将CryptoStream解密为MemoryStream

Question

我已经写了一个过程，其中一个文件被加密并上传到Azure，然后下载过程必须解密，这是失败的，并出现“填充无效且无法删除”错误，或“要解密的数据的长度无效”。错误。

我在网上尝试了许多解决方案，包括C# Decrypting mp3 file using RijndaelManaged and CryptoStream，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跳跃。加密过程使用与解密相同的密钥/IV对，因为它将解密流的一部分，所以我觉得它工作得很好-它最终死于上面的错误。

这是我的代码，有什么想法吗？请注意，这三个变体(cryptoStream.CopyTo(decryptedStream)、do {}和while)不能一起运行-它们在这里显示了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();
    }
}

其中一条评论提到想知道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();
    }
}

然而，代码永远不会达到这一点--我还没来得及达到这一点，它就死了。

Answer 1

在各种博客来回奔波之后，我发现我在上面的代码中确实有几个错误，让我很头疼。首先，加密过程错误地写入了数组-它被包装在一个CryptoStream实例中，但实际上并没有利用它，所以我将未加密的数据写入Azure。下面是实现这一点的正确方法(fileKey是我为生成密钥/IV对而创建的自定义类的一部分，因此无论在哪里引用它，都可以更改为来自RijndaelManaged的内置进程，或者您用来生成密钥/IV对的任何其他东西)：

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;
    }
}

其次，由于我的加密过程涉及多个步骤(每个文件总共有三个密钥-容器、文件名和文件本身)，所以当我尝试解密时，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的密钥，而不是文件本身。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();
    }
}

我研究过Azure加密扩展(http://www.stefangordon.com/introducing-azure-encryption-extensions/)，但它更多的是以本地文件为中心，而不是我感兴趣的--我这端的所有东西都是流/内存中的，而翻新这个实用程序的工作将会比它的价值更多。

希望这能帮助任何希望对底层文件系统零依赖地加密Azure blob的人！

Answer 2

有点晚了，但如果这对找到这个帖子的人有用：

下面的方法对我来说很有效。

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();
        }
    }

并解密：

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);
        }
    }

这适用于从hex解码为byte[]时的固定长度十六进制字符串，以及使用Encoding.UTF8.GetBytes()解码时的utf8可变长度字符串。