Add DH key exchange example.

examples/dh.rs

@@ -0,0 +1,34 @@
+// This is an example of three-party Diffie-Hellman key exchange
+// Requires two rounds
+
+extern crate bn;
+extern crate rand;
+
+use bn::*;
+
+fn main() {
+    let rng = &mut rand::thread_rng();
+
+    // Construct private keys
+    let alice_sk = Scalar::random(rng);
+    let bob_sk = Scalar::random(rng);
+    let carol_sk = Scalar::random(rng);
+
+    // Construct public keys
+    let alice_pk = G1::one() * &alice_sk;
+    let bob_pk = G1::one() * &bob_sk;
+    let carol_pk = G1::one() * &carol_sk;
+
+    // Round one:
+    let alice_dh_1 = &bob_pk * &carol_sk;
+    let bob_dh_1 = &carol_pk * &alice_sk;
+    let carol_dh_1 = &alice_pk * &bob_sk;
+
+    // Round two:
+    let alice_dh_2 = alice_dh_1 * &alice_sk;
+    let bob_dh_2 = bob_dh_1 * &bob_sk;
+    let carol_dh_2 = carol_dh_1 * &carol_sk;
+
+    // All parties should arrive to the same shared secret
+    assert!(alice_dh_2 == bob_dh_2 && bob_dh_2 == carol_dh_2);
+}