Dynamic Password Generation

[Inquisitive]

Looking for a script, javascript, etc...., for generating passwords dynamicaly as part of an email system. The password should be generated from the previous password used based on an expression formulated by the user. For example, assume initial password is the letter "a" and the expression is "x + 7" when the user logs in, intially, with password is "a" , however, at the next login, the script on the server side should have changed the password to letter "h", x+7.

[beetle]

Uh, you want to change a server-side password with javascript? Gimme some of what you're on, it must be good! (just kidding...)

What authentication system are you using for these passwords? How are they stored?

[Inquisitive]

.....well, thats what I am looking for, the whole picture. Someone with the indepth knowledge to explain to me how it can be accomplished. ...cgi, php, perl, etc. Please, do not focus on the word javascript, that is simply the "bait" to get the ball rolling.