18: Cryptanalysis

Question 1

What is cryptanalysis ?

Answer 1

It is the process of discovering

• an input text or
• a key or
• a principle

of an encryption.

Question 2

What is Brute-force attack ?

How many possible keys are there for a 128 bit key ?

Answer 2

It tries to guess a key by trying all possibilities.

2^128.

Question 3

What is chosen plain text attack ?

Answer 3

Encrypt some specially chosen text to get clues (eg repeated blocks) from resulting codes about the key.

Question 4

What is differential cryptanalysis ?

Answer 4

Encrypt several texts which differ only slightly and look for differences in the resulting codes.

Question 5

What is differential fault analysis ?

Answer 5

Attack the hardware of the encryption computer to force it to make mistakes and reveal the key.

Question 6

What does a rotor machine have ?

Answer 6

Several cylinders which independently rotate and simulate substitutions.

26 input pins, and 26 output pins. 26^3.

Question 7

Who broke enigma and when?

Answer 7

Alan turing during WW2.

Question 8

What is the Turing machine ?

Answer 8

A model of a computer.

Question 9

What does a Turing test do ?

Answer 9

Checks if experts can not distinguish a machine from a human.

Question 10

4 components of a Turing machine ?

Answer 10

• Infinite tape
• Head
• State register
• Rules

Question 11

Which works best:

• Substitution over substitution
• Transposition over transposition
• Transposition over substitution

?

Answer 11

Transposition over substitution