The Beauty Of Public Secrets

Introduction public

Getting the signal through and understood by the right person(s)

'Illegitimate' (from Whitfields talk - before during and after Crypto..)



Zero Knowledge Proof

There is a well-known story presenting some of the ideas of zero-knowledge proofs, first published by Jean-Jacques Quisquater et al. in their "How to Explain Zero-Knowledge Protocols to Your Children".[1] It is common practice to label the two parties in a zero-knowledge proof as Peggy (the prover of the statement) and Victor (the verifier of the statement). Sometimes P and V are known instead as Pat and Vanna.

In this story, Peggy has uncovered the secret word used to open a magic door in a cave. The cave is shaped like a circle, with the entrance in one side and the magic door blocking the opposite side. Victor says he'll pay her for the secret, but not until he's sure that she really knows it. Peggy says she'll tell him the secret, but not until she receives the money. They devise a scheme by which Peggy can prove that she knows the word without telling it to Victor.

First, Victor waits outside the cave as Peggy goes in. We label the left and right paths from the entrance A and B. She randomly takes either path A or B. Then, Victor enters the cave and shouts the name of the path he wants her to use to return, either A or B, chosen at random. Providing she really does know the magic word, this is easy: she opens the door, if necessary, and returns along the desired path. Note that Victor does not know which path she has gone down.

However, suppose she does not know the word. Then, she can only return by the named path if Victor gives the name of the same path that she entered by. Since Victor chooses A or B at random, she has at most a 50% chance of guessing correctly. If they repeat this trick many times, say 20 times in a row, her chance of successfully anticipating all of Victor's requests becomes vanishingly small, and Victor is convinced that she knows the secret.

You may ask, why not just make Peggy take a known path that will force her through the door, and make Victor wait at the entrance? Certainly, that will prove that Peggy knows the secret word, but it also opens the door for eavesdropping. By randomising the initial path that Peggy takes and preventing Victor from knowing it, it reduces the chances that Victor can follow Peggy and learn not just that she knows the secret word, but what the secret word actually is. This part of the exchange is important for keeping the amount of information revealed to a minimum.


Snuffle showed how to use a cryptographic hash function, which was legal to export, as a strong encryption system, which was illegal to export. The irony of the case was that it was not the hash that was illegal, but the software that showed how to use it.


Philip R. "Phil" Zimmermann (born February 12, 1954) is the creator of Pretty Good Privacy (PGP), the most widely used email encryption software in the world.

Dining cryptographers protocol

The dining cryptographers protocol is a method of anonymous communication. It offers untraceability of both the sender and the recipient.

Man-in-the-middle attack

In cryptography, a man-in-the-middle attack (MITM) is an attack in which an attacker is able to read, insert and modify at will, messages between two parties without either party knowing that the link between them has been compromised. The attacker must be able to observe and intercept messages going between the two victims. The MITM attack is particularly applicable to the original Diffie-Hellman key exchange protocol, when used without authentication

Hash Trees


Whitfield Diffie

Key transport/exchange

defense with evidence of attack

increase in distributed calculations require authenticated services

James Ellis



illegal primes..


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