C# 逐块解密AES文件

我有一个用256比特AES加密的PDF文件。如果我将整个文件读入内存中的字节数组，我可以非常轻松地对其进行解密，并且工作正常：

public static async Task<StorageFile> DecryptFile(IStorageFile file, string key, string destFilename)
{
    var buffer = await FileIO.ReadBufferAsync(file);

    var pwBuffer = CryptographicBuffer.ConvertStringToBinary(key, BinaryStringEncoding.Utf8);
    pwBuffer = pwBuffer.ToArray().Take(16).ToArray().AsBuffer();

    var symProvider = SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithmNames.AesEcbPkcs7);
    var cryptographicKey = symProvider.CreateSymmetricKey(pwBuffer);

    var res = CryptographicEngine.Decrypt(cryptographicKey, buffer, null);
    var destFile = await ApplicationData.Current.TemporaryFolder.CreateFileAsync(destFilename,CreationCollisionOption.ReplaceExisting);
    await FileIO.WriteBufferAsync(destFile, res);
    res = null;

    return destFile;
}

---

有什么办法让WinRT代码工作吗？

如评论中所述，WinRT不支持解密文件。使用

Portable.BouncyCastle

Nuget包，我成功地编写了工作正常的代码

public static async Task<StorageFile> DecryptFile(IStorageFile file, string key, string destFilename)
{
    var destFile = await ApplicationData.Current.TemporaryFolder.CreateFileAsync(destFilename, CreationCollisionOption.ReplaceExisting);
    var pwBuffer = CryptographicBuffer.ConvertStringToBinary(key, BinaryStringEncoding.Utf8);            

    using (var inputStream = await file.OpenStreamForReadAsync())
    {
        using (var outputStream = await destFile.OpenStreamForWriteAsync())
        {
            var engine = CipherUtilities.GetCipher("AES/ECB/PKCS7Padding");
            engine.Init(false, new KeyParameter(pwBuffer.ToArray().Take(16).ToArray()));

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

            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;

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

    return destFile;
}

公共静态异步任务解密文件（IStorageFile文件、字符串密钥、字符串文件名）
{
var destFile=wait ApplicationData.Current.TemporaryFolder.CreateFileAsync（destFilename，CreationCollisionOption.ReplaceExisting）；
var pwBuffer=cryptographicsbuffer.ConvertStringToBinary（key，BinaryStringEncoding.Utf8）；
使用（var inputStream=wait file.OpenStreamForReadAsync（））
{
使用（var outputStream=await destFile.OpenStreamForWriteAsync（））
{
var engine=cipherputilities.GetCipher（“AES/ECB/PKCS7Padding”）；
engine.Init（false，新的键参数（pwBuffer.ToArray（）.Take（16.ToArray（）））；
变量大小=inputStream.Length；
无功电流=输入流位置；
var chunkSize=1024*1024L；
var lastChunk=false；
等待任务；
//初始化DataReader和DataWriter以实现可靠的读写
//直接写入流是不可靠的。
使用（变量读取器=新二进制读取器（inputStream））
使用（var writer=newbinarywriter（outputStream））
{
while（当前<大小）
{
if（大小-当前<块大小）
{
chunkSize=（uint）（大小-当前）；
lastChunk=true；
}
var chunk=新字节[chunkSize]；
reader.Read（chunk，0，（int）chunkSize）；
//最后一个块在附加额外字节时必须调用DoFinal（）
var processedBytes=lastChunk？engine.DoFinal（chunk）：engine.ProcessBytes（chunk）；
writer.Write（processedBytes）；
电流=输入流位置；
等待任务；
}
等待outputStream.FlushAsync（）；
}
}
}
返回文件；
}

看起来它不受支持。你可以试试这个：谢谢你给我指出了正确的方向

var bytes = Encoding.UTF8.GetBytes(key);

var aes256 = new AesCryptoServiceProvider
{
    Mode = CipherMode.ECB,
    Key = bytes.Take(16).ToArray(),
    Padding = PaddingMode.PKCS7
};
aes256.GenerateIV();
var encryptor = aes256.CreateDecryptor();

using (var dest = File.Create(destFile))
{
    using (CryptoStream csEncrypt = new CryptoStream(dest, encryptor, CryptoStreamMode.Write))
    {
        csEncrypt.Write(aes256.IV, 0, aes256.IV.Length);

        using (Stream source = File.OpenRead(file)
        {
            byte[] buffer = new byte[2048];
            int bytesRead;
            while ((bytesRead = source.Read(buffer, 0, buffer.Length)) > 0)
            {                
                csEncrypt.Write(buffer, 0, bytesRead);
            }
        }

        csEncrypt.FlushFinalBlock();
    }
}

public static async Task<StorageFile> DecryptFile(IStorageFile file, string key, string destFilename)
{
    var destFile = await ApplicationData.Current.TemporaryFolder.CreateFileAsync(destFilename, CreationCollisionOption.ReplaceExisting);
    var pwBuffer = CryptographicBuffer.ConvertStringToBinary(key, BinaryStringEncoding.Utf8);            

    using (var inputStream = await file.OpenStreamForReadAsync())
    {
        using (var outputStream = await destFile.OpenStreamForWriteAsync())
        {
            var engine = CipherUtilities.GetCipher("AES/ECB/PKCS7Padding");
            engine.Init(false, new KeyParameter(pwBuffer.ToArray().Take(16).ToArray()));

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

            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;

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

    return destFile;
}