Keyword Substitution Cipher

How Keyword Substitution Cipher works

Keyword Substitution Cipher handles the ordinary alphabet through a mixed alphabet made from unique keyword letters followed by every unused letter from A through Z. Encoding maps plain alphabet positions to the keyed alphabet; decoding reverses that lookup. Nonletters pass through unchanged and do not alter the mapping. The Keyword Substitution Cipher exposes its message, keyword, operation controls so this particular convention stays inspectable instead of hiding behind an unexplained preset.

The ZEBRA alphabet transforms HELLOWORLD into FAJJMVMPJR, which returns to HELLOWORLD when decode mode uses the same keyword. The explicit mixed alphabet helps puzzle solvers reproduce newspaper-style substitution systems without manually crossing duplicate key letters out. The Keyword Substitution Cipher presents a deterministic plain-text result that can be copied and compared with the worked value before it enters another workflow.

Limits and private processing

Every occurrence of a letter receives the same substitute, preserving frequency patterns. The cipher is educational and should never protect passwords or sensitive text. The Keyword Substitution Cipher performs its complete operation locally in your browser; neither the source text nor its settings are uploaded, stored remotely, or sent through an external request.