Breaking Ciphers and Zero Knowledge Proofs

This hands-on workshop from the Cryptocurrency Village has attendees break classic ciphers themselves instead of only reading about them. The session starts with the shift cipher, where there are only 25 useful alphabets and a couple of letters can reveal the shift. Participants work through encrypted messages from a handout, and the presenters use each one to show why the weakness exists.

The middle section moves to substitution ciphers. The presenters explain why brute force fails against a random alphabet, since the possible keys number roughly 26 factorial, and then show how frequency analysis narrows the search. Useful clues include letter counts compared with English text, short common words, apostrophes followed by an S, and vowel patterns in two-letter words. The recurring point is that human habits leak into implementations, and statistics can shrink a huge key space.

The session then covers polyalphabetic substitution, using a keyword to shift letters in the Vigenère cipher. It ends by introducing the Kasiski method: find repeated strings, measure the distances between them, and use common factors to estimate the key length. The presenters ran short of time and said the Kasiski walkthrough would continue the next day. The takeaway is that each cipher upgrade fixes one weakness and exposes another, which mirrors how real cryptography is tested and improved.