private byte[] GenerateIv(MBusHeader header)
{
if (header.EncryptionScheme == EncryptionScheme.AesCtr)
{
return(GenerateCounterModeIV(header));
}
return(GenerateGenericIV(header));
}
private byte[] GenerateGenericIV(MBusHeader header)
{
var initializationVector = new List <byte>();
initializationVector.AddRange(header.GetMAVDBytes);
for (var i = 0; i < 8; i++)
{
initializationVector.Add(header.GetAccessNumber); //Access number is one byte
}
return(initializationVector.ToArray());
}
/// <summary>
/// parse the payload.
/// </summary>
/// <param name="header">the mbus header. Used for manufacturer specific parsing.</param>
/// <param name="payload">the payload.</param>
/// <param name="decryptionKey">the decryption key.</param>
/// <param name="initializationVector">the initialization vector.</param>
/// <returns>the mbus telegram.</returns>
public MBusTelegram ParsePayload(MBusHeader header, IList <byte> payload, byte[] decryptionKey = null)
{
double?rssi = null;
// todo refactor to be able to return rssi
if (header.IsWireless)
{
rssi = -payload.Last() / 2;
payload = payload.Take(payload.Count - 1).ToArray();
}
IList <VariableDataRecord>?records = this.ParseRecords(
header,
payload,
decryptionKey);
return(new MBusTelegram(header, records, rssi));
}
private byte[] GenerateCounterModeIV(MBusHeader header, byte[]?frameNumber = null, byte blockCounter = 0b00000000)
{
var extendedLinkLayer = header.ExtendedLinkLayer;
if (frameNumber == null)
{
frameNumber = new byte[] { 0x00, 0x00 };
}
var initializationVector = new List <byte>();
initializationVector.AddRange(header.GetMAVDBytes);
byte commControl = extendedLinkLayer.GetCommunicationControlByte.Mask(0b1110_1111);
initializationVector.Add(commControl);
initializationVector.AddRange(extendedLinkLayer.GetSessionNumberBytes);
initializationVector.AddRange(frameNumber);
initializationVector.Add(blockCounter);
return(initializationVector.ToArray());
}
/// <summary>
/// parse the records.
/// </summary>
/// <param name="header">the mbus header. Useful for manufacturer specific parsing.</param>
/// <param name="payload">the payload.</param>
/// <param name="decryptionKey">the decryption key.</param>
/// <param name="initializationVector">the initialization vector.</param>
/// <returns>a IList<MbusRecord> containing the parse records.</returns>
private IList <VariableDataRecord> ParseRecords(MBusHeader header, IList <byte> payload, byte[] decryptionKey)
{
List <byte> payloadBody;
// Todo find out whats wrong with this.
if (header.ExtendedLinkLayer != null)
{
payloadBody = payload.Skip(header.PayloadStartsAtIndex - 2).ToList();
}
else
{
payloadBody = payload.Skip(header.PayloadStartsAtIndex).ToList();
}
if (decryptionKey != null)
{
payloadBody = DecryptPayload(header, payloadBody, decryptionKey);
}
if (payloadBody == null)
{
return(null);
}
if (header.ExtendedLinkLayer != null)
{
var frameType = ControlInformationLookup.Find(payloadBody.First()).frameType;
if (frameType != FrameType.Full)
{
return(null);
}
payloadBody = payloadBody.Skip(1).ToList();
}
while (payloadBody.Last() == 0x2F)
{
payloadBody.RemoveAt(payloadBody.Count() - 1);
}
var list = new List <VariableDataRecord>();
// MBus has a maximum length of 255.
byte indexer = 0;
while (indexer < payloadBody.Count)
{
var difFieldByte = payloadBody[indexer++];
// TODO Handle special case stuff
if (difFieldByte == 0x1F || difFieldByte == 0x0F)
{
break;
}
var dataInformationField = new DataInformationField(difFieldByte);
var dataInformationFieldExtensions = new List <DataInformationExtensionField>();
var difesAvailable = dataInformationField.HasExtensionBit;
while (difesAvailable)
{
var extension = new DataInformationExtensionField(payloadBody[indexer++]);
dataInformationFieldExtensions.Add(extension);
difesAvailable = extension.HasExtensionBit;
}
var valueInformationField = new PrimaryValueInformationField(payloadBody[indexer++], dataInformationField.DataField);
var valueInformationFieldExtensions = new List <ValueInformationExtensionField>();
var vifesAvailable = valueInformationField.HasExtensionBit;
while (vifesAvailable)
{
ValueInformationExtensionField?extension = null;
if (!valueInformationFieldExtensions.Any())
{
switch (valueInformationField.Type)
{
case PrimaryValueInformation.FBValueInformationExtension:
extension = new FBValueInformationExtensionField(payloadBody[indexer++]);
break;
case PrimaryValueInformation.FDValueInformationExtension:
extension = new FDValueInformationExtensionField(payloadBody[indexer++]);
break;
case PrimaryValueInformation.ManufacturerSpecific:
switch (header.ManufacturerName.ToLowerInvariant())
{
case "kam":
extension = new KamstrupValueInformationExtensionField(payloadBody[indexer++]);
break;
}
break;
default:
extension = new UnknownValueInformationExtensionField(payloadBody[indexer++]);
break;
}
}
else
{
extension = new OrthogonalValueInformationExtensionField(payloadBody[indexer++]);
}
valueInformationFieldExtensions.Add(extension);
vifesAvailable = extension.HasExtensionBit;
}
// is LVAR, the length of the data is in the first byte of the "real" data.
