Encryption

Question 1

Describe what is meant by ‘encryption’.

Answer 1

The process of converting data into a format that cannot be understood by an unauthorised viewer, unless you have access to the key needed to decrypt it

(conversion of plaintext into ciphertext)

Question 2

What is meant by ‘plaintext’?

Answer 2

Plaintext describes the original unencrypted text

Question 3

What is the need for encrypting data?

Answer 3

To protect the data’s confidentiality

Question 4

Give examples of two forms of encryption.

Answer 4

• Symmetric encryption
• Asymmetric encryption

Question 5

Describe the difference between symmetric and asymmetric encryption.

Answer 5

• Symmetric uses the same key to encrypt and decrypt the data
• Asymmetric uses two different keys - public key to encrypt the data and a private key, which only the recipient knows, to decrypt it

Question 6

Describe how a Caesar cipher works.

Answer 6

Realigns the alphabet, substituting each letter of the original message with a letter further down the alphabet

(systematic shift, all letters affected in the same way)

Question 7

(Exam-style question)

Explain one reason why the Caesar cipher is a weak encryption algorithm. (2)

Answer 7

The number of keys are limited, making it easy to use brute force to decrypt

Question 8

(Exam-style question)

Answer 8

State:

• Yes

Justification:

• Each letter is represented
• The symbol is a unique representation

Question 9

(Exam-style question)

Give the key used in the first stage of the encryption process. (1)

Answer 9

5

Question 10

(Exam-style question)

Give the ciphertext that is produced by this Rail Fence cipher encryption algorithm.

Answer 10

TIHYSEMNEEERNA

Question 11

On a Vigenere square, what axes do the plaintext and the keyword go on?

Answer 11

• Plaintext - x-axis
• Keyword - y-axis

Question 12

In regard to a Vigenere cipher, what is a keystream?

Answer 12

A version of the keyword that is repeated over and over