Computer security is often advertised in the abstract: “This system is secure.” A product vendor might say: “This product makes your network secure.” Or: “We secure e-commerce.” Inevitably, these claims are naïve and simplistic. They look at the security of the product, rather than the security of the system. The first questions to ask are: “Secure from whom?” and “Secure against what?”

They're real questions. Imagine a vendor selling a secure operating system. Is it secure against a hand grenade dropped on top of the CPU? Against someone who positions a video camera directly behind the keyboard and screen? Against someone who infiltrates the company? Probably not; not because the operating system is faulty, but because someone made conscious or unconscious design decisions about what kinds of attacks the operating system was going to prevent (and could possibly prevent) and what kinds of attacks it was going to ignore.

Problems arise when these decisions are made without consideration. And it's not always as palpable as the preceding example. Is a secure telephone secure against a casual listener, a well-funded eavesdropper, or a national intelligence agency? Is a secure banking system secure against consumer fraud, merchant fraud, teller fraud, or bank manager fraud? Does that other product, when used, increase or decrease the security of whatever needs to be secured? Exactly what a particular security technology does, and exactly what it does not do, is ...

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