(PHP 5 >= 5.6.0, PHP 7, PHP 8)
openssl_spki_export — Exports a valid PEM formatted public key signed public key and challenge
Exports PEM formatted public key from encoded signed public key and challenge
spkiExpects a valid signed public key and challenge
   Returns the associated PEM formatted public key or false on failure.
  
   Emits an E_WARNING level error if an invalid argument
   is passed via the spki parameter.
  
Example #1 openssl_spki_export() example
      Extracts the associated PEM formatted public key or null on failure.
   
<?php
$pkey = openssl_pkey_new('secret password');
$spkac = openssl_spki_new($pkey, 'challenge string');
$pubKey = openssl_spki_export(preg_replace('/SPKAC=/', '', $spkac));
if ($pubKey) {
    echo $pubKey;
}
?>Example #2 openssl_spki_export() example from <keygen>
Extracts the associated PEM formatted public key issued from the <keygen> element
<?php
$spkac = openssl_spki_export(preg_replace('/SPKAC=/', '', $_POST['spkac']));
if ($spkac != NULL) {
    echo $spkac;
} else {
    echo "Extraction of pub key failed";
}
?>
<keygen name="spkac" challenge="challenge string" keytype="RSA">