“The internet is the most liberating tool for humanity ever invented, and also the best for surveillance. It’s not one or the other. It’s both.”—John Perry Barlow, co-founder of the Electronic Frontier Foundation


In Chapter 15, you learned that the affine cipher has about a thousand possible keys but that computers can still brute-force through all of them easily. We need a cipher that has so many possible keys that no computer can brute-force through them all.

The simple substitution cipher is one such cipher that is effectively invulnerable to a brute-force attack because it has an enormous number ...

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