How i can create a self-signed certificate using phpseclib - php

Question

How i can create a self-signed certificate using phpseclib from a existing .csr file, only i can use a .csr file.
I've read the manual and the method use a private key, but in my assignment i only can use a .csr file.
I hope you can help me.
Here's my code:
<?php
include('File/X509.php');
include('Crypt/RSA.php');
if ($_FILES["file"]["error"] > 0)
{
echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
}
else
{
//This is the content of the file
$csr = file_get_contents($_FILES["file"]["name"]);
}
// create private key / x.509 cert for stunnel / website
$privKey = new Crypt_RSA();
extract($privKey->createKey());
$privKey->loadKey($privatekey);
$pubKey = new Crypt_RSA();
$pubKey->loadKey($publickey);
$pubKey->setPublicKey();
$subject = new File_X509();
$subject->loadCSR('...'); // see csr.pem
// calling setPublicKey() is unnecessary when loadCSR() is called
$issuer = new File_X509();
$issuer->setPrivateKey($privKey);
$issuer->setDN($subject->getDN());
$x509 = new File_X509();
//$x509->setStartDate('-1 month'); // default: now
//$x509->setEndDate('+1 year'); // default: +1 year
$result = $x509->sign($issuer, $subject);
echo "the stunnel.pem contents are as follows:\r\n\r\n";
echo $privKey->getPrivateKey();
echo "\r\n";
echo $x509->saveX509($result);
echo "\r\n";
?>

Answer 1

You need a private key, plain and simple. Otherwise, what are you going to sign it with? The signature field of an X.509 cert is mandatory.
I mean, if all you want is a public key, you don't need to bother with the X.509 overhead. You can just pony up a public key that looks like this:
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqGKukO1De7zhZj6+H0qtjTkVxwTCpvKe4eCZ0
FPqri0cb2JZfXJ/DgYSF6vUpwmJG8wVQZKjeGcjDOL5UlsuusFncCzWBQ7RKNUSesmQRMSGkVb1/
3j+skZ6UtW+5u09lHNsj6tQ51s1SPrCBkedbNf0Tp0GbMJDyR4e9T04ZZwIDAQAB
-----END PUBLIC KEY-----
But X.509 is more than just a public key - it's a signed public key. Technically, a CSR is, too, but CSR's are always self-signed whereas X.509 certs can be signed by anyone.