Encode and decode classical polyalphabetic substitution ciphers with secret key phrases.
Execution runs 100% locally inside the browser sandbox using HTML5 Canvas, Web Cryptography Subtle API, and Web Workers. Zero egress.
Zero network latency. Operates completely offline with zero dependencies on third-party backend servers or cloud services.
Built according to official RFC specifications, cryptographic test vectors, and enterprise-grade data transformation standards.
Choose Encrypt or Decrypt mode.
Input your secret passphrase key (e.g. LEMON, CIPHERKEY).
View the instant polyalphabetic substitution result and copy the transformed payload.
The Vigenère cipher is a method of encrypting alphabetic text by using a series of interwoven Caesar ciphers based on the letters of a secret keyword.
Because it uses multiple shift values (one for each letter in the keyword), it resists simple frequency analysis that easily breaks monoalphabetic ciphers.
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