Question

How convert RSA public key, from XML to PEM (PHP)?

Answer 1

we know

.pem – (Privacy Enhanced Mail) Base64
encoded DER certificate, enclosed
between “—–BEGIN CERTIFICATE—–”
and “—–END CERTIFICATE—–“

X.509

The SignatureValue element contains
the Base64 encoded signature result –
the signature generated with the
parameters specified in the
SignatureMethod element – of the
SignedInfo element after applying the
algorithm specified by the
CanonicalizationMethod.

XML_Signature

so we end up with

$xml = simplexml_load_file($xmlFile); // or simplexml_load_string

$pem = "-----BEGIN CERTIFICATE-----\n";
$pem .= $xml->SignatureValue;
$pem .= "\n-----END CERTIFICATE-----";

// save to file

if your xml-file isn’t a XML_Signature

$xml = simplexml_load_file($xmlFile); // or simplexml_load_string
$pem = "-----BEGIN CERTIFICATE-----\n";
$pem .= $xml->nodeWithWantedValue; // use base64_encode if needed
$pem .= "\n-----END CERTIFICATE-----";