将 CryptoStream 解密为 MemoryStream

Question

我已经编写了一个过程，其中文件被加密并上传到 Azure，然后下载过程必须被解密，这导致 "Padding is invalid and cannot be removed" 错误或 "Length of the data to decrypt is invalid." 错误。

我在网上尝试了很多解决方案，包括，但其中 none 似乎有效，我最终只是在这两个错误之间来回跳动。加密过程使用与解密相同的 key/IV 对，并且由于它会解密一部分流，我觉得它工作正常 - 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，这三个变体（cryptoStream.CopyTo(decryptedStream)、do {} 和 while）并不是运行在一起的——它们在这里是为了展示我已经尝试过的所有选项失败了。

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，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();
    }
}

尽管代码从未达到此目的 - 它在我达到这一点之前就死了。

Answer 1

在各种博客上来回反复之后，我发现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——它用 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。这是正确的方法（fileKey 是我创建的用于生成 Key/IV 对的自定义 class 的一部分，因此无论在哪里引用都可以更改为内置过程来自 RijndaelManaged 或任何你用来得到 key/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;
    }
}

其次，由于我的加密过程涉及多个步骤（每个文件共有三个密钥 - 容器、文件名和文件本身），当我尝试解密时，我使用了错误的密钥（在我引用 blobKey解密，其实是加密文件名的密钥，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/)，但它比我感兴趣的更以本地文件为中心 - 我这边的一切都只是 streams/in-memory，并且正在改装该实用程序的工作量将超过其价值。

希望这可以帮助任何希望在零依赖基础文件系统的情况下加密 Azure blob 的人！

Answer 2

晚会有点晚了，但如果这对发现此主题的人有用：

以下对我来说效果很好。

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 encrypting/decrypting 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() 解码时的 utf8 可变长度字符串。

将 CryptoStream 解密为 MemoryStream

Decrypting CryptoStream into MemoryStream

c#

encryption

aes

cryptostream

azure-blob-storage