RSA Sign & Verify v2

<?php
include 'vendor/autoload.php';
$plaintext  = 'Hello, this is a text written by me, John Doe.' . "\n" . time();
//RSA-2048
$privatekey = '-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----';
$publickey  = '-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAzANst0RirmL3vrPHIGxH
+1fQMmEemcS7N+Gq5QY34m7imyc4wELe2DGQ0O8r5fcO3wO+1MlDwrZiTOvPBJZt
Tid4lGN5rjGJIIXrZ2eXEboUC3QN+gsZHTLQ5asJOMVEQYKRJN/TuMgmvvZmtEUD
ngsgXdoddqELld6Ha7DMV87/RUiSwD270XukDO+tnpjPiyiMwvaJGYtvBCKK9mAy
ctyWvcTt3j2cwD7NqzlokmTSWcoltS+xEHly5IcE+tFRag6wMSxhVzkDyz2D4Q3Z
wSg/Opvd1AN85eo5ybaxZ0gdgBWslRk2X4zNs7vJfVrIL0g8UKEg196UqZHxHLDq
AQIDAQAB
-----END PUBLIC KEY-----';
$signature = '';
$status = '';

if (isset($_GET['action'])) {
    $rsa = new \phpseclib\Crypt\RSA();
    $rsa->setHash('sha512');
    $rsa->setMGFHash('sha512');
    $plaintext  = $_GET['plaintext'];
    if ($_GET['action'] == 'sign') {
        $privatekey = $_GET['privatekey'];
        $rsa->loadKey($privatekey);
        $signature = $rsa->sign($plaintext);
        $signature = base64_encode($signature);
    } else {
        $publickey = $_GET['publickey'];
        $signature = $_GET['signature'];
        $rsa->loadKey($publickey);
        $res = $rsa->verify($plaintext, base64_decode($signature));
        $status = $res ? "Verification OK" : "Verification Failed";
    }
}
?>

<html>
<head>
    <title>RSA Sign & Verify v2</title>
</head>
<body>
    <h1>Sign a text</h1>
    <form action="rsa-sign-verify-v2.php">
        <p><b>Input plain text</b></p>
        <textarea name="plaintext" style="height:100px;width:600px;"><?php echo $plaintext;?></textarea><br>
        <p><b>Input Private Key</b></p>
        <textarea name="privatekey" style="height:100px;width:600px;"><?php echo $privatekey;?></textarea><br>
        <input type="hidden" name="action" value="sign">
        <input type="submit" value="Submit">
    </form>
    <p><b>Signature</b></p>
    <textarea name="signature" style="height:100px;width:600px;"><?php echo $signature;?></textarea><br></p>
    <br>
    <hr><br>

    <h1>Verify a text</h1>
    <form action="rsa-sign-verify-v2.php">
        <p><b>Input plain text</b></p>
        <textarea name="plaintext" style="height:100px;width:600px;"><?php echo $plaintext;?></textarea><br>
        <p><b>Input Public Key</b></p>
        <textarea name="publickey" style="height:100px;width:600px;"><?php echo $publickey;?></textarea><br>
        <p><b>Input Signature</b></p>
        <textarea name="signature" style="height:100px;width:600px;"><?php echo $signature;?></textarea><br></p>
        <input type="hidden" name="action" value="verify">
        <input type="submit" value="Submit">
    </form>
    <p><b>Verification result: </b><font color='red'><?php echo $status;?></font></p>
    <p></p>
</body>
</html>