Authentication using a key encrypted with a passphrase in JSch

Question

I'd like to use JSch to open an SFTP connection to download some files.

String SFTPPRIVATEKEY = "/folder/privatekeyfile";
String SFTPUSER = "user";
String SFTPPASS = "";
String SFTPHOST = "server.tld";
String SFTPPORT = "22";
int usePrivateKey = 1;

public boolean connect() {
    boolean isConnected = false;
    try {
        JSch jsch = new JSch();
        
        if (usePrivateKey) {
            jsch.addIdentity(SFTPPRIVATEKEY);
        }
        
        session = jsch.getSession(SFTPUSER,SFTPHOST,SFTPPORT);
        if (!usePrivateKey) {
            session.setPassword(SFTPPASS);
        }
        
        java.util.Properties config = new java.util.Properties();
        config.put("StrictHostKeyChecking", "no"); 
        session.setConfig(config);
        session.connect();
        if (session.isConnected() == true) {
            log.println("Connection to Session server is successfully");
        }
        channel = session.openChannel("sftp");
        channel.connect();
        channelSftp = (ChannelSftp)channel;
        isConnected = true;
    } catch (JSchException e) {
        log.println("SFTPClient Connect ERROR: "+e.getMessage());
        e.printStackTrace();
        
    }
    return isConnected;
}

If i run my code i get:

com.jcraft.jsch.JSchException: USERAUTH fail

I tried to connect using sftp on the shell on the same client where my Java code runs. I run

sftp -i privatekeyfile user@server.tld

It prompts for a passphrase for the privatekeyfile. I entered the passphrase and the connection works great.

But JSch did not connect. I found no option to set the passphrase in JSch. Maybe this is the problem?

Can some of you help?
Thanks

Answer 1

There's JSch.addIdentity overload that takes the passphrase:

public void addIdentity(String prvkey, String passphrase)

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Obligatory warning: Do not use StrictHostKeyChecking=no to blindly accept all host keys. That is a security flaw. You lose a protection against MITM attacks . For the correct (and secure) approach, see: How to resolve Java UnknownHostKey, while using JSch SFTP library?