/// <summary>
/// This method uses the Windows Runtime APIs to provide the crypto algorithm.
/// HMAC computes a Hashed Message Authentication Code with the
/// crypto hash algorithm as a parameter.
/// </summary>
/// <param name="crypto">The crypto algorithm.</param>
/// <param name="keyBytes">The bytes to use for the HMAC key.</param>
/// <param name="text">The message or text to be authenticated.</param>
/// <returns></returns>
public static byte[] HmacSha(MacAlgorithmEnum crypto, byte[] keyBytes,
byte[] text)
{
// Select crypto algorithm
MacAlgorithmProvider macAlgorithmProvider = null;
switch (crypto)
{
case MacAlgorithmEnum.HmacSha1:
macAlgorithmProvider = MacAlgorithmProvider.OpenAlgorithm(MacAlgorithmNames.HmacSha1);
break;
case MacAlgorithmEnum.HmacSha256:
macAlgorithmProvider = MacAlgorithmProvider.OpenAlgorithm(MacAlgorithmNames.HmacSha256);
break;
case MacAlgorithmEnum.HmacSha512:
macAlgorithmProvider = MacAlgorithmProvider.OpenAlgorithm(MacAlgorithmNames.HmacSha512);
break;
}
if (macAlgorithmProvider == null)
{
throw new InvalidOperationException("MacAlgorithmProvider failed to initialize.");
}
// Get buffer
var keyBuffer = CryptographicBuffer.CreateFromByteArray(keyBytes);
if (keyBuffer == null)
{
throw new InvalidOperationException("Invaild Key buffer.");
}
var key = macAlgorithmProvider.CreateKey(keyBuffer);
if (key == null)
{
throw new InvalidOperationException("Invaild Key.");
}
// Get hash
var dataBuffer = CryptographicBuffer.CreateFromByteArray(text);
if (dataBuffer == null)
{
throw new InvalidOperationException("Invaild data buffer.");
}
// Sign hash
var dataBufferSigned = CryptographicEngine.Sign(key, dataBuffer);
if (dataBufferSigned == null)
{
throw new InvalidOperationException("Invaild signed data.");
}
byte[] hashBytes;
CryptographicBuffer.CopyToByteArray(dataBufferSigned, out hashBytes);
return(hashBytes);
}
/// <summary>
/// This method generates a TOTP value for the given
/// set of parameters.
/// </summary>
/// <param name="key">The shared secret, HEX encoded</param>
/// <param name="time">A value that reflects a time</param>
/// <param name="returnDigits">Number of digits to return</param>
/// <param name="crypto">The crypto function to use</param>
/// <returns>A numeric string in base 10 that includes
/// {@link truncationDigits} digits
/// </returns>
public static string GenerateTotp(string key,
string time,
int returnDigits,
MacAlgorithmEnum crypto)
{
var codeDigits = returnDigits;
// Using the counter
// First 8 bytes are for the movingFactor
// Compliant with base RFC 4226 (HOTP)
while (time.Length < 16)
{
time = "0" + time;
}
// Get the HEX in a Byte[]
var msg = StringToByteArray(time);
var k = StringToByteArray(key);
var hash = HmacSha(crypto, k, msg);
// put selected bytes into result int
var offset = hash[hash.Length - 1] & 0xf;
var binary =
((hash[offset] & 0x7f) << 24) |
((hash[offset + 1] & 0xff) << 16) |
((hash[offset + 2] & 0xff) << 8) |
(hash[offset + 3] & 0xff);
var otp = binary % DigitsPower[codeDigits];
var result = otp.ToString();
while (result.Length < codeDigits)
{
result = "0" + result;
}
return(result);
}
