A properly implemented security mechanism will provide the following functionality:
Prevent unauthorized access to application functions and business or personal data (authentication)
Hold system users accountable for operations they perform (non-repudiation)
Protect a system from service interruptions and other breaches that affect quality of service (QoS)
Ideally, properly implemented security mechanisms will also provide the following functionality:
Easy to administer
Transparent to system users
Interoperable across application and enterprise boundaries