how to encode/encrypt a string

still doing my switch from MySQL to PgSQL, and can't figure out what
the comparable function would be for this:

In MySQL, to store a big secret (like a credit card number) in the
database that I didn't want anyone to be able to see without knowing
the salt/password value, I would do this into a blob-type field:

INSERT INTO clients(ccnum) VALUES (ENCODE(''433904123121309319', 'xyzzy'));

Then it would be stored as binary jumble in the database, only able to
be decoded with my "xyzzy" password.

SELECT DECODE(ccnum, 'xyzzy') FROM clients;

How would I do this same thing in PostgreSQL?