if (dataInformationField.DataLength == null && dataInformationField.DataField == DataField.VariableLength)
{
dataInformationField.DataLength = payloadBody[indexer++];
}
var dataBlock = new DataBlock(payloadBody.Skip(indexer).Take(dataInformationField.DataLength.Value).ToArray(), dataInformationField, dataInformationFieldExtensions, valueInformationField, valueInformationFieldExtensions);
indexer = (byte)(indexer + dataInformationField.DataLength.Value);
list.Add(new VariableDataRecord(dataBlock));
}
return(list);
}
private List <byte> DecryptPayload(MBusHeader header, List <byte> payloadBody, byte[] decryptionKey)
{
var encryptionScheme = header.EncryptionScheme;
if (encryptionScheme == EncryptionScheme.NoEncryption)
{
return(payloadBody);
}
var initializationVector = GenerateIv(header);
List <byte>? decryptionResult = null;
IEnumerable <byte> bytesToBeDecrypted;
var remainderBytes = new List <byte>();
// For CTR we need to decrypt the entire payload from the Extended linklayer. Plus the two CRC bytes before the payload (these need to be removed after decryption)
if (encryptionScheme == EncryptionScheme.AesCtr)
{
bytesToBeDecrypted = payloadBody;
}
else
{
// It is CBC, DES, or something else than CTR
// These encryption schemes can be implemented in two ways:
// 1 - All of the payload is encrypted, and if the payload isnt exactly a fit with encryption-block sizes, it puts "fill bytes" (2F) in the trailer of the (unencrypted) payload.
// 2 - It encrypts what it can, and leaves a remainder of unencrypted bytes in the end of the payload.
int decryptionBlockSize;
// For 128-bit AES a decryption blocksize is 16
// For 128-bit DES it is 8
if (encryptionScheme == EncryptionScheme.DesCbcIvIsZero || encryptionScheme == EncryptionScheme.DesCbc)
{
decryptionBlockSize = 8;
}
else
{
decryptionBlockSize = 16;
}
// Find out how many encrypted blocks the payload contains
var numberOfBlocks = header.Configuration.NumberOfEncryptedBlocks;
// Find out how many of the bytes in the payload are actually encrypted
var numberOfBytesToDecrypt = decryptionBlockSize * numberOfBlocks;
// Retrieve the number of bytes to decrypted
bytesToBeDecrypted = payloadBody.Take(numberOfBytesToDecrypt);
// If there is a remainder, keep it for later use.
remainderBytes = payloadBody.Skip(numberOfBytesToDecrypt).ToList();
}
decryptionResult = DecryptBytes(decryptionKey, initializationVector, bytesToBeDecrypted, encryptionScheme);
int decryptionValidationSize = 2;
// The first two bytes of CTR decryption is CRC bytes, and first two bytes of any other is "validation bytes" (2 x 0x2F), extract these in order to validate if decryption was successful.
if (!DecryptionSuccessful(decryptionResult.ToArray(), encryptionScheme))
{
//throw new MBusDecryptionException($"Decryption-check failed. Key: {key.ToHexString()}, IV: {initializationVector.ToHexString()}");
return(null);
}
// Remove the two validation bytes
decryptionResult = decryptionResult.Skip(decryptionValidationSize).ToList();
// Add the last bunch of bytes which were sent unencrypted, if there is any
decryptionResult.AddRange(remainderBytes);
return(decryptionResult);
}
/// <summary>
/// Initializes a new instance of the <see cref="MBusTelegram"/> class.
/// </summary>
/// <param name="header"><see cref="MBusHeader"/>.</param>
/// <param name="records">A list of <see cref="MbusRecord"/>'s.</param>
/// <param name="rssi">RSSI-value if the telegram was from a wireless mbus.</param>
public MBusTelegram(MBusHeader header, IList <VariableDataRecord>?records, double?rssi)
{
Header = header;
Rssi = rssi;
Records = records;
}