AesBCryptModes.cs

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using System;
using System.Security.Cryptography;
using Internal.NativeCrypto;
 
namespace Internal.Cryptography;
 
internal static class AesBCryptModes
{
    private static readonly Lazy<SafeAlgorithmHandle> s_hAlgCbc = OpenAesAlgorithm("ChainingModeCBC");
 
    private static readonly Lazy<SafeAlgorithmHandle> s_hAlgEcb = OpenAesAlgorithm("ChainingModeECB");
 
    private static readonly Lazy<SafeAlgorithmHandle> s_hAlgCfb128 = OpenAesAlgorithm("ChainingModeCFB", 16);
 
    private static readonly Lazy<SafeAlgorithmHandle> s_hAlgCfb8 = OpenAesAlgorithm("ChainingModeCFB", 1);
 
    internal static SafeAlgorithmHandle GetSharedHandle(CipherMode cipherMode, int feedback)
    {
        switch (cipherMode)
        {
        case CipherMode.CFB:
            switch (feedback)
            {
            case 16:
                return s_hAlgCfb128.Value;
            case 1:
                return s_hAlgCfb8.Value;
            }
            break;
        case CipherMode.CBC:
            return s_hAlgCbc.Value;
        case CipherMode.ECB:
            return s_hAlgEcb.Value;
        }
        throw new NotSupportedException();
    }
 
    internal static Lazy<SafeAlgorithmHandle> OpenAesAlgorithm(string cipherMode, int feedback = 0)
    {
        return new Lazy<SafeAlgorithmHandle>(delegate
        {
            SafeAlgorithmHandle safeAlgorithmHandle = Cng.BCryptOpenAlgorithmProvider("AES", null, Cng.OpenAlgorithmProviderFlags.NONE);
            safeAlgorithmHandle.SetCipherMode(cipherMode);
            if (feedback > 0 && feedback != 1)
            {
                try
                {
                    safeAlgorithmHandle.SetFeedbackSize(feedback);
                }
                catch (CryptographicException inner)
                {
                    throw new CryptographicException(System.SR.Cryptography_FeedbackSizeNotSupported, inner);
                }
            }
            return safeAlgorithmHandle;
        });
    }
}