What should every web developer know about encryption?

Question

I've just landed a PHP5 gig. I won't be handling the parts of the application that involve super sensitive data, but I still know embarrassingly little about security and encryption methods. I only know the very basics (don't store passwords in plaintext, don't allow users to run code using post data, etc). What do I need to know to keep my applications secure, and where can I learn it?

Answer 1

Learn the difference between hashes and encryption. Encryptions are generally two-way interpretations of a string. I can encrypt my password, and then decrypt it to plaintext again. The idea behind hashes are that they become a one-way 'encryption.'

On my sites I store passwords as hashes. Anytime a user signs on, I re-hash their provided password, test it against the hash stored in the database and approve if they match. I cannot send them their password if they forget it, since (generally) there is no way for me to know.Two different strings can translate into the same hash, which makes it (generally) impossible to find out what the original string was.

This is one issue that is good to get a firm understanding of, and discern when to use encryption vs. hashes.

Answer 2

Know not to write your own encryption functionality. An existing, trusted library is best way to go wherever possible. Avoid cool, bleeding edge technologies that lack many successful programmer-hours and user-hours behind them. Know not to trust the functionality you choose until you've thoroughly tested it yourself, first-person. Keep abreast of new developments which may antiquate your chosen functionality overnight. Know that just because you're using the best encryption technology available today that you've protected nothing if you leave the keys on the table (e.g., cleartext is not in a cache or stored in another table in the same database, private keys not left in the open)