required_keys.php

<?php
function f($in, $required) {
    $keys = array_keys(array_intersect_key(($in), array_flip($required)));
    sort($keys);
    sort($required);
    return $keys === $required;
}

$required = array('key1', 'key2');

$in1 = array(
    'key2' => 200,
    'key1' => 100,
    'key3' => 333,
);
$in2 = array(
    'key1' => 100,
    'key3' => 333,
);


$result = f($in1, $required);
var_dump($result);
$result = f($in2, $required);
var_dump($result);