InMemoryKey.cs

using System;
using System.Security.Cryptography;

namespace Fire.Authentication.Private;

public class InMemoryKey : IKeyProvider
{
	private readonly byte[] _keyData;

	public InMemoryKey(byte[] key)
	{
		_keyData = key ?? throw new ArgumentNullException(nameof(key));
		if (_keyData.Length <= 0)
		{
			throw new ArgumentException("The key must not be empty");
		}
	}

	internal byte[] GetCopyOfKey()
	{
		return (byte[])_keyData.Clone();
	}

	public byte[] ComputeHmac(OtpHashMode mode, byte[] data)
	{
		using HMAC hmac = CreateHmacHash(mode);
		byte[] key = GetCopyOfKey();
		try
		{
			hmac.Key = key;
			return hmac.ComputeHash(data);
		}
		finally
		{
			KeyUtilities.Destroy(key);
		}
	}

	private static HMAC CreateHmacHash(OtpHashMode otpHashMode)
	{
		return otpHashMode switch
		{
			OtpHashMode.Sha256 => new HMACSHA256(),
			OtpHashMode.Sha512 => new HMACSHA512(),
			_ => new HMACSHA1() // OtpHashMode.Sha1 or default
		};
	}
}