Cryptography (Parents/Teachers)

Alphabet Shift Cipher: This would be done using a cipher that looks at the letter you start with an changes it to another letter that is a set number of letters away. In the cipher think about the alphabet as moving and just circling back on itself, let’s look at an alphabet shift cipher that shifts by six letters:

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In this shift A becomes G, B becomes H, C becomes I and so forth. The cipher will change the letters from their first source to their changed letter. Let’s go through and encrypt a simple message using this cipher.

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Now looking at what the phrase has become unless you knew the cipher or were very good and figuring out what the cipher could be this phrase would no longer make any sense, hence the phrase has now been encrypted. But now we need to decrypt our message. Since we know our first cipher all we have to do is reverse it and go from the encrypted message back to the original decrypted message. Let’s look at what our reverse cipher would look like:

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From here we can simply apply the decryption cipher to our encrypted message and get our original message out:

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Problem 1: Your challenge will be to encrypt to phrase “The Blue Moon is Bright tonight” using the cipher above and write it in the spaces shown below.

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Problem 2: Knowing that the same alphabet shift cipher that was described above was used to create this message, can you decrypt the following message?

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Substitution Cipher: This cipher is based off of the alphabet but instead of simply doing a shift to the letters in the alphabet it randomizes the letters more. A common way of making this cipher is to pick a work that has no repeating letters and use it to start your cipher, then take the remaining letters and use them in order for the rest of the cipher. I like the word dinosaur (this word has no repeating letters so it should work just fine) and will use it to encode my first letters then have the rest of the alphabet follow in order, an example of this is shown below:

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So using this cipher if I had the phrase: Purple is an awesome color, it would become:

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From there I can work backwards and decrypt that message.

Problem 3: Knowing that the same cipher as above needs to be used, can you encrypt the following message “Cats are felines”?

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Problem 4: Knowing that the same cipher as above was used to encrypt this message, can you decrypt this message?

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Rail-fence cipher: In the rail fence cipher, the plain text is written downwards and diagonally on successive "rails" of an imaginary fence, then moving up when it reaches the bottom rail. When it reaches the top rail again, the message is written downwards until the whole plaintext is written out. The message is then read off in rows. Let’s try the message “Candy is sweet but apples are sweetest!” on a fence that has 5 rails (this means there are 5 lines or rows):

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From here you would take the letters across each line and make the final message: 

CWPS!ASEAPEWTNSETLRESDITUEAEEYBST

Problem 5: Now you have a fence with 3 rails(rows), can you encrypt the following message “Fall is cold”?

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And the message would be read as:

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Problem 6: Now this will be very tricky but I know you can do it. You know that your encrypted message comes from a 4 rail(row) fence, can you decrypt the following message?

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And the secret message is:

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Route Cipher: In a route cipher the text of your message is written out in a grid ignoring spaces between the words. Think about a grid as a table with a set number of rows and columns. You create your message to fit in this table. Let’s look at a simple example with the message “Dogs snow down town” (odd message but will make it easy to show a route cipher). For this message a table of 4 columns by 4 rows would be perfect to fit the message and make an easy example to look at. Put the first word down the first column then put the next word on the next column again with each letter in its own row, continue with this until you are done putting the entire message in the grid. The grid for this message should look like this:

D	S	D	T
O	N	O	O
G	O	W	W
S	W	N	N

Now to encrypt the message you will pick a cipher that take a route or path through the text and write the letters that it encounters on its path. Let’s use the route of circling clockwise from the top left, this would give you the encoded message of:

DSDTOWNNWSOGNOWO

From here to decipher the text you would use the cipher in reverse, writing the text out into the grid and pulling back out the original message.

Problem 7: Using a 5 row by 5 column grid encode the message “Times Change very fast Peterc”, and using the cipher spiraling clockwise inwards from the top left.

T	C	E	F	E
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D	G	Y	P	C

And the encoded message is:

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Problem 8: This message came from a 4 row by 4 column grid and used the cipher spiraling clockwise outward from the top right center, decode the following message:

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And the message is:

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