private static int GetHashLength(OtpAlgorithm algorithm)
{
switch (algorithm)
{
case OtpAlgorithm.MD5: return(32);
case OtpAlgorithm.SHA1: return(20);
case OtpAlgorithm.SHA256: return(32);
case OtpAlgorithm.SHA512: return(64);
}
throw new InvalidOperationException();
}
private static HMAC GetHMAC(OtpAlgorithm algorithm, byte[] key)
{
switch (algorithm)
{
case OtpAlgorithm.MD5: return(new HMACMD5(key));
case OtpAlgorithm.SHA1: return(new HMACSHA1(key));
case OtpAlgorithm.SHA256: return(new HMACSHA256(key));
case OtpAlgorithm.SHA512: return(new HMACSHA512(key));
}
throw new InvalidOperationException();
}
public OtpAuthenticator(OtpType type, OtpAlgorithm algorithm = OtpAlgorithm.SHA1, byte[] key = null)
{
HMAC = GetHMAC(algorithm, key ?? GenerateKey(algorithm));
Type = type;
}
public static byte[] GenerateKey(OtpAlgorithm algorithm)
{
return(GenerateKey(GetHashLength(algorithm)));
}
public static string GetUri(OtpType type, byte[] key, string accountName, string issuer = "", OtpAlgorithm algorithm = OtpAlgorithm.SHA1,
int codeLength = 6, long counter = 0, int period = 30)
{
StringBuilder SB = new StringBuilder();
SB.AppendFormat("otpauth://{0}/", type.ToString().ToLower());
if (!string.IsNullOrEmpty(issuer))
{
SB.AppendFormat("{0}:{1}?issuer={0}&", Uri.EscapeUriString(issuer), Uri.EscapeUriString(accountName));
}
else
{
SB.AppendFormat("{0}?", Uri.EscapeUriString(accountName));
}
SB.AppendFormat("secret={0}&algorithm={1}&digits={2}&", Base32.Encode(key), algorithm, codeLength);
if (type == OtpType.HOTP)
{
SB.AppendFormat("counter={0}", counter);
}
else
{
SB.AppendFormat("period={0}", period);
}
return(SB.ToString());
}
