Why this tool is useful
Use the Affine Cipher Tool for classroom examples that need a keyed substitution with an explicitly invertible multiplier.
Text & List Tools · runs locally
Affine Cipher Tool
Encode or decode Latin letters with validated affine multiplier and offset keys using arithmetic modulo 26.
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How it works
The encoder calculates (a·x+b) mod 26; decoding finds the modular inverse of a, and rejects multipliers that are not coprime with 26.
Practical example
With multiplier 5 and offset 8, AFFINE CIPHER encodes as IHHWVC SWFRCP and decodes back without changing the space.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.