Implement challenge 34
parent
9e568ac97c
commit
ad3a292e0e
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@ -83,7 +83,7 @@ impl Bytes {
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pub fn pad_pkcs7(&mut self, block_size: usize) {
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let Bytes(v) = self;
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let padding_value = (block_size - v.len() % block_size)
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let padding_value = (block_size - (v.len() % block_size))
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.try_into()
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.expect("Padding value has to be an u8");
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for _ in 0..padding_value {
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32
src/rsa.rs
32
src/rsa.rs
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@ -1,12 +1,26 @@
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pub fn expmod(base: u32, exp: u32, m: u32) -> u32 {
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if exp == 0 {
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return 1;
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}
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use num_bigint::BigUint;
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use num_bigint::RandBigInt;
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if exp % 2 == 0 {
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let s = expmod(base, exp / 2, m);
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(s * s) % m
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} else {
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(expmod(base, exp - 1, m) * base) % m
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#[derive(Clone)]
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pub struct PublicKey(pub BigUint);
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#[derive(Clone)]
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pub struct PrivateKey(pub BigUint);
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#[derive(Clone)]
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pub struct Keypair {
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pub private: PrivateKey,
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pub public: PublicKey,
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}
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impl Keypair {
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pub fn make(p: &BigUint, g: &BigUint) -> Self {
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let mut rng = rand::thread_rng();
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let private = rng.gen_biguint_below(p);
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let public = g.modpow(&private, p);
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Self {
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private: PrivateKey(private),
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public: PublicKey(public),
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}
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}
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}
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225
src/set5.rs
225
src/set5.rs
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@ -1,12 +1,41 @@
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use crate::bytes::Bytes;
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use crate::cbc;
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use crate::rsa;
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use num_bigint::{BigUint, RandBigInt, ToBigUint};
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use crate::sha1::Sha1;
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use num_bigint::ToBigUint;
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use rand::Rng;
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use std::fs;
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mod challenge33 {
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use num_bigint::BigUint;
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use std::fs;
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pub fn load_large_prime() -> BigUint {
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let s = fs::read_to_string("data/33.txt").expect("run from git root dir");
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let b: Vec<u8> = s
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.chars()
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.filter(|c| *c != '\n')
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.map(|c| c.to_digit(16).unwrap().try_into().unwrap())
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.collect();
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BigUint::from_radix_be(&b, 16).unwrap()
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}
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}
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pub fn challenge33() {
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#![allow(non_snake_case)]
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fn expmod(base: u32, exp: u32, m: u32) -> u32 {
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if exp == 0 {
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return 1;
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}
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if exp % 2 == 0 {
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let s = expmod(base, exp / 2, m);
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(s * s) % m
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} else {
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(expmod(base, exp - 1, m) * base) % m
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}
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}
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fn simple_diffie_hellman() {
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#![allow(non_snake_case)]
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let mut rng = rand::thread_rng();
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// Set a variable "p" to 37 and "g" to 5.
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@ -16,18 +45,18 @@ pub fn challenge33() {
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// Generate "a", a random number mod 37. Now generate "A", which is "g" raised to the "a"
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// power mode 37 --- A = (g**a) % p.
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let a: u32 = rng.gen::<u32>() % p;
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let A = rsa::expmod(g, a, p);
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let A = expmod(g, a, p);
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// Do the same for "b" and "B".
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let b: u32 = rng.gen::<u32>() % p;
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let B = rsa::expmod(g, b, p);
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let B = expmod(g, b, p);
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// "A" and "B" are public keys. Generate a session key with them; set "s" to "B" raised to
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// the "a" power mod 37 --- s = (B**a) % p.
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let s = rsa::expmod(B, a, p);
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let s = expmod(B, a, p);
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// Do the same with A**b, check that you come up with the same "s".
