/// <summary>
/// Create Session Key
/// </summary>
/// <param name="bdk">Base Derivation Key</param>
/// <param name="ksn">Key Serial Number</param>
/// <param name="dukptVariant">DUKPT variant used to determine session key creation method</param>
/// <returns>Session Key</returns>
private static BigInteger CreateSessionKey(string bdk, string ksn, DUKPTVariant dukptVariant)
{
BigInteger ksnBigInt = ksn.HexToBigInteger();
BigInteger ipek = CreateIpek(ksnBigInt, bdk.HexToBigInteger());
BigInteger sessionKey;
if (dukptVariant == DUKPTVariant.Data)
{
sessionKey = CreateSessionKeyDEK(ipek, ksnBigInt);
}
else
{
sessionKey = CreateSessionKeyPEK(ipek, ksnBigInt);
}
return(sessionKey);
}
/// <summary>
/// Decrypt data using TDES DUKPT.
/// </summary>
/// <param name="bdk">Base Derivation Key</param>
/// <param name="ksn">Key Serial Number</param>
/// <param name="encryptedData">Data to decrypt</param>
/// <param name="variant">DUKPT transaction key variant</param>
/// <returns>Decrypted data</returns>
/// <exception cref="ArgumentNullException">Thrown for null or empty parameter values</exception>
public static byte[] Decrypt(string bdk, string ksn, byte[] encryptedData, DUKPTVariant variant)
{
if (string.IsNullOrEmpty(bdk))
{
throw new ArgumentNullException(nameof(bdk));
}
if (string.IsNullOrEmpty(ksn))
{
throw new ArgumentNullException(nameof(ksn));
}
if (encryptedData == null)
{
throw new ArgumentNullException(nameof(encryptedData));
}
return(Transform("TripleDES", false, CreateSessionKey(bdk, ksn, variant), encryptedData.ToBigInteger()).GetBytes());
}