"Back doors to encryption"? IIRC, Zimmerman and his Pretty Good Privacy (PGP) based on Rivest-Shamir-Adleman (RSA) public key encryption is open source without back doors.

And the RSA paper is no doubt still on the shelves of the libraries. And it is in various books, e.g., IIRC one by B. Schneier. IIRC, the main number theory is just Fermat's little theorem in even elementary books on number theory.

IIRC, breaking RSA is equivalent to being able to factor a large integer into a product of prime numbers. As soon as some mathematician finds how to do that quickly enough to be practical, likely we will hear about it via an Abel Prize of just the front page of the NYT. I haven't heard yet.

Comey: Good luck on getting your back doors in DIY, roll your own, open source PGP RSA encryption! The open source part? That is much of why Zimmerman did his work.