Principles of Cryptography

Question 1

What is the key in a Caeser Cipher?

Answer 1

The number of times you need to shift the alphabet

Question 2

What is Symmetric encryption?

Answer 2

The encryption and decryption happen using same key. Key is secret.

Question 3

What does Symmetric encryption guarantee?

Answer 3

Confidentiality of the message being sent

Question 4

What is Asymmetric encryption?

Answer 4

The encryption and decryption happen with two different keys (I have two keys, one used to encrypt and one used to decrypt)

Question 5

What is an example of Symmetric encryption?

Answer 5

Advanced Encryption Standard

Question 6

What is an issue with Asymmetric encryption?

Answer 6

A lot of work to create the keys

Question 7

Asymmetric Encryption (4 steps)

Answer 7

1) Alice encrypts message with Bob’s public key 2) Bob decrypts this with his private key 3) Bob encrypts with Alice’s public key 4) Alice decrypts with her private key

Question 8

What are the 2 uses for Public Key encryption?

Answer 8

Symmetric key distribution, Digital Signatures (DSA)

Question 9

What are 2 ways of Public Key encryption?

Answer 9

RSA, DSA

Question 10

RSA Public Key Encryption (4 Steps)

Answer 10

1) Alice calculates a public key and a private key, 2) Bob sends a message to Alice, encrypting it with her public key, 3) Alice decrypts using her private key, 7) If they match up, the message has not been tampered with and Alice really did send it

Question 11

DSA Public Key Encryption (7 Steps)

Answer 11

1) Alice calculates a hash of the message she wants to send, 2) She encrypts this with her own private key. This is her signature. 3) She takes (her signature + message) and encrypts it with Bob’s public key, 4) Bob decrypts with his private key, to get the message and Alice’s signature, 5) Bob decrypts Alice’s signature to get her hash, 6) He hashes the message he recieved, and compared it to the hash from Alice

Question 12

What 3 things does DSA guarantee?

Answer 12

Integrity of message send, source authentication, non-repudiation (cannot pretend you didn’t send)

Question 13

How does DSA differ to Assymetric?

Answer 13

Asymmetric, you encrypt with the other person’s public. DSA, the signature itself is encrypted with your own signature. Asymmetric =
1) Encrypt with the other person’s public key
2) That person decrypts with their private key

DSA =
1) Encrypt your signature with your private key
2) That person decrypts with your public key

Question 14

What are 2 ways of sharing shared secret keys in symmetric cryptography?

Answer 14

Public Key Cryptography, Diffie-Hellman key exchange protocol

Question 15

What are the 2 overall steps of Public Key Encryption?

Answer 15

1) Alice sends her public key to Bob 2) Bob sends back the shared key encrypted with Alice’s public key

Question 16

What is the issue with Public Key Encryption?

Answer 16

It’s susceptible to a Man in the Middle Attack, after step 1 someone could get Alice’s public key and replace it with their own, before sending to Bob

Question 17

Diffie Hellman Key Exchange

Answer 17

1) Alice and Bob each make a private and public key. 2) They share each other’s public key 3) alculate their shared private key using the public key given to them and their own private key.

Question 18

For the Diffie- Hellman key exchange protocol, what does its effectiveness depend on?

Answer 18

The difficulty that in computing discrete logarithms

Question 19

What is the issue with Diffie Hellman?

Answer 19

It’s susceptible to a Man in the Middle Attack, after step 2 someone could get Alice’s public key and replace it with their own, before sending to Bob. Same with intercepting Bob’s public key and putting in his own