// Server -> Client
// - only sequence number
// - error code (optional)
func (verify *VerifyServerController) handlePairVerifyFinish(in util.Container) (util.Container, error) {
	verify.step = VerifyStepFinishResponse

	data := in.GetBytes(TagEncryptedData)
	message := data[:(len(data) - 16)]
	var mac [16]byte
	copy(mac[:], data[len(message):]) // 16 byte (MAC)
	log.Debug.Println("->     Message:", hex.EncodeToString(message))
	log.Debug.Println("->     MAC:", hex.EncodeToString(mac[:]))

	decryptedBytes, err := chacha20poly1305.DecryptAndVerify(verify.session.EncryptionKey[:], []byte("PV-Msg03"), message, mac, nil)

	out := util.NewTLV8Container()
	out.SetByte(TagSequence, verify.step.Byte())

	if err != nil {
		verify.reset()
		log.Info.Panic(err)
		out.SetByte(TagErrCode, ErrCodeAuthenticationFailed.Byte()) // return error 2
	} else {
		in, err := util.NewTLV8ContainerFromReader(bytes.NewBuffer(decryptedBytes))
		if err != nil {
			return nil, err
		}

		username := in.GetString(TagUsername)
		signature := in.GetBytes(TagSignature)
		log.Debug.Println("    client:", username)
		log.Debug.Println(" signature:", hex.EncodeToString(signature))

		entity, err := verify.database.EntityWithName(username)
		if err != nil {
			return nil, fmt.Errorf("Client %s is unknown", username)
		}

		if len(entity.PublicKey) == 0 {
			return nil, fmt.Errorf("No LTPK available for client %s", username)
		}

		var material []byte
		material = append(material, verify.session.OtherPublicKey[:]...)
		material = append(material, []byte(username)...)
		material = append(material, verify.session.PublicKey[:]...)

		if crypto.ValidateED25519Signature(entity.PublicKey, material, signature) == false {
			log.Debug.Println("signature is invalid")
			verify.reset()
			out.SetByte(TagErrCode, ErrCodeUnknownPeer.Byte()) // return error 4
		} else {
			log.Debug.Println("signature is valid")
		}
	}

	return out, nil
}
// Server -> Client
// - B: server public key
// - encrypted message
//      - username
//      - signature: from server session public key, server name, client session public key
//
// Client -> Server
// - encrypted message
//      - username
//      - signature: from client session public key, server name, server session public key,
func (verify *VerifyClientController) handlePairStepVerifyResponse(in util.Container) (util.Container, error) {
	serverPublicKey := in.GetBytes(TagPublicKey)
	if len(serverPublicKey) != 32 {
		return nil, fmt.Errorf("Invalid server public key size %d", len(serverPublicKey))
	}

	var otherPublicKey [32]byte
	copy(otherPublicKey[:], serverPublicKey)
	verify.session.GenerateSharedKeyWithOtherPublicKey(otherPublicKey)
	verify.session.SetupEncryptionKey([]byte("Pair-Verify-Encrypt-Salt"), []byte("Pair-Verify-Encrypt-Info"))

	fmt.Println("Client")
	fmt.Println("->   B:", hex.EncodeToString(serverPublicKey))
	fmt.Println("     S:", hex.EncodeToString(verify.session.PrivateKey[:]))
	fmt.Println("Shared:", hex.EncodeToString(verify.session.SharedKey[:]))
	fmt.Println("     K:", hex.EncodeToString(verify.session.EncryptionKey[:]))

	// Decrypt
	data := in.GetBytes(TagEncryptedData)
	message := data[:(len(data) - 16)]
	var mac [16]byte
	copy(mac[:], data[len(message):]) // 16 byte (MAC)

	decryptedBytes, err := chacha20poly1305.DecryptAndVerify(verify.session.EncryptionKey[:], []byte("PV-Msg02"), message, mac, nil)
	if err != nil {
		return nil, err
	}

	decryptedIn, err := util.NewTLV8ContainerFromReader(bytes.NewBuffer(decryptedBytes))
	if err != nil {
		return nil, err
	}

	username := decryptedIn.GetString(TagUsername)
	signature := decryptedIn.GetBytes(TagSignature)

	fmt.Println("    Username:"******"   Signature:", hex.EncodeToString(signature))

	// Validate signature
	var material []byte
	material = append(material, verify.session.OtherPublicKey[:]...)
	material = append(material, username...)
	material = append(material, verify.session.PublicKey[:]...)

	entity := verify.database.EntityWithName(username)
	if entity == nil {
		return nil, fmt.Errorf("Server %s is unknown", username)
	}

	if len(entity.PublicKey()) == 0 {
		return nil, fmt.Errorf("No LTPK available for client %s", username)
	}

	if crypto.ValidateED25519Signature(entity.PublicKey(), material, signature) == false {
		return nil, fmt.Errorf("Could not validate signature")
	}

	out := util.NewTLV8Container()
	out.SetByte(TagSequence, VerifyStepFinishRequest.Byte())

	encryptedOut := util.NewTLV8Container()
	encryptedOut.SetString(TagUsername, verify.client.Name())

	material = make([]byte, 0)
	material = append(material, verify.session.PublicKey[:]...)
	material = append(material, verify.client.Name()...)
	material = append(material, verify.session.OtherPublicKey[:]...)

