如何在 php 中将输入字段与提交时的变量进行比较？

Question

我创建了一个随机字符串并将其用作验证码但无法验证。我在 PHP 中非常菜鸟。在这里我使用 isset($_POST['submit']) 但是没有点击提交这个表单显示错误（变量）（strCaptcha 是必需的）。我的逻辑是，在提交时，点击代码会将 'strCaptcha' 的值与 $str 进行比较，并显示错误或运行表单。

$error = '';
if (isset($_POST['submit'])){
  if (empty($_POST["strCaptcha"]) || $_POST["strCaptcha"] != $str) {
    $error = "strCaptcha is required";
   }
}
<form method="post" action="<?php echo $action; ?>" >
    <p><label><b>COA Number:</b></label><br>
    <input type="text" name="number" class="text"><br><be>
    <span id="realcap" style="visibility:hidden;"><?php echo implode(' ',str_split($str)); ?></span><be>
    <span style="color:red;"><?php echo $error; ?></span><br>
    <img src="" id="captch" alt="This Is a CAPTCHA Image"><br>
    <label><b>Enter the text of the image above:</b></label><br>
    <input name="strCaptcha" type="text" class="text" value="" maxlength="5"><br><br>
    <input type="submit" class="awesome medium" name="submit" value="Verify Now"></p>
</form>

添加图片

<script src="//cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.min.js"></script>
<script>
  html2canvas(document.getElementById("realcap"), {
    onrendered: function(canvas) {
      var screenshot = canvas.toDataURL("image/png");
      document.getElementById("captch").setAttribute("src", screenshot);
    }
  });
</script>

随机字符串

$n=5; 
function getName($n) { 
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; 
    $randomString = ''; 
    for ($i = 0; $i < $n; $i++) { 
        $index = rand(0, strlen($characters) - 1); 
        $randomString .= $characters[$index]; 
    } 
    return $randomString; 
} 

$str = getName($n);

Answer 1

如果您在 html.

的隐藏字段中以纯文本形式提供验证码值，那么您的脚本很容易被欺骗

您必须创建随机字符串并将值保存到会话中，这样该值就不会暴露给用户，您可以稍后使用它进行比较。

页面代码

<?php 
session_start();
$captcha = $_SESSION['captcha'];
$error = '';
if (isset($_POST['submit'])){
  if (empty($_POST["strCaptcha"]) || $_POST["strCaptcha"] != $captcha) {
    $error = "strCaptcha is required";
   }
}
<form method="post" action="<?php echo $action; ?>" >
    <p><label><b>COA Number:</b></label><br>
    <input type="text" name="number" class="text"><br>
    <span style="color:red;"><?php echo $error; ?></span><br>
    <img src="image.php" id="captch" alt="This Is a CAPTCHA Image"><br>
    <label><b>Enter the text of the image above:</b></label><br>
    <input name="strCaptcha" type="text" class="text" value="" maxlength="5"><br><br>
    <input type="submit" class="awesome medium" name="submit" value="Verify Now"></p>
</form>

图片必须在服务器端生成。

示例未经测试。 image.php

<?php 
$n=5; 
function getName($n) { 
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; 
    $randomString = ''; 
    for ($i = 0; $i < $n; $i++) { 
        $index = rand(0, strlen($characters) - 1); 
        $randomString .= $characters[$index]; 
    } 
    return $randomString; 
} 


$str = getName($n);
session_start();
$_SESSION['captcha'] = $str;

// Generate image using the $str to create the image.
$im = imagecreate(100, 30);

// White background and blue text
$bg = imagecolorallocate($im, 255, 255, 255);
$textcolor = imagecolorallocate($im, 0, 0, 255);

// Write the string at the top left
imagestring($im, 5, 0, 0, $str, $textcolor);

// Output the image
header('Content-type: image/png');

imagepng($im);
imagedestroy($im);

如何在 php 中将输入字段与提交时的变量进行比较？

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