You CAN list all keys in the keyring, you only have to pass an empty string ''.
<?php
$gpg = new gnupg();
$info = $gpg -> keyinfo('');
print_r($info);
?>
That's it! ;)(PECL gnupg >= 0.1)
gnupg_keyinfo — Retorna un array con las informaciones acerca de todas las claves que coinciden con el patrón dado
identifierEl identificador gnupg, generado por una llamada a la función gnupg_init() o a la función gnupg.
patternLa máscara a utilizar sobre las claves.
   Retorna un array con las informaciones acerca de todas las claves que
   coinciden con el patrón dado o retorna false si ha ocurrido un error.
  
Ejemplo #1 Ejemplo con gnupg_keyinfo() (Estilo procedimental)
<?php
$res = gnupg_init();
$info = gnupg_keyinfo($res, 'test');
print_r($info);
?>Ejemplo #2 Ejemplo con gnupg_keyinfo() (Estilo orientado a objetos)
<?php
$gpg = new gnupg();
$info = $gpg->keyinfo("test");
print_r($info);
?>You CAN list all keys in the keyring, you only have to pass an empty string ''.
<?php
$gpg = new gnupg();
$info = $gpg -> keyinfo('');
print_r($info);
?>
That's it! ;)Returns an array of information blocks. An information block looks like
<?php
array (
    'disabled' => <bool>,
    'expired' => <bool>,
    'revoked' => <bool>,
    'is_secret' => <bool>,
    'can_sign' => <bool>,
    'can_encrypt' => <bool>,
    'uids' => <array of uid blocks>,
    'subkeys' => <array of subkey blocks>,
)
?>
An uid data block looks like
<?php
array (
    'name' => <string>,
    'comment' => <string>,
    'email' => <string>,
    'uid' => <string>,
    'revoked' => <bool>,
    'invalid' => <bool>,
)
?>
A subkey block looks like
<?php
array (
    'fingerprint' => <string>,
    'keyid' => <string>,
    'timestamp' => <int>,
    'expires' => <int>,
    'is_secret' => <bool>,
    'invalid' => <bool>,
    'can_encrypt' => <bool>,
    'can_sign' => <bool>,
    'disabled' => <bool>,
    'expired' => <bool>,
    'revoked' => <bool>,
),
?>