You are what you know

‘You are what you know’ is a byte sized spy story by Paul Curzon of Queen Mary University of London to make you think cyber security. A spy has set up a meeting with their new handler. A pass phrase has been agreed …

The trouble with using spy novel style pass phrases to prove who you are is you still have to trust the other person. If they might have nefarious intentions, you want to prove who you are without giving anything else away. You certainly don’t want them to be able to take the information you give and use it to pretend to be you. Unfortunately, this story is pretty much how passwords work, and why attacks like phishing, where someone sends emails pretending to be from your bank, are such a problem.

The story outlines the essential problem faced by all authentication systems trying to prove who someone is or that they possess some secret information. You give up the secret in the process to anyone there to hear. Security protocols somehow need ways one agent can prove to another who they are in a way that no one can masquerade as them in future. Creating a secure authentication system is harder than you might think! To do it well takes serious skill. What you don’t do is just send a password!

A simple solution for some situations is used by banks. Rather than ask you for a whole account number, they ask you for a random set of its digits: perhaps, the third, fifth and eighth digit one time, but completely different ones the next. Though they have learnt some of the secret, anyone listening in can’t masquerade as you as they will be asked for different digits when they do. Take this idea to an extreme and you get the Zero Knowledge Proof where none of the secret is given up: possibly one of the cleverest ideas of computer science.

More computational thinking tales…

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