Finish challenge 38 SRP dictionary attack

src/main.rs

@@ -61,8 +61,9 @@ fn main() {
         set5::challenge33();
         set5::challenge34();
         set5::challenge35();
+        set5::challenge36();
     }
-    set5::challenge36();
     set5::challenge37();
     set5::challenge38();
+    set5::challenge39();
 }

src/set5.rs

@@ -433,7 +433,7 @@ pub fn challenge38() -> Option<()> {
     // Client and Server
     let n = challenge33::load_large_prime();
     let g = 2_u8.to_biguint()?;
-    let password = "horse planet carpet country";
+    let password = "bar";
 
     // Server: x = SHA256(salt|password); v = g**x % n;
     let salt: u32 = rng.gen();
@@ -445,7 +445,8 @@ pub fn challenge38() -> Option<()> {
     let a_public = g.modpow(&a, &n);
 
     // S->C: salt, B = g**b % n, u = 128 bit random number
-    let b = rng.gen_biguint_below(&n);
+    // Pose as the server and use arbitrary values for b, B, u, and salt.
+    let b = 11_u8.to_biguint()?;
     let b_public = g.modpow(&b, &n);
     let u: u128 = rng.gen();
 
@@ -455,45 +456,59 @@ pub fn challenge38() -> Option<()> {
     let k_client = sha256(&s_client.to_bytes_be());
 
     // Server: S = (A * v ** u)**b % n; K = SHA256(S);
-    let s_server = (a_public * v.modpow(&u.to_biguint()?, &n)).modpow(&b, &n);
+    let s_server = (&a_public * v.modpow(&u.to_biguint()?, &n)).modpow(&b, &n);
     let k_server = sha256(&s_server.to_bytes_be());
 
     assert_eq!(k_client, k_server);
 
     // C->S
     //   Send HMAC-SHA256(K, salt)
-    let salt = Bytes(salt.to_be_bytes().to_vec());
-    let mac_client = sha1::hmac_sha1(&Bytes(k_client.to_vec()), &salt);
+    let salt_bytes = Bytes(salt.to_be_bytes().to_vec());
+    let mac_client = sha1::hmac_sha1(&Bytes(k_client.to_vec()), &salt_bytes);
 
     // S->C
-    let mac_server = sha1::hmac_sha1(&Bytes(k_server.to_vec()), &salt);
+    let mac_server = sha1::hmac_sha1(&Bytes(k_server.to_vec()), &salt_bytes);
     assert_eq!(mac_server, mac_client, "HMAC verification failed");
 
-    //fn crack_password(mac_client: &Bytes, salt: u32, B: &BigUint, u: BigUint) -> Option<String> {
-    //    let dict = ["foo", "bar", "lol"];
-    //    for password in dict {
-    //        let x = srp::hash_password(salt, &password)?;
-    //        let s_client = b_public.modpow(&(a + &u * x), &n);
-    //        let k_client = sha256(&s_client.to_bytes_be());
-    //    }
+    fn crack_password(
+        mac_client: &Bytes,
+        salt: u32,
+        a_public: &BigUint,
+        u: u128,
+    ) -> Option<String> {
+        // Now, run the protocol as a MITM attacker: pose as the server and use arbitrary values
+        // for b, B, u, and salt.  Crack the password from A's HMAC-SHA256(K, salt).
+        let dict = ["foo", "bar", "lol"];
+        let g = 2_u8.to_biguint()?;
+        let n = challenge33::load_large_prime();
+        let b = 11_u8.to_biguint()?;
+        let salt_bytes = Bytes(salt.to_be_bytes().to_vec());
 
+        for password in dict {
+            let x = srp::hash_password(salt, &password)?;
+            let v = g.modpow(&x, &n);
+            let s_attack = (a_public * v.modpow(&u.to_biguint()?, &n)).modpow(&b, &n);
+            let k_attack = sha256(&s_attack.to_bytes_be());
+            let mac_attack = sha1::hmac_sha1(&Bytes(k_attack.to_vec()), &salt_bytes);
+            if mac_attack == *mac_client {
+                return Some(password.to_owned());
+            }
+        }
 
-    //    "foo".to_string()
-    //}
+        None
+    }
 
-    // TASK:
-    //
-    // Note that in this protocol, the server's "B" parameter doesn't depend on the password (it's
-    // just a Diffie Hellman public key).
-    //
-    // Make sure the protocol works given a valid password.
-    //
-    // Now, run the protocol as a MITM attacker: pose as the server and use arbitrary values for b,
-    // B, u, and salt.
-    //
-    // Crack the password from A's HMAC-SHA256(K, salt).
+    let cracked_password = crack_password(&mac_client, salt, &a_public, u);
+    match cracked_password {
+        Some(p) if p == password => {
+            println!("[okay] Challenge 38: offline dictionary attack on SRP");
+        }
+        _ => println!("[FAIL] Challenge 38: offline dictionary attack on SRP"),
+    };
 
-
-    println!("[xxxx] Challenge 38: offline dictionary attack on SRP");
     Some(())
 }
+
+pub fn challenge39() {
+    println!("[xxxx] Challenge 39: Implement RSA");
+}