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let s_ = rsa::expmod(A, b, p);
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let s_ = expmod(A, b, p);
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assert_eq!(s, s_, "crypto is broken");
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// To turn "s" into a key, you can just hash it to create 128 bits of key material (or
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@ -35,25 +64,14 @@ pub fn challenge33() {
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}
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fn serious_diffie_hellman() {
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let mut rng = rand::thread_rng();
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let s = fs::read_to_string("data/33.txt").expect("run from git root dir");
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let b: Vec<u8> = s
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.chars()
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.filter(|c| *c != '\n')
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.map(|c| c.to_digit(16).unwrap().try_into().unwrap())
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.collect();
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let p = BigUint::from_radix_be(&b, 16).unwrap();
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let p = challenge33::load_large_prime();
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let g = 2_u8.to_biguint().unwrap();
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let a = rng.gen_biguint_below(&p);
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let A = g.modpow(&a, &p);
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let a = rsa::Keypair::make(&p, &g);
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let b = rsa::Keypair::make(&p, &g);
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let b = rng.gen_biguint_below(&p);
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let B = g.modpow(&b, &p);
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let s = B.modpow(&a, &p);
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let s_ = A.modpow(&b, &p);
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let s = b.public.0.modpow(&a.private.0, &p);
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let s_ = a.public.0.modpow(&b.private.0, &p);
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assert_eq!(s, s_, "crypto is broken");
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}
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@ -62,6 +80,163 @@ pub fn challenge33() {
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println!("[okay] Challenge 33: implemented Diffie-Hellman");
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}
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pub fn challenge34() {
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println!("[xxxx] Challenge 34: tbd");
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mod challenge34 {
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use crate::bytes::Bytes;
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use crate::cbc;
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use crate::rsa;
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use crate::sha1::Sha1;
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use num_bigint::BigUint;
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pub struct Bot {
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p: BigUint,
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keypair: rsa::Keypair,
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pub s: Option<BigUint>,
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pub key: Option<Bytes>,
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}
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impl Bot {
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pub fn new(p: BigUint, g: &BigUint) -> Self {
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let keypair = rsa::Keypair::make(&p, g);
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Bot {
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p: p,
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keypair: keypair,
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s: None,
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key: None,
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}
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}
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pub fn get_public_key(&self) -> rsa::PublicKey {
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self.keypair.public.clone()
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}
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pub fn exchange_keys(&mut self, public: &rsa::PublicKey) -> rsa::PublicKey {
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let s = public.0.modpow(&self.keypair.private.0, &self.p);
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self.s = Some(s);
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self.make_encryption_key();
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self.keypair.public.clone()
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}
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fn make_encryption_key(&mut self) {
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assert!(self.s.is_some(), "keys have not been exchanged");
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if self.key.is_some() {
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return;
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}
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let mut sha1 = Sha1::default();
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let key = &sha1.hash(&Bytes(self.s.clone().unwrap().to_bytes_be())).0[0..16];
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self.key = Some(Bytes(key.to_vec()));
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}
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pub fn encrypt(&mut self, message: &Bytes) -> Bytes {
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assert!(self.key.is_some(), "keys have not been exchanged");
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const BLOCK_SIZE: usize = 16;
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let key = self.key.as_ref().unwrap();
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let mut iv = Bytes::random(16);
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let mut message = Bytes(message.0.clone());
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message.pad_pkcs7(BLOCK_SIZE);
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// AES-CBC(SHA1(s)[0:16], iv=random(16), msg) + iv
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let mut cipher = cbc::encrypt(&key, &iv, &message).0;
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cipher.append(&mut iv.0);
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Bytes(cipher)
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}
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pub fn decrypt(&mut self, cipher: &Bytes) -> Bytes {
