Add intro-crypto exercise 04

school/intro-crypto/uebung/04/lfsr/src/main.rs

@@ -0,0 +1,177 @@
+struct Lfsr {
+    reg: Vec<bool>,
+    p: Vec<bool>,
+}
+
+impl Lfsr {
+    fn new(iv: &[bool], p: &[bool]) -> Self {
+        assert_eq!(iv.len(), p.len());
+        Self {
+            reg: iv.iter().cloned().collect(),
+            p: p.iter().cloned().collect(),
+        }
+    }
+
+    fn next(&mut self) -> bool {
+        // let res = self.reg[self.len - 1];
+        let next = self
+            .reg
+            .iter()
+            .zip(self.p.iter())
+            .map(|(n, m)| n & m)
+            .fold(false, |acc, v| acc ^ v);
+        self.reg.insert(0, next);
+        let ret = self.reg.pop().unwrap();
+        assert_eq!(self.reg.len(), self.p.len());
+        ret
+    }
+
+    fn state(&self) -> &[bool] {
+        &self.reg
+    }
+}
+
+fn convert_state(s: &[bool]) -> String {
+    s.iter()
+        .map(|x| if *x { "1".to_string() } else { "0".to_string() })
+        .collect::<Vec<String>>()
+        .join(" & ")
+}
+
+/// helper for 3c)
+fn recover_keystream(plain: &[bool], cipher: &[bool]) -> Vec<bool> {
+    assert_eq!(plain.len(), cipher.len());
+    plain
+        .iter()
+        .zip(cipher.iter())
+        .map(|(a, b)| a ^ b)
+        .collect()
+}
+
+fn decrypt(l: &mut Lfsr, c: &[bool]) -> u8 {
+    let s: String = c
+        .into_iter()
+        .map(|c| c ^ l.next())
+        .map(|c| if c { "1" } else { "0" })
+        .collect();
+    u8::from_str_radix(&s, 2).unwrap()
+}
+
+/// main for 3d)
+fn main() {
+    let p = &[false, true, true, false, false, false, true, true];
+    // let s = &[true, false, true, true, true, false, true, true];
+    // let s = &[true, false, true, false, false, false, false, true];
+    // let s = &[true, false, false, false, false, true, false, true];
+    let s = &[true, true, false, true, true, true, false, true];
+    let mut l = Lfsr::new(s, p);
+    // for _ in 0..17 {
+    //     println!("{}", if lfsr.next() { "1" } else { "0" });
+    // }
+    // 00010011
+    // 11010100
+    let c = &[true, true, false, true, false, true, false, false];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 00010011 = 0x13
+    let c = &[false, false, false, true, false, false, true, true];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 00010000 = 0x10
+    let c = &[false, false, false, true, false, false, false, false];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 01110101 = 0x75
+    let c = &[false, true, true, true, false, true, false, true];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 01100000 = 0x60
+    let c = &[false, true, true, false, false, false, false, false];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 00000101 = 0x05
+    let c = &[false, false, false, false, false, true, false, true];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 01111100 = 0x7c
+    let c = &[false, true, true, true, true, true, false, false];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 01010000 = 0x50
+    let c = &[false, true, false, true, false, false, false, false];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 11011011 = 0xdb
+    let c = &[true, true, false, true, true, false, true, true];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+
+    // 01110011 = 0x73
+    let c = &[false, true, true, true, false, false, true, true];
+    let d = decrypt(&mut l, c);
+    println!("{}: {}", d, d as char);
+}
+
+// fn main() {
+//     let plain = &[
+//         false, true, false, false, true, true, false, true, false, true, true, false, true, true,
+//         true, true,
+//     ];
+//     let cipher = &[
+//         true, true, true, false, true, true, false, false, true, true, false, true, false, true,
+//         false, false,
+//     ];
+//     let key_stream = recover_keystream(plain, cipher);
+//     println!(
+//         "{}",
+//         key_stream
+//             .iter()
+//             .map(|k| if *k { "1, " } else { "0, " })
+//             .collect::<String>()
+//     );
+// }
+
+/// main for exercise 1
+fn main1() {
+    // 1a)
+    // let mut lfsr = Lfsr::new(
+    //     &[true, true, false, false, false, false],
+    //     // &[true, true, true, true, true, true],
+    //     // &[true, false, false, false, false, false],
+    //     &[false, true, false, true, true, true],
+    // );
+
+    // 1b)
+    // let mut lfsr = Lfsr::new(
+    //     // &[true, true, true, true, true, true],
+    //     &[true, false, false, false, false, false],
+    //     &[false, false, false, false, true, true],
+    // );
+
+    // 1c)
+    let mut lfsr = Lfsr::new(
+        // &[true, true, true, false, false, false],
+        // &[true, true, false, false, false, false],
+        &[true, false, true, true, false, true],
+        // &[true, true, true, true, true, true],
+        // &[true, false, false, false, false, false],
+        &[false, false, true, true, true, true],
+    );
+    let mut seen = Vec::new();
+    let mut i = 0;
+    while !seen.contains(&lfsr.state().iter().cloned().collect::<Vec<_>>()) {
+        seen.push(lfsr.state().iter().cloned().collect::<Vec<_>>());
+        print!("{}", convert_state(lfsr.state()));
+        println!(" & {} \\\\", if lfsr.next() { 1 } else { 0 });
+        i += 1;
+    }
+    eprintln!("Repetition after {} iterations", i);
+}