John works as a cryptography consultant. He finds that people often misunderstand the reality of breaking a cipher. What is the definition of breaking a cipher?

Finding any method that is more efficient than brute force. https://en.wikipedia.org/wiki/Cryptanalysis Bruce Schneier notes that even computationally impractical attacks can be considered breaks: "Breaking a cipher simply means finding a weakness in the cipher that can be exploited with a complexity less than brute force. Never mind that brute-force might require 2^128 encryptions; an attack requiring 2^110 encryptions would be considered a break...simply put, a break can just be a certificational weakness: evidence that the cipher does not perform as advertised."