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Security Fundamentals & Crypto · Foundational

Transposition Cipher

Cipher that rearranges the order of plaintext characters without changing the characters themselves.

Definition

Transposition (permutation) ciphers, such as rail fence and columnar transposition, keep letter frequencies intact but scramble positions. Combined with substitution, they provide the diffusion used in modern product ciphers.

Example

A rail fence cipher writes 'ATTACKATDAWN' in a zigzag across three rows and reads it off row by row.

Exam tip

Transposition changes position; substitution changes the symbols.

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