Xts.cs

using System;
using System.Security.Cryptography;

namespace XTSSharp;

public class Xts
{
    private readonly SymmetricAlgorithm _key1;
    private readonly SymmetricAlgorithm _key2;

    protected Xts(Func<SymmetricAlgorithm> create, byte[] key1, byte[] key2)
    {
        if (create == null)
        {
            throw new ArgumentNullException(nameof(create));
        }
        if (key1 == null)
        {
            throw new ArgumentNullException(nameof(key1));
        }
        if (key2 == null)
        {
            throw new ArgumentNullException(nameof(key2));
        }
        _key1 = create();
        _key2 = create();
        if (key1.Length != key2.Length)
        {
            throw new ArgumentException("Key lengths don't match");
        }
        _key1.KeySize = key1.Length * 8;
        _key2.KeySize = key2.Length * 8;
        _key1.Key = key1;
        _key2.Key = key2;
        _key1.Mode = CipherMode.ECB;
        _key2.Mode = CipherMode.ECB;
        _key1.Padding = PaddingMode.None;
        _key2.Padding = PaddingMode.None;
        _key1.BlockSize = 128;
        _key2.BlockSize = 128;
    }

    public XtsCryptoTransform CreateEncryptor()
    {
        return new XtsCryptoTransform(_key1.CreateEncryptor(), _key2.CreateEncryptor(), false);
    }

    public XtsCryptoTransform CreateDecryptor()
    {
        return new XtsCryptoTransform(_key1.CreateDecryptor(), _key2.CreateEncryptor(), true);
    }

    protected static byte[] VerifyKey(int expectedSize, byte[] key)
    {
        if (key == null)
        {
            throw new ArgumentNullException(nameof(key));
        }
        if (key.Length * 8 != expectedSize)
        {
            throw new ArgumentException($"Expected key length of {expectedSize} bits, got {key.Length * 8}");
        }
        return key;
    }
}