ssh_pki_import_privkey_file always returns -1

[Eric Lemasson <eric.lemasson@xxxxxxxxxxxxxx>]

Hello

I hope this is the right place to ask this kind of question, apologizes in advance if I should send my question somewhere else.
I am new to libssh and trying to use it properly in a windows application that needs to do sftp.
I have followed samples found online (mostly in the tutorial section of libssh website) and came up with the following piece of code:

                ssh_session my_ssh_session = ssh_new();
                if (my_ssh_session == NULL) {
                                exit(-1);
                }
                ssh_options_set(my_ssh_session, SSH_OPTIONS_HOST, serverIP.GetBuffer());
                ssh_options_set(my_ssh_session, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
                ssh_options_set(my_ssh_session, SSH_OPTIONS_PORT, &port);
                ssh_options_set(my_ssh_session, SSH_OPTIONS_USER, User.GetBuffer());

                rc = ssh_connect(my_ssh_session);
                if (rc != SSH_OK)
                {
                                ssh_free(my_ssh_session);
                                exit(-1);
                }
                if (verify_knownhost(my_ssh_session) < 0)
                {
                                ssh_disconnect(my_ssh_session);
                                ssh_free(my_ssh_session);
                                exit(-1);
                }
                rc = ssh_userauth_publickey_auto(my_ssh_session, NULL, NULL);
                if (rc != SSH_AUTH_SUCCESS)
                {
                                ssh_key pubKey, privKey;
                                rc = ssh_pki_import_pubkey_file("C:\\Users\\XXXX\\.ssh\\key.pub", &pubKey);
                                if (rc == SSH_OK) {
                                                rc = ssh_userauth_try_publickey(my_ssh_session, NULL, pubKey);
                                                if (rc == SSH_AUTH_SUCCESS) {
                                                                rc = ssh_pki_import_privkey_file("C:\\Users\\XXXX\\.ssh\\key", NULL, NULL, NULL, &privKey);
                                                                if (rc == SSH_OK) {
                                                                                rc = ssh_userauth_publickey(my_ssh_session, NULL, privKey);
                                                                                ssh_key_free(privKey);
                                                                }
                                                }
                                                ssh_key_free(pubKey);
                                }
                                if (!authenticated) {
                                                rc = ssh_userauth_password(my_ssh_session, NULL, password.GetBuffer());
                                                if (rc != SSH_AUTH_SUCCESS)
                                                {
                                                                ssh_disconnect(my_ssh_session);
                                                                ssh_free(my_ssh_session);
                                                                exit(-1);
                                                }
                                }
                }

The key pair have been generated with puttygen tool, and I understand that putty uses a different format to store the private key, so I have used the Conversion / Export OpenSSH key (force new file format) option to have the private key in standard format.
The public key has been added to the authorized_key file on the remote server and the manual connection using putty works fine, using a password, or using the putty key agent (pageant) without having to enter a password.

In my code above, the call to the function ssh_pki_import_privkey_file always return -1. I have tried different key type but I still get the same thing. Also tried to remove the line (--- BEGIN OPENSSH PRIVATE KEY ----) in the key file but no luck.
I know that on linux / unix, permission checking on key files are very strict in .ssh directory and may be a reason for failing to authenticate.

The fact that I am getting SSH_ERROR and not SSH_EOF tells me that it is able to find the file, so I am thinking it is a file format or a file permission issue.

I don't know if the same permission checks are done on Windows and if so, what the permission should be.

The password authentication in the code works fine so I am still able to connect to the server but I would like to have the key method to work.

If you have any suggestion or tips, that would be greatly appreciated,

Thanks
Eric