A security culture is a set of customs shared by a community whose members may be targeted by the government, designed to minimize risk. Having a security culture in place saves everyone the trouble of having to work out safety measures over and over from scratch, and can help offset paranoia and panic in stressful situations—hell, it might keep you out of prison, too. The difference between protocol and culture is that culture becomes unconscious, instinctive, and thus effortless; once the safest possible behavior has become habitual for everyone in the circles in which you travel, you can spend less time and energy emphasizing the need for it, or suffering the consequences of not having it, or worrying about how much danger you’re in, as you’ll know you’re already doing everything you can to be careful. If you’re in the habit of not giving away anything sensitive about yourself, you can collaborate with strangers without having to agonize about whether or not they are informers; if everyone knows what not to talk about over the telephone, your enemies can tap the line all they want and it won’t get them anywhere. 1
The greater the number of people who know something that can put individuals or projects at risk—whether that something be the identity of a person who committed an illegal act, the location of a private meeting, or a plan for future activity—the more chance there is of the knowledge getting into the wrong hands. Sharing such information with people who do not need it does them a disservice as well as the ones it puts at risk: it places them in the uncomfortable situation of being able to mess up other people’s lives with a single misstep. If they are interrogated, for example, they will have something to hide, rather than being able to honestly claim ignorance.