Subjects (active) use computers and programs to access (information flow) objects (passive repository of data). A trusted path must be established between the subject and the object.
Access controls are technical controls, administrative controls, or physical controls. Controls are driven by threats and are implemented to deter, delay, prevent, detect, assess, respond (correct, recover), compensate, or direct.
Controls of various types should be implemented in layers. Remember: Defense in depth.
AAA = authentication (something you know, something you have, and something you are), authorization, and accounting. (The third A is also auditing or accountability.)
Attacks on authentication include the brute force, the dictionary, the hybrid, ...