RSA

Question 1

Symmetric key algorithms advantages

Answer 1

Simpler algorithm structure
Shorter key lengths
Very fast to implement

Question 2

Symmetric key algorithms disadvantages

Answer 2

Key distribution must be via a secure channel
Cannot offer non- repudiation

Question 3

Public key algorithms advantages

Answer 3

Does not need a shared secret key
Offers non repudiation (as can be used as digital signature)

Question 4

Public key algorithms disadvantages

Answer 4

Complex algorithms based on number
Long key lengths
Very slow to implement

Question 5

In symmetric key cryptography an algorithm which has a key length of n-bit has n bit security level

Answer 5

True

Question 6

Two techniques used to speed up the performance of RSA

Answer 6

Square and multiply- reduces number of multiplications needed therefore speeding up encryption and decryption

Small public exponent (e)- choosing small e allows faster encryption by reducing number of operations required in modular exponentiation step.

Question 7

Encryption in triple DES

Answer 7

Encrypt plaintext using key 1
Decrypt output using key 2
Encrypt the output from step 2 using key 3

Question 8

Decryption in triple DES

Answer 8

Decrypt the cipher text using key 3
Encrypt the output using key 2
Decrypt the output from step 2 using key 1

Question 9

How can triple DES operate with three different keys

Answer 9

Encrypt the plaintext with key 1
Decrypt result using key 2
Encrypt the result again with key 3