You need both the private and *public* key file in "ssh\keys" folder under Token2Shell/Mobile data home path. (You can check your current data home path by opening [ Menu ] -> [ Home Folder ].)

When those key files are recognized by Token2Shell/Mobile, you should see a list of file names when you select "For 'publickey' method" or "For 'hostbased' method" option in SSH settings.

If you do not see file names or "publickey" authentication method fails, please check the followings:

[*] Check private/public key file format.

Token2Shell/Mobile supports private/public key file formats used in OpenSSH(http://www.openssh.org) and SSH Corp.(http://www.ssh.com). Make sure your private/public keys are generated using the application that came with your server.

[*] Check private/public file names.

In order for Token2Shell/Mobile to recognize a key file, a public key file *must* have a ".pub" file extension while the file name itself is the same as its corresponding private key file. For example, if you named your private key file as "myserver-key", its corresponding public key file *must* be named "myserver-key.pub". Make sure *both* of your private and public key files are in the same "ssh\keys" folder.

[*] Add your public key to your server config file.

You must install your public key on your server to use it with Token2Shell/Mobile.
Installing a public key varies from SSH server to server, hence please check your SSH server manual or contact your system administrator for more details. It could be as simple as copying the public key file to a specific folder on your server.

Hope this helps.