlbmN5LCBvcGVuLWhlYXJ0IHN1cmdlcnk=
+T3BlbiB5b3VyIG1pbmQsIHlvdSB3aWxsIGZpbmQgZXZlcnkgd29yZCdsbCBiZSAvIEZ1cmllciB0aGFuIGV2ZXIsIEkgcmVtYWluIHRoZSBmdXJ0dXJl
+QmF0dGxlJ3MgdGVtcHRpbmcuLi53aGF0ZXZlciBzdWl0cyB5YSEgLyBGb3Igd29yZHMgdGhlIHNlbnRlbmNlLCB0aGVyZSdzIG5vIHJlc2VtYmxhbmNl
+WW91IHRoaW5rIHlvdSdyZSBydWZmZXIsIHRoZW4gc3VmZmVyIHRoZSBjb25zZXF1ZW5jZXMhIC8gSSdtIG5ldmVyIGR5aW5nLXRlcnJpZnlpbmcgcmVzdWx0cw==
+SSB3YWtlIHlhIHdpdGggaHVuZHJlZHMgb2YgdGhvdXNhbmRzIG9mIHZvbHRzIC8gTWljLXRvLW1vdXRoIHJlc3VzY2l0YXRpb24sIHJoeXRobSB3aXRoIHJhZGlhdGlvbg==
+Tm92b2NhaW4gZWFzZSB0aGUgcGFpbiBpdCBtaWdodCBzYXZlIGhpbSAvIElmIG5vdCwgRXJpYyBCLidzIHRoZSBqdWRnZSwgdGhlIGNyb3dkJ3MgdGhlIGp1cnk=
+WW8gUmFraW0sIHdoYXQncyB1cD8gLyBZbywgSSdtIGRvaW5nIHRoZSBrbm93bGVkZ2UsIEUuLCBtYW4gSSdtIHRyeWluZyB0byBnZXQgcGFpZCBpbiBmdWxs
+V2VsbCwgY2hlY2sgdGhpcyBvdXQsIHNpbmNlIE5vcmJ5IFdhbHRlcnMgaXMgb3VyIGFnZW5jeSwgcmlnaHQ/IC8gVHJ1ZQ==
+S2FyYSBMZXdpcyBpcyBvdXIgYWdlbnQsIHdvcmQgdXAgLyBaYWtpYSBhbmQgNHRoIGFuZCBCcm9hZHdheSBpcyBvdXIgcmVjb3JkIGNvbXBhbnksIGluZGVlZA==
+T2theSwgc28gd2hvIHdlIHJvbGxpbicgd2l0aCB0aGVuPyBXZSByb2xsaW4nIHdpdGggUnVzaCAvIE9mIFJ1c2h0b3duIE1hbmFnZW1lbnQ=
+Q2hlY2sgdGhpcyBvdXQsIHNpbmNlIHdlIHRhbGtpbmcgb3ZlciAvIFRoaXMgZGVmIGJlYXQgcmlnaHQgaGVyZSB0aGF0IEkgcHV0IHRvZ2V0aGVy
+SSB3YW5uYSBoZWFyIHNvbWUgb2YgdGhlbSBkZWYgcmh5bWVzLCB5b3Uga25vdyB3aGF0IEknbSBzYXlpbic/IC8gQW5kIHRvZ2V0aGVyLCB3ZSBjYW4gZ2V0IHBhaWQgaW4gZnVsbA==
+VGhpbmtpbicgb2YgYSBtYXN0ZXIgcGxhbiAvICdDdXogYWluJ3QgbnV0aGluJyBidXQgc3dlYXQgaW5zaWRlIG15IGhhbmQ=
+U28gSSBkaWcgaW50byBteSBwb2NrZXQsIGFsbCBteSBtb25leSBpcyBzcGVudCAvIFNvIEkgZGlnIGRlZXBlciBidXQgc3RpbGwgY29taW4nIHVwIHdpdGggbGludA==
+U28gSSBzdGFydCBteSBtaXNzaW9uLCBsZWF2ZSBteSByZXNpZGVuY2UgLyBUaGlua2luJyBob3cgY291bGQgSSBnZXQgc29tZSBkZWFkIHByZXNpZGVudHM=
+SSBuZWVkIG1vbmV5LCBJIHVzZWQgdG8gYmUgYSBzdGljay11cCBraWQgLyBTbyBJIHRoaW5rIG9mIGFsbCB0aGUgZGV2aW91cyB0aGluZ3MgSSBkaWQ=
+SSB1c2VkIHRvIHJvbGwgdXAsIHRoaXMgaXMgYSBob2xkIHVwLCBhaW4ndCBudXRoaW4nIGZ1bm55IC8gU3RvcCBzbWlsaW5nLCBiZSBzdGlsbCwgZG9uJ3QgbnV0aGluJyBtb3ZlIGJ1dCB0aGUgbW9uZXk=
+QnV0IG5vdyBJIGxlYXJuZWQgdG8gZWFybiAnY3V6IEknbSByaWdodGVvdXMgLyBJIGZlZWwgZ3JlYXQsIHNvIG1heWJlIEkgbWlnaHQganVzdA==
+U2VhcmNoIGZvciBhIG5pbmUgdG8gZml2ZSwgaWYgSSBzdHJpdmUgLyBUaGVuIG1heWJlIEknbGwgc3RheSBhbGl2ZQ==
+U28gSSB3YWxrIHVwIHRoZSBzdHJlZXQgd2hpc3RsaW4nIHRoaXMgLyBGZWVsaW4nIG91dCBvZiBwbGFjZSAnY3V6LCBtYW4sIGRvIEkgbWlzcw==
+QSBwZW4gYW5kIGEgcGFwZXIsIGEgc3RlcmVvLCBhIHRhcGUgb2YgLyBNZSBhbmQgRXJpYyBCLCBhbmQgYSBuaWNlIGJpZyBwbGF0ZSBvZg==
+RmlzaCwgd2hpY2ggaXMgbXkgZmF2b3JpdGUgZGlzaCAvIEJ1dCB3aXRob3V0IG5vIG1vbmV5IGl0J3Mgc3RpbGwgYSB3aXNo
+J0N1eiBJIGRvbid0IGxpa2UgdG8gZHJlYW0gYWJvdXQgZ2V0dGluJyBwYWlkIC8gU28gSSBkaWcgaW50byB0aGUgYm9va3Mgb2YgdGhlIHJoeW1lcyB0aGF0IEkgbWFkZQ==
+U28gbm93IHRvIHRlc3QgdG8gc2VlIGlmIEkgZ290IHB1bGwgLyBIaXQgdGhlIHN0dWRpbywgJ2N1eiBJJ20gcGFpZCBpbiBmdWxs
+UmFraW0sIGNoZWNrIHRoaXMgb3V0LCB5byAvIFlvdSBnbyB0byB5b3VyIGdpcmwgaG91c2UgYW5kIEknbGwgZ28gdG8gbWluZQ==
+J0NhdXNlIG15IGdpcmwgaXMgZGVmaW5pdGVseSBtYWQgLyAnQ2F1c2UgaXQgdG9vayB1cyB0b28gbG9uZyB0byBkbyB0aGlzIGFsYnVt
+WW8sIEkgaGVhciB3aGF0IHlvdSdyZSBzYXlpbmcgLyBTbyBsZXQncyBqdXN0IHB1bXAgdGhlIG11c2ljIHVw
+QW5kIGNvdW50IG91ciBtb25leSAvIFlvLCB3ZWxsIGNoZWNrIHRoaXMgb3V0LCB5byBFbGk=
+VHVybiBkb3duIHRoZSBiYXNzIGRvd24gLyBBbmQgbGV0IHRoZSBiZWF0IGp1c3Qga2VlcCBvbiByb2NraW4n
+QW5kIHdlIG91dHRhIGhlcmUgLyBZbywgd2hhdCBoYXBwZW5lZCB0byBwZWFjZT8gLyBQZWFjZQ==

