c# - 使用 CryptoStreams 加密和 HMAC 数据

Question

假设我们有一条使用 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，我将数据写入两次，一次写入 HMAC.TransformBlock，然后再次写入 aesStream，但我想避免这种情况。有什么想法吗？

Answer 1

因为我在处理类似的话题atm，所以我会在这里回答:

正如 Maarten Bodewes 所写，我建议您先加密然后再 MAC。

然后您可以在对 aesStream 执行 FlushFinalBlock() 之后写入 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();