note 27656 rejected from function.md5 by betz

I am having trouble understand this whole encryption thing with md5. I have figured out how to create a public and secret key for rsa take a digit and encrypt it. But I can't find out how to use md5. Does md5 encrypt? If I have a site where I don't want to bother with ssl and I want to authenticate users by passwords stored in a database how would I use md5 to securly encrypt the password send it in a post and then unencrypt it in my php code and see if they match. BTW I have a javascript md5 script that will do the encryption client side at http://pajhome.org.uk/crypt/md5/index.html My biggest concern is that the encrypted password for the users will always be the same. So if bob has a password of password, the md5 will always be the same everytime he logs in. Thus all a hacker will need to do is capture the password in its encrypted form and then pass it on someother time when he wants in. Or am I totally wrong and the md5 is different every time? Thank you for your help