I was finally able to match Authorize.net's hash value. It seems as though their Advanced Integration Method uses straight MD5 rather than HMAC-MD5 ... and upper and lower case characters make a HUGE difference! <g>

>We're using the AIM method (Advanced Integration Method). The AIM documentation just referred to it as MD5 Hash but I bet they're using the HMAC-M5 just as their SIM does.
>
>I'll have to try that and see if the hash values match.
>
>Thanks for your help!
>
>Rodd
>
>>Rodd,
>>That is correct Authorize.net is using HMAC-M5 as per there documentation on page: 7 of the Simple Integration Method Implementation Guide v1.0
>>
>>Chad Newman