Classical Ciphers

Question 1

Assume all algorithms are ____

Answer 1

public

Question 2

Security is determined ____ by key size

Answer 2

only

Question 3

Making your own security is _______

Answer 3

insecure

Question 4

Simplest and earliest known use of substitution cipher

Answer 4

Caesar Cipher

Question 5

Replace each letter in alphabet with another letter $n mod |A|$ places down

Answer 5

Caesar Cipher

Question 6

Vulnerable to word / letter frequency analysis

Answer 6

Substitution Ciphers

Question 7

Different monoalphabetic substitutions as one proceeds through plaintext message

Answer 7

Polyalphabetic cipher

Question 8

Key determines which particular rule is chosen for given transformation

Answer 8

Polyalphabetic cipher

Question 9

Key is required that is as long as the word

Answer 9

Vigenere Cipher

Question 10

Usually a repeating keyword

Answer 10

Vigenere Cipher

Question 11

Key: dogdogdog
Plaintext: abcdefghi

Answer 11

Ciphetext: dpigsljvo

Question 12

Key and plaintext share same frequency distribution of letters

Answer 12

Vigenere Cipher

Question 13

Plaintext written down as sequence of diagonals, read off as sequence of rows

Answer 13

Rail fence cipher

Question 14

Plaintext (depth = 3):
whatsgoingonpal

Answer 14

Ciphertext: whtogpasioagnnl

Question 15

Write messages in rectangle, row by row, and read message off column by column, permuting order of columns

Answer 15

Row transposition cipher

Question 16

Order of the columns becomes key to algorithm

Answer 16

Row transposition cipher

Question 17

Processes one bit or byte at a time

Answer 17

Stream cipher

Question 18

Substitution and permutation techniques, one block at a time

Answer 18

Block cipher

Question 19

Make the relationship between plaintext, key input and ciphertext output as complex as possible

Answer 19

Confusion

Question 20

Spread the influence of each input bit across many output bits

Answer 20

Diffusion

Question 21

Achieved mainly via substitutions

Answer 21

Confusion

Question 22

Achieved via permutations

Answer 22

Diffusion

Question 23

Each character of ciphertext depends on several parts of key

Answer 23

Confusion

Question 24

Changing plaintext character should result in several changed ciphertext characters

Answer 24

Diffusion