PHP Programming/Encryption

PHP provides several functions to encrypt data.

Symmetrical encryption
Storing passwords in clear (unencrypted), in a file or a database, constitutes a security breach. To be able to encrypt and decrypt them, a can be done by:

Asymmetrical encryption
The est used to check an identity, via a public and a private key. In PHP, it's done with:

Hashing
crypt is a for a string, which can add a  as an optional second parameter.