OATH.Net is a .NET library to perform OATH authentication.

Built for .NET Standard 2.0, so it should work on .NET Framework 4.6.1 or .NET Core 2.0.

Add to your project with "Install-Package OATH.Net".

// Time-based OTP

public bool CreateTOTPCode(User user)
{
    string secretKey = user.SecretKey;
    int otpDigits = 8;

    Key key = new Key();         // Generate a new key
    user.SecretKey = key.Base32; // Persist this for later

    TimeBasedOtpGenerator otp = new TimeBasedOtpGenerator(key, otpDigits);
    return otp.GenerateOtp(DateTime.UtcNow);
}

public bool AuthorizedWithTOTP(string userSuppliedCode, User user)
{
    int otpDigits = 8;
    Key key = new Key(user.SecretKey);

    TimeBasedOtpGenerator otp = new TimeBasedOtpGenerator(key, otpDigits);
    return otp.ValidateOtp(userSuppliedCode, DateTime.UtcNow);
}


// Counter-based OTP

public bool AuthorizedWithHOTP(string userSuppliedCode, User user)
{
    int otpDigits = 8;
    int counterValue = user.NextCounterValue();
    Key key = new Key(user.SecretKey);

    CounterBasedOtpGenerator otp = new CounterBasedOtpGenerator(key, otpDigits);
    string validCode = otp.GenerateOtp(counterValue);

    return userSuppliedCode == validCode;
}

Visual Studio should build the project correctly with no effort.

A Psake build script is included for running tests and creating NuGet packages. To use Psake:

1. Open Psake by importing Psake.psm1 into a PowerShell session, or run Psake.cmd to create a session with Psake already imported.

2. Run Invoke-psake build to build the project.

3. Run Invoke-psake test to run all unit tests.

OATH.Net is on GitHub:

https://github.com/jennings/OATH.Net

Copyright 2011 Stephen Jennings

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.