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const BLOCK_SIZE: usize = 16;
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assert!(self.key.is_some(), "keys have not been exchanged");
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let key = self.key.as_ref().unwrap();
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let cipher_len = cipher.len();
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let iv = Bytes(cipher.0[(cipher_len - BLOCK_SIZE)..cipher_len].to_vec());
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let cipher = Bytes(cipher.0[0..cipher_len - BLOCK_SIZE].to_vec());
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let mut message = cbc::decrypt(&key, &iv, &cipher);
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message.remove_pkcs7(BLOCK_SIZE);
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message
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}
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}
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}
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pub fn challenge34() {
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fn echo() {
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let p = challenge33::load_large_prime();
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let g = 2_u8.to_biguint().unwrap();
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let mut a = challenge34::Bot::new(p.clone(), &g);
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// A->B: Send "p", "g", "A"
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let mut b = challenge34::Bot::new(p.clone(), &g);
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// B->A: Send "B"
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a.exchange_keys(&b.exchange_keys(&a.get_public_key()));
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assert_eq!(a.s, b.s, "crypto is broken");
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// A->B: Send AES-CBC(SHA1(s)[0:16], iv=random(16), msg) + iv
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let message_a = Bytes::from_utf8("Will this work? Let's make it longer.");
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let cipher_a = a.encrypt(&message_a);
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// B->A: Send AES-CBC(SHA1(s)[0:16], iv=random(16), A's msg) + iv
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let message_b = b.decrypt(&cipher_a);
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let cipher_b = b.encrypt(&message_b);
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let roundtrip = a.decrypt(&cipher_b);
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assert_eq!(message_a, roundtrip, "we broke it fam");
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}
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fn echo_mitm() {
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let p = challenge33::load_large_prime();
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let g = 2_u8.to_biguint().unwrap();
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let p_public = rsa::PublicKey(p.clone());
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// A->M Send "p", "g", "A"
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let mut a = challenge34::Bot::new(p.clone(), &g);
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let mut m = challenge34::Bot::new(p.clone(), &g);
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m.exchange_keys(&a.get_public_key());
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// M->B Send "p", "g", "p"
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// B->M Send "B"
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let mut b = challenge34::Bot::new(p.clone(), &g);
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b.exchange_keys(&p_public);
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// M->A Send "p"
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a.exchange_keys(&p_public);
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// A->M Send AES-CBC(SHA1(s)[0:16], iv=random(16), msg) + iv
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// M->B Relay that to B
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let message_a = Bytes::from_utf8("Will this work again? I don't doubt it.");
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let cipher_a = a.encrypt(&message_a);
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// B->M Send AES-CBC(SHA1(s)[0:16], iv=random(16), A's msg) + iv
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let message_b = b.decrypt(&cipher_a);
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let cipher_b = b.encrypt(&message_b);
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// M->A Relay that to A
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let roundtrip = a.decrypt(&cipher_b);
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assert_eq!(message_a, roundtrip, "we broke it fam");
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let restored_a = attack(&cipher_a);
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let restored_b = attack(&cipher_b);
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assert_eq!(message_a, restored_a, "attack didn't work");
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assert_eq!(message_b, restored_b, "attack didn't work");
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}
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fn attack(cipher: &Bytes) -> Bytes {
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const BLOCK_SIZE: usize = 16;
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// Do the DH math on this quickly to see what that does to the predictability of the key.
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// Math: with p = A; s = (A ** b) % p becomes (p ** b) % p = 0 => s = 0
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let s = 0_u8.to_biguint().unwrap();
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let mut sha1 = Sha1::default();
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let key = Bytes(sha1.hash(&Bytes(s.to_bytes_be())).0[0..16].to_vec());
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let cipher_len = cipher.len();
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let iv = Bytes(cipher.0[(cipher_len - BLOCK_SIZE)..cipher_len].to_vec());
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let cipher = Bytes(cipher.0[0..cipher_len - BLOCK_SIZE].to_vec());
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let mut message = cbc::decrypt(&key, &iv, &cipher);
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message.remove_pkcs7(BLOCK_SIZE);
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message
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}
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echo();
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echo_mitm();
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println!("[okay] Challenge 34: implement MITM key-fixing attack on DH");
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}
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