Has anyone done encryption of attachments using crypto class?  What we want to do is encrypt attachments to all users and give only specific users to decrypt.  Can someone share their code?  I am new to this functionality and I would like to get some sample codes to get me started.  Unfortunately, I can't find a whole lot of this use case here.  And the sample codes provided here http://wiki.developerforce.com/page/Apex_Crypto_Class doesn't help me much either. 

Any info is appreciated.  

Thanks,

John