By the end of 1969, Ellis appears to have reached the same impasse that the Stanford trio would reach in 1975. He had proved to himself that public key cryptography (or nonsecret encryption, as he called it) was possible, and he had developed the concept of separate public keys and private keys. He also knew that he needed to find a special one-way function, one that could be reversed if the receiver had access to a piece of special information. Unfortunately, Ellis was not a mathematician. He experimented with a few mathematical functions, but he soon realized that he would be unable to
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