Public Key Crypto

Question 1

What is the additive inverse of 8 MOD 20

Answer 1

12The number that when we add 8 to, 8 MOD 20 results in 0P2 L7

Question 2

what is the multiplicative inverse of 3 MOD 17

Answer 2

6Given X, find Y such that X*Y MOD N = 1P2 L7

Question 3

if n=21, what is totient(n)

Answer 3

12find relatively prime factors of n21 = 3 * 7, (3-1)*(7-1) = 12P2 L7

Question 4

Use the totient technique to find c:c = 7^27 MOD 30

Answer 4

this is the same as 7 ^ (27 MOD totient(30))totient(30) = totient(3) * totient(10) = 2 * (2-1)(5-1) = 2 * 4 = 827 MOD 8 = 37^3 (MOD 30) = 343 MOD 30 = 13P2 L7

Question 5

RSAGiven p = 3 and q = 11A) compute nB) compute totient(n)Assume e = 7C) compute dD) what is the public keyE) what is the private key

Answer 5

A) n = pq = 33B) totient(n) = (3-1)(11-1) = 20C) d = (e * d) MOD totient(n) = 1 = (7 * d) MOD 21 = 1; d = 3D) (e, n) = (7, 33)E) (d, n) = (3, 33)P2 L7

Question 6

What is the RSA encryption formula for value X?

Answer 6

public key = (e, n)(X ** e) MOD nP2 L7

Question 7

What is the RSA decryption formula for value X?

Answer 7

private key = (d, n)(X ** d) MOD nP2 L7

Question 8

When implementing RSA, it is best to use:A) Your own custom software, to ensure a secure systemB) use the standard libraries for RSA

Answer 8

B)P2 L7

Question 9

In Diffie Helman, Alice and Bob agree to use prime q = 23 and primitive root alpha = 5Alice choses secret A = 6, and Bob chooses secret B = 15.What number does Alice send Bob?What number does Bob send Alice?

Answer 9

Alice sends bob (5^6) mod 23 = 8Bob sends Alice (5^15) mod 23 = 19P2 L7

Question 10

RSA is a block cipher in which the plaintext and ciphertext are integers between 0 and n-1 for some n

Answer 10

trueP2 L7

Question 11

If someone invents a very efficient method to factor large integers, then RSA becomes insecure

Answer 11

trueP2 L7

Question 12

The Diffie-Helman algorithm depends for its effectiveness on the difficulty of computing discrete logarithms

Answer 12

trueP2 L7

Question 13

The Diffie-Helman key exchange protocol is vulnerable to a man-in-the-middle attack because it does not authenticate the participants

Answer 13

trueP2 L7

Question 14

RSA and Diffie-Helman are the only public-key algoritms

Answer 14

falseP2 L7