“You can start from here and go to the end of the world and never have a repetition,” Elizebeth said. In theory, the only way to read a message was to know the starting configuration of the machine’s internal parts—the “key”—which only the sender and recipient would possess. What’s more, the machines were designed to survive capture and study. Even if you got your hands on a copy and took it apart like a broken clock, examining each gear for as long as you pleased, you would still not be able to read messages produced by another such machine. Many inventors of cipher machines were private
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