Introducing the lockboxfile gem

require 'lockboxfile'

key = Lockbox.generate_key
#=> "d506414ad742dbdb64208aa89e18a121fa351238ac857183dc5f5dffa74b2162" 

LockboxFile.new(key).write '/tmp/funtime2.txt', 'Hello World!'

LockboxFile.new(key).read '/tmp/funtime2.txt'
#=> 'Hello World!'

key = "d506414ad742dbdb64208aa89e18a121fa351238ac857183dc5f5dffa74b2162" 
# encrypt a unencrypted file and then delete the unencrypted file
LockboxFile.new(key).encrypt('/tmp/funtime.txt','/tmp/funtime3.txt', delete: true)

LockboxFile.new(key).read '/tmp/funtime3.txt'