src/bytes.rs

@@ -93,6 +93,16 @@ impl Bytes {
         r
     }
 
+    pub fn guess_key(&self) -> u8 {
+        // Assuming all bytes have been xor-encrypted by the same u8 key, find that key
+        // by trying all u8 values and compute an ascii score for the resulting "plaintext".
+        // The u8 key for the "plaintext" with the highest score is returned as the guessed
+        // key.
+        let mut h: Vec<(Bytes, u8)> = (0..=255).map(|i| (Bytes::xor_byte(self, i), i)).collect();
+        h.sort_by(|a, b| a.0.ascii_score().partial_cmp(&b.0.ascii_score()).unwrap());
+        h.last().unwrap().1
+    }
+
     pub fn pad_pkcs7(&mut self, block_size: usize) -> () {
         let Bytes(v) = self;
         let padding_value = (block_size - v.len() % block_size) as u8;

src/main.rs

@@ -31,7 +31,8 @@ fn main() {
         set3::challenge18();
         set3::challenge19();
         set3::challenge20();
+        set3::challenge21();
     } else {
-        set3::challenge20();
+        set3::challenge21();
     }
 }

src/set1.rs

@@ -138,17 +138,16 @@ pub fn challenge6() {
         result
     }
 
-    fn guess_key(bytes: &Bytes) -> u8 {
-        let mut h: Vec<(Bytes, u8)> = (0..=255).map(|i| (Bytes::xor_byte(bytes, i), i)).collect();
-        h.sort_by(|a, b| a.0.ascii_score().partial_cmp(&b.0.ascii_score()).unwrap());
-        h.last().unwrap().1
-    }
-
     _test_roundtrip();
     let bytes = read("data/6.txt");
     let key_size = guess_key_size(&bytes);
     let bytes_tranposed = transpose(&bytes, key_size);
-    let key = Bytes(bytes_tranposed.iter().map(|b| guess_key(&b)).collect());
+    let key = Bytes(
+        bytes_tranposed
+            .iter()
+            .map(|b| Bytes::guess_key(&b))
+            .collect(),
+    );
     let msg = Bytes::xor_cycle(&bytes, &key).to_utf8();
 
     let partial_msg = msg[..20].to_string();

src/set3.rs

@@ -268,5 +268,38 @@ pub fn challenge19() {
 }
 
 pub fn challenge20() {
-    println!("[xxxx] Challenge 20: 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()
+    }
+
+    fn attack(ciphers: Vec<Bytes>) -> Vec<Bytes> {
+        let min_cipher_len = ciphers.iter().map(|c| c.len()).min().unwrap_or(0);
+        let mut key: Vec<u8> = vec![];
+        for byte_index in 0..min_cipher_len {
+            let bytes = Bytes(ciphers.iter().map(|c| c.0[byte_index]).collect());
+            let key_char = Bytes::guess_key(&bytes);
+            key.push(key_char);
+        }
+        let key = Bytes(key);
+        ciphers
+            .iter()
+            .map(|cipher| Bytes::xor(&key, cipher))
+            .collect()
+    }
+
+    let plaintexts = read("data/20.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 plaintexts = attack(ciphers);
+
+    println!("[okay] Challenge 20: {}", plaintexts[0].to_utf8());
+}
+
+pub fn challenge21() {
+    println!("[xxxx] Challenge 21: TBD");
 }