<?php
/*
 * Copyright 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

require_once 'Google/Auth/Exception.php';
require_once 'Google/Verifier/Abstract.php';

/**
 * Verifies signatures using PEM encoded certificates.
 *
 * @author Brian Eaton <beaton@google.com>
 */
class Google_Verifier_Pem extends Google_Verifier_Abstract {
    private $publicKey;

    /**
     * Constructs a verifier from the supplied PEM-encoded certificate.
     *
     * $pem: a PEM encoded certificate (not a file).
     * @param $pem
     * @throws Google_Auth_Exception
     * @throws Google_Exception
     */
    public function __construct($pem) {
        if (!function_exists('openssl_x509_read')) {
            throw new Google_Exception('Google API PHP client needs the openssl PHP extension');
        }
        $this->publicKey = openssl_x509_read($pem);
        if (!$this->publicKey) {
            throw new Google_Auth_Exception("Unable to parse PEM: $pem");
        }
    }

    public function __destruct() {
        if ($this->publicKey) {
            openssl_x509_free($this->publicKey);
        }
    }

    /**
     * Verifies the signature on data.
     *
     * Returns true if the signature is valid, false otherwise.
     * @param $data
     * @param $signature
     * @return bool
     * @throws Google_Auth_Exception
     */
    public function verify($data, $signature) {
        $hash = defined("OPENSSL_ALGO_SHA256") ? OPENSSL_ALGO_SHA256 : "sha256";
        $status = openssl_verify($data, $signature, $this->publicKey, $hash);
        if ($status === -1) {
            throw new Google_Auth_Exception('Signature verification error: ' . openssl_error_string());
        }
        return $status === 1;
    }
}