CipherInputStream冻结的ObjectInputStream，挂起 [英] ObjectInputStream with CipherInputStream freezing, hanging

问题描述

我正在编程基于客户端-服务器的Java应用程序，但遇到了一个问题，因为在客户端和服务器中构造ObjectInputStream时，该挂起.

I'm programming client-server based Java application and I've got a problem, because it hangs when constructing ObjectInputStream both in client and server.

客户:

Socket socket = new Socket("localhost", 9999);

outCiph = new CipherOutputStream(socket.getOutputStream(), AES.getEncryptCipher("key"));
out = new ObjectOutputStream(outCiph);
inCiph = new CipherInputStream(socket.getInputStream(), AES.getDecryptCipher("key"));
in = new ObjectInputStream(inCiph);

try
{
String text = "test!";

out.writeObject(text);
out.flush();

if (out != null)
out.close();

if (in != null)
in.close();
}
catch (IOException ex)
{
System.err.println(ex.toString());
}

服务器:

ServerSocket serverSocket = new ServerSocket(9999);
Socket socket = serverSocket.accept();

outCiph = new CipherOutputStream(socket.getOutputStream(), AES.getEncryptCipher("key"));
out = new ObjectOutputStream(outCiph);
inCiph = new CipherInputStream(socket.getInputStream(), AES.getDecryptCipher("key"));
in = new ObjectInputStream(inCiph);

try
{
String rec = (String) in.readObject();
System.out.println("Received from client: " + rec);

if (out != null)
out.close();

if (in != null)
in.close();

}
catch (IOException ex)
{
System.err.println(ex.toString() + " in start()");
}
catch (ClassNotFoundException ex)
{
System.err.println(ex.toString());
}

AES:

// I'm not author of generateKey method so I've no idea if is it correct
private static byte[] generateKey(String pass) throws UnsupportedEncodingException, NoSuchAlgorithmException
{
MessageDigest sha = MessageDigest.getInstance("SHA-256");
byte[] passBytes = pass.getBytes("ASCII");
byte[] sha256Bytes = sha.digest(passBytes);


byte[] key = new byte[16];
int j = 0;
for (int i = 0; i < sha256Bytes.length; i++)
{
    if (i % 2 == 0)
    {
    key[j] = sha256Bytes[i];
    j++;
    }
}
return key;
}

public static Cipher getEncryptCipher(String pass)
{
try
{
    SecretKeySpec skeySpec = new SecretKeySpec(generateKey(pass), "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
    return cipher;
}
catch (Exception ex) // just for clarity
{
    Logger.getLogger(AES.class.getName()).log(Level.SEVERE, null, ex);
}
return null;
}

public static Cipher getDecryptCipher(String pass)
{
try
{
    SecretKeySpec skeySpec = new SecretKeySpec(generateKey(pass), "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec);
    return cipher;
}
catch (Exception ex) // just for clarity
{
    Logger.getLogger(AES.class.getName()).log(Level.SEVERE, null, ex);
}
return null;
}

当我不使用CipherInput/OutputStream时，一切正常，因此问题与CipherInput/OutputStream某种程度上有关.

When I don't use CipherInput/OutputStream everything works fine so the problem is somehow related with CipherInput/OutputStream.

推荐答案

仅在向 all 发送完信息后，才需要创建ObjectInputStream，因为ObjectInputStream的构造函数需要阻塞读取标题.

You need to create the ObjectInputStream only after you've send all the information over, because the constructor of ObjectInputStream blocks because it needs to read the header.

通常，所有字节都会由ObjectOutputStream写入，但是现在CipherOutputStream一直等待，直到它有一个完整的16字节块(对于AES而言)，然后才发送(最后一部分)标头.也许采用流密码模式(CTR或GCM)的AES在这里会更有用，因为它使用每字节加密，并且能够直接发送每个字节.

Normally, all the bytes would have been written by the ObjectOutputStream, but now the CipherOutputStream is waiting until it has a full 16 byte block (in the case of AES) before it sends the (last part of the) header over. Maybe AES in stream cipher mode (CTR or GCM) would be more useful here as it uses per byte encryption, and would be able to directly send each byte.

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