I have a web site which stores passwords as sha1 hashes in the database and I'd like to increase the security by adding salts. Is there a way to convert existing passwords in sha1 to sha1 with a salt? My guess is not but I want to make sure. My current plan is to do conversion individually at the moment a user logs in - he has to provide the password so then the system can hash it again with a salt and store it. Are there any better options? Ideally I'd like to convert all passwords in one go.