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Mathematics

Numbers That Keep Secrets

Clock arithmetic, a cost that will not run backwards, and a padlock you can publish

Gauss · Diffie and Hellman · Rivest, Shamir and Adleman · GCHQ · 3 chapters · 8 min read

Arithmetic on a clock, a sum that will not run backwards, and a padlock you can post publicly.

Free to read: every chapter below is open

Cryptography

  1. 01Arithmetic on a ClockOn a number system where eleven plus four is three, exactly.
  2. 02Easy Forwards, Hard BackwardsOn a gap between two costs, and the fact that nobody has proved it is there.
  3. 03A Padlock You Can Post PubliclyOn handing out open padlocks, and the one place the metaphor leaks.