Implement challenge 26 ez katka

src/set4.rs

@@ -1,4 +1,4 @@
-use crate::{bytes::Bytes, ctr, utils};
+use crate::{bytes::Bytes, ctr, parser, utils};
 
 pub fn challenge25() {
     let cipher = utils::read_base64("data/25.txt");
@@ -43,5 +43,42 @@ pub fn challenge25() {
 }
 
 pub fn challenge26() {
-    println!("[xxxx] Challenge 26: TBD");
+    fn encrypt(input: &str, key: &Bytes) -> Bytes {
+        let mut r = String::new();
+        for c in input.chars() {
+            if c == ';' || c == '=' {
+                panic!("encrypt: invalid char {}", c);
+            }
+        }
+        r.push_str("comment1=cooking%20MCs;userdata=");
+        r.push_str(input);
+        r.push_str(";comment2=%20like%20a%20pound%20of%20bacon");
+        let data = Bytes(r.as_bytes().to_vec());
+        ctr::encrypt(key, 0, &data)
+    }
+
+    let key = Bytes::random(16);
+
+    // 0               16              32              48              64
+    // 0..34..78..bc..f0..34..78..bc..f0..34..78..bc..f0..34..78..bc..f0..34..78..bc..f
+    // comment1=cooking%20MCs;userdata=aaaaaaaaaaaaaaaa;comment2=%20like%20a%20pound%20of%20bacon
+    // comment1=cooking%20MCs;userdata=fobar;admin=true;comment2=%20like%20a%20pound%20of%20bacon
+    let input = "aaaaaaaaaaaaaaaa";
+    let cipher = encrypt(&input, &key);
+    let keystream = utils::xor(&cipher.0[32..48], &Bytes::from_utf8(input).0);
+
+    let input = "fobar;admin=true";
+    let mut flipped_cipher = cipher.0[0..32].to_vec();
+    flipped_cipher.append(&mut utils::xor(&keystream, &input.as_bytes()));
+    flipped_cipher.append(&mut cipher.0[48..cipher.len()].to_vec());
+
+    let cleartext = ctr::decrypt(&key, 0, &Bytes(flipped_cipher));
+    let dict = parser::parse_key_value(&cleartext.to_utf8());
+    let admin_status = dict.get("admin").unwrap();
+    assert_eq!(admin_status, "true");
+    println!("[okay] Challenge 26: admin={}", admin_status);
+}
+
+pub fn challenge27() {
+    println!("[xxxx] Challenge 27: tbd");
 }