When integrating with Chase Payemtech E-Xact Pay-Pages, I could not get the HMAC-MD5 hash to generate properly and match what their Hash Generator was producing. After reading up on HMAC (http://en.wikipedia.org/wiki/HMAC)

I ran some of their samples and found that what was being generated from the HMAC-MD5 was the same result as HMAC SHA1 and NOT what the wiki said should be produced for HMAC-MD5.

Solution? change the Pay-Page configuration to use SHA1 and use SHA1 to generate all the request and response validation hashes.

x_fp_hash