Login failure using private key

[Pieter Cardoen <pieter.cardoen@xxxxxxxxxxx>]

Hello

I am trying to authenticate to my target system using libssh. My target system is configured to use login without password. Using openssh ssh client, I can login: "ssh -i <path to private key file> root@<ip address>" gives me the prompt.

However I am not succeeding to login to the target system using libssh. I was following this tutorial but it wasn't that helpful because I ran into multiple errors:
http://api.libssh.org/master/libssh_tutor_authentication.html

I am able to load the public key using ssh_pki_import_pubkey_file with "id_rsa.pub". Return value SSH_OK. However if I try to execute ssh_userauth_try_publickey, I get:
[2018/09/26 13:15:06.226731, 1] ssh_packet_userauth_failure:  Access denied for 'publickey'. Authentication that can continue: publickey,password
[2018/09/26 13:15:06.226816, 2] ssh_packet_userauth_failure:  Access denied for 'publickey'. Authentication that can continue: publickey,password

This seams fairly reasonable as I used the public key of my PC to authenticate. However, I don't have a public key of my target system, only the private key.

How do I handle this?
 
Thanks
Pieter