From caf6d35b59169036b50419ec147f64ba4a88873d Mon Sep 17 00:00:00 2001
From: Felix Martin <mail@felixm.de>
Date: Mon, 15 Aug 2022 20:21:40 -0400
Subject: [PATCH] Implement challenge 26 ez katka

---
 src/main.rs   |  3 ++-
 src/parser.rs | 15 +++++++--------
 src/set4.rs   | 41 +++++++++++++++++++++++++++++++++++++++--
 3 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index d1861cc..f8bbcc7 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -41,7 +41,8 @@ fn main() {
         set3::challenge24();
         set4::challenge25();
         set4::challenge26();
+        set4::challenge27();
     } else {
-        set4::challenge26();
+        set4::challenge27();
     }
 }
diff --git a/src/parser.rs b/src/parser.rs
index a6de9dd..60f1327 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -40,14 +40,13 @@ fn scan(code: &str, mut ix: usize, mut tokens: Tokens) -> Tokens {
     let c: char = code[ix..ix + 1].chars().next().unwrap();
     if c.is_ascii_alphanumeric() || SPECIAL_CHARS.contains(&c) {
         return scan_identifier(code, ix, tokens);
-    } else if c == '&' {
-        tokens.push(Token::Ampersand);
-    } else if c == '=' {
-        tokens.push(Token::Equal);
-    } else if c == ';' {
-        tokens.push(Token::Semicolon);
-    } else {
-        panic!("Unexpected char '{}' at index {}", c, ix);
+    }
+
+    match c {
+        '&' => tokens.push(Token::Ampersand),
+        '=' => tokens.push(Token::Equal),
+        ';' => tokens.push(Token::Semicolon),
+        _ => panic!("Unexpected char '{}' at index {}", c, ix),
     }
     ix += 1;
     scan(code, ix, tokens)
diff --git a/src/set4.rs b/src/set4.rs
index 820a56f..34e3f77 100644
--- a/src/set4.rs
+++ b/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");
 }