Modifying WordPress Password Encryption

Hi,

I recently came across a client who had me migrate their site from Joomla to WordPress. I was able to migrate all their content and find plugins that matched the ones they were using in Joomla. However, the client also wants me to migrate all the users from Joomla to WordPress, so that they don’t all have to reregister.

Of course, the only way to do this would be to modify WordPress’s password encryption to match the encryptions used with their Joomla installation. I was able to find what encryptions Joomla was using, but now I’m stuck. What functions/files do I need to change in WordPress to use the new encryption?

Any help at all is appreciated – all I really need is a starting point and I can do the rest. Thanks!