P2L5: Intro To Cryptography

Question 1

What is Ciphertext?

Answer 1

Ciphertext is plaintext that has been encrypted

Question 2

What other services does Encryption/Decryption provide?

Answer 2

* Integrity checking (no tampering) * Authenticity (verified authorship) * Authentication (not an imposter)

Question 3

Most protocols use Symmetric ciphers and Asymmetric Ciphers (True or False)

Answer 3

True

Question 4

What are Asymmetric ciphers used for?

Answer 4

Authentication, key exchange and digital signatures

Question 5

What are Symmetric ciphers used for?

Answer 5

Encryption of data/traffic

Question 6

What types of attack methods exist related to Encryption/Decryption?

Answer 6

* Brute force - trying all possibilities * Cryptanalysis - analysis of algorithm and data characteristics used to decode a message * Implementation attacks - side channel analysis * Social Engineering attacks - the easiest way to get into a system

Question 7

If the only form of an attack against encryption was brute force, then the solution would be to do what?

Answer 7

Use a longer key length so they just can’t find it in a reasonable amount of time

Question 8

What is another name for the Caesar Cipher?

Answer 8

Shift Cipher

Question 9

What is a Caesar cipher called when each letter isn’t shifted a specific amount but is instead mapped arbitrarily?

Answer 9

Mono-alphabetic cipher

Question 10

What is the Vigenere cipher?

Answer 10

A matrix-like cipher.

Question 11

What weaknesses exist for the Vigenere cipher?

Answer 11

It uses repeating letters and the length of the key can be determined using frequency analysis

Question 12

What is Kerckhoff’s principle?

Answer 12

• A cryptosystem should be secure even if the attacker knows all the details about the system with exception of the secret key
• AKA “obscurity shouldn’t be used for security”

Question 13

What types of ciphers should you use in real life based on the Kerckhoff principle?

Answer 13

Only use widely known ciphers that have been crypto analyzed for many years

Question 14

What are the different types of Cryptography?

Answer 14

• Secret Key - ONE Key is used for encryption/decryption
• Public Key - TWO Keys are used
  
  • Public for encryption & verification
  • Private for decryption & signing
• Hash functions - easy to compute and infeasible to crack (weak collision resistant property)

Question 15

What is the one-way property of a hash function?

Answer 15

It’s easy to compute the hash, but computably infeasible to crack it

Question 16

What is the most commonly used encryption type?

Answer 16

block ciphers

Question 17

What does DES stand for?

Answer 17

Data Encryption Standard

Question 18

What does AES stand for?

Answer 18

Advanced Encryption Standard

Question 19

DES with a key size of 56 bits is breakable with a super computer. True/False

Answer 19

True

Question 20

What’s the difference between differential cryptanalysis and linear cryptanalysis?

Answer 20

• Differential analyzes the changes in input on the encrypted output
• Linear analyzes known phrases and maps them to the encrypted output