Vigenere Cipher

Tool Introduction

The Vigenère Cipher is a famous polyalphabetic substitution encryption technique. It originated in the 16th century and was considered an "unbreakable" cipher for a long time. Unlike the simple Caesar cipher (monoalphabetic substitution), the Vigenère cipher uses a keyword to encrypt plaintext, greatly enhancing security by **cyclically using multiple different letter substitution tables, effectively resisting frequency analysis attacks.

This tool is an online Vigenère cipher encryptor and decryptor. You only need to enter the text to be processed and the key, select the encryption or decryption mode, and the tool will automatically complete the calculation, helping you quickly and accurately experience how this classic cipher works. Whether for cryptography learning, CTF competitions, or simple fun games, this tool can provide convenience.

 

How to use this tool

Using this tool is very simple, just three steps:

1.  Enter text: Enter the original text you want to encrypt in the "Plaintext" box, or enter the text you want to decrypt in the "Ciphertext" box.
2.  Enter key: Enter a word or phrase consisting of letters in the "Key" box. **Please note: The key usually only uses letters, and the tool will automatically ignore non-letter characters in it.
3.  Select mode and execute:
       Click the "Encrypt" button to encrypt your plaintext into ciphertext.
       Click the "Decrypt" button to decrypt your ciphertext back to plaintext.

 

Frequently Asked Questions (FAQ)

Q1: Can the key contain numbers or symbols?

A: The standard Vigenère cipher only uses letters (A-Z). This tool will automatically filter out non-letter characters in the key. For example, if you enter the key `MyKey123!`, the tool will only use `MYKEY` as the valid key.

Q2: Is case sensitive during encryption?

A: To simplify calculations, this tool usually converts all input text (plaintext, ciphertext, key) uniformly to uppercase (or lowercase) before processing, and the output result defaults to uppercase. Please refer to the specific instructions on the tool page.

Q3: Why is the decrypted result incorrect?

A: Please check:
    Whether the key you entered is exactly the same as the key used for encryption.
   Whether the ciphertext you entered is complete and accurate, without extra spaces or incorrect characters.
   Whether you have selected the correct mode ("Decrypt" mode).

Q4: Is the Vigenère cipher secure?

A: No, it is no longer secure against modern computers. Although it is much more secure than the Caesar cipher, it was successfully broken in the mid-19th century by methods proposed by Charles Babbage and Friedrich Kasiski, among others. Modern encryption (such as AES) is much more secure. This tool is for educational purposes only.

 

Notes

1.  Educational purposes: This tool is intended for cryptography education and historical research. Please do not use it for any communication scenarios that require real security.

2.  Key management: Encryption and decryption must use **exactly the same key. Please keep your key safe; once lost, the ciphertext will be difficult to decrypt.

3.  Character limitations: This tool usually only processes letters (A-Z). Numbers, punctuation, and spaces in plaintext and ciphertext may be kept as is or ignored directly. Please check the specific rules of the tool before use.

4.  Key strength: The longer and more random the key, the better the encryption effect. Avoid using short or common words (such as `KEY`, `ABC`, `PASSWORD`) as keys, as they will reduce security and be easier to break.