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Paper 2 - Computer Science > Encryption > Flashcards

Flashcards in Encryption Deck (12)
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1

What is encryption?

The process of converting a message into ciphertext so it can't be understood by an unauthorised third party

2

What are the advantages of encryption?

It stops data being stolen.
It stops data being changed.

3

What is Ciphertext and plaintext

Plaintext is the data before it's encrypted. Ciphertext is the data after it's been encrypted.

4

How is does a Caesar Cipher work?

Each letter is replaced with a different letter in the alphabet by shifting all the letters along by a certain amount.

5

How is does a Vernam Cipher work?

It uses a one time pad that is the same length or longer than the data to be encrypted. Then an XOR operation is performed to create the cipher text

6

Why is using a Vernam Cipher more secure than using a Caesar Cipher?

A Caesar Cipher can only shift 25 times so could be decoded easier than a Vernam Cipher that uses a key once (one time pad) and an XOR operation, making it impossible to decrypt without the key.

7

What is computational security

is used to describe the effectiveness of a cipher

8

What type of cipher is a caesar cipher?

It's a substitution cipher

9

What is a disadvantage of caesar ciphers?

They can be easily cracked due to frequency analysis

10

What are the two requirements of a key used for a vernam cipher?

- must be completely random
- must not be reused

11

What are the requirements of for a computationally secure vernam cipher?

It can be cracked, but not in a reasonable amount of time

12

What is a requirement of the one time pad?

It must be at least as long or longer than the data that's being encrypted