Generate HMAC-SHA256 hash with BouncyCastle

Question

I need to generate a HMAC-SHA256 hash in a PCL (developing for Xamarin Forms) which doesn't support the .NET built-in HMAC/cryptography classes, so I'm working with BouncyCastle to implement my cryptography classes.

I need to generate a HMAC-SHA256 hash, but I haven't been able to find any example on Google, nor does BouncyCastle seem to have any documentation for this. Can anyone help me out?

Answer 1

Thanks to the solution here I came up with this code:

public class HmacSha256
{
    public byte[] Hash(string text, string key)
    {
        var hmac = new HMac(new Sha256Digest());
        hmac.Init(new KeyParameter(Encoding.UTF8.GetBytes(key)));
        byte[] result = new byte[hmac.GetMacSize()];
        byte[] bytes = Encoding.UTF8.GetBytes(text);

        hmac.BlockUpdate(bytes, 0, bytes.Length);
        hmac.DoFinal(result, 0);

        return result;
    }
}

Corresponding unit test (uses FluentAssertions):

[TestClass]
public class HmacSha256Tests
{
    private readonly HmacSha256 _hmac = new HmacSha256();

    [TestMethod]
    public void Hash_GeneratesValidHash_ForInput()
    {
        // Arrange
        string input = "hello";
        string key = "test";
        string expected = "F151EA24BDA91A18E89B8BB5793EF324B2A02133CCE15A28A719ACBD2E58A986";

        // Act
        byte[] output = _hmac.Hash(input, key);

        string outputHex = BitConverter.ToString(output).Replace("-", "").ToUpper();

        // Assert
        expected.Should().Be(outputHex);
    }
}