I am working on integration to a Credit Card Gateway. The Gateway provider has provided me with a "Hash Key". All values I send to the gateway need to be "md5 hashed against the Hash Key".
How am I best to "MD5 hash my values using the supplied key"? I have been investigating both hash() and Encrypt(), but can't really be sure which is going to give me exactly what I need and how exactly to go about it.
Thanks in advance for all advice.