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Paper 2 - Computer Science > Encryption > Flashcards

Flashcards in Encryption Deck (12)
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What is encryption?

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


What are the advantages of encryption?

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


What is Ciphertext and plaintext

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


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.


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


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.


What is computational security

is used to describe the effectiveness of a cipher


What type of cipher is a caesar cipher?

It's a substitution cipher


What is a disadvantage of caesar ciphers?

They can be easily cracked due to frequency analysis


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

- must be completely random
- must not be reused


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

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


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