77

I've just set up the new google recaptcha with checkbox, it's working fine on front end, however I don't know how to handle it on server side using PHP. I've tried to use the old code below but the form is sent even if the captcha is not valid.

require_once('recaptchalib.php');
$privatekey = "my key";
$resp = recaptcha_check_answer ($privatekey,
        $_SERVER["REMOTE_ADDR"],
        $_POST["recaptcha_challenge_field"],
        $_POST["recaptcha_response_field"]);

if (!$resp->is_valid) {
 $errCapt='<p style="color:#D6012C ">The CAPTCHA Code wasnot entered correctly.</p>';}
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4
  • Check it's been filled in. if( strlen($_POST['recaptcha_challenge_field']) > 0) {}
    – ʰᵈˑ
    Dec 3, 2014 at 14:30
  • thank you for response but can you give me more details please...
    – Moatez
    Dec 3, 2014 at 15:06
  • 1
    I just implemented this myself on a contact form. I'd suggest using the new Google-supplied recaptchalib.php along with their example at this link: github.com/google/ReCAPTCHA/tree/master/php
    – Ed Stenger
    Dec 3, 2014 at 15:18
  • thank you, but i am sorry i didn't understand yet, i have two files contact.html and contact.php, the first call the second, in thé first i put the following : before </head> : <script src='google.com/recaptcha/api.js'></script> before the submit button <div class="g-recaptcha" data-sitekey="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"></div> but in contact.php i dont know what i should put ??
    – Moatez
    Dec 5, 2014 at 0:25

12 Answers 12

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131

Private key safety

While the answers here are definately working, they are using a GET request, which exposes your private key (even though https is used). On Google Developers the specified method is POST.

For a little bit more detail: https://stackoverflow.com/a/323286/1680919

Verification via POST

function isValid() 
{
    try {

        $url = 'https://www.google.com/recaptcha/api/siteverify';
        $data = ['secret'   => '[YOUR SECRET KEY]',
                 'response' => $_POST['g-recaptcha-response'],
                 'remoteip' => $_SERVER['REMOTE_ADDR']];
                 
        $options = [
            'http' => [
                'header'  => "Content-type: application/x-www-form-urlencoded\r\n",
                'method'  => 'POST',
                'content' => http_build_query($data) 
            ]
        ];
    
        $context  = stream_context_create($options);
        $result = file_get_contents($url, false, $context);
        return json_decode($result)->success;
    }
    catch (Exception $e) {
        return null;
    }
}

Array Syntax: I use the "new" array syntax ( [ and ] instead of array(..) ). If your php version does not support this yet, you will have to edit those 3 array definitions accordingly (see comment).

Return Values: This function returns true if the user is valid, false if not, and null if an error occured. You can use it for example simply by writing if (isValid()) { ... }

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9
  • 2
    If you need the old array syntax, change the $data = ... and $options = ... declarations to this: $data = array('secret' => '[YOUR SECRET KEY]', 'response' => $_POST['g-recaptcha-response'], 'remoteip' => $_SERVER['REMOTE_ADDR']); $options = array( 'http' => array( 'header' => "Content-type: application/x-www-form-urlencoded\r\n", 'method' => 'POST', 'content' => http_build_query($data) ) );
    – Levite
    Jun 10, 2015 at 7:06
  • 4
    You can save a request to the server and bail ahead of time: if (empty($_POST['g-recaptcha-response'])) { return false; }
    – Westy92
    Nov 28, 2016 at 3:47
  • 6
    https urls are actually encrypted, so the private key is not exposed even when using a GET request, see: stackoverflow.com/questions/499591/are-https-urls-encrypted
    – Varga Tamas
    Dec 8, 2016 at 14:06
  • 1
    Please note, for debugging purposes, you can only call isValid() once. If called a second time, it will return false. Found this out the hard way with an echo statement...
    – Sablefoste
    May 12, 2017 at 16:58
  • 1
    None of the function used throw exceptions so the try{}catch() is pointless
    – chris
    Feb 2, 2018 at 10:59
116

this is solution

index.html

<html>
  <head>
    <title>Google recapcha demo - Codeforgeek</title>
    <script src='https://www.google.com/recaptcha/api.js'></script>
  </head>
  <body>
    <h1>Google reCAPTHA Demo</h1>
    <form id="comment_form" action="form.php" method="post">
      <input type="email" placeholder="Type your email" size="40"><br><br>
      <textarea name="comment" rows="8" cols="39"></textarea><br><br>
      <input type="submit" name="submit" value="Post comment"><br><br>
      <div class="g-recaptcha" data-sitekey="=== Your site key ==="></div>
    </form>
  </body>
</html>

verify.php

<?php
    $email; $comment; $captcha;

    if(isset($_POST['email']))
        $email=$_POST['email'];
    if(isset($_POST['comment']))
        $comment=$_POST['comment'];
    if(isset($_POST['g-recaptcha-response']))
        $captcha=$_POST['g-recaptcha-response'];

    if(!$captcha){
        echo '<h2>Please check the the captcha form.</h2>';
        exit;
    }

