Substitution Cipher Explained
A substitution cipher replaces each plaintext letter with a unique ciphertext letter according to a permutation of the alphabet. Use Cipher Portal with a 26-letter key, or visit the substitution cipher decoder page.
What is a substitution cipher?
Each A–Z symbol maps to a different symbol; the mapping stays fixed for the entire message (monoalphabetic). Newspaper cryptograms often preserve spaces and punctuation.
Caesar is a special substitution where the tableau is a cyclic shift. Atbash is the reversal tableau. General substitution allows any permutation.
How substitution encryption works
Cipher Portal expects a 26-character key listing the ciphertext alphabet in order corresponding to plaintext A..Z. Encrypt walks plaintext letters through the map; decrypt inverts it.
Security is weak for long English text: letter frequencies survive. The Frequency Analysis Lab and frequency analysis decoder guide demonstrate attacks.
Compare with other classical ciphers
Vigenère changes the map over time; Rail Fence permutes order without changing symbols. Enigma composes stepping permutations electrically.
To solve without the tableau, read the substitution cipher cracker and identify a cipher checklist.
Study substitution cipher examples and contrast Caesar / Atbash special cases.
Frequently asked questions
What is a substitution cipher?
A cipher that replaces each letter with another letter via a fixed permutation for the whole message.
What is the substitution cipher key?
A 26-letter alphabet listing the ciphertext equivalents of A through Z.
How do you break substitution?
Frequency analysis, pattern matching, and automated solvers score plaintext likelihood.
How do I encrypt substitution online?
Cipher Portal → substitution → enter text and 26-letter key → encrypt or decrypt.