Hey friends! @lemony-cricket here, and even though cryptography is the stuff that powers our collective rocket lambo ride to the moon… encryption has ** absolutely nothing to do with that**. That’s it. End of post.

**You can stop reading now.**

^{Rocket graphic extracted from this CC0 image from OpenClipart-Vectors on Pixabay.}

# But I want to understand… please teach me.

**Fair enough.** In this series (of which this is the inaugural post), I will attempt to teach the *beginner* about the basic building blocks of cryptography. Note that this series is *not* about **cryptocurrency,** but about the field of computer and information science known as **cryptography**. But despair not, dear reader, because learning about *cryptography* now will actually help you understand better how *cryptocurrency* works, if that’s your thing! I will probably do a series on that too, after this one.

**We are starting from the ground up here.** I’ll stress *beginner* again. If you *cringed* at the title, knowing full well what a Caesar cipher is and wondering why it’s being mentioned in this millenium, you might get a little bored with this post. If so, come back in a few posts when we should be getting into more modern encryption.

# The Caesar Cipher

^{a brief introduction to the concept of encryption}

**The first occurrences** of what we today call 𝕖𝕟𝕔𝕣𝕪𝕡𝕥𝕚𝕠𝕟^{d1} utilised the group of 𝕒𝕝𝕘𝕠𝕣𝕚𝕥𝕙𝕞𝕤^{d2} we now know as **classical ciphers**. There are a few different types of classical ciphers, all of which are *no longer useful* in the Information Age. They do, however, provide an interesting bit of history, as well as an easy way to exemplify the concept of encryption.

**The most famous classical cipher** is most likely the **Caesar cipher**, which you might have guessed was used by the Roman dictator Julius Caesar. Also known as the **shift cipher**, this algorithm is extremely simple and can be performed using only a pencil and paper (or even your favourite word processor!).

**The shift cipher** worked much better when nobody really knew what it was. It’s distant history today. But what I would like to do, is use is as an *example* to introduce some words and concepts you’ll need to know for future installments.

**Now, together, let’s encrypt a message**, by hand, using the shift cipher.

# Interactive exercise

^{You should have paper and something to write with for this portion.}

**First, let’s write down the English alphabet.** Write it in a straight line, like shown below:

```
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
```

**Next, pick a number from 1 to 23.** This number will be your 𝕜𝕖𝕪^{d3}. As an example, I’m going to use a 𝕣𝕠𝕥𝟙𝟛^{d4} cipher, which means my key is 13. Starting with `A`

as zero, count forward in the alphabet to your key, and write `A`

beneath the letter you end up on:

```
0 1 2 3 4 5 6 7 8 9 0 1 2 3
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
```

**Now fill in the rest of the alphabet.** When you get to the end, wrap around to below the `A`

and keep going. Be sure to keep the letters lined up neatly! Leave some space between them or draw lines between the columns to distinguish them.

```
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
N O P Q R S T U V W X Y Z A B C D E F G H I J K L M
```

**Write a message down on the paper.** It should consist only of the 26 letters above, no punctuation. This message is your 𝕡𝕝𝕒𝕚𝕟𝕥𝕖𝕩𝕥^{d4}. Here’s an example:

```
I WANT A RUSTY AXE
```

**For each letter in your plaintext,** find that letter on the top line above, and write down the letter directly beneath it. For instance, for `I`

we would write `V`

, for `W`

we would write `J`

, and so on:

```
V JNAG N EHFGL NKR
```

**We did it!** What I have just done, and what you’ve done too if you’ve been following along, is technically encryption (albeit a very unsafe variety!).

**Now, we can prove it worked** by reversing the process: find each letter of the 𝕔𝕚𝕡𝕙𝕖𝕣𝕥𝕖𝕩𝕥^{d5} in the ** bottom** row and replace it with the letter immediately

*above*it. You should end up with the original message again:

```
I WANT A RUSTY AXE
```

**At this point, you’ve not only done encryption,** but you’ve performed a 𝕕𝕖𝕔𝕣𝕪𝕡𝕥𝕚𝕠𝕟^{d6} operation as well! We’re on a roll!

**Here’s your chance for an upvote if you’re paying attention.** Think of a short message you’d like to give me. *Pick your own key and message*; don’t use mine! Then encrypt it with a shift cipher using the steps above, and send your ciphertext in the comments. ** I like a challenge, so don’t tell me what the key is!** 🍋

# Definitions

^{From my personal knowledge and experience unless otherwise noted.}

**encryption**: the act of transforming data in a reversible way in order to hide information from others.**algorithm**: a specific process with a strict set of rules which, when applied, generates some desired result. There are algorithms for every kind of problem a computer can solve. A**cipher**is a*type*of algorithm, used for encryption.**key**: a secret that is used along with the cipher algorithm. In general,*algorithms*do not change, but keys*do*. The “13” part of the rot13 example above is the*key*.**rot13**: a specific Caesar cipher using a shift of 13, so that the encrypt and decrypt operations are functionally the same algorithm with the standard English alphabet (since 13 is half of 26).**plaintext**: the actual message or data; this is the thing you are trying to hide by encrypting.**ciphertext**: the encrypted message or data; the output of the*cipher*. If your cipher is secure (shift ciphers are*not*secure!), this is what is safe to send over the Internet, store in public places, etc.