    $response = json_decode(file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=YOUR SECRET KEY&response=".$captcha."&remoteip=".$_SERVER['REMOTE_ADDR']), true);
    if($response['success'] == false)
    {
        echo '<h2>You are spammer ! Get the @$%K out</h2>';
    }
    else
    {
        echo '<h2>Thanks for posting comment.</h2>';
    }
?>

http://codeforgeek.com/2014/12/google-recaptcha-tutorial/

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6
  • 15
    The reCAPTCHA form field value is being concatenated directly into the verify URL. An attacker could use that to inject arbitrary form parameters on the verify request, potentially circumventing the CAPTCHA. To solve this problem, sanitize the captcha variable like this: urlencode($captcha)
    – sffc
    Oct 1, 2015 at 8:19
  • 2
    this code does not encode the parameters which can be used by attackers to break your code.
    – Paul
    Mar 25, 2016 at 7:53
  • 6
    The data should be POSTed as specified in the docs. This code uses a GET method. I'd go with a variation on Levit's answer.
    – ͢bts
    Jun 23, 2016 at 11:59
  • 2
    Worked well for me. Except (in index.html) on the form line: action="form.php", it should be action="verify.php".
    – Joe
    Apr 14, 2018 at 21:50
  • This codes works on my Shared hosting & not on VPS server. Are there any requirements linked to server?
    – Mohammed Kumel
    Mar 27, 2019 at 0:41
28

I'm not a fan of any of these solutions. I use this instead:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://www.google.com/recaptcha/api/siteverify");
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, [
    'secret' => $privatekey,
    'response' => $_POST['g-recaptcha-response'],
    'remoteip' => $_SERVER['REMOTE_ADDR']
]);

$resp = json_decode(curl_exec($ch));
curl_close($ch);

if ($resp->success) {
    // Success
} else {
    // failure
}

I'd argue that this is superior because you ensure it is being POSTed to the server and it's not making an awkward 'file_get_contents' call. This is compatible with recaptcha 2.0 described here: https://developers.google.com/recaptcha/docs/verify

I find this cleaner. I see most solutions are file_get_contents, when I feel curl would suffice.

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2
  • 2
    This is a good working solution if you are unable to use the file_get_contents() due to 'allow_url_fopen' being disabled in php.ini. Works for me. +1.
    – Gregory R.
    Mar 28, 2017 at 5:54
  • Straightforward and simple, and uses POST as required by Google
    – John Contarino
    Mar 28, 2019 at 19:16
8

Easy and best solution is the following.
index.html 

<form action="submit.php" method="POST">
   <input type="text" name="name" value="" />
   <input type="text" name="email" value="" />
   <textarea type="text" name="message"></textarea>
   <div class="g-recaptcha" data-sitekey="Insert Your Site Key"></div>
   <input type="submit" name="submit" value="SUBMIT">
</form>

submit.php 

<?php
if(isset($_POST['submit']) && !empty($_POST['submit'])){
  if(isset($_POST['g-recaptcha-response']) && !empty($_POST['g-recaptcha-response'])){
    //your site secret key
    $secret = 'InsertSiteSecretKey';
    //get verify response data
    $verifyResponse = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret='.$secret.'&response='.$_POST['g-recaptcha-response']);
    $responseData = json_decode($verifyResponse);
    if($responseData->success){
        //contact form submission code goes here

        $succMsg = 'Your contact request have submitted successfully.';
    }else{
        $errMsg = 'Robot verification failed, please try again.';
    }
  }else{
    $errMsg = 'Please click on the reCAPTCHA box.';
  }
}
?>

I have found this reference and full tutorial from here - Using new Google reCAPTCHA with PHP

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0
7

I liked Levit's answer and ended up using it. But I just wanted to point out, just in case, that there is an official Google PHP library for new reCAPTCHA: https://github.com/google/recaptcha

The latest version (right now 1.1.2) supports Composer and contains an example that you can run to see if you have configured everything correctly.

