# Rail Fence Cipher

Cryptography is the writing and decoding of secret messages, called ciphers. Now for governments these secret ciphers are a matter of national security. They hire special cryptanalysts who work on these ciphers using cryptanalysis. The secret is, solving substitution ciphers can be pretty entertaining! Ciphers are published daily in newspapers everywhere. If you practice encoding and decoding ciphers, you too can become a really great cryptanalyst.

In this video, I’ll show you how to use the Rail Fence Cipher. Before you start, say this three times fast: cryptanalysts use cryptanalysis to crack ciphers!

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# Twisted Path Cipher

In this video, I demonstrate a Twisted Path Cipher. It uses a matrix and a path in order to encode your message. The shape of the path you create within the matrix of a Twisted Path Cipher determines how difficult it will be to break the code. Watch the video to learn exactly how it works.

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# Shift Cipher

Shift ciphers were used by Julius Caesar in Roman times. The key is a number which tells you how many letters you’ll shift the alphabet. These are fairly simple to encode and decode. However, you have to be extra careful when encoding because mistakes can throw off the decoding process. Watch the video to see why it’s important to double check your work!

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# Date Shift Cipher

The Date Shift cipher is a much harder code to break than, for example, the more simple Shift cipher. This is because the shift number varies from letter to letter, and also because it’s *polyalphabetic* (this means that a single number can represent multiple letters). I’ll explain it all in the video.

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# Pig Pen Cipher

The Pig Pen cipher is of the most historically popular ciphers. It was used by Freemasons a century ago and also by Confederate soldiers during the Civil War. Since it’s so popular, it’s not a very good choice for top secret messages. Lots of people know how to use this one! It starts with shapes: tic-tac-toe grids and X shapes. I really like it because coded messages look like they’re written an entirely different language! Watch the video to learn how it works.

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# Polybius Checkerboard Cipher

Polybius was an ancient Greek who first figured out a way to substitute different two-digit numbers for each letter. In the Polybius cipher we’ll use a 5×5 square grid with the columns and rows numbered. Take a look at the video and I’ll show you how it works.

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# Cracking Ciphers

Cryptograms are solved by making good guesses and testing them to see if the results make sense. Through a process of trial and error, you can usually figure out the answer. Knowing some facts about the English language can help you to solve a simple substitution cipher. For example, did you know that an **E** is the most commonly-used letter in the English alphabet? It’s also the most commonly-used letter to end a word. Watch the video below to learn some more tips and tricks to get you on the right track to being an expert cryptogram solver!

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# Playfair Cipher

This is a super hard cipher to break. It’s encoded by taking pairs of letters and numbers from a matrix. There are three rules to follow.

- If both letters are in the same row, then use the letters immediately to the right of each other. (Think of the rows as wrapping from the right end back around to that same row’s left end).
- If both letters are in the same column, then use the letters immediately below them. If necessary, the bottom letter wraps back around to the top of the same row.
- If the two letters or numbers are in different rows
**and**in different columns, then each letter is replaced by the letter in the same row that’s also in the same column of the other letter. Basically, you find each intersection of the pair. Use the letter or number below the pair and then the one above the pair.

Play Fair sounds really complicated, but that also makes it a tough code to crack! Watch the video and I’ll explain it all for you.

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# Telephone Cipher

Code machines – or cipher machines – can be used to encode and decode messages. One everyday example of a code machine that you can easily access is a telephone. Watch this video and I’ll show you how it works.

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# Invisible Writing

This is an alternate method of secret writing that’s completely different from encoding and decoding message ciphers. It involves using special inks that are invisible until something is done to make them appear on the paper. There are hundreds of formulas to make these special inks and some formulas even have multiple ways to develop the ink. Some recipes involve special chemicals, but many invisible inks can be made using materials that you have in your home. Watch the video and I’ll share a few recipes and teach you more about this method.

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# Scytale

In this video I’ll show you how to use a actual cipher machine called a *scytale*. This was first used in ancient Greek and Roman times, most notably by the Spartans. To make a scytale, use a cylinder with a piece of paper wrapped around it. Then simply print your message in rows that run along the length of the cylinder. When the paper is unwrapped, the message is scrambled! Watch the video and I’ll show you the trick to proper message decoding.

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# Secret Math Code

If only you could keep better track of big numbers, adding and multiplying your head wouldn’t be such a problem! But fear not… I have a trick that might be just the ticket for your brain!

Use this secret phonetic math code to code and decode sentences into numbers. Developed over a hundred years ago, this is *the *code that the expert mathematicians use when doing large calculations in their head. This is exactly how Arthur Benjamin squares 5-digit numbers *without* a calculator!

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