c# - 使用 StreamWriter 写入 Stream(用于大 Stream 加密)

Question

我正在关注 MSDN Example of Rijndael Encryption ，只是我想加密并返回一个流。

以下不起作用。

它没有抛出异常，但是单步执行代码后，返回值没有数据。

        public static Stream EncryptStream(Stream plainStream, byte[] Key, byte[] IV)
        {

            var encrypted = new MemoryStream()

            // Create an RijndaelManaged object 
            // with the specified key and IV. 
            using (RijndaelManaged rijAlg = new RijndaelManaged())
            {
                rijAlg.Key = Key;
                rijAlg.IV = IV;

                // Create a decrytor to perform the stream transform.
                ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV);

                // Create the streams used for encryption. 
                using (MemoryStream msEncrypt = new MemoryStream())
                {
                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                    {
                        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                        {

                            //Write all data to the stream.
                            swEncrypt.Write(plainStream);
                        }
                        msEncrypt.CopyTo(encrypted);
                    }
                }
            }
            return encrypted;


        }

我查看了 documentation for the Stream.Writer class ，以为跟不支持写入Stream有关系。

我注意到有一个“object”类型的参数，所以我假设它会起作用……对吗？如果没有，我该怎么做？

顺便说一句，我将一个 FileStream 传递给它。单步执行代码，plainStream 确实包含数据。

Answer 1

以下是一些用于对流进行加密和解密的示例函数(将算法替换为您喜欢的算法):

public static void Decrypt(Stream input, Stream output, byte[] key, byte[] iv)
{
    using (SymmetricAlgorithm algo = SymmetricAlgorithm.Create()) // Creates the default implementation, which is RijndaelManaged. 
    {
        using (CryptoStream stream = new CryptoStream(input, algo.CreateDecryptor(key, iv), CryptoStreamMode.Read))
        {
            byte[] bytes = new byte[16];
            int read;
            do
            {
                read = stream.Read(bytes, 0, bytes.Length);
                output.Write(bytes, 0, read);
            }
            while (read > 0);
        }
    }
}

public static void Encrypt(Stream input, Stream output, byte[] key, byte[] iv)
{
    using (SymmetricAlgorithm algo = SymmetricAlgorithm.Create()) //Creates the default implementation, which is RijndaelManaged. 
    {
        using (CryptoStream stream = new CryptoStream(output, algo.CreateEncryptor(key, iv), CryptoStreamMode.Write))
        {
            byte[] bytes = new byte[16];
            int read;
            do
            {
                read = input.Read(bytes, 0, bytes.Length);
                stream.Write(bytes, 0, read);
            }
            while (read > 0);
        }
    }
}

您可以将它们用于任何输出流。如果你想写入一个大的输出流，你可以直接使用那个输出流(例如 FileStream 或 ASP.NET Response.OutputStream 等)，你不应该使用中间的 MemoryStream，它会无意义地消耗内存.

也就是说，如果您真的想使用 MemoryStream，您可以这样做:

MemoryStream output = new MemoryStream();
Encrypt(input, output, key, iv);
output.Position = 0; // rewind the stream, so you can use it from the beginning