Security Protocols

Question 1

What 3 things are needed to communicate securely over the internet

Answer 1

the users must mutually authenticate each other
establish and exchangekeys
agree on cryptographic operations & algoirithms

Question 2

What’s the process for message authentication with shared secret key for a session

Answer 2

1. User 1 request to communicate w User2
2. User 2 sends back a Challenge R1
3. User 1 Sends an encrypted R1 using their shared secret key
4. User 1 sends to User 2 a Challenge

Question 3

The challenges and responses for multiple sessions should be:

Answer 3

random, not easily repeatable or predictable

R1 & R2 should be large random values and
secret key should be protected

Question 4

In message authentication, what is a reflection attack

Answer 4

over multiple sessions, the attacker, not knowing the encrypted R1, can challenge the victim with R1, upon which the victim will automatically respond with encrypted R1. Attacker then uses that encrypted R1 as the response to the initial challenge

Question 5

How to defend against a reflection attack

Answer 5

use 2 separate keys, an initiator secret key and a response secret key
OR
use even #challenges for User1 and odd # challenges for User2

Question 6

How might mutual authentication work for asymmetric encryption?

Answer 6

1. User1 sends encrypted message using User2’s public key

2. User2 responds with decrypted message and also sends an encrypted message using User1’s public key

Question 7

How are session keys made?

Answer 7

Encrypt a shared session key w the shared master key and send over OR
encrypt a shared session key w the public keys

this encrypted shared key w public key can be also signed (digital signature) by the author’s private key for authentication

Diffie Hellman could also be used as their “shared session key”

Question 8

Key Distribution Center help to deal with scalability with master keys. How does session making and mutual authentication work in this case?

Answer 8

upon a request N1 & UserID,

KDC sends back encrypted: E(Ka,Ks|Request|N1|Encrypted(Kb,Ks|”Alice”))

Question 9

What is Kerberos

Answer 9

authentication and access control in network
it is the Key Distribution Center
Shared Master key is the user’s master key stored on the KDC