Week 9

Question 1

Appreciate that cryptography is a broad term that includes tools for providing a wide range of security properties

Question 2

Give examples of scenarios in which secrecy, authentication and data integrity would be desirable

Question 3

Describe the basic structure and requirements of a symmetric encryption scheme, vs asymmetric

Answer 3

[confirm this is what the notes says]

Symmetric:

• the same key is used to encrypt or decrypt a message
• both Alice and Bob hold a copy of the key
• if the key is stolen, game over

Asymmetric:

• a pair of different keys used for encryption and decryption
• Bob shares the encryption key publicly; only the intended message recipient holds the decryption key
• it’s fine if the public key is “stolen”; if private key is stolen then game over

Question 4

Describe the Caesar Cipher, perform encryption and decryption using the Caesar Cipher and discuss its weaknesses

Question 5

Describe the Substitution Cipher, perform encryption and decryption using the Substitution Cipher, and discuss its weaknesses

Question 6

Define a brute force attack on a symmetric encryption scheme

Question 7

Describe how to use frequency analysis to attack a Substitution Cipher

Question 8

Appreciate that an attack is said to break a cipher if it can be carried out faster than a brute force attack on the same cipher