I know beginners often screw up encryption, and I'm certainly a beginner so I'd like some feedback on my approach.I wrote a small PHP app to store passwords in a database for a group of sys admins ...

"You will need an experienced PHP developer to help you fix their broken code in order to use the key and reverse the encryption," said Mark Maunder, Wordfence CEO.

One use for symmetric encryption is an encrypted file system. Since modern computers can perform complex calculations easily and quickly, they have the ability to encrypt and decrypt data on demand.