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<openssl_spki_exportopenssl_spki_new>
^OpenSSL FunctionsLast updated: Mon, 26 Oct 2026

openssl_spki_export_challenge

(PHP 5 >= 5.6.0, PHP 7, PHP 8)

openssl_spki_export_challenge — Exports the challenge associated with a signed public key and challenge

Description

function openssl_spki_export_challenge(string $spki): string|false

Exports challenge from encoded signed public key and challenge

Parameters

spki

Expects a valid signed public key and challenge

Return Values

Returns the associated challenge string or false on failure.

Errors/Exceptions

Emits an E_WARNING level error if an invalid argument is passed via the spki parameter.

Examples

Example #1 openssl_spki_export_challenge() example

Extracts the associated challenge string or NULL on failure. 

<?php
$pkey = openssl_pkey_new('secret password');
$spkac = openssl_spki_new($pkey, 'challenge string');
$challenge = openssl_spki_export_challenge(preg_replace('/SPKAC=/', '', $spkac));
?>

Example #2 openssl_spki_export_challenge() example from <keygen>

Extracts the associated challenge string issued from the <keygen> element 

<?php
$challenge = openssl_spki_export_challenge(preg_replace('/SPKAC=/', '', $_POST['spkac']));
?>
<keygen name="spkac" challenge="challenge string" keytype="RSA">

See Also


<openssl_spki_exportopenssl_spki_new>
^OpenSSL FunctionsLast updated: Mon, 26 Oct 2026