Enums and Masks – Encryption

The RFM69CW/RFM69HCW module (based on the Semtech SX1231/SX1231H) has built in support for 128bit Advanced Encryption Standard(AES) encoding of message payloads. To make encryption easy to configure I added some additional constants and enumerations for the other settings configured in RegPacketConfig2.

// RegPacketConfig2
private const byte InterPacketRxDelayDefault = 0;
public const byte InterPacketRxDelayMinimum = 0x0;
public const byte InterPacketRxDelayMaximum = 0xF;

private const bool RestartRxDefault = false;
[Flags]
private enum RegPacketConfig2RestartRxDefault : byte
{
	Off = 0b00000000,
	On = 0b00000100,
}

private const bool AutoRestartRxDefault = true;
[Flags]
private enum RegPacketConfig2AutoRestartRxDefault : byte
{
	Off = 0b00000000,
	On = 0b00000010,
}

[Flags]
private enum RegPacketConfig2Aes : byte
{
	Off = 0b00000000,
	On = 0b00000001,
}
public const byte AesKeyLength = 16;

I then added some guard conditions to the initialise method to validate the InterPacketRxDelay and the encryption key length.

public void Initialise(RegOpModeMode modeAfterInitialise,
	BitRate bitRate = BitRateDefault,
	ushort frequencyDeviation = frequencyDeviationDefault,
	double frequency = FrequencyDefault,
	ListenModeIdleResolution listenModeIdleResolution = ListenModeIdleResolutionDefault, ListenModeRXTime listenModeRXTime = ListenModeRXTimeDefault, ListenModeCrieria listenModeCrieria = ListenModeCrieriaDefault, ListenModeEnd listenModeEnd = ListenModeEndDefault,
	byte listenCoefficientIdle = ListenCoefficientIdleDefault,
	byte listenCoefficientReceive = ListenCoefficientReceiveDefault,
	bool pa0On = pa0OnDefault, bool pa1On = pa1OnDefaut, bool pa2On = pa2OnDefault, byte outputpower = OutputpowerDefault,
	PaRamp paRamp = PaRampDefault,
	bool ocpOn = OcpOnDefault, byte ocpTrim = OcpTrimDefault,
	LnaZin lnaZin = LnaZinDefault, LnaCurrentGain lnaCurrentGain = LnaCurrentGainDefault, LnaGainSelect lnaGainSelect = LnaGainSelectDefault,
	byte dccFrequency = DccFrequencyDefault, RxBwMant rxBwMant = RxBwMantDefault, byte RxBwExp = RxBwExpDefault,
	byte dccFreqAfc = DccFreqAfcDefault, byte rxBwMantAfc = RxBwMantAfcDefault, byte bxBwExpAfc = RxBwExpAfcDefault,
	ushort preambleSize = PreambleSizeDefault,
	bool syncOn = SyncOnDefault, SyncFifoFileCondition syncFifoFileCondition = SyncFifoFileConditionDefault, byte syncSize = SyncSizeDefault, byte syncTolerance = SyncToleranceDefault, byte[] syncValues = null,
	RegPacketConfig1PacketFormat packetFormat = RegPacketConfig1PacketFormat.FixedLength,
	RegPacketConfig1DcFree packetDcFree = RegPacketConfig1DcFreeDefault,
	bool packetCrc = PacketCrcOnDefault,
	bool packetCrcAutoClearOff = PacketCrcAutoClearOffDefault,
	RegPacketConfig1CrcAddressFiltering packetAddressFiltering = PacketAddressFilteringDefault,
	byte payloadLength = PayloadLengthDefault,
	byte addressNode = NodeAddressDefault, byte addressbroadcast = BroadcastAddressDefault,
	TxStartCondition txStartCondition = TxStartConditionDefault, byte fifoThreshold = FifoThresholdDefault,
	byte interPacketRxDelay = InterPacketRxDelayDefault, bool restartRx = RestartRxDefault, bool autoRestartRx = AutoRestartRxDefault,
	byte[] aesKey = null
)
{
	RegOpModeModeCurrent = modeAfterInitialise;
	PacketFormat = packetFormat;

	#region Guard Conditions
	if ((interPacketRxDelay < InterPacketRxDelayMinimum ) || (interPacketRxDelay &gt; InterPacketRxDelayMaximum))
	{
		throw new ArgumentException($"The interPacketRxDelay must be between {InterPacketRxDelayMinimum} and {InterPacketRxDelayMaximum}", "interPacketRxDelay");
	}
	if ((aesKey != null) &amp;&amp; (aesKey.Length != AesKeyLength))
	{
		throw new ArgumentException($"The AES key must be {AesKeyLength} bytes", "aesKey");
	}
	#endregion

This required some modifications to the run method to catch the new exceptions gracefully.

public void Run(IBackgroundTaskInstance taskInstance)
{
	byte[] syncValues ={0xAA, 0x2D, 0xD4};
	byte[] aesKeyValues = {0x0, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0X0E, 0X0F };

	rfm69Device.RegisterDump();

	try
	{
		rfm69Device.Initialise(Rfm69HcwDevice.RegOpModeMode.StandBy,
			bitRate: Rfm69HcwDevice.BitRate.bps4K8,
			frequency: 915000000.0, frequencyDeviation: 0X023d,
			dccFrequency: 0x1,rxBwMant: Rfm69HcwDevice.RxBwMant.RxBwMant20, RxBwExp:0x2,
			preambleSize: 16,
			syncSize: 3,
			syncValues: syncValues,
			packetFormat: Rfm69HcwDevice.RegPacketConfig1PacketFormat.VariableLength,
			packetCrc:true,
			aesKey: aesKeyValues
			);

		rfm69Device.RegisterDump();

		// RegDioMapping1
		rfm69Device.RegisterManager.WriteByte(0x26, 0x01);

		rfm69Device.RegisterDump();
		while (true)
		{
			string message = "hello world " + DateTime.Now.ToLongTimeString();

			byte[] messageBuffer = UTF8Encoding.UTF8.GetBytes(message);

			Debug.WriteLine("{0:HH:mm:ss.fff} Send-{1}", DateTime.Now, message);
			rfm69Device.SendMessage(messageBuffer);

			Debug.WriteLine("{0:HH:mm:ss.fff} Send-Done", DateTime.Now);

			Task.Delay(5000).Wait();
		}
	}
	catch( Exception ex)
	{
		Debug.WriteLine(ex.Message);
	}
}

The Arduino client code works though I need modify it so I can do more testing of the initialise method parameter options.