Question

Which of the following statement correctly differentiates substitution and transposition ciphers ?

• A. Substitution changes the order of symbols; transposition replaces symbol
• B. Both change symbol order and values simultaneously
• C. Substitution replaces symbol with others; transposition rearranges their position
• D. Substitution is always weaker than transposition in modern cryptography

Hint:

Think of it this way: Substitution is like a Costume Party (same person, different look). Transposition is like Musical Chairs (same people, different seats).

Answer 1

The Correct Option is C

Concept:
• Classical encryption algorithms are built on two fundamental building blocks: Substitution and Transposition (also called Permutation).
• Claude Shannon identified these as the mechanisms to achieve "Confusion" and "Diffusion" respectively.

Step 1: Define Substitution Ciphers
In a substitution cipher, the identity of the characters is changed, but their relative positions remain the same.
For example, the Caesar cipher replaces 'A' with 'D'.
This replaces a symbol with another symbol.

Step 2: Define Transposition Ciphers
In a transposition cipher, the identity of the characters remains unchanged, but their order (positions) is shuffled.
For example, the word "CAT" might become "TAC".
This rearranges their position without altering the symbols themselves.

Step 3: Select the accurate differentiation
Option (C) correctly describes substitution as replacing symbols and transposition as rearranging positions.
Option (A) has the definitions swapped.