e.g. if we had the php code:
<?php $sign = hash_hmac('sha512', $post_data, $secret); echo $sign;
var shaObj = new jsSHA("SHA-512", "TEXT"); shaObj.setHMACKey(secret, "TEXT"); shaObj.update(post_data); var hmac = shaObj.getHMAC("HEX");
I hope this helps.