This is a simple example of a Procedural use of import addencryptkey and encrypt. Obviously in a real world use you would only be importing the key once.
<?php
putenv("GNUPGHOME=/tmp");
$pubkey = "-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.2.6 (GNU/Linux)
mQGiBEe68W8RBACVuFuv4d+roDSCdRO1SuO8dQwds4VTjVOqgVKQtq6+8Fe95RY8
BAf1IyLj4bxvWPhr0wZdVwTosD/sFoPtdCyhVcF932nP0GLHsTEeVwSz9mid22HI
O4Kmwj2kE+I+C9QdzAg0zaWQnVaF9UC7pIdMR6tEnADI8nkVDdZ+zb2ziwCg6Yqu
tk3KAzKRT1SNUzTE/n9y2PED/1tIWiXfGBGzseX0W/e1G+MjuolWOXv4BXeiFGmn
8wnHsQ4Z4Tzk+ag0k+6pZZXjcL6Le486wpZ9MAe6LM31XDpQDVtyCL8t63nvQpB8
TUimbseBZMb3TytCubNLGFe5FnNLGDciElcD09d2xC6Xv6zE2jj4GtBW1bXqYWtl
jm0PA/4u6av6o6pIgLRfAawspr8kaeZ8+FU4NbIiS6xZmBUEQ/o7q95VKGgFVKBi
ugDOlnbgSzBIwSlsRVT2ivu/XVWnhQaRCotSm3AzOc2XecqrJ6F1gqk0n+yP/1h1
yeTvvfS5zgqNTG2UmovjVsKFzaDqmsYZ+sYfwc209z9PY+6FuLQnQXBhY2hlVGVz
dCAoVGVzdGluZykgPGFwYWNoZUBsb2NhbGhvc3Q+iF4EExECAB4FAke68W8CGwMG
CwkIBwMCAxUCAwMWAgECHgECF4AACgkQJE9COu2PFIEGDwCglArzAza13xjbdR04
DQ1U9FWQhMYAnRrWQeGTRm+BYm6SghNpDOKcmMqruQENBEe68XAQBADPIO+JFe5t
BQmI4l60bNMNSUqsL0TtIP8G6Bpd8q2xBOemHCLfGT9Y5DN6k0nneBQxajSfWBQ5
ZdKFwV5ezICz9fnGisEf9LPSwctfUIcvumbcPPsrUOUZX7BuCHrcfy1nebS3myO/
ScTKpW8Wz8AjpKTBG55DMkXSvnx+hS+PEwADBQP/dNnVlKYdNKA70B4QTEzfvF+E
5lyiauyT41SQoheTMhrs/3RIqUy7WWn3B20aTutHWWYXdYV+E85/CarhUmLNZGA2
tml1Mgl6F2myQ/+MiKi/aj9NVhcuz38OK/IAze7kNJJqK+UEWblB2Wfa31/9nNzv
ewVHa1xHtUyVDaewAACISQQYEQIACQUCR7rxcAIbDAAKCRAkT0I67Y8UgRwEAKDT
L6DwyEZGLTpAqy2OLUH7SFKm2ACgr3tnPuPFlBtHx0OqY4gGiNMJHXE=
=jHPH
-----END PGP PUBLIC KEY BLOCK-----";
$enc = (null);
$res = gnupg_init();
echo "gnupg_init RTV = <br/><pre>\n";
var_dump($res);
echo "</pre>\n";
$rtv = gnupg_import($res, $pubkey);
echo "gnupg_import RTV = <br/><pre>\n";
var_dump($rtv);
echo "</pre>\n";
$rtv = gnupg_addencryptkey($res, "C25F29936D9046D73A77DCF8244F423AED8F1481");
echo "gnupg_addencryptkey RTV = <br /><pre>\n";
var_dump($rtv);
echo "</pre>\n";
$enc = gnupg_encrypt($res, "just a test to see if anything works");
echo "Encrypted Data: " . $enc . "<br/>";
?>
