Java: InvalidAlgorithmParameterException Prime size must be multiple of 64

Question

I implemented a Java program that will connect and execute a command in a remote server using JSCH. The problem is that whenever I tried to connect to the server, I got the

Answer 1

Add this line of code after you have the Session instance:

public static Session createSession(Server srv){
   JSch js = new JSch();
   try {
      Session s = js.getSession(srv.getUser().getUsername(), srv.getAddress(), 22);
      s.setPassword(srv.getUser().getPassword());
      Properties config = new Properties();
      config.put("StrictHostKeyChecking", "no");
      config.put("PreferredAuthentications", "password");
      config.put("kex", "diffie-hellman-group1-sha1");
      s.setConfig(config);
      ...

The line to be added is: config.put("kex", "diffie-hellman-group1-sha1");

Answer 2

I was getting this error

ERROR: Message form the remote server : Session.connect: java.security.InvalidAlgorithmParameterException: Prime size must be multiple of 64, and can only range from 512 to 1024 (inclusive)

I was able to solve it by setting the client version as in this line

session.setClientVersion("SSH-2.0-OpenSSH_2.5.3");

The default value that was causing the error is

session.setClientVersion("SSH-2.0-JSCH-0.1.54");

Answer 3

My solution to this problem was putting in the first line of my main method the following:

public static void main(String[] args) {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    ...
}

If you are using Spring you can add instead:

@Configuration
public class AppConfig {
    @PostConstruct
    public void init(){
        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    }
}