W3 - Historical Ciphers

Question 1

Caesar Cipher

Answer 1

Shift 3 places down

Question 2

Mono-alphabetic substitution Cipher

Answer 2

Permutation if a finite set S of elements. Mapping each letter to a distinct letter

Question 3

Homophonic Substitution Cipher

Answer 3

Each letter mapped to a set of different series of letters

Question 4

Playfair Cipher

Answer 4

5x5 matrix
Fill with key (w/out doubles)
Fill in alphabetic order
Intersect (row of first priority)

Question 5

Polyalphabetic Substitution Cipher

Answer 5

Use different monoalphabetic substitutions as you encrypt text (e.g. Vigenere)

Question 6

Vigenere Cipher

Answer 6

parse plaintext and key

Add each p_i with k_i (mod 26)

Question 7

Vernam Cipher

Answer 7

p_i ⊕ k_i

Question 8

Rail Fence Cipher (Zig-Zag)

Answer 8

Write the plaintext as diagonals. Key = depth

Question 9

Cardano Grille

Answer 9

Use a mask (“grille”) with precut holes. Example of stenography (hiding a message in another)

Question 10

Rotating (turning) grille

Answer 10

6x6 grid
9 holes
Write then rotate 90°

Question 11

Columnar Transposition Cipher

Answer 11

Write message in a rectangles. Key = order columns should be read

Question 12

Multistage columnar Transposition Cipher

Answer 12

Perform Columnar Transposition more than one stage

Question 13

Substitution Permutation Networks (SPN)

Answer 13

• Blocks length l
• Sub
• Perm
• Repeat

Question 14

Fiestal Network

Answer 14

L_i = R_(i-1)
R_i = L_(i-1) ⊕ f(sk_i, R_(i-1))

Question 15

Electronic Code Book (ECB)

Answer 15

c_i = f(m_i)
c = c1c2…

Question 16

Cipher Block Chaining (CBC)

Answer 16

c_i = f(c_(i-1) ⊕ m_i)

c = c1c2…

Question 17

Counter Mode

Answer 17

c_i = f(IV + i) ⊕ m_i