Vigenère Cipher
Encrypt and decrypt text online using the polyalphabetic Vigenère cipher with a custom keyword.
Run tool
Apply the classic polyalphabetic Vigenere cipher to encipher or decipher messages using a custom keyword. Each letter in your text shifts according to the matching letter of the repeating key, while uppercase and lowercase capitalization remains intact. Punctuation, numerals, spaces, and special symbols are preserved in their original positions and do not advance the keyword index. If you provide text without specifying a key, the tool automatically uses the default keyword key to perform the shift. You can switch between forward encryption and reverse decryption to test historical cryptography concepts, solve puzzle ciphers, or verify manual polyalphabetic calculations. Because the Vigenere cipher is a historical substitution method rather than a modern cryptographic standard, it is intended for educational exploration, recreational puzzles, and cipher study. Enter your message, define your keyword, select your conversion direction, and inspect the transformed text immediately in the result display.
Instructions
- Enter or paste your text into the Text field.
- Enter your shift keyword into the Key field, or leave it blank to use the default keyword.
- Set Mode to encrypt for forward shifting or decrypt for reverse shifting.
- Click Run to process your text and review the shifted output in the result panel.
Examples
- Encrypting "Hello, World!" with key "SECRET" in encrypt mode produces "Zincs, Pcfdh!".
- Decrypting "Zincs, Pcfdh!" with key "SECRET" in decrypt mode restores "Hello, World!".
FAQ
How does the cipher treat spaces, numbers, and punctuation?
Non-alphabetic characters such as spaces, digits, and punctuation marks are copied directly to the output without changes. The key position only advances when an alphabetic letter is processed.
What happens if I leave the key field blank?
When the input text is not empty and no key is entered, the tool automatically applies the default keyword "key".
Is the key case-sensitive?
No. The key is normalized to uppercase before shifts are computed, so typing "key", "Key", or "KEY" produces identical shifts.
Can the Vigenere cipher secure confidential data?
No. The Vigenere cipher is an early classical substitution cipher susceptible to frequency analysis and Kasiski examination. It is intended for educational, puzzle, and historical demonstration purposes, not secure modern data protection.