Implement challenge 10.

data/10.txt

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src/cbs.rs

@@ -0,0 +1,59 @@
+use crate::bytes::Bytes;
+use openssl::symm;
+
+fn xor(a: &[u8], b: &[u8]) -> Vec<u8> {
+    Iterator::zip(a.iter(), b.iter())
+        .map(|z| *(z.0) ^ *(z.1))
+        .collect()
+}
+
+fn enrypt_aes_128_ecb_block(key: &[u8], data: &[u8]) -> Vec<u8> {
+    let cipher_type = symm::Cipher::aes_128_ecb();
+    let block_size = cipher_type.block_size();
+    let mut encrypter = symm::Crypter::new(cipher_type, symm::Mode::Encrypt, key, None).unwrap();
+    if data.len() == block_size {
+        encrypter.pad(false);
+    }
+    let mut cipher = vec![0; data.len() + block_size];
+    let mut count = encrypter.update(data, &mut cipher).unwrap();
+    count += encrypter.finalize(&mut cipher).unwrap();
+    cipher[0..count].to_vec()
+}
+
+fn decrypt_aes_128_ecb_block(key: &[u8], data: &[u8]) -> Vec<u8> {
+    let cipher_type = symm::Cipher::aes_128_ecb();
+    let block_size = cipher_type.block_size();
+    let mut encrypter = symm::Crypter::new(cipher_type, symm::Mode::Decrypt, key, None).unwrap();
+    encrypter.pad(false);
+    let mut cipher = vec![0; data.len() + block_size];
+    encrypter.update(data, &mut cipher).unwrap();
+    cipher[0..block_size].to_vec()
+}
+
+pub fn encrypt(Bytes(key): &Bytes, Bytes(iv): &Bytes, Bytes(data): &Bytes) -> Bytes {
+    let block_size = 16;
+    let mut result: Vec<u8> = vec![];
+    let mut prev_cipher: Vec<u8> = iv.to_vec(); // first xor input is IV
+    for data in data.chunks(block_size) {
+        let xored = xor(&prev_cipher, data);
+        let mut cipher = enrypt_aes_128_ecb_block(key, &xored);
+        prev_cipher = cipher.to_vec(); // cipher is input for next xor
+        result.append(&mut cipher);
+    }
+    Bytes(result)
+}
+
+pub fn decrypt(Bytes(key): &Bytes, Bytes(iv): &Bytes, Bytes(data): &Bytes) -> Bytes {
+    // XXX: does not handle padding for last block
+    let cipher_type = symm::Cipher::aes_128_ecb();
+    let block_size = cipher_type.block_size();
+    let mut result: Vec<u8> = vec![];
+    let mut prev_cipher: Vec<u8> = iv.to_vec(); // first xor input is IV
+    for cipher in data.chunks(block_size) {
+        let xored = decrypt_aes_128_ecb_block(key, &cipher);
+        let data = xor(&xored, &prev_cipher);
+        result.extend(data.to_vec());
+        prev_cipher = cipher.to_vec();
+    }
+    Bytes(result)
+}

src/main.rs

@@ -1,17 +1,19 @@
 mod bytes;
 mod bytes_base64;
+mod cbs;
 mod set1;
 mod set2;
 
 fn main() {
-    set1::challenge1();
-    set1::challenge2();
-    set1::challenge3();
-    set1::challenge4();
-    set1::challenge5();
-    set1::challenge6();
-    set1::challenge7();
-    set1::challenge8();
-    set2::challenge9();
+    // set1::challenge1();
+    // set1::challenge2();
+    // set1::challenge3();
+    // set1::challenge4();
+    // set1::challenge5();
+    // set1::challenge6();
+    // set1::challenge7();
+    // set1::challenge8();
+    // set2::challenge9();
     set2::challenge10();
+    set2::challenge11();
 }

src/set2.rs

@@ -1,4 +1,7 @@
+#![allow(dead_code)]
 use crate::bytes::Bytes;
+use crate::bytes_base64::BytesBase64;
+use crate::cbs;
 
 pub fn challenge9() {
     let mut bytes = Bytes::from_utf8("YELLOW SUBMARINE");
@@ -7,5 +10,26 @@ pub fn challenge9() {
 }
 
 pub fn challenge10() {
-    println!("[TBD] Challenge 10: TBD");
+    fn read(path: &str) -> Bytes {
+        let s = std::fs::read_to_string(path).unwrap();
+        BytesBase64::from_base64(&s).to_bytes()
+    }
+    let iv = Bytes(vec![0; 16]);
+    let key = Bytes::from_utf8("YELLOW SUBMARINE");
+
+    let text = Bytes::from_utf8("aaaabbbbccccddddeeeeffffgggghhhh");
+    let ciphertext = cbs::encrypt(&key, &iv, &text);
+    let roundtrip = cbs::decrypt(&key, &iv, &ciphertext);
+    if text == roundtrip {
+        let ciphertext = read("data/10.txt");
+        let cleartext = cbs::decrypt(&key, &iv, &ciphertext);
+        let output = cleartext.to_utf8()[..10].to_string();
+        println!("[okay] Challenge 10: {}", output);
+    } else {
+        println!("[fail] Challenge 10: rountrip failed");
+    }
+}
+
+pub fn challenge11() {
+    println!("[tbd] Challenge 11: TBD!");
 }