Lecture 4 - Public Key Encryption

Question 1

Describe the steps involved in ensuring confidentiality of a message.

Answer 1

1. Bob encrypts the plaintext message using Alices public key
2. The produced ciphertext message is transmitted by Bob to Alice.
3. Alice decrypts the ciphertext message using her private key

Secure message format uses the recipient’s private key to protect message confidentiality.

Question 2

Describe the steps involved in ensuring authenticity of a message.

Answer 2

1. Bob encrypts the plaintext message using his private key
2. The produced ciphertext message is transmitted by Bob to Alice.
3. Alice decrypts the ciphertext message using Bobs public key

Open message format uses the sender’s private key to ensure authenticity.

Question 3

Describe the steps involved in ensuring both confidentiality and authenticity of a message.

Answer 3

1. Bob encrypts the plaintext message using Alice’s public key and then his own private key.
2. The produced ciphertext message is transmitted by Bob to Alice.
3. Alice uses Bobs public key to verify the authenticity of the message and then decrypts the ciphertext message using her private key.

Question 4

True / False

Public key encryption is too slow for real-time communication

Answer 4

True

Question 5

List three aspects that describe public key encryption

Answer 5

1. Is an asymmetric key method
2. Uses a Public key and a Private Key
3. Is excellent for keeping data secure

Question 6

List the three maths methods that Public Key encryption use

Answer 6

1. Integer Factorisation (RSA)
2. Discrete Logarithms (ElGamal)
3. Elliptic Curve Relationships (Elliptic Curve)

Question 7

Provide a definition for RSA

Answer 7

RSA is an asymmetric key algorithm based on factoring prime numbers

Question 8

What is the greatest common divisor (gcd)

Answer 8

The greatest common divisor (gcd) between two numbers is the largest integer that will divide both numbers.

Example gcd(4,10) = 2

Question 9

Provide a definition for a prime number

Answer 9

Defined as a number that can only be divided without a remainder by itself and 1

Question 10

List two advantages to public key encryption

Answer 10

1. The main advantage of this type of cryptography is its increased data security. Because users never need to transmit or reveal their private keys to anyone.
2. Digital signatures that cannot be repudiated

Question 11

List two disadvantages to public key encryption

Answer 11

1. computational overhead means it is slow
2. As computers get faster, brute force attacks will become more practical

Question 12

RECAP LECTURE

MD5 hashing is vulnerable to what type of attacks?

Answer 12

Collision attacks

Question 13

RECAP LECTURE

Diffie-Helman key exchange is vulnerable to what type of attacks?

Answer 13

MITM Attacks

Question 14

RECAP LECTURE

The RSA algorithm involves three steps. List them

Answer 14

1. Key generation
2. Encryption
3. Decryption

Question 15

RECAP LECTURE

Fill in the blanks

RSA creates a ___ ___ (public and private) for a single user

Answer 15

RSA creates a key pair (public and private) for a single user