C# 使用CryptoStreams加密和HMAC数据

假设我们有一条用HMAC签名的消息，然后该消息和HMAC被加密，然后通过TCP套接字发送：

// endpoint info excluded
TcpClient client = new TcpClient();
var stream = client.GetStream();

// assume pre-shared keys are used and set at this point
AesManaged aes = new AesManaged();
var aesEncryptor = aes.CreateEncryptor();
CryptoStream aesStream = new CryptoStream(
    stream, aesEncryptor, CryptoStreamMode.Write);

// assume pre-shared keys here too
HMACSHA256 mac = new HMACSHA256();
CryptoStream macStream = new CryptoStream(
    aesStream, mac, CryptoStreamMode.Write);

// assume a message with actual data is written to the macStream
// which updates the hash of the HMAC and also pipes the message
// to the aesStream which encrypts the data and writes it to the
// TCP socket stream
byte[] message = new byte[1024];
macStream.Write(message, 0, message.Length);
macStream.FlushFinalBlock();

// flushing the final block of the macStream actually flushes the
// final block of the aesStream, so I get an error when trying to
// write the HMAC hash to the aesStream
aesStream.Write(mac.Hash, 0, mac.Hash.Length);
aesStream.FlushFinalBlock();

---

我提取了很多代码，所以这不是一个有效的示例。我可能可以解决这个问题，将数据写入两次，一次写入HMAC.TransformBlock，另一次写入aesStream，但我希望避免这种情况。有什么想法吗？

您真的应该在MAC之前执行加密，以创建一个安全的解决方案，特别是如果您通过套接字发送数据（因为您可能容易受到oracle附件的攻击）。因此，尽管您的问题是正确的，但最好改变流的顺序。

因此，我提出了一个暂时可行的方法。我创建了一个名为

ProtectedStream

的流包装类。要点如下：

public class ProtectedStream : Stream
{
  private Stream stream;

  public ProtectedStream(Stream stream)
  {
    if(stream == null)
      throw new ArgumentNullException("stream");

    this.stream = stream;
  }

  public override void Close()
  {
    this.stream.Close();
    base.Close();
  }

  public override int Read(byte[] buffer, int offset, int count)
  {
    return this.stream.Read(buffer, offset, count);
  }

  public override void Write(byte[] buffer, int offset, int count)
  {
    this.stream.Write(buffer, offset, count);
  }

  // and continue overriding every other overridable Stream member
  // in the same fashion
}

然后原始代码如下所示：

// assume pre-shared keys are used and set at this point
AesManaged aes = new AesManaged();
var aesEncryptor = aes.CreateEncryptor();
CryptoStream aesStream = new CryptoStream(
    stream, aesEncryptor, CryptoStreamMode.Write);

// assume pre-shared keys here too
HMACSHA256 mac = new HMACSHA256();
CryptoStream macStream = new CryptoStream(
    new ProtectedStream(aesStream), mac, CryptoStreamMode.Write);

---

请注意，

aesStream

被包装在

ProtectedStream

中。这隐藏了一个事实，即

aestream

是

macStream

的

CryptoStream

，因此当你在

macStream

上调用

FlushFinalBlock

时，它不会在

aestream

上调用

FlushFinalBlock

，因为我正在处理类似的主题，我会在这里给出一个答案：

就像Maarten Bodewes写的，我建议你加密MAC

然后，您可以在

aesStream

上执行

FlushFinalBlock（）

后写入HMAC字节

不要忘记处理CryptoStreams和Algorithms对象

var stream = client.GetStream();

HMACSHA256 mac = new HMACSHA256();
CryptoStream macStream = new CryptoStream(stream, mac, CryptoStreamMode.Write);

AesManaged aes = new AesManaged();
var aesEncryptor = aes.CreateEncryptor();
CryptoStream aesStream = new CryptoStream(macStream, aesEncryptor, CryptoStreamMode.Write);

byte[] message = new byte[1024];
aesStream.Write(message, 0, message.Length);
aesStream.FlushFinalBlock();

//No need to FlushFinalBlock() on macStream, would throw

//Write HMAC here
stream.Write(mac.Hash, 0, mac.Hash.Length);

//Dispose
aesStream.Dispose();
aes.Dispose();
macStream.Dispose();
mac.Dispose();

---

谢谢你的洞察力。我将对此做一些研究。我将此标记为答案，但这不是加密，而是MAC。这是加密和MAC。微妙的区别在于，您正在散列明文而不是密文。再见，谢谢。

aestream

将

macStream

作为参数。据我所知，它散列加密流，而不是原始输入（消息）。也许我弄错了。哦，对不起，你是对的。流被加密，然后散列。对不起，当我读到这篇文章时，它看起来像是hmac流接受了明文流，aesStream接受了hmac流，所以看起来明文被加密了。我错过什么了吗？编辑nvm它正在写入而不是读取，因此消息会写入aesStream，aesStream会写入hmacStream，hmacStream会写入客户端。别担心。