The currency of computer security is Trust – the degree to which you can believe that your system is doing what you expect it to. There are a lot of properties that comprise trust, including integrity, reliability, etc., each of which is made up of smaller properties like non-repudiation, auditability, resistance to replay attacks, ad infinitum. We talk about trust loosely; it’s like Liberty or Good Cinematography – it’s a useful concept for describing the relationship between ourselves and the systems we use – whether they work right for any given notion of “right.”