|MadSci Network: Computer Science|
Government computers that contain secret information do, in fact, scramble their communications in ways similar to what the questioner suggests. Perhaps the real question is, "If government secrets are being competently protected, why do we keep seeing the headline, 'Hackers Penetrate Computer at Secret Government Site'?" The answer to that question is that the vast majority of government computers never touch secret information, are protected only about as well as computers in a not-very-careful big company, and are occasionally penetrated by hackers in incidents that journalists make more interesting by suggesting that official secrets may have been exposed.
Our federal government's approach to protecting secrets starts by dividing information into two categories: secret (often called "classified") and non-secret ("unclassified"). Secret information is protected energetically, while non-secret information is pretty much left to fend for itself. The protection of secret information is dictated by strict rules initially developed by competent experts, though often garbled when interpreted by successive layers of bureaucracy. I believe these rules have been very effective at preventing exposure of secrets to hackers, but the rules are so strict as to be somewhat crippling, with the result that workers do as much work as possible on computers that never touch secret data and are therefore not so restricted. These secret-free computers -- the vast majority of the government's computers -- get no attention from the government's best experts, are often managed by system managers with little tranining in computer security, and are occasionally penetrated by hackers.
The federal government's data scramblers have names like KG81, KG84, and KG94. Information about them is not widely available.
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