ssh2_auth_pubkey_file authentication always fails - php

Question

I'm trying to connect to another machine using PHP's ssh2 functions. I know the ssh keys have been created with no passwords and are distributed correctly, I can ssh user#host in the terminal on my machine to the server.
The PHP function tries to connect to a ip address using an ssh key file:-
function minnerConnect($miner_serial) {
$port = '7822';
$miner_ip = $this->getMinerIp($miner_serial);
$methods = array(
'kex' => 'diffie-hellman-group1-sha1',
'hostkey' => 'ssh-dss',
'client_to_server' => array(
'crypt' => '3des-cbc',
'mac' => 'hmac-md5',
'comp' => 'none'),
'server_to_client' => array(
'crypt' => '3des-cbc',
'mac' => 'hmac-md5',
'comp' => 'none'));
$connection = ssh2_connect($miner_ip, $port, $methods);
if (ssh2_auth_pubkey_file($connection, 'root',
'/root/.ssh/id_dsa.pub',
'/root/.ssh/id_dsa','')) {
echo "Public Key Authentication Successful\n";
} else {
echo "Public Key Authentication Failed";
}
but the error shown is:-
( ! ) Warning: ssh2_auth_pubkey_file(): Authentication failed for root using public key: Callback returned error in /var/www/application/models/miner_model.php on line 95
line 95 is '/root/.ssh/id_dsa','')) {.
Can anybody suggest a fix?

Answer 1

The error in this case was that the keys were generated by the root user, but they need to be accessible by the web server group/owner www-data.
I didn't like the idea of keeping ssh keys in a web folder open to www-data, so I moved the key files to a new user's home directory (/home/keyuser/) then made them accessible to www-data. Authentication was successful.
Even though the original error was saying it found the file, it couldn't read the file.
A better debug method is to try reading the file via php:
$prv_key = file_get_contents('/var/www/application/files/id_dsa');
print "<pre>";
var_export($prv_key);
print "</pre>";