Algorithms

Question 1

What is the Formula for Encryption for RSA

Answer 1

C = M^e % n

Question 2

What is the Formula for Decryption for RSA

Answer 2

M=C^d % n = (M^e)^d % n

Question 3

Explain Key Generation for RSA

Answer 3

1. take distinct Prime Numbers p q, let n=p.q
2. let phi(n) = (p-1)(q-1)
3. calculate d so that de % phi(n) = 1

Public Key KU = {e ,n}
private Key KR = {d, n}

Question 4

How can you break RSA

Answer 4

Brute Force Attacks
find p and q for n

Question 5

Points about the security of RSA

Answer 5

Relies on factoring algorithms
big numbers cannot be factored easily

Question 6

Requirements for DH algorithm

Answer 6

2 known numbers
1. Prime Number (q)
2. Primitive root of q (a)

Question 7

Steps Of DH Encryption

Answer 7

1. A and B Select random numbers secretly
2. A Calculates Y_a = alpha ^X_a% q
3. B calculates Y_b = alpha ^X_b% q
4. send those over
5. they calculate a common secret key using
   K = (Y_a/b^X_b/X_a)

Question 8

What does MAC Stand For

Answer 8

Message Authentication Code

Question 9

How does MAC work

Answer 9

a hash is found for a message using a shared secret key and added to the end of the message by the sender, the receiver then also calculates the MAC and compares their results

Question 10

Compare MAC to encryption

Answer 10

MAC is easier to implement and is less vunerable to being broken but cannot be reversed

Question 11

Compare One-Way Hash functions and MAC

Answer 11

• hash functions do not use a secret key to find the hash unlike MAC
• both easy to implement

Question 12

Requirements for one way Hash Functions in message authentication

Answer 12

• function must be able to be applied to a block of any size
• function must produce a fixed length
  -H(x) must be easy to compute
  -for a given h it must be difficult to find x such that H(x) = h
  -Strong collision resistance