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Programs must use the javax.net.ssl.SSLSocket class rather than the java.net.Socket class when transferring sensitive data over insecure communication channels. The class SSLSocket provides security protocols such as Secure Sockets Layer/Transport Layer Security (SSL/TLS) to ensure that the channel is not vulnerable to eavesdropping and malicious tampering.

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• Integrity Protection: SSL protects against modification of messages by an active wiretapper.
• Authentication: In most modes, SSL provides peer authentication. Servers are usually authenticated, and clients may be authenticated as requested by servers.
• Confidentiality (privacy protection): In most modes, SSL encrypts data being sent between client and server. This protects the confidentiality of data so that passive wiretappers cannot observe won't see sensitive data such as financial information or personal information of many kinds.

It is also important to use SSL for secure remote method invocation (RMI) communications because RMI depends on object serialization, and serialized data must be safeguarded in transit. Gong, Ellison, and Dageforde [Gong 2003] describe how to secure RMI communications using SSLSocket.

Note that this rule lacks any assumptions about the integrity of the data being sent down a socket. For information about ensuring data integrity, see rule SER02-J. Sign then seal sensitive objects before sending them outside a trust boundary.

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// Exception handling has been omitted for the sake of brevity
class EchoServer { 
  public static void main(String[] args) throws IOException {
    ServerSocket serverSocket = null;
    try {
      serverSocket = new ServerSocket(9999); 
      Socket socket = serverSocket.accept();
      PrintWriter out = new PrintWriter(socket.getOutputStream(), true); 
      BufferedReader in = new BufferedReader(
          new InputStreamReader(socket.getInputStream())); 
      String inputLine; 
      while ((inputLine = in.readLine()) != null) { 
        System.out.println(inputLine); 
        out.println(inputLine); 
      }
    } finally {
      if (serverSocket != null) {
        try {
          serverSocket.close();
        } catch (IOException x) {
          // handleHandle error
        }
      }
    }
  }
}

class EchoClient {
  public static void main(String[] args) 
                          throws UnknownHostException, IOException {
    Socket socket = null;
    try {
      socket = new Socket("localhost", 9999);
      PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
      BufferedReader in = new BufferedReader(
          new InputStreamReader(socket.getInputStream()));
      BufferedReader stdIn = new BufferedReader(
          new InputStreamReader(System.in));
      String userInput;
      while ((userInput = stdIn.readLine()) != null) {
        out.println(userInput);
        System.out.println(in.readLine());
      } 
    } finally {
      if (socket != null) {
        try {
          socket.close();
        } catch (IOException x) {
          // handleHandle error
        }
      }
    }
  }
}

Note that the sockets are properly closed in accordance with rule ERR05-J. Do not let checked exceptions escape from a finally block.

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This compliant solution uses SSLSocket to protect packets using the SSL/TLS security protocols.:

// Exception handling has been omitted for the sake of brevity
class EchoServer {
  public static void main(String[] args) throws IOException {
    SSLServerSocket sslServerSocket = null;
    try {
      SSLServerSocketFactory sslServerSocketFactory =
          (SSLServerSocketFactory) SSLServerSocketFactory.getDefault();
      sslServerSocket = (SSLServerSocket) sslServerSocketFactory.
                        createServerSocket(9999);
      SSLSocket sslSocket = (SSLSocket) sslServerSocket.accept();
      PrintWriter out = new PrintWriter(sslSocket.getOutputStream(),true);
      BufferedReader in = new BufferedReader(
          new InputStreamReader(sslSocket.getInputStream()));
      String inputLine;
      while ((inputLine = in.readLine()) != null) { 
        System.out.println(inputLine); 
        out.println(inputLine); 
      } 
    } finally {
      if (sslServerSocket != null) {
        try {
          sslServerSocket.close();
        } catch (IOException x) {
          // handleHandle error
        }
      }
    }
  }
}

class EchoClient {
  public static void main(String[] args) throws IOException {
    SSLSocket sslSocket = null;
    try {
      SSLSocketFactory sslSocketFactory =
          (SSLSocketFactory) SSLSocketFactory.getDefault();
      sslSocket = 
          (SSLSocket) sslSocketFactory.createSocket("localhost", 9999);
      PrintWriter out = new PrintWriter(sslSocket.getOutputStream(), true);
      BufferedReader in = new BufferedReader(
          new InputStreamReader(sslSocket.getInputStream()));
      BufferedReader stdIn = new BufferedReader(
          new InputStreamReader(System.in));
      String userInput;
      while ((userInput = stdIn.readLine()) != null) {
        out.println(userInput);
        System.out.println(in.readLine());
      }
    } finally {
      if (sslSocket != null) {
        try {
          sslSocket.close();
        } catch (IOException x) {
          // handleHandle error
        }
      }
    }
  }
}

Programs that use SSLSocket will block indefinitely if they attempt to connect to a port that is not using SSL. Similarly, a program that does not use SSLSocket will block when attempting to establish a connection through a port that does use SSL.

Note that SSLSocket does not validate host names, so providing an arbitrary host name to an SSLSocket is still vulnerable to a Manman-in-the-middle attack. Host names should be validated separately. The HttpsURLConnection class validates host names and is a suitable solution for secure web sockets.

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MSC00-EX0: Because of the mechanisms that SSLSocket provides to ensure the secure transfer of packets, significant performance overhead may result. Regular sockets are sufficient whenunder the following circumstances:

• The the data being sent over the socket is not sensitive.
• the The data is sensitive , but properly encrypted . See rule (see SER02-J. Sign then seal sensitive objects before sending them outside a trust boundary for more information).
• the The network path of the socket never crosses a trust boundary. This could happen when, for example, the two endpoints of the socket are within the same local network and the entire network is trusted.

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Automated Detection

The general case of automated detection appears to be infeasible because determining which specific data may be passed through the socket is not statically computable. An approach that introduces a custom API for passing sensitive data via secure sockets may be feasible. User tagging of sensitive data is a necessary requirement for such an approach.

Related Guidelines

Bibliography

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