Converting stream encryption method from .NET to RT

问题

I'm trying to convert Encryption/Decryption methods from managed .NET to WinRT version for use in Windows Store app. The managed .NET encryption methods are already used largely in production, so the assumption is they work correctly.

This is the managed .NET encryption method:

    public static byte[] iv = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 };

    public static void EncryptFile(string sInputFilename, string sOutputFilename, string sKey)
    {
        FileStream fsInput = null;
        FileStream fsOutput = null;
        CryptoStream cryptostream = null;

        try
        {
            #region Prep
            fsInput = new FileStream(sInputFilename, FileMode.Open, FileAccess.Read);
            fsOutput = new FileStream(sOutputFilename, FileMode.Create, FileAccess.Write);
            var cryptoDes = new DESCryptoServiceProvider { IV = iv, Key = Convert.FromBase64String(sKey), Mode = CipherMode.CBC };

            var desEncrypt = cryptoDes.CreateEncryptor();

            #endregion

            cryptostream = new CryptoStream(fsOutput, desEncrypt, CryptoStreamMode.Write);
            long startIndex = 0;
            var bytearrayinput = new byte[64];
            var byteCount = bytearrayinput.Length;
            while (startIndex < fsInput.Length)
            {
                if (fsInput.Length - startIndex < byteCount)
                {
                    byteCount = (int)(fsInput.Length - startIndex);
                }

                fsInput.Read(bytearrayinput, 0, byteCount);
                cryptostream.Write(bytearrayinput, 0, byteCount);

                startIndex += byteCount;
            }
            cryptostream.FlushFinalBlock();
        }
        finally
        {
            if (fsInput != null) { fsInput.Close(); }
            if (cryptostream != null) { cryptostream.Close(); }
            if (fsOutput != null) { fsOutput.Close(); }
        }
    }

This is the WinRT version that uses CryptographicEngine.

    public static async Task EncryptContentFile(IRandomAccessStream inputStream, IRandomAccessStream outputStream, string key)
    {
        var iv = CryptographicBuffer.CreateFromByteArray(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 });
        var keyMaterial = CryptographicBuffer.DecodeFromBase64String(key);

        var cryptoProvider = SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithmNames.DesCbcPkcs7);
        var symmetricKey = cryptoProvider.CreateSymmetricKey(keyMaterial);

        var inStream  = inputStream.AsStreamForRead();
        var outStream = outputStream.AsStreamForWrite();

        try
        {
            var size = (long)inputStream.Size;
            var chunkSize = 64L;
            //var finalChunk = false;
            while (inStream.Position < size)
            {
                if (size - inStream.Position < chunkSize)
                {
                    chunkSize = size - inStream.Position;
                    //finalChunk = true;
                }
                var chunk = new byte[chunkSize];
                await inStream.ReadAsync(chunk, 0, (int)chunkSize);

                var writeBuffer = CryptographicEngine.Encrypt(symmetricKey, chunk.AsBuffer(), iv).ToArray();

                await outStream.WriteAsync(writeBuffer, 0, (int)chunkSize);
                //await outStream.WriteAsync(writeBuffer, 0, finalChunk ? writeBuffer.Length : (int)chunkSize);
            }
            await outputStream.FlushAsync();
        }
        catch (Exception e)
        {
            Debug.WriteLine(e.Message);
        }
    }

The goal is to be able to encrypt large files by reading and encrypting chunks of bytes. The problem that I have with the RT method is that everytime it encrypts a chunk, the encrypted bytes are larger by 8 bytes. I understand on the .NET side this is what CryptoStream.FlushFinalBlock() adds. I tried trimming the bytes to the original size (the commented finalChunk code), but it didn't help.

How can I reliably encrypt in WinRT and have the final encrypted file be identical with what the .NET method produces.

Thank you

回答1:

To answer my question, I found the problem. Windows Runtime doesn't support buffered encryption and will always treat data as a whole. While the .NET ICryptoTransform contains methods like TransformBlock and TransformFinalBlock, the RT API always uses treats data as final, which makes it impossible to encrypt large streams by chunks. I ended up using BouncyCastle PCL library which worked out perfectly. Similarly, DesEngine in BouncyCastle has method ProcessBytes and DoFinal which correspond to the above mentioned .NET methods in ICryptoTransform.

Hope this helps someone.

    private Task TransformStream_DesCbcPkcs7_WithProgress(bool forEncryption, Stream inputStream, Stream outputStream, byte[] key, byte[] iv, IProgress<int> progress)
    {
        return Task.Run(async () =>
        {
            // Initialize symmetric crypto engine
            // Algorithm:           DES
            // Mode of operation:   CBC
            // Byte padding:        PKCS#7
            var engine = new PaddedBufferedBlockCipher(new CbcBlockCipher(new DesEngine()), new Pkcs7Padding());
            engine.Init(forEncryption, new ParametersWithIV(new DesParameters(key), iv));

            // Report progress if available
            Action<int> report = x =>
            {
                if (progress != null)
                    progress.Report(x);
            };

            var size = inputStream.Length;
            var current = inputStream.Position;
            var chunkSize = 1024 * 1024L;
            var lastChunk = false;

            report(0);
            await Task.Yield();

            // Initialize DataReader and DataWriter for reliable reading and writing
            // to a stream. Writing directly to a stream is unreliable.
            using (var reader = new BinaryReader(inputStream))
            using (var writer = new BinaryWriter(outputStream))
            {
                while (current < size)
                {
                    if (size - current < chunkSize)
                    {
                        chunkSize = (uint)(size - current);
                        lastChunk = true;
                    }

                    var chunk = new byte[chunkSize];
                    reader.Read(chunk, 0, (int)chunkSize);

                    // The last chunk must call DoFinal() as it appends additional bytes
                    var processedBytes = lastChunk ? engine.DoFinal(chunk) : engine.ProcessBytes(chunk);

                    writer.Write(processedBytes);

                    current = inputStream.Position;
                    report((int)(current * 100F / size));

                    await Task.Yield();
                }
                await outputStream.FlushAsync();
            }
        });
    }

来源：https://stackoverflow.com/questions/25186350/converting-stream-encryption-method-from-net-to-rt