Below you can see part of the example that comes with this official library (with my minor modifications for clarity):

// Make the call to verify the response and also pass the user's IP address
    $resp = $recaptcha->verify($_POST['g-recaptcha-response'], $_SERVER['REMOTE_ADDR']);

    if ($resp->isSuccess()) {
// If the response is a success, that's it!
        ?>
        <h2>Success!</h2>
        <p>That's it. Everything is working. Go integrate this into your real project.</p>
        <p><a href="/">Try again</a></p>
        <?php
    } else {
// If it's not successful, then one or more error codes will be returned.
        ?>
        <h2>Something went wrong</h2>
        <p>The following error was returned: <?php
            foreach ($resp->getErrorCodes() as $code) {
                echo '<tt>' , $code , '</tt> ';
            }
            ?></p>
        <p>Check the error code reference at <tt><a href="https://developers.google.com/recaptcha/docs/verify#error-code-reference">https://developers.google.com/recaptcha/docs/verify#error-code-reference</a></tt>.
        <p><strong>Note:</strong> Error code <tt>missing-input-response</tt> may mean the user just didn't complete the reCAPTCHA.</p>
        <p><a href="/">Try again</a></p>
    <?php
    }

Hope it helps someone.

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3

To verify at server side using PHP. Two most important thing you need to consider.

1. $_POST['g-recaptcha-response']

2.$secretKey = '6LeycSQTAAAAAMM3AeG62pBslQZwBTwCbzeKt06V';

$verifydata = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret='.$secretKey.'&response='.$_POST['g-recaptcha-response']);
        $response= json_decode($verifydata);

If you get $verifydata true, You done.
For more check out this
Google reCaptcha Using PHP | Only 2 Step Integration

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0
2

In the example above. For me, this if($response.success==false) thing does not work. Here is correct PHP code: 

$url = 'https://www.google.com/recaptcha/api/siteverify';
$privatekey = "--your_key--";
$response = file_get_contents($url."?secret=".$privatekey."&response=".$_POST['g-recaptcha-response']."&remoteip=".$_SERVER['REMOTE_ADDR']);
$data = json_decode($response);

if (isset($data->success) AND $data->success==true) {
            // everything is ok!
} else {
            // spam
}
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2
  • 2
    This is because you're not passing true as the 2nd parameter to json_decode. By default, json_decode returns an object (jsOn), but passing true will allow it to return an array.
    – Curtis Mattoon
    Apr 23, 2015 at 13:11
  • "In the example above..." please note that the StackExchange platform sorts answers according to their ranking by votes. The example above is clearly not the one you were referring to.
    – Nicolas
    Jul 18, 2018 at 3:41
1

it is similar with mattgen88, but I just fixed CURLOPT_HEADER, and redefine array for it work in domain.com host server. this one doesn't work on my xampp localhost. Those small error but took long to figure out. this code was tested on domain.com hosting.

   $privatekey = 'your google captcha private key';

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://www.google.com/recaptcha/api/siteverify");
    curl_setopt($ch, CURLOPT_HEADER, 'Content-Type: application/json');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, array(
        'secret' => $privatekey,
        'response' => $_POST['g-recaptcha-response'],
        'remoteip' => $_SERVER['REMOTE_ADDR']
    )
               );

    $resp = json_decode(curl_exec($ch));
    curl_close($ch);

    if ($resp->success) {
        // Success
        echo 'captcha';
    } else {
        // failure
        echo 'no captcha';
    }
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1

Here you have simple example. Just remember to provide secretKey and siteKey from google api.

<?php
$siteKey = 'Provide element from google';
$secretKey = 'Provide element from google';

if($_POST['submit']){
    $username = $_POST['username'];
    $responseKey = $_POST['g-recaptcha-response'];
    $userIP = $_SERVER['REMOTE_ADDR'];
    $url = "https://www.google.com/recaptcha/api/siteverify?secret=$secretKey&response=$responseKey&remoteip=$userIP";
    $response = file_get_contents($url);
    $response = json_decode($response);
    if($response->success){
        echo "Verification is correct. Your name is $username";
    } else {
        echo "Verification failed";
    }
} ?>

<html>
<meta>
    <title>Google ReCaptcha</title>
</meta>
<body>
    <form action="index.php" method="post">
        <input type="text" name="username" placeholder="Write your name"/>
        <div class="g-recaptcha" data-sitekey="<?= $siteKey ?>"></div>
        <input type="submit" name="submit" value="send"/>
    </form>
    <script src='https://www.google.com/recaptcha/api.js'></script>
</body>

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1

Source Tutorial Link

V2 of Google reCAPTCHA.

Step 1 - Go to Google reCAPTCHA

Login then get Site Key and Secret Key

Step 2 - Download PHP code here and upload src folder on your server.

