looking for a good solution

I haven't been able to find a good solution to my a problem. I want to be able to email, through php, a report as a file attachment to a client of mine and it needs to be SECURE and easy for them to open. Right now he get's a password protected zip file for something similar. I can easily use mcrypt to encrypt it, but can't find an easy way to decrypt it on that end.

Anyone have any suggestions?