Encryption: the fated story of Alice and Bob

The secrets of how we keep information secure

Today’s world runs on data. We’ve generated more data in the past two years than in our entire history combined. This data revolution has also allowed us to communicate more than ever before. Humanity revolves around communication, especially private communication — but how do we keep communication data private?

Gone are the days where spies secretly exchanged envelopes with secret codes in them at a nondescript park bench. Gone are the days of the Enigma machine and substitution ciphers. Encryption has evolved quite a bit, and it holds some very interesting math. I love math, and the math involved in encryption is very elegant — and very clever.

What is encryption?

The goal of encryption is to take a message (in plain text) and scramble it so no one except the person you want to send the message to can read it. To understand this better, let’s take the example of the immortal Alice and Bob.

Alice is madly in love with Bob, and she wants to tell him. However, she doesn’t want anyone else to know, just in case Bob doesn’t love her back. How can she send the message to Bob?

One way would be to use a simple 1-to-1 encoding system — we map each character to another character and encrypt the message. Let’s say a = 1 , b = 2 and so on. So:

'i love you' = 9 0 12 15 ...

Cool! Alice now has a nice, garbled message that no one can read! The only problem, of course, is that Bob can’t read it either. How does she tell Bob how to decrypt the message? Simple encryption schemes like this fail because there is no way to send the common key without using a more advanced encryption system. If Alice tries to encrypt the key, then the key to that key has to be sent too. So unless Alice is willing to pluck up the courage to talk to Bob in-person (secretly at a nondescript park bench of course), she can’t encrypt her message in such a simple way.

This is how kids make “secret codes”. Both parties have to be in on the cipher for it to work, but this throws us into the realm of paradox.