Font size
WorksheetsEncryption - AQA A Level Computer Science
Total questions: 10
Worksheet time: 3mins
Definition of encryption
Using an algorithm and a key to convert message data into a form that is not understandable without that key.
A method of trying to find the plain text from the cipher text without the decryption key.
Process of turning legible text into gobbledygook.
Using an algorithm and a key to convert encrypted message data into its plain text equivalent.
Definition of decryption
Using an algorithm and a key to convert message data into a form that is not understandable without that key.
A method of trying to find the plain text from the cipher text without the decryption key.
Process of turning legible text into gobbledygook.
Using an algorithm and a key to convert encrypted message data into its plain text equivalent.
A Caesar cipher encrypts the plaintext Et tu, Brute into the ciphertext ix xy, fvyxi. What would the same cipher encrypt it was Greek to me into?
mx aew kviio xs qi
ny bfx lwjjp yt rj
ep swo cnaag pk ia
qb eia ozmms bw um
Why are Caesar ciphers so easy to crack?
There are only 25 possible 'shifts', so a brute force attack will easily find the key required.
Use of frequency analysis will be able to find common letters and words.
Each key is only used once.
The number of shifts is calculated from the number of characters in the plaintext.
The Caesar cipher is an example of what type of cipher?
Substitution cipher
Transposition cipher
Public key encryption
Vernam cipher
What are the conditions required for a Vernam cipher to be 100% mathematically secure?
The key is used only once, and then destroyed/
The key is made up of truly random characters/
The key must be made up of fewer characters than the plaintext message.
Different keys must be used to encrypt and decrypt a message.
Which Boolean operator is used to produce the cipher text from the plaintext and the key?
XOR
NOR
OR
NAND
The letter m has an ascii code of 1101101. As part of a Vernam cipher, the key 0101001 is applied to that letter. What is the resulting ciphertext?
1000100
0111011
1100101
1101001
Which cipher is considered to be 100% mathematically secure?
Caesar cipher
Vernam cipher
Transposition cipher
Railfence cipher
If a cipher is theoretically possible to break, but not when using current technology in a timeframe that would be useful is known as what?
Computationally secure
Intractably resistant
Algorithmically impossible
Cryptographically unbreakable
