Does anyone know if I can encrypt files using Ruby?

I want to make my students' grades available for them on-line.  But this 
is private information.  I thought that perhaps I could have each 
student's marks in an encrypted file which can be decrypted by Ruby using 
a passphrase.  The passphrase would be the student's Social Security 
Number.

I suppose that a symmetric cypher would good for this, since I don't have 
to worry about transmitting the passphrase.

Thanks for the help.

-- 
Daniel Carrera
Graduate Teaching Assistant.  Math Dept.
University of Maryland.  (301) 405-5137