difference between authorize.net and authorize.net direct post in magento

[cmartin19]

Hi, my authorize.net account has just been activated earlier today and I have my magento shop almost ready to launch.  The issue I'm having is I cannot seem to get the authorize.net to display as a payment option when I enable authorize.net from the admin panel.  I notice that  if I enable authorize.net direct post it will show but I do not have a Merchant MD5 key so it declines test transactions.  I would rather use authorize.net as the way to go but I can also fall back on authorize.net direct post if that is the only way to display the credit card fields on check out page.   Can someone explain the difference between the two payment methods?

Another thing I noticed is that when I enter in the API Login id and the Transaction Key in the respective fields and then press save, the password 'dots' that represent the characters I entered always show '6' dots in each field.  Is this correct?  Shouldn't it be showing the number of dots related to number of characters in Transaction Key and API Login Id?  Thanks for help.  Charles

[TJPride]

I believe the default Authorize.net is AIM. AIM and DPM both have the form display on your site, but AIM has the credit card info pass through your site on its way to Authorize.net, while DPM pretends to do everything through your site but really passes it directly to Authorize.net. The former method has slightly less PCI requirements, the latter runs slightly slower on some connections. Take your pick.

As for the 6 dots, my guess is the software is passing a verification hash rather than including the ID and key you entered as hidden field values (which could theoretically be a security hole - anyone with access to your computer could just access your cache and retrieve them). I wouldn't worry too much about it unless you hit submit and get an error.