Читать книгу Alice and Bob Learn Application Security - Tanya Janca - Страница 9

If Alice’s insulin measuring device was unavailable due to malfunction, tampering, or dead batteries, her device would not be “available.” Since Alice usually checks her insulin levels several times a day, but she is able to do manual testing of her insulin (by pricking her finger and using a medical kit designed for this purpose) if she needs to, it is somewhat important to her that this service is available. A lack of availability of this system would be quite inconvenient for her, but not life-threatening.

Bob, on the other hand, has irregular heartbeats from time to time and never knows when his arrhythmia will strike. If Bob’s pacemaker was not available when his heart was behaving erratically, this could be a life-or-death situation if enough time elapsed. It is vital that his pacemaker is available and that it reacts in real time (immediately) when an emergency happens.

Bob works for the federal government as a clerk managing secret and top-secret documents, and has for many years. He is a proud grandfather and has been trying hard to live a healthy life since his pacemaker was installed.

NOTE Medical devices are generally “real-time” software systems. Real-time means the system must respond to changes in the fastest amount of time possible, generally in milliseconds. It cannot have delays—the responses must be as close as possible to instantaneous or immediate. When Bob’s arrhythmia starts, his pacemaker must act immediately; there cannot be a delay. Most applications are not real-time. If there is a 10-millisecond delay in the purchase of new running shoes, or in predicting traffic changes, it is not truly critical.

Figure 1-4: Resilience improves availability.

NOTE Many customers move to “the cloud” for the sole reason that it is extremely reliable (almost always available) when compared to more traditional in-house data center service levels. As you can see in Figure 1-4, resilience improves availability, making public cloud an attractive option from a security perspective.

The following are security concepts that are well known within the information security industry. It is essential to have a good grasp of these foundational ideas in order to understand how the rest of the topics in this book apply to them. If you are already a security practitioner, you may not need to read this chapter.