Decrypting CryptoStream into MemoryStream

Question

我写了一个文件加密并上传到Azure的过程，然后下载过程必须解密，这就是失败的"填充无效且无法删除"错误，或"要解密的数据长度无效"错误。

我在网上尝试了许多解决方案，包括c#使用RijndaelManaged和CryptoStream解密mp3文件，但它们似乎都不起作用，我最终只是在这两个错误之间来回弹跳。加密过程使用与解密相同的密钥/IV对，并且由于它将解密流的一部分，我觉得它工作得很好-它最终会因上述错误而死亡。

这是我的代码，有什么想法吗?请注意，三个变体(cryptoStream.CopyTo(decryptedStream), do {}和while)没有一起运行-它们在这里显示我已经尝试过的选项，所有这些选项都失败了。

byte[] encryptedBytes = null;
using (var encryptedStream = new MemoryStream())
{
    //download from Azure
    cloudBlockBlob.DownloadToStream(encryptedStream);
    //reset positioning for reading it back out
    encryptedStream.Position = 0;
    encryptedBytes = encryptedStream.ConvertToByteArray();
}
//used for the blob stream from Azure
using (var encryptedStream = new MemoryStream(encryptedBytes))
{
    //stream where decrypted contents will be stored
    using (var decryptedStream = new MemoryStream())
    {
        using (var aes = new RijndaelManaged { KeySize = 256, Key = blobKey.Key, IV = blobKey.IV })
        {
            using (var decryptor = aes.CreateDecryptor())
            {
                //decrypt stream and write it to parent stream
                using (var cryptoStream = new CryptoStream(encryptedStream, decryptor, CryptoStreamMode.Read))
                {
                    //fails here with "Length of the data to decrypt is invalid." error
                    cryptoStream.CopyTo(decryptedStream);
                    int data;
                    //fails here with "Length of the data to decrypt is invalid." error after it loops a number of times,
                    //implying it is in fact decrypting part of it, just not everything
                    do
                    {
                        data = cryptoStream.ReadByte();
                        decryptedStream.WriteByte((byte)cryptoStream.ReadByte());
                    } while (!cryptoStream.HasFlushedFinalBlock);
                    //fails here with "Length of the data to decrypt is invalid." error after it loops a number of times,
                    //implying it is in fact decrypting part of it, just not everything
                    while ((data = cryptoStream.ReadByte()) != -1)
                    {
                        decryptedStream.WriteByte((byte)data);
                    }
                }
            }
        }
        //reset position in prep for reading
        decryptedStream.Position = 0;
        return decryptedStream.ConvertToByteArray();
    }
}

其中一个评论提到想知道ConvertToByteArray是什么，它只是一个简单的扩展方法:

/// <summary>
/// Converts a Stream into a byte array.
/// </summary>
/// <param name="stream">The stream to convert.</param>
/// <returns>A byte[] array representing the current stream.</returns>
public static byte[] ConvertToByteArray(this Stream stream)
{
    byte[] buffer = new byte[16 * 1024];
    using (MemoryStream ms = new MemoryStream())
    {
        int read;
        while ((read = stream.Read(buffer, 0, buffer.Length)) > 0)
        {
            ms.Write(buffer, 0, read);
        }
        return ms.ToArray();
    }
}

代码从来没有达到这一点——在我到达这一点之前它就死了。

Answer 1

在与各种博客进行了大量的交流之后，我发现上面的代码中确实有几个错误困扰着我。首先，加密过程错误地写入数组-它被CryptoStream实例包装，但实际上并没有利用它，所以我将未加密的数据写入Azure。以下是正确的路线(fileKey是我创建的自定义类的一部分，用于生成密钥/IV对，因此无论引用何处，都可以从RijndaelManaged更改为内置进程或其他任何您用于提出密钥/IV对的东西):

using (var aes = new RijndaelManaged { KeySize = 256, Key = fileKey.Key, IV = fileKey.IV })
{
    using (var encryptedStream = new MemoryStream())
    {
        using (ICryptoTransform encryptor = aes.CreateEncryptor())
        {
            using (CryptoStream cryptoStream = new CryptoStream(encryptedStream, encryptor, CryptoStreamMode.Write))
            {
                using (var originalByteStream = new MemoryStream(file.File.Data))
                {
                    int data;
                    while ((data = originalByteStream.ReadByte()) != -1)
                        cryptoStream.WriteByte((byte)data);
                }
            }
        }
        var encryptedBytes = encryptedStream.ToArray();
        return encryptedBytes;
    }
}

第二，由于我的加密过程涉及多个步骤(每个文件三个密钥-容器，文件名和文件本身)，当我试图解密时，我使用了错误的密钥(当我引用blobKey进行解密时可以看到，这实际上是用于加密文件名而不是文件本身的密钥。正确的解密方法是:

//used for the blob stream from Azure
using (var encryptedStream = new MemoryStream(encryptedBytes))
{
    //stream where decrypted contents will be stored
    using (var decryptedStream = new MemoryStream())
    {
        using (var aes = new RijndaelManaged { KeySize = 256, Key = blobKey.Key, IV = blobKey.IV })
        {
            using (var decryptor = aes.CreateDecryptor())
            {
                //decrypt stream and write it to parent stream
                using (var cryptoStream = new CryptoStream(encryptedStream, decryptor, CryptoStreamMode.Read))
                {
                    int data;
                    while ((data = cryptoStream.ReadByte()) != -1)
                        decryptedStream.WriteByte((byte)data);
                }
            }
        }
        //reset position in prep for reading
        decryptedStream.Position = 0;
        return decryptedStream.ConvertToByteArray();
    }
}

我曾研究过Azure加密扩展(http://www.stefangordon.com/introducing-azure-encryption-extensions/)，但它比我感兴趣的更以本地文件为中心——我的终端上的所有东西都是流/内存中的，而改造这个实用程序将是比它的价值更多的工作。

希望这能帮助任何想要加密Azure blob而不依赖底层文件系统的人!

Answer 2

有点晚了，但如果这对发现这个线程的人有用:

下面的方法对我很有效。

internal static byte[] AesEncryptor(byte[] key, byte[] iv, byte[] payload)
    {
        using (var aesAlg = Aes.Create())
        {
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;
            var encryptor = aesAlg.CreateEncryptor(key, iv);
            var encrypted = encryptor.TransformFinalBlock(payload, 0, payload.Length);
            return iv.Concat(encrypted).ToArray();
        }
    }

和解密:

internal static byte[] AesDecryptor(byte[] key, byte[] iv, byte[] payload)
    {
        using (var aesAlg = Aes.Create())
        {
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;
            var decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
            return decryptor.TransformFinalBlock(payload, 0, payload.Length);
        }
    }

这适用于加密/解密从hex解码到byte[]的固定长度十六进制字符串以及使用Encoding.UTF8.GetBytes()解码的utf8可变长度字符串。