Week 2 - Public Key Cryptography

Question 1

What is the key distribution problem?

Answer 1

trying to agree on shared key over an insecure network

Question 2

What are some solutions to the Key distribution problem?

Answer 2

1/ Diffie Hellman key exchange algorithm
2. Public key cryptography

Question 3

What are the properties of public keys?

Answer 3

• Each entity has their own private and public key
• Data is encrypted with private key and decrypted with a corresponding public key
• mathematically impossible to get the private key from the public key

Question 4

How does public key cryptography provide authenticity?

Answer 4

sender encrypts a message with their private key, allowing anyone with the senders public key to decrypt it, verifying it is them

also ensures sender cannot deny creating message, as only their private key could have signed it (Non repudiation)

Question 5

How is Confidentiality and Authenticity achieved?

Answer 5

Layered Encryption

1st, encrypt message with bob’s private key (authenticity)

2nd, encrypt it with receivers public key, (confidentiality)

receiver decrypts with their private key and senders public key

Question 6

Why might an entity have multiple key pairs?

Answer 6

single session communications

Question 7

What should be done if a key pair is compromised or lost?

Answer 7

revoke key and generate new key pair