Method Exchange

src/network/network_crypto.cpp:64–92

* Perform the actual key exchange. * @param peer_public_key The public key chosen by the other participant of the key exchange. * @param side Whether we are the client or server; used to hash the public key of us and the peer in the right order. * @param our_secret_key The secret key of us. * @param our_public_key The public key of us. * @param extra_payload Extra payload to put into the hash

 * @return True when the key exchange has succeeded, false when an illegal public key was given.
 */
bool X25519DerivedKeys::Exchange(const X25519PublicKey &peer_public_key, X25519KeyExchangeSide side,
		const X25519SecretKey &our_secret_key, const X25519PublicKey &our_public_key, std::string_view extra_payload)
{
	X25519Key shared_secret;
	crypto_x25519(shared_secret.data(), our_secret_key.data(), peer_public_key.data());
	if (std::all_of(shared_secret.begin(), shared_secret.end(), [](auto v) { return v == 0; })) {
		/* A shared secret of all zeros means that the peer tried to force the shared secret to a known constant. */
		return false;
	}

	crypto_blake2b_ctx ctx;
	crypto_blake2b_init(&ctx, this->keys.size());
	crypto_blake2b_update(&ctx, shared_secret.data(), shared_secret.size());
	switch (side) {
		case X25519KeyExchangeSide::SERVER:
			crypto_blake2b_update(&ctx, our_public_key.data(), our_public_key.size());
			crypto_blake2b_update(&ctx, peer_public_key.data(), peer_public_key.size());
			break;
		case X25519KeyExchangeSide::CLIENT:
			crypto_blake2b_update(&ctx, peer_public_key.data(), peer_public_key.size());
			crypto_blake2b_update(&ctx, our_public_key.data(), our_public_key.size());
			break;
		default:
			NOT_REACHED();
	}
	crypto_blake2b_update(&ctx, reinterpret_cast<const uint8_t *>(extra_payload.data()), extra_payload.size());
	crypto_blake2b_final(&ctx, this->keys.data());
	return true;
}

/**
 * Encryption handler implementation for monocypher encryption after a X25519 key exchange.