JSchException: UnknownHostKey

Question

I'm trying to use Jsch to establish an SSH connection in Java. I have set "StrictHostKeyChecking" to yes. I understand that the hostkey of the server has to be obtained before hand and store in the hostkey file before the first attempt to connect to the server. How can I get the HostKey of the server. My code produces the following exception:

com.jcraft.jsch.JSchException: UnknownHostKey: ASY-PC RSA key fingerprint is 22:fb:ee:fe:18:cd:aa:9a:9c:78:89:9f:b4:78:75:b4

How can I make connection with StrictHostKeyChecking Yes. Here is my code.

package sshexample;

import com.jcraft.jsch.*;
import java.io.*;

public class SSHexample 
{
public static void main(String[] args) 
{
    String user = "user";
    String password = "password";
    String host = "192.168.100.103";
    int port=22;
    try
    {
        JSch jsch = new JSch();
        Session session = jsch.getSession(user, host, port);
        session.setPassword(password);
        session.setConfig("StrictHostKeyChecking", "yes");
        System.out.println("Establishing Connection...");
        session.connect();
        System.out.println("Connection established.");
        System.out.println("Crating SFTP Channel.");
        ChannelSftp sftpChannel = (ChannelSftp) session.openChannel("sftp");
        sftpChannel.connect();
}catch(Exception e) {
e.printStackTrace();
}
}

Answer 1

You have to supply a KnownHostKeys file by calling following function

jsch.setKnownHosts(new FileInputStream(knownHostsFile));

this file should have all the the known hosts' fingerprints separated by new lines.

for example

hostname,10.1.1.120, ssh-rsa AAAAC3NzaC1yc2EAAAADAQABAAABAQCi5b647581SwC0uUDQw1ENjKSz3rhJMRRZEgIjHylvF4fbuAEzj645YoAf9SItb51MhetFAJrq98jYsHpedSm3IoMG+aR/P1CjsBz1RtJKlfR2NfYDCZ7Dyx11P8FnJbwbYif/GeG0xEujekwF1pyL0tNPmf0H4/GPR4mwrv/llGlB3Lo3BzxrGtl4f4X/oSHDoo7FrQkDwqOfeSM++3vPPHxyVO5zhFJ5u9f7M/uuxUeHS+YS5JWAI7NLXKgbiM9dluGzZU/6Awo3ux4x5ojL+kf29JEVxK+o6GfW2bIW+LhgIGZNThnN5nHzBVfNNHvQ7KC5ic0h2z2gbVpwJr1h

you can obtain this key from server by using any sftp client however following command may help if you are using linux or unix

ssh-keyscan -t rsa 10.1.1.120