Tait Hoyem
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author: tait
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title: "How Does Encryption Work, in Theory?"
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---
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There are many kinds of encryption used in our everyday communication. Online and offline, over the internet and in person. In this article, I will explain the basics of how encryption should work in theory. I explain in [this article](/2020/01/26/rsa1.html) why encryption is important, and why *you* should care about it.
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We will start by looking at in-person, offline encryption.
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## Cryptography We Do Everyday
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We encrypt things all the time without even thinking about it.
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If you spend a significant amount of time with the same group of friends, your will tend of develop common codes that may not make sense to others outside the group.
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For example: for years, my family called sombody falling from a sitting position "doing a Don". There is a story of course---We knew a guy named Don who fell from his plastic beach chair in a rather hilarious way; "doing a Don" was born.
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These kind of minor dialects in speech are cryptographic in their own way. The truth is though, that we use cryptography much more than that!
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> "Is cryptography any different than talking?
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> We say something other than what we mean, and then expect everyone is able to decipher the true meaning behind the words.
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> Only, I never do..." --- Adapted from a scene in [The Imitation Game (p. 39-40)](https://www.benedictcumberbatch.co.uk/wordpress/wp-content/uploads/ScreenplayTIG.pdf)
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How many times have you hinted, flirted, and innuendoed to try to say "I find you very physically attractive"?
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Have you told your friend that always stinks to wear more deoderent?
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Have you ever had someone say the words "I'm fine" when you know *for certain* that they are indeed not okay?
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Words Said | Meaning
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--- | ---
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What can you do? | I don't want to talk about this anymore.
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I don't want to overstay my welcome. | I want to go home now.
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I don't like them and don't know why. | They threaten my ego.
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Creepy | Unattractive and friendly
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All of these scenarios are perfect examples of ~~lies~~ encryption! If we have the key to these codes, we can start to understand what people really mean.
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Hopefully I have convinced you that you use ~~deceit~~ cryptography on a regular basis in your life, so let us consider what a basic encryption method might be:
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## Grade-School Encryption
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Back when I was in middle school I used to pass notes like these:
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PIC
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This is a messege encrypted using the Caesar cipher. This encryption technique was used by Julius Caesar during the reign of the Roman Empire to "encrypt messeges of military significance."<a class="citation-link" href="https://en.wikipedia.org/wiki/Caesar_chipher/">[1]</a>
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This is one of the oldest and simplest methods of encryption known to us today.
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You can try this out yourself by moving some letters forward in the alphabet.
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An 'A' turns into a 'B', 'B' into 'C', 'C' into 'D', et cetera.
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In this case, "Hello!" would become "Ifmmp!"
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That is just using a shift of one. You can use a shift of seven, for example, and then you would shift letters like so:
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- `A -> +7 -> H`
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- `Q -> +7 -> X`
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- `T -> +7 -> A`
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We should wrap-around to the beginning of the alphabet if there are no letters left.
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## Example of a Caesar Cipher
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Let's setup a little story to illustrate the problems of encryption. We will have three characters:
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* Alice, a little girl with feelings for Bob
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* Bob, a young boy with an addiction to pancakes
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* Eve, a wee jealous girl scout who sits between Bob and Alice
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Alice really likes Bob and wants to tell Bob her feelings, so she writes "I love you, Bob! Please eat healthier!" on a sticky note.
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She passes it to Eve, so Eve can pass it to Alice's love interest.
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However, in an unfortunate turn of events Eve reads the note herself, and decides not to give it to Bob.
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Oh the horror! Alice is without young love! How could she remedy this so that Bob can read her messege, but evil Eve can not?
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Let's use the Caesar cipher to fix this problem.
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Let us assume that Alice and Bob already have a shared key, 7 for example. To encrypt this messege, we should shift our letters seven letters forward in the alphabet---just like the example above.
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PIC2
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Now Alice's messege reads "P svcl fvb, Ivi! Wslhzl lha olhsaoply!"
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Now, when Alice sends her Romeo a little note, all he has to do is decrypt the text by shifting the letters down by 7.
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[Here is a site](https://www.xarg.org/tools/caesar-cipher/) which can do longer pieces of text for you instead of doing it manually.
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## Problems
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Before the two love-birds start smooching on the branch of a big pine tree in the schoolyard, perhaps we should consider some problems with the Ceasar cipher.
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#### It is Very Easy to Break
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Even Eve with her measly grade 4 math skills could easily start going through this messege with pen and paper and figure out any combination in a couple hours at maximum.
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Imagine how easy this is for a computer?
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This could be broken in a few microseconds even on an older processor like the Intel Core 2 Duo.
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#### No Secure Way of Sharing Keys
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We assumed in our previous example that Bob and Alice already have a shared key (seven) to encrypt and decrypt all of their messeges.
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If Bob and Alice did not have a previous friendship and time to share secrets of this sort, there is no way to share their key with eachother without Eve also knowing.
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This would defeat the entire purpose of obscuring the messege in the first place.
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#### Universal Vulnerability of Messeges
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Every messege sent between the two parties uses the same code to encrypt and decrypt. If someone finds out the code once, all previous communications are comprimised.
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## Better Encryption Methods
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To combat the issues with easily breakable, shared-key cryptography, we can turn to the beautiful beast that is [Asymetric Cryptography](https://en.wikipedia.org/wiki/Public-key_cryptography).
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I will discuss this more in another article, but for the technically inclined:
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1. [RSA](https://en.wikipedia.org/wiki/RSA_(cryptosystem))/[EC](https://en.wikipedia.org/wiki/Elliptic-curve_cryptography) provides *very* large cryptographic keys. It would be impossible for a human to encrypt or decrypt a messege manually.
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2. [Asymetric cryptography](https://www.youtube.com/watch?v=GSIDS_lvRv4) provides four keys, instead of just one; stopping evesdroppers from listening in on your secret conversations---even if you do not have the change to exchange keys in advance.
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