	signature, err = crypto.ED25519Signature(verify.client.PrivateKey(), material)
	if err != nil {
		return nil, err
	}

	encryptedOut.SetBytes(TagSignature, signature)

	encryptedBytes, mac, _ := chacha20poly1305.EncryptAndSeal(verify.session.EncryptionKey[:], []byte("PV-Msg03"), encryptedOut.BytesBuffer().Bytes(), nil)

	out.SetBytes(TagEncryptedData, append(encryptedBytes, mac[:]...))

	return out, nil
}
// Client -> Server
// - encrypted tlv8: entity ltpk, entity name and signature (of H, entity name, ltpk)
// - auth tag (mac)
//
// Server
// - Validate signature of encrpyted tlv8
// - Read and store entity ltpk and name
//
// Server -> Client
// - encrpyted tlv8: bridge ltpk, bridge name, signature (of hash, bridge name, ltpk)
func (setup *SetupServerController) handleKeyExchange(in util.Container) (util.Container, error) {
	out := util.NewTLV8Container()

	setup.step = PairStepKeyExchangeResponse

	out.SetByte(TagSequence, setup.step.Byte())

	data := in.GetBytes(TagEncryptedData)
	message := data[:(len(data) - 16)]
	var mac [16]byte
	copy(mac[:], data[len(message):]) // 16 byte (MAC)
	log.Debug.Println("->     Message:", hex.EncodeToString(message))
	log.Debug.Println("->     MAC:", hex.EncodeToString(mac[:]))

	decrypted, err := chacha20poly1305.DecryptAndVerify(setup.session.EncryptionKey[:], []byte("PS-Msg05"), message, mac, nil)

	if err != nil {
		setup.reset()
		log.Info.Panic(err)
		out.SetByte(TagErrCode, ErrCodeUnknown.Byte()) // return error 1
	} else {
		decryptedBuf := bytes.NewBuffer(decrypted)
		in, err := util.NewTLV8ContainerFromReader(decryptedBuf)
		if err != nil {
			return nil, err
		}

		username := in.GetString(TagUsername)
		clientltpk := in.GetBytes(TagPublicKey)
		signature := in.GetBytes(TagSignature)
		log.Debug.Println("->     Username:"******"->     ltpk:", hex.EncodeToString(clientltpk))
		log.Debug.Println("->     Signature:", hex.EncodeToString(signature))

		// Calculate hash `H`
		hash, _ := hkdf.Sha512(setup.session.PrivateKey, []byte("Pair-Setup-Controller-Sign-Salt"), []byte("Pair-Setup-Controller-Sign-Info"))
		var material []byte
		material = append(material, hash[:]...)
		material = append(material, []byte(username)...)
		material = append(material, clientltpk...)

		if crypto.ValidateED25519Signature(clientltpk, material, signature) == false {
			log.Debug.Println("ed25519 signature is invalid")
			setup.reset()
			out.SetByte(TagErrCode, ErrCodeAuthenticationFailed.Byte()) // return error 2
		} else {
			log.Debug.Println("ed25519 signature is valid")
			// Store entity ltpk and name
			entity := db.NewEntity(username, clientltpk, nil)
			setup.database.SaveEntity(entity)
			log.Debug.Printf("Stored ltpk '%s' for entity '%s'\n", hex.EncodeToString(clientltpk), username)

			ltpk := setup.device.PublicKey()
			ltsk := setup.device.PrivateKey()

			// Send username, ltpk, signature as encrypted message
			hash, err := hkdf.Sha512(setup.session.PrivateKey, []byte("Pair-Setup-Accessory-Sign-Salt"), []byte("Pair-Setup-Accessory-Sign-Info"))
			material = make([]byte, 0)
			material = append(material, hash[:]...)
			material = append(material, []byte(setup.session.Username)...)
			material = append(material, ltpk...)

			signature, err := crypto.ED25519Signature(ltsk, material)
			if err != nil {
				log.Info.Panic(err)
				return nil, err
			}

			tlvPairKeyExchange := util.NewTLV8Container()
			tlvPairKeyExchange.SetBytes(TagUsername, setup.session.Username)
			tlvPairKeyExchange.SetBytes(TagPublicKey, ltpk)
			tlvPairKeyExchange.SetBytes(TagSignature, []byte(signature))

			log.Debug.Println("<-     Username:"******"<-     ltpk:", hex.EncodeToString(tlvPairKeyExchange.GetBytes(TagPublicKey)))
			log.Debug.Println("<-     Signature:", hex.EncodeToString(tlvPairKeyExchange.GetBytes(TagSignature)))

			encrypted, mac, _ := chacha20poly1305.EncryptAndSeal(setup.session.EncryptionKey[:], []byte("PS-Msg06"), tlvPairKeyExchange.BytesBuffer().Bytes(), nil)
			out.SetByte(TagSequence, PairStepKeyExchangeRequest.Byte())
			out.SetBytes(TagEncryptedData, append(encrypted, mac[:]...))
		}
	}

	return out, nil
}