What is Alice and Bob?

Cartoon by John Richardson in Physics World, March 1998. When the interaction between two hypothetical characters is needed to explain or describe a trope, they are nearly always called Alice and Bob. Alice and Bob — A and B. This duo originally started out as a standardized way to explain cryptography.

What is the role of Alice and Bob in cryptology?

Over the next decade of academic research in cryptology, Alice and Bob would become ubiquitous and a key epistemic tool.

How does Bob know if Alice has sent a message?

When Bob sees his transactions held in the blockchain, he can be sure that Alice has sent her message to the network preventing duplicate transactions. This is a very important part of the Bitcoin protocol, as Alice would need to collaborate with friends or become herself more powerful than over half the network.

How does Alice and Bob use Diffie-Hellman?

That is, Alice and Bob use the mechanism of Diffie-Hellman to send messages rather than simply agreeing on a key. The current industry standard cryptosystem in this family is known as the Integrated Encryption Scheme (IES).