Vigenere Cipher
Vigenere cipher applies a repeating letter key supplied by you; encrypt and decrypt on this page with the same key and alphabet rules.
Ready. Supply a key; this page does not guess or recover keys.
Original keyed encryption and decryption checks
We ran four text-and-key pairs through this page’s function. We encrypted each text, decrypted the result with the same key and compared the recovered text with the original, including case and nonletters. Every recovered text matched. A separate Python calculation also matched every encrypted result. This table was generated from those calculations rather than copied from another tool.
| Plaintext | Key | Encrypted text | Decrypted text |
|---|---|---|---|
| ATTACKATDAWN | LEMON | LXFOPVEFRNHR | ATTACKATDAWN |
| Hello World | KEY | Rijvs Uyvjn | Hello World |
| Abc, xyz! 09 é 🚀 | b | Bcd, yza! 09 é 🚀 | Abc, xyz! 09 é 🚀 |
| Line 1\nLine 2 | Ab | Ljnf 1\nLjnf 2 | Line 1\nLine 2 |
The ATTACKATDAWN sample with LEMON produced LXFOPVEFRNHR and decrypted back to ATTACKATDAWN. The mixed-case samples retained case. Digits, punctuation, spaces, line breaks, the accented character and emoji stayed unchanged. The table displays a line break as \n; the tool keeps the actual line break.
To reproduce a row, paste its plaintext and key, select Encrypt and apply the key. Use Swap direction and result without changing the key, then compare the decrypted output with the original. Do not remove spaces or change key alignment in another implementation when comparing results.
Key and alphabet rules
Keys must contain one or more English letters A–Z or a–z, without spaces, digits or punctuation. Key case has no effect. The key repeats across text letters, using A as zero shift, B as one shift and so on. Plaintext and ciphertext use separate uppercase and lowercase English alphabets, preserving case.
Only A–Z and a–z are transformed. Other characters stay unchanged and do not advance the key. This rule includes digits, punctuation, whitespace, accented letters and emoji. Other alphabet or alignment conventions can produce different results.
Can this page decrypt without the key?
No. It requires the key you supply. There is no automatic cracking, key search or claim of recovery without a key. A wrong key can produce another letter sequence; this tool does not authenticate the result or identify the correct key.
Does Vigenere protect private information?
This is a historical cipher for exercises and demonstrations, not modern protection for confidential data. Do not treat the output as authenticated or use this tool as a password-storage system.
Input, output and limits
Paste one text sequence and supply one key; copy the resulting text. Text input is limited to 20,000 characters and the key to 1,000 letters. Invalid keys produce an error and clear the previous result. Encryption and decryption run locally without login, file upload, batch mode or saved history. Text and keys are not uploaded.
Related representation walkthrough
This existing video demonstrates hexadecimal byte input and Base64 output. It is a related representation walkthrough, not a Vigenere tutorial or key-recovery demonstration.
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For fixed alphabet reversal rather than shifts, use the Atbash alphabet reversal tool.
To display separate classical transformations without identifying or cracking a cipher, use the Classic cipher result comparison tool.