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I'm using below code to connect remote server and I followed below steps to connect private/public key generation & concatenate of public key with authorized key.

Code: 

private Session createSession() throws JSchException {
        JSch jsch = new JSch();
            jsch.addIdentity(privateKey);                   //add private key path as ~/.ssh/id_rsa
            Session session;
            session = jsch.getSession(user, host, port);
            java.util.Properties config = new java.util.Properties();

        Properties cfg = new Properties();
            cfg.put("trust", "true");
            cfg.put("StrictHostKeyChecking", "no");
            cfg.put("HashKnownHosts", "yes");

            session.setConfig(cfg);
            session.connect();
            return session;
    }

Steps:

1. I can able to generate private/public key in the path ~/.ssh/id_rsa(private key) and ~/.ssh/id_rsa.pub(public key)
    >> ssh-keygen (or) ssh-keygen -t rsa -b 4096
   Note: Generated key with no passphrase
2. I have added public key with authorized_keys with below command
    >> ssh user@host "echo \"`cat ~/.ssh/id_rsa.pub`\" >> .ssh/authorized_keys"

Still I'm facing the exception "com.jcraft.jsch.JSchException: Auth fail". Please guide me to proceed.

Shailu
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2 Answers2

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I believe this can happen for several reasons:

  • The private key is password protected, which you have already verified is not the case.

  • The directory containing the keys is encrypted.

  • The file permissions on the .ssh directory and or public/private keys are too open. They should be:

    • ssh directory: 700
    • public key: 644
    • private key: 600 (possibly even 400)

  • What also might be going on is the format of the public key within the authorized keys file is incompatible. You might need to convert it to a different format. Assuming OpenSSH:

    • Convert to SSH2: ssh-keygen -i -f /path/to/private/key ssh-keygen -i -f /path/to/public/key
    • Convert from SSH2: ssh-keygen -e -f /path/to/private/key ssh-keygen -e -f /path/to/public/key
Murph
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JSch does not support rsa-sha2. And as JSch seems not to be updated anymore, it quite likely never will. Try this ssh-keygen -m PEM -t rsa -b 2048 its work.

Indravijaysinh
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  • Jcraft hasn't updated since 2018, but a fork in https://github.com/mwiede/jsch is current and includes rsa-sha2-# signatures -- _and_ 'new' format keyfiles (OPENSSH PRIVATE KEY), which Jcraft's 1.55 does not, and is the _only_ thing you changed by `-m PEM` (exactly the same RSA keys, in either old or new format, can be used for both rsa-sha2-# and ssh-rsa signatures in OpenSSH, except in 8.8 up ssh-rsa is disabled by default and must be reenabled). – dave_thompson_085 Apr 29 '23 at 01:54