Change password fields

Hi all

I’ve tried to find this in the docs and in this community but without luck.

I have a form where details can be updated. Part of this is two fields - password and password2. If they are left empty then I want the password to be unchanged. But, if anything is entered into the password field, then the same must be entered in password2 and then it’s encrypted (SHA1) and updated in the database.

But, how do I set it to only update when something is entered?

And how do I check the values of password and password2 are the same?

Thanks again in anticipation.