Answer to Question #167340 in Computer Networks for Ali

Question

Describe an autokey cipher and use it with initial key K1=6 to 

encrypt a plaintext “Information”.

2. Describe Random Mapping Cipher and use the following table 

to encrypt a plaintext ‘tutorial’ and ‘Homework’

3. Use the additive cipher with K=10 to encrypt a plaintext

“Homework”.

Note that: Operation is in modulo 26

4. Describe Playfair Cipher, and use the following table to encrypt 

a plaintext ‘university’

Explain and Use Vigenere cipher to encrypt the message 

“homework” using keyword “student”.

6. Use an affine cipher with K=(7,2) to encrypt “security”.

Explain and Use Unkey Transpositional ciphering to encrypt the 

message “Information Technology”

Note that both parties agreed on the number of columns which 

is 4 

8. Explain and Use Keyed columnar transposition cipher to encrypt 

a plaintext “Meet me at the park” with key “Study”

Note: both parties agreed on the number of columns is 5.

Answer 1

Autokey cipher:

The autokey cipher is used by members of the American Cryptogram Association, starts with a relatively-short keyword, the primer, and appends the message to it. If, for example, the keyword is "QWERTY" and the message is "ATTACK ", the key would be "QWERTYATTACK".

1) use it with initial key K1=6 to encrypt a plaintext “Information”.

Ans: K1=6 to encrypt a plaintext “Information” is converted to QAKCIYAMQCA.

the plaintext is converted into ciphertext as shown in the figure.

2. Describe Random Mapping Cipher and use the following table to encrypt a plaintext ‘tutorial’ and ‘Homework’.

ANS: tutorial and Homework is converted as follows:

3. Use the additive cipher with K=10 to encrypt a plaintext “Homework”.

ANS: Using the cipher with K=10 to encrypt a plaintext “Homework” then it will be converted to OCYISCIU.

4. Describe Playfair Cipher, and use the following table to encrypt a plaintext ‘university’

ANS: The Playfair cipher is a written code or symmetric encryption technique that was the first substitution cipher used for the encryption of data. it involved the use of keys that arrange alphabetical letters in geometric patterns in order to encode messages this process is also known as the Playfair square.

5) Explain and Use Vigenere cipher to encrypt the message “homework” using the keyword “student”.

ANS: Vigenere Cipher is a method of encrypting alphabetic text. It uses a simple form of polyalphabetic substitution. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The encryption of the original text is done using the Vigenère table.

These are the few things need to know about the Vigenere cipher.

it consists of the alphabets written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet, corresponding to the 26 possible Caesar Ciphers. At different points in the encryption process, the cipher uses a different alphabet from one of the rows. The alphabet used at each point depends on a repeating keyword.

encrypting the plaintext “homework” using the keyword “student” is converted to ZHGHABKR.

6) Use an affine cipher with K=(7,2) to encrypt “security”.

Using an affine cipher with Key=(7,2) to encrypt “security” is converted to KIEOIQMW.

7) Transposition Cipher:

Transposition Cipher is a cryptographic algorithm where the order of alphabets in the plaintext is rearranged to form a ciphertext. In this process, the actual plain text alphabets are not included.

8) In a transposition cipher, the order of the alphabets is re-arranged to obtain the cipher-text.

1. The message is written out in rows of a fixed length, and then read out again column by column, and the columns are chosen in some scrambled order.
2. The width of the rows and the permutation of the columns are usually defined by a keyword.
3. Finally, the message is read off in columns, in the order specified by the keyword.

cipher to encrypt a plaintext “Meet me at the park” with key “Study” is converted to BEVD YI EM FLE ITYO.