[Plugin: eShop] Authorize.net MD5 hash help

I haven’t been able to find instructions on using the MD5 hash in the Authorize.net payment settings, so now I need help (trying to launch store today.) Everything works fine but I’m getting these errors on the return from Authorize.net. I know it has to do with the MD5 hash. I have set the has value at Authorize and put the same value in the MD5-Hash Phrase field on the cart, but it does not work. I would really appreciate help on this! I’m stuck!

Warning: hash_hmac() expects at least 3 parameters, 2 given in /home/pedalpoc/public_html/wp-content/plugins/eshop/authorizenet.php on line 203

Fatal error: Call to undefined function mhash() in /home/pedalpoc/public_html/wp-content/plugins/eshop/authorizenet.php on line 207