# Cryptography: Homework #1

- Due Apr 18, 2018 by 11:59pm
- Points 10
- Submitting a text entry box, a website url, or a file upload
- Available after Apr 9, 2018 at 12am

Changing Placement - Problem Set

There are a total of 5 problems.

1) Encrypt the plaintext ‘MATHEMATICS IS THE GATE AND KEY TO SCIENCE’ using a

permutation cipher.

a. Determine all possible grid sizes. Explain.

b. How many different keys are there if you use a grid with 7 columns?

c. Encrypt the given plaintext with this key 2345671.

d. Explain how to decrypt the ciphertext message.

2) Sometimes people use a keyword as a key so that it is easy to remember. The key is the

alphabetical order of the letters in the keyword. For example, if the keyword is ‘MATH’, the

corresponding key is 3142.The following ciphertext was encrypted with a permutation

cipher. What does the plaintext say?

COPRTY GYPRHA IUHSET LTMTAI EORFMO FVNN-O ITEONL DTEICR ANICOT

(Keyword: CRYPTO)

3) Come up with your own permutation cipher.

a. Explain your algorithm step-by-step.

b. Give an example of using your algorithm: write an original message and then show what

the message looks like when it is enciphered.

4) How many different ways can the letters from the word “LIME” be arranged in a row from

left to right? How many of those arrangements form English words? How many of those

arrangements form non-English words?

5) Otto is sending a secret message to his best friend Izzy by scrambling the letters of the

words in the intended message so that if the scrambled message is intercepted by someone

else, it would not be obvious what the message is saying.

a. Create an organized list of all the arrangements of the letters in the word “BATH”.

Explain the organization of your list. How do you know you have counted all the

arrangements exactly once?

b. How many arrangements of the letters in the name “IZZY” are possible? How about

“OTTO”?