Science & ideas · Inventions & technology

The code that guarded Rome now just hides punchlines

A shift of three letters was once good enough for the private correspondence of a Roman general — and today the same trick survives as ROT13, used not to keep secrets but to politely blur a spoiler or a joke's punchline. It is the rare encryption method that outlived its own security by two thousand years and found a second job as a courtesy. It is also a building block: the shift step lives inside more serious schemes like the Vigenère cipher. Worth five minutes for how cleanly it shows what "secure" actually depends on — not the cleverness of the method, but who is looking.

Every single-alphabet substitution cipher, Caesar's included, is trivially breakable — in modern terms it provides essentially no security at all.

Read the whole of Caesar cipher on Wikipedia

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