Crypt为两个不同(相似）的密码返回相同的散列

我在使用crypt（）时遇到问题，如果用户有密码（本例中为password1），并且他们将其更改为password2，则哈希将返回相同的结果。您可以在此处测试：旧链接输入password1作为当前密码，输入password2作为新密码并确认密码，您将看到结果。如果输入了完全不相似的密码，则没有问题。我知道还有其他方法可以破解密码等。我比任何事情都好奇。我的代码如下：

<?php
$oldpassword="password1";
echo "<form method='"post'">
<p>Enter Current Password: <input type='"password'" name='"currentpassword'" /></p>
<p>Enter New Password: <input type='"password'" name='"password'" /></p>
<p>Confirm New Password: <input type='"password'" name='"confirmpassword'" /></p>
<p><input type='"submit'" value='"Change Password'"></p>
</form>";
$user_id = $_SESSION['user_id'];
$pass=$_POST['password'];
$salt = 'xxxxx';
$currentpassword = crypt($_POST['currentpassword'], $salt);
$oldpassword = crypt($oldpassword, $salt);
if(isset($_POST['password'])) {
    if ($currentpassword !== $oldpassword) {
        echo "The password you entered for current password does not match our records.";
    }
    else {
        if ($_POST['password'] && $_POST['confirmpassword']) {
            if ($_POST['password'] == $_POST['confirmpassword']) {
            $hash = crypt($pass, $salt);
                if ($hash == $currentpassword) {
                    echo "Current Password:&nbsp;";
                    var_dump($_POST['currentpassword']);
                    echo "<br/>";
                    echo "New Password:&nbsp;";
                    var_dump($_POST['password']);
                    echo "<br/>";
                    echo "New Hash:&nbsp";
                    var_dump($hash);
                    echo "<br/>";
                    echo "Current Password Hash:&nbsp";
                    var_dump($currentpassword);
                    echo "<br/>";
                    echo "<hr/>";
                    echo "Your new password cannot be the same as your current password.";
                }
                else {
                    echo "Your password has been changed successfully<br/>";
                }
            } else {
                echo "Your passwords do not match. Please try again.";
            }
        }
    }
}
?>