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Homework answers / question archive / Homework 3 SECURITY AND PRIVACY HOMEWORK Layered Security Problem (15 points) Suppose you are a medium size health care service provider and have installed a EMR

Homework 3 SECURITY AND PRIVACY HOMEWORK Layered Security Problem (15 points) Suppose you are a medium size health care service provider and have installed a EMR

Computer Science


Layered Security Problem (15 points)

  1. Suppose you are a medium size health care service provider and have installed a EMR. This EMR has no network connection and consists of workstations in exam rooms that are connected to a server with the EMR database.  Propose a layered security system to protect patient information. You should have at least 4 layers.


Encryption Problems (30 Points)



The Caesar cipher (aka “shift cipher”) is a type of substitution cipher.  Messages are encrypted by “shifting” letters or numbers.  Letters can be represented as numbers. For example, if a message was encoded using a shift of five, A would be replaced by F, B would become G, and so on.  This same concept can be used with numbers.  Letters can also be converted to a number code. For example: A = 1, B = 2, C = 3 , …  .  Then we do the shift. Using a shift of four, A would be replaced with 5, B would become 6, etc.  You can also do multiple shifts within a message.  Known as a Vignère cipher or a polyalphabetic substitution cipher, these can be a bit harder to break.  For example, we could shift the first character by 22, the second by 15, the third by 4, and then repeat the pattern.  You may represent a space with a “ “ or a “_”.

Hint: Writing down the alphabet may help.




Instructions: Please encrypt the following messages.

Hint: It helps to write out the regular alphabet (plain text) and then the cipher text.


Encrypt using a 3 letter shift.

1. I like the zoo.


Encrypt using a 5 letter shift.

2. The sky is blue.


Decryption (15 Points)

Instructions: Please decode the following messages.



Using a 4 letter shift the encoded message “LM” becomes the decoded message “HI”. Remember that going from Z à A is only 1 letter. (Hint – The Vignère table below might be helpful). Use a 4 letter shift.




          The Vigenère square is a form of the Caesar cipher contained within a 26x26 box, corresponding to each row and column beginning with different letters of the alphabet, in consecutive order, beginning from A.  Each alphabet is shifted cyclically to the left compared to the previous alphabet by some repeating pattern.  At different points in the encryption or decryption process, the cipher uses a different alphabet from one of the rows.

          The alphabet used is determined by a keyword that repeats until it matches the length of the plaintext to be encrypted/decrypted.  Each number/letter in the keyword corresponds to a position within the square.

          In the square below, the row atop refers to the letter being encrypted while the numerated column on the side corresponds to the letters position within the word.  For example, if we were trying to encrypt an ‘A’ with a key of 1, the result would be B, which is given in the table.. 

Example: Use the square below to encrypt the word “HELLO” with the key 1,2,3.

Solved: Using the square below, we begin by matching up the letter H, with the number 1 since H is the first letter; this would give us the letter I.  Next is matching E and 2, which gives us G; L3=O, L4=M (we start the key pattern again) , L5=Q.  Thus our answer would be IGOMQ.  To use this for decryption, you would reverse the process.  For the letter I in the 1st position, you would find the column heading under which the letter I falls in the 1st row, thus the letter H.  If, for example you were decrypting the letter Q in spot 5, you would first look at row 2 (the key is being used for the second time) until you found the letter Q, at this point you would find the letter whose column this is, in this case it would be O.



Encrypt with the Vignère cipher using a 2, 0, 1, 3 letter shift pattern.

1. Help.



Example: Using the Vignère cipher with the key 2,5,2,5. For example the encrypted text UYCW is the word STAR.

2. Message: U F H J


  1. Using the Vigenère Square below, please encrypt “PRIVACY” with the key 1,2,3. 



  1. Once this is completed, then decrypt “TGFYWOAG.” With the key 1,2,3,4,5,6,7,8



One Time Pad (10 Points)

One way to use the Vigenere Square is as a “one time pad”  This means that the key can only be used one time and is the same length as the message.  If I use the Vigenere Square as a one time pad is it possible to break the code?   If so how?






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