Step 3 - Use below code in your form.php

        <head>
            <title>FreakyJolly.com Google reCAPTCHA EXAMPLE form</title>
            <script src='https://www.google.com/recaptcha/api.js'></script>
        </head>

        <body>
            <?php

            require('src/autoload.php');

            $siteKey = '6LegPmIUAAAAADLwDmXXXXXXXyZAJVJXXXjN';
            $secret = '6LegPmIUAAAAAO3ZTXXXXXXXXJwQ66ngJ7AlP';

            $recaptcha = new \ReCaptcha\ReCaptcha($secret);

            $gRecaptchaResponse = $_POST['g-recaptcha-response']; //google captcha post data
            $remoteIp = $_SERVER['REMOTE_ADDR']; //to get user's ip

            $recaptchaErrors = ''; // blank varible to store error

            $resp = $recaptcha->verify($gRecaptchaResponse, $remoteIp); //method to verify captcha
            if ($resp->isSuccess()) {

               /******** 

                Add code to create User here when form submission is successful

               *****/

            } else {

                /****

                // This variable will have error when reCAPTCHA is not entered correctly.

                ****/

               $recaptchaErrors = $resp->getErrorCodes(); 
            }


            ?>
                <form autcomplete="off" class="form-createuser" name="create_user_form" action="" method="post">
                    <div class="panel periodic-login">
                        <div class="panel-body text-center">
                            <div class="form-group form-animate-text" style="margin-top:40px !important;">
                                <input type="text" autcomplete="off" class="form-text" name="new_user_name" required="">
                                <span class="bar"></span>
                                <label>Username</label>
                            </div>
                            <div class="form-group form-animate-text" style="margin-top:40px !important;">
                                <input type="text" autcomplete="off" class="form-text" name="new_phone_number" required="">
                                <span class="bar"></span>
                                <label>Phone</label>
                            </div>
                            <div class="form-group form-animate-text" style="margin-top:40px !important;">
                                <input type="password" autcomplete="off" class="form-text" name="new_user_password" required="">
                                <span class="bar"></span>
                                <label>Password</label>
                            </div>
                            <?php 
                                    if(isset($recaptchaErrors[0])){
                                        print('Error in Submitting Form. Please Enter reCAPTCHA AGAIN');
                                    }
                              ?>
                            <div class="g-recaptcha" data-sitekey="6LegPmIUAAAAADLwDmmVmXXXXXXXXXXXXXXjN"></div>
                            <input type="submit" class="btn col-md-12" value="Create User">
                        </div>
                    </div>
                </form>
        </body>

        </html>
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0

In response to @mattgen88's answer ,Here is a CURL method with better arrangement:

   //$secret= 'your google captcha private key';
    $curl = curl_init();
    curl_setopt_array($curl, array(
        CURLOPT_URL             => "https://www.google.com/recaptcha/api/siteverify",
        CURLOPT_HEADER          => "Content-Type: application/json",
        CURLOPT_RETURNTRANSFER  => true,
        CURLOPT_SSL_VERIFYPEER  => FALSE, // to disable ssl verifiction set to false else true
        //CURLOPT_ENCODING      => "",
        CURLOPT_MAXREDIRS       => 10,
        CURLOPT_TIMEOUT         => 30,
        CURLOPT_HTTP_VERSION    => CURL_HTTP_VERSION_1_1,
        CURLOPT_CUSTOMREQUEST   => "POST",
        CURLOPT_POSTFIELDS      => array(
            'secret' => $secret,
            'response' => $_POST['g-recaptcha-response'],
            'remoteip' => $_SERVER['REMOTE_ADDR']
        )
    ));

    $response = json_decode(curl_exec($curl));
    $err = curl_error($curl);

    curl_close($curl);

    if ($response->success) {
        echo 'captcha';
    } 
    else if ($err){
        echo $err;
    }   
    else {
        echo 'no captcha';
    }
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0

Check below example

<script src='https://www.google.com/recaptcha/api.js'></script>
<script>

function get_action(form) 
{
    var v = grecaptcha.getResponse();
    if(v.length == 0)
    {
        document.getElementById('captcha').innerHTML="You can't leave Captcha Code empty";
        return false;
    }
    else
    {
         document.getElementById('captcha').innerHTML="Captcha completed";
        return true; 
    }
}

</script>
<form autocomplete="off" method="post" action=submit.php">

    <input type="text" name="name">
    <input type="text" name="email">
    <div class="g-recaptcha" id="rcaptcha"  data-sitekey="site key"></div>
    <span id="captcha" style="color:red" /></span> <!-- this will show captcha errors -->
    <input type="submit" id="sbtBrn" value="Submit" name="sbt" class="btn btn-info contactBtn" />
</form>
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