Cryptography

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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How did you like the Rail Fence Cipher? Pretty neat, right? Would you rather encode or decode a cipher? I think both parts are fun. But if you’re encoding, just make sure the decoder knows the correct formula to use!

Exercises

Write the cipher of the following message:

1. COME TOMORROW AT 2PM
2. HE HAS ARRIVED AT THE AIRPORT
3. HE IS CARRYING A BAG
4. THEY ARE HERE NOW
5. COME AT MY PLACE

Write the cipher of the following message (use a three row zigzag)

6. COME TOMORROW IN MY OFFICE
7. LEAVE THEM BEHIND
8. WE WILL BE THERE SOON
9. The cipher below was encoded using a two rows zigzag method with six letters in every row. Decode it.
   IMOIG OACMN NW
10. The cipher below was encoded using a three rows zigzag method with four letters in every row. Decode it.
    ICINA ONOMM GW

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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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What did you think of the Twisted Path Cipher? Remember that it will be easier to break your code if you use straight lines, so consider using some extra tricks to make it more difficult. For example, spirals, and zigzags are super hard to crack, and paths don’t have to be continuous! If you’re encoding, just make sure that the decoder knows the correct path shape (or shapes) to use!

Exercises

Given the following message, what would be the best size of the table to use?

1. COME TOMORROW
2. WE ARE WAITING AT THE BUS STATION
3. THE LETTER IS IN HIS BRIEFCASE
4. HE WILL COME LATE TODAY

Identify the type of path indicated in the diagrams below

Write the cipher of the following message using the path in #5 above.

7. I WILL LEAVE FOR UK TODAY
8. AM ON MY WAY TO THE SCENE
9. I WILL ATTEND THE OPENNING DAY
10. I WILL BE THERE AT 2

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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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Do you see why it’s important to double check the encoding?  This is a simple code, but it’s easy to shift and end up with a jumble when your message is decoded. So always check your cipher with a practice decoding prior to sharing it.

Exercises

Use the key shift number 4 on the letters of alphabet to code or decode the following:

Encode the following statement:

1. OUR SCHOOL WAS THE BEST
2. I WAS THE BEST IN MATHEMATICS
3. I AM THREE FEET TALL
4. OUR SCHOOL HAS GOOD TEACHERS
5. COME TO MY RESCUE

Decode the following:

6. SAWNA HAWRE JCXQZ
7. SDWQE OQDAM PAOQE KJXQZ
8. LHAWO AYKIA QKZWU
9. EWIKJ IUSWU
10. ODAEO WCKKZ OEJCA NMXQZ

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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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What do you think about the Date Shift cipher? The possibilities for numerical keys are endless. You can use the date you’re sending the message, birth dates, phone numbers, and more! Just remember to start decoding by writing the key numbers over the top of the encoded cipher. And always makes sure the decoder has the correct numerical key!

Exercises

1. Which kind of key is used in date-shift ciphers?
2. In which direction is the cipher shifted when decoding?
3. How do you describe a cipher where a specific alphabetical letter represents more than one letter?

What would be the date shift key codes for the following?

4. April 4^th  1998 (Don’t forget that the key needs six digits! Use “04” for the date.)
5. Jan. 28^th 2012
6. Nov. 30^th 2011

Encode the following:

7. COME TO MY HOME : March 16^th 1999
8. THEY HAVE JUST LEFT : June 1^st 2001

What are the original messages? (These messages were sent on July 16^th 1992)

9. GUBZC GOGNZ
10. MKFZV GAZTO GROZQ

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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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Isn’t this a fun one!  To make the cipher a little harder to crack, arrange the encoded message in groups of five characters. As always, remember that your intended recipient needs the Pig Pen key in order to decode your message.

Exercises

1. What’s the difference between the second and the fourth pig pen?

Draw the following:

2. The third pig pen
3. The first pig pen

Using the following pig pen key, encode #4-7:

4. GO TO SCHOOL
5. COME BACK
6. I WILL SLEEP LATER
7. NORTHERN AMERICA

Using the pig pen key, decode the following messages:

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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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To make the Polybius more difficult to crack, you can write the alphabet backwards or in an up and down pattern rather than left to right. Just be sure the decoder knows if you’ve used a different path or pattern to encode.

Exercises

1. Write the grid that is used to encode and decode messages in the Polybius Cipher. (Can you think up your own?)
2. Identify the codes representing the following letters using the grid from the example in the lesson: A, O and C.

Encode the following statements using the Polybius Cipher grid from the main lesson:

3. LET US LEAVE
4. I AM LEAVING
5. THEY WILL COME
6. SHE IS HERE

Decode the following messages using the Polybius Cipher grid from the main lesson.

7. 32-35-35-31-11-45-45-23-15-45-11-12-32-15
8. 24-45-24-44-23-24-14-14-15-34
9. 23-15-43-15-24-44-45-23-15-41-11-41-15-43
10. 32-35-35-31-11-45-33-55-12-35-35-31

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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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So, it helps to have a lot of words to work with so that you can begin to recognize patterns in the code.  Here are some examples from the video:

• single letter words will most likely be either A or I
  
• the most frequent two-letter words in English are OF, TO, and IN
  
• the most frequently used three-letter words are THE and AND
  
• finally, the most frequently occurring four-letter word in English is THAT

Additional tips include the fact that Q is almost always followed by U, and that N often (but not always) follows a vowel. Finally, if two code symbols occur in a row, they could be a consonant combination such as  LL, EE, SS, OO, TT, etc. The real trick to this is to try something, and then if it doesn’t work, go back and try something else. Get lots of practice by checking in newspapers and magazines for these popular puzzles. If you really like them, you can find puzzle books full of cryptograms. You’ll be an expert cipher solver in no time!

Exercises

1. What does it mean by “cracking a cipher?”
2. In there a difference between cracking and decoding a cipher?
3. What is very important that a person should know before beginning the cracking process?
4. What is the most common letter of alphabet that is usually at the end of a word?
5. What is the most common letter that is usually at the beginning of a word?
6. If you have a letter all by itself, what is it most likely to be?
7. What are two of the most common two character words in sentences?
8. What are two of the most common three character words in sentences?
9. What is the most common four character word in sentences?

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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.

1. 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).
2. 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.
3. 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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Isn’t this cool? It makes a lot more sense when you see it in action, right? Remember: when decoding the Playfair cipher, you have to shift up instead of down and left instead of right. And it’s easy to make a mistake by encoding in the incorrect order. So always  double check your cipher before sending it on to the recipient. Mistakes make messages much harder for the decoder to interpret!

Exercises

1. What is the name given to the following table?

Use the table in 1 above to answer question 2 – 10.

What will be the cipher for the following?

2. KB
3. HR
4. AR
5. EU
6. COME TO SCHOOL
7. GO HOME THEN

Decode the following messages

8. 73 3N SG YZ 6X
9. SG MN YK A7 JO HD
10. Why is it important the number of letters in the message to be encoded be even?

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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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What do you think about the Telephone Code? Remember to get those slash codes just right in order to make decoding easier for the message receiver. (No pun intended!)

Exercises

Encode the following using the telephone keypad:

1. COME BACK
2. LEAVE TODAY
3. HE ARRIVED
4. THEY WENT
5. HE IS COMING
6. REVEAL
7. GO AHEAD

Decode the following ciphers

8. 1 6 3 7 4   2  2
9. 8 64  8 3   3 5 4 6 4   3 6  6
10. 2 8 7  8 7   2 5 4 2

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