openssl_pkcs12_read失败

Question

I am trying to read a p12 formatted certificate file with php function openssl_pkcs12_read. My code looks like this:

<?php

$fname  = "./client-cert.p12";
$handle = fopen($fname, "r") or die ("Unable to open file!");
$p12buf = fread($handle, filesize($fname));
fclose($handle);
$certs = array();
$pass  = "bliblablup";

$result = openssl_pkcs12_read($p12buf, $certs, $pass);

if ( $result ) {
    print_r( $certs );
} else {
    print_r( "Error!
");
}

I am always running into the error-branch of if($result) ... and cannot find any information how to get more details on the error condition. Any hints welcome.