Question

假设我们有一条与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();

我抽象了很多代码，所以这不是一个有效的例子。我可以解决这个问题，我将数据写入两次，一次是HMAC.TransformBlock，再次是aesStream，但我想避免这种情况。有什么想法吗？

Answer 1

如果您通过套接字发送数据（因为您可能容易填充oracle attacs），您真的应该在MAC之前执行加密以创建安全解决方案，尤其是。因此，尽管您的问题是有效的，但最好更改流的顺序。

Answer 2

由于我正在处理类似的主题，我会在这里给出答案：

就像Maarten Bodewes所写，我建议你加密 - 然后MAC。

然后，您可以在FlushFinalBlock()上执行aesStream后编写HMAC-Bytes。

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();

Answer 3

所以我放了一个似乎正在工作的黑客。我创建了一个名为ProtectedStream的流包装类。这是要点：

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包含在ProtectedStream内。这隐含了aesStream来自CryptoStream的{{1}}这一事实，因此当您在macStream上致电FlushFinalBlock时，它不会在macStream上调用FlushFinalBlock {1}}。

使用CryptoStreams加密和HMAC数据

3 个答案: