Encrypting cookies in PHP

Question

How can i encrypt and later decrypt a value of a cookie in PHP (how secure will the encryption be )

Answer 1

I am in full agreement with the other answers: If the data is truly sensitive it should be stored server side in a session, not in a cookie.

As far as ways to encrypt cookie contents, the Suhosin PHP extension provides the ability to transparently encrypt all cookies. If you have the ability to install PHp extensions this may or may not be easier for you than writing your own encryption scheme.