Extract public key from a PFX certificate to a .cer file with PHP OPENSSL

Question

I'm trying to create an encryption PHP-OPENSSL module to sign data and communicate with a third-party app. I have a digital .PFX certificate (cert.pfx) for this purpose.

I can open it and read it with openssl_pkcs12_read() with my passphrase.

The setup of the third party app ask me to upload the .cer public key of my certificate.

Because, i only have a .pfx file. I'm trying to extract the .cer public key from the PFX to create and upload the .cer file.

I'm using PHP-OPENSSL.

I tried to do it with this command :

 $pkeydet = openssl_pkey_get_details(openssl_pkey_get_public(file_get_contents("/path/to/cert.pfx")));

But it doesn't give the expected result (openssl_pkey_get_details() expects parameter 1 to be resource, boolean given). I'm not sure the reason why...

What this the correct way to achieve the creation of the .cer file?

Thank you :)

Answer 1

I think i found the solution, I need to make a conversion from PFX to PEM to CER because the function openssl_pkey_get_details() only works with a .pem certificate.

Here is what I did :

$pass = "thisismypass"; // my pfx is pwd protected
$cert_info = array();

I read the certificate

if (!$cert_store = file_get_contents(/path/to/cert.pfx")) {
echo "Error: Unable to read the cert file\n";
exit;
}

if (openssl_pkcs12_read($cert_store, $cert_info, $pass)) {
echo "Certificate loaded\n";
}else{
echo "Error: Unable to read the cert store.\n";
exit;
}

I write the .CER certificate

$cert = $cert_info['pkey'].$cert_info['cert'].implode('', $cert_info['extracerts']);
file_put_contents(/path/to/cert.cer',$cert);

I write the .PEM certificate

$cert = $cert_info['cert'].implode('', $cert_info['extracerts']);
file_put_contents(/path/to/cert.pem', $cert);

Now, I can extract the public key from the .PEM :

$pkeydet = openssl_pkey_get_details(openssl_pkey_get_public(file_get_contents(/path/to/cert.pem')));
file_put_contents(/path/to/publick.pem', $pkeydet['key']);

Because my .CER PK is supposed to be binary, i need to use this function found on php.net to make the conversion :

function pem2der($pem_data){
   $begin = "KEY-----";
   $end   = "-----END";
   $pem_data = substr($pem_data, strpos($pem_data, $begin)+strlen($begin));   
   $pem_data = substr($pem_data, 0, strpos($pem_data, $end));
   $der = base64_decode($pem_data);
   return $der;
}

$pem_data = file_get_contents(/path/to/publick.pem');
$pem2der = pem2der($pem_data);
file_put_contents(/path/to/publick.cer', $pem2der);

NOTE: i read that a .cer file can be binary or not

I hope it is correct. I've not yet tested the generated CER but i think i'm maybe close to the solution !

Any comments/advices are welcome :)