Codebusters Test Codebusters Transposition Ciphers 1 — Questions and Answers
Question 1: What is the defining characteristic of a transposition cipher?
- Letters are replaced with different letters using a fixed alphabet
- The positions of letters are rearranged without changing the letters themselves (Correct answer)
- Each letter is shifted by a numeric key value
- Letters are converted into pairs of symbols using a grid
Correct answer: The positions of letters are rearranged without changing the letters themselves
Transposition ciphers rearrange the positions of plaintext letters without substituting them, so the same alphabet of letters appears but in a different order.
Question 2: How does the rail fence cipher encipher a message?
- It shifts each letter by the number of its rail position
- It writes the plaintext in a zigzag pattern across multiple rails and reads off each rail in sequence (Correct answer)
- It fills columns with plaintext and reorders them using a keyword
- It writes the message in reverse along a diagonal path
Correct answer: It writes the plaintext in a zigzag pattern across multiple rails and reads off each rail in sequence
The rail fence cipher writes plaintext letters diagonally up and down across a set number of rails, then reads off each rail left to right to produce the ciphertext.
Question 3: Why is frequency analysis alone insufficient to break a transposition cipher?
- Transposition ciphers eliminate repeated letters
- Transposition preserves letter frequencies, so the distribution looks like normal English (Correct answer)
- Transposition ciphers always produce a flat frequency distribution
- Frequency analysis only applies to polyalphabetic ciphers
Correct answer: Transposition preserves letter frequencies, so the distribution looks like normal English
Since transposition only rearranges letters without changing them, each letter appears exactly as often in the ciphertext as in the plaintext, so frequency analysis reveals English-like frequencies rather than exposing the key.
Question 4: In a columnar transposition cipher, how is the ciphertext generated?
- The plaintext is written in a single column and read diagonally
- The plaintext is written row by row into a grid and the columns are read out in a key-determined order (Correct answer)
- The plaintext is written column by column and rows are read in a keyword order
- Each column is individually encrypted with the corresponding keyword letter
Correct answer: The plaintext is written row by row into a grid and the columns are read out in a key-determined order
Columnar transposition writes the plaintext across rows in a rectangular grid, then reads out the columns in the order dictated by alphabetizing the keyword letters.
Question 5: What ancient cipher device used a cylinder to implement a transposition cipher?
- The Polybius square
- The Enigma rotor
- The scytale (Correct answer)
- The Jefferson wheel
Correct answer: The scytale
The scytale, used by ancient Spartans, was a cylinder around which a leather strip was wound; the message written across the strip was only readable when wound around a cylinder of the same diameter.
Question 6: What is the route cipher?
- A cipher where letters travel through a series of substitution tables
- A cipher where plaintext is written into a grid and read out following a specified geometric path (Correct answer)
- A cipher that routes letters through multiple transposition stages simultaneously
- A cipher based on reading alternate letters from the plaintext
Correct answer: A cipher where plaintext is written into a grid and read out following a specified geometric path
A route cipher fills plaintext into a rectangular grid and then reads it out by tracing a predetermined route, such as spiraling inward, reading columns alternately top-down and bottom-up, or following a diagonal.
Question 7: If the index of coincidence (IC) of a ciphertext is approximately 0.065, what does this suggest?
- The cipher is a polyalphabetic substitution like Vigenère
- The cipher is most likely a transposition or monoalphabetic substitution cipher (Correct answer)
- The cipher has a very short keyword
- The cipher uses a completely random key
Correct answer: The cipher is most likely a transposition or monoalphabetic substitution cipher
An IC of ~0.065 matches the expected value for English text; since transposition does not alter letter identities, the IC of a transposition ciphertext matches plain English, as does a monoalphabetic substitution.
Codebusters Test Codebusters Transposition Ciphers 1
What is the defining characteristic of a transposition cipher?