Encrypt Files at Rest for Storage

Hi All,

Since these files are being stored in the cloud, one of the things my client was looking for was encryption of the files while they are at rest.

I was thinking of using something like this: http://stackoverflow.com/questions/6033972/encrypting-files-with-php-mcr...

Additional Notes on Key Generation: http://www.itnewb.com/v/PHP-Encryption-Decryption-Using-the-MCrypt-Libra...

Would this be useful to include the ability to encrypt a file while stored on rackspace/amazon/etc?

Any thoughts on if there is a better way to do this?