Affine Cipher

Encode or decode an Affine substitution cipher: E(x) = (a×x + b) mod 26. The multiplicative key must be coprime with 26.

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Multiplicative key a

Additive key b (0–25)

Operation

Result

Try every valid key

312 candidate decryptions (12 valid a values × 26 b values). Results can be filtered by a word fragment.

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Affine cipher guide

Each letter is converted to A=0 through Z=25, then transformed with two keys. A valid a must have a modular inverse, so only the listed values are possible. Spaces, numbers and punctuation are preserved.