A Few Parting Lessons

Now that we've covered the critical concepts, here are a few more basic lessons in security-think that you should consider before reading the rest of this guide:

Knowledge is Power. Good security decisions can't be made without good information. Your security tradeoffs are only as good as the information you have about the value of your assets, the severity of the threats from different adversaries to those assets, and the risk of those attacks actually happening. We're going to try to give you the knowledge you need to identify the threats to your computer and communications security that are posed by the government, and judge the risk against possible security measures.

The Weakest Link. Think about assets as components of the system in which they are used. The security of the asset depends on the strength of all the components in the system. The old adage that "a chain is only as strong as its weakest link" applies to security, too: The system as a whole is only as strong as the weakest component. For example, the best door lock is of no use if you have cheap window latches. Encrypting your email so it won't get intercepted in transit won't protect the confidentiality of that email if you store an unencrypted copy on your laptop and your laptop is stolen.

Simpler is Safer and Easier. It is generally most cost-effective and most important to protect the weakest component of the system in which an asset is used. Since the weak components are much easier to identify and understand in simple systems, you should strive to reduce the number and complexity of components in your information systems. A small number of components will also serve to reduce the number of interactions between components, which is another source of complexity, cost, and risk.

More Expensive Doesn't Mean More Secure. Don't assume that the most expensive security solution is the best, especially if it takes away resources needed elsewhere. Low-cost measures like shredding trash before leaving it on the curb can give you lots of bang for your security buck.

There is No Perfect Security — It's Always a Trade-Off. Set security policies that are reasonable for your organization, for the risks you face, and for the implementation steps your group can and will take. A perfect security policy on paper won't work if it's too difficult to follow day-to-day.

What's Secure Today May Not Be Secure Tomorrow. It is also crucially important to continually re-evaluate the security of your assets. Just because they were secure last year or last week doesn't mean they're still secure!

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