UPDATE: @Martin Prikryl's answer is correct however I asked the question because I was getting IllegalStateException with the message encrypted key has not been decrypted yet. when I called getKeyType() so I thought that you can't get info about locked keys. After some more trial and error I found out that the problem was specific to the fork of JSch I use (com.github.mwiede:jsch:0.2.1) that adds support for ED25519 keys and the problem is specific to ED25519 keys. I solved my problem this way:

private static int getKeyType(Path keyFilePath) {
    try {
        Path keyFile = keyFilePath;
        final byte[] key = Files.readAllBytes(keyFile);
        final JSch jSch = new JSch();
        final KeyPair keyPair = KeyPair.load(jSch, key, null);
        return keyPair.getKeyType();
    } catch (final IOException | JSchException e) {
        System.err.println(e.getMessage());
        return 0; // 0 is the key type of ERROR defined in the KeyPair class
    } catch (IllegalStateException e) {
        if (e.getMessage().equals("encrypted key has not been decrypted yet."))
            return 5; // 5 is the key type of ED25519 defined in the KeyPair class
        e.printStackTrace();
        return 0;
    }
}

Can I get the type (RSA, DSA, ECDSA, ED25519...) or the fingerprint of a passphrase protected private ssh key without unlocking it with JSch (like you can in Linux with ssh-keygen -l -f <key_file>)?

I'm writing an Android app and JSch is pretty much the only lib that I managed to get to work with Android so it has to be done with JSch or manually.

CodePudding user response：

Use KeyPair.load to load the key.

And then KeyPair.getKeyType and KeyPair.getFingerPrint to access its properties.

JSch jSch = new JSch();
KeyPair keypair = KeyPair.load(jSch, filename);
System.out.println(keypair.getKeyType());
System.out.println(keypair.getFingerPrint(jSch));