add noise handshake example

protocols/v2/noise-sv2/examples/noise_handshake.rs

@@ -0,0 +1,68 @@
+// # Noise Protocol Handshake
+//
+// This example demonstrates how to use the `noise-sv2` crate to establish a Noise handshake
+// between and initiator and responder, and encrypt and decrypt a secret message. It showcases how
+// to:
+//
+// - Generate a cryptographic keypair using the `secp256k1` library.
+// - Perform a Noise handshake between an initiator and responder.
+// - Transition from handshake to secure communication mode.
+// - Encrypt a message as the initiator role.
+// - Decrypt the message as the responder role.
+//
+// ## Run
+//
+// ```sh
+// cargo run --example noise_handshake
+// ```
+
+use noise_sv2::{Initiator, Responder};
+use secp256k1::{Keypair, Parity, Secp256k1};
+
+// Even parity used in the Schnorr signature process
+const PARITY: Parity = Parity::Even;
+// Validity duration of the responder's certificate, seconds
+const RESPONDER_CERT_VALIDITY: u32 = 3600;
+
+// Generates a secp256k1 public/private key pair for the responder.
+fn generate_key() -> Keypair {
+    let secp = Secp256k1::new();
+    let (secret_key, _) = secp.generate_keypair(&mut rand::thread_rng());
+    let kp = Keypair::from_secret_key(&secp, &secret_key);
+    if kp.x_only_public_key().1 == PARITY {
+        kp
+    } else {
+        generate_key()
+    }
+}
+
+fn main() {
+    let mut secret_message = "Ciao, Mondo!".as_bytes().to_vec();
+
+    let responder_key_pair = generate_key();
+
+    let mut initiator = Initiator::new(Some(responder_key_pair.public_key().into()));
+    let mut responder = Responder::new(responder_key_pair, RESPONDER_CERT_VALIDITY);
+
+    let first_message = initiator
+        .step_0()
+        .expect("Initiator failed first step of handshake");
+
+    let (second_message, mut responder_state) = responder
+        .step_1(first_message)
+        .expect("Responder failed second step of handshake");
+
+    let mut initiator_state = initiator
+        .step_2(second_message)
+        .expect("Initiator failed third step of handshake");
+
+    initiator_state
+        .encrypt(&mut secret_message)
+        .expect("Initiator failed to encrypt the secret message");
+    assert!(secret_message != "Ciao, Mondo!".as_bytes().to_vec());
+
+    responder_state
+        .decrypt(&mut secret_message)
+        .expect("Responder failed to decrypt the secret message");
+    assert!(secret_message == "Ciao, Mondo!".as_bytes().to_vec());
+}