Chapter 2: Cryptographic Tools

Question 1

What are the five ingredients of a symmetric encryption scheme?

Answer 1

Plaintext
Encryption Algorithm
Secret Key
Ciphertext
Decryption Algorithm

Question 2

What are two requirements for secure use of symmetric encryption?

Answer 2

A strong encryption algorithm

Sender and receiver must have obtained copies of the secret key in a secure fashion

Question 3

What are the two general approaches to attacking a symmetric encryption scheme and a secure hash function?

Answer 3

Cryptanalysis

Brute-Force Attack

Question 4

What are the most important symmetric algorithms (all of which are block ciphers)?

Answer 4

Data Encryption Standard (DES)
Triple DES (3DES)
Advanced Encryption Standard (AES)

Question 5

What are two concerns over the Data Encryption Standard?

Answer 5

that this algorithm uses a 56-bit key

as this is the most-studied encryption algorithm, that a fatal weakness may be discovered due to cryptanalysis (none has yet been discovered as of today 01/2015)

Question 6

Running a brute-force attack is not as simple as running through all possible keys. What other challenges must an attacker overcome?

Answer 6

unless known plaintext is provided, the analyst must be able to recognize plaintext as plaintext

if the message is just plain text in English the whole process is easy, but the task of recognizing English would have to be automated

if the message is compressed before encryption, recognition is made even more difficult

if the message is a general type of data (a numerical file), recognition is made even more difficult

Question 7

Which group made the “DES cracker” machine that broke DES in less than 3 days in 1998?

Answer 7

Electronic Frontier Foundation (EFF)

Question 8

What are two reasons that 3DES has not been adopted as the appropriate choice for a standardized encryption algorithm?

Answer 8

3DES is relatively sluggish

both 3DES and DES use a 64-bit block size. A larger block size is desirable for efficiency and security

Question 9

What were the five evaluation criteria categories that NIST used to grade the new Advanced Encryption Standard (AES)?

Answer 9

security
computational efficiency
memory requirements
hardware and software suitability
flexibility