Method decrypt

src/microReticulum/Identity.cpp:494–540

Decrypts information for the identity. :param ciphertext: The ciphertext to be decrypted as *bytes*. :returns: Plaintext as *bytes*, or *None* if decryption fails. :raises: *KeyError* if the instance does not hold a private key. */

:raises: *KeyError* if the instance does not hold a private key.
*/
const Bytes Identity::decrypt(const Bytes& ciphertext_token) const {
	assert(_object);
	TRACE("Identity::decrypt: decrypting data...");
	if (!_object->_prv) {
		throw std::runtime_error("Decryption failed because identity does not hold a private key");
	}
	if (ciphertext_token.size() <= Type::Identity::KEYSIZE/8/2) {
		DEBUGF("Decryption failed because the token size %lu was invalid.", ciphertext_token.size());
		return {Bytes::NONE};
	}
	Bytes plaintext;
	try {
		//peer_pub_bytes = ciphertext_token[:Identity.KEYSIZE//8//2]
		Bytes peer_pub_bytes = ciphertext_token.left(Type::Identity::KEYSIZE/8/2);
		//peer_pub = X25519PublicKey.from_public_bytes(peer_pub_bytes)
		//Cryptography::X25519PublicKey::Ptr peer_pub = Cryptography::X25519PublicKey::from_public_bytes(peer_pub_bytes);
		TRACEF("Identity::decrypt: peer public key:      %s", peer_pub_bytes.toHex().c_str());


		// CRYPTO: create shared key for key exchange using peer public key
		//shared_key = _object->_prv->exchange(peer_pub);
		Bytes shared_key = _object->_prv->exchange(peer_pub_bytes);
		TRACEF("Identity::decrypt: shared key:           %s", shared_key.toHex().c_str());

		Bytes derived_key = Cryptography::hkdf(
			DERIVED_KEY_LENGTH,
			shared_key,
			get_salt(),
			get_context()
		);
		TRACEF("Identity::decrypt: derived key:          %s", derived_key.toHex().c_str());

		Cryptography::Token token(derived_key);
		//ciphertext = ciphertext_token[Identity.KEYSIZE//8//2:]
		Bytes ciphertext(ciphertext_token.mid(Type::Identity::KEYSIZE/8/2));
		TRACEF("Identity::decrypt: Token decrypting data of length %lu", ciphertext.size());
		TRACEF("Identity::decrypt: ciphertext: %s", ciphertext.toHex().c_str());
		plaintext = token.decrypt(ciphertext);
		TRACEF("Identity::decrypt: plaintext:  %s", plaintext.toHex().c_str());
		//TRACEF("Identity::decrypt: Token decrypted data of length %lu", plaintext.size());
	}
	catch (const std::exception& e) {
		DEBUGF("Decryption by %s failed: %s", toString().c_str(), e.what());
	}
		
	return plaintext;
}

/*
Signs information by the identity.