Encryption

Question 1

[PPQ] What is the difference between a symmetric and an asymmetric cipher system?

Answer 1

Symmetric: The same key is used for encryption and decryption
Asymmetric: Different keys are used for encryption and decryption

Question 2

[PPQ] State two benefits of including a digital signature

Answer 2

So that B can check if the message has been modified, and also so they can confirm who sent it

Question 3

[PPQ] Explain what it means for a cipher to be described as being computationally secure

Answer 3

Messages cannot be decoded in polynomial time

Question 4

[PPQ] What is the key exchange problem?

Answer 4

How to pass the key from the sender to the receiver without it getting intercepted

Question 5

How does the Vernam cipher work?

Answer 5

Original message XOR key. The key is randomly generated and must be exchanged with the receiver before sending

Question 6

What is the difference between the Vernam cipher and other ciphers?

Answer 6

Vernam cipher is the only one to have been mathematically proved to be completely secure. The worth of all other ciphers ever devised is based on computational security. In theory, every cryptographic algorithm except for Vernam cipher can be broken, given enough ciphertext and time.