How to Encode and Decode Using the Vigènere Cipher

Last Updated: May 31, 2022 References

The Vigenère cipher is a method of encryption that uses a series of different "Caesar ciphers" based on the letters of a keyword. In a Caesar cipher, each letter in the passage is moved a certain number of letters over, to be replaced by the corresponding letter. For example, this would mean that in a Caesar cipher shift of three: A would become D; B would become E; C would become F etc. A Vigenère cipher builds on this method by using multiple Caesar ciphers at different points in the message; this article shows you how to use it.^{[1]
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Sample Cipher and Messages

Sample Vigenere Square

Method 1

Method 1 of 2:

Encipher

1
Obtain a Vigenère Square (see Sample) or create a Vigenère Square on your own.^{[2]
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2
Think of a keyword that is shorter than the phrase or phrases you want to encipher. For this example we will use:
```
LIME
```
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3
Write down your message without spaces. For this example, we will use:
```
WIKIHOWISTHEBEST
```
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4
Write the keyword under your message, carefully lining each letter up with a letter from your message. Do this until you run out of message:
```
WIKIHOWISTHEBEST
```
```
LIMELIMELIMELIME
```
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5
Cut the keyword to fit the phrase if needed. In the example used for this article, the word
```
LIME
```
fits perfectly but when the keyword is not a perfect fit, there is no need to use the full word. For example:
```
WIKIHOWISTHEBESTOFTHEBEST
```
```
LIMELIMELIMELIMELIMELIMEL
```
6
Go to the row of the first letter of the keyword in the Vigenère Square and go to the column of the first letter of the actual message and find the intersection point of the row and column. That's your cipher letter.^{[6]
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7
Continue on in this fashion until your entire phrase is ciphered. Using the sample Vigenère square given above, the first ciphertext letter is an H coming from row L and column W. So the ciphertext is:
```
HQWMSWIMDBTIMMEX
```

Method 2

Method 2 of 2:

Decipher

1
Perform the above steps in reverse to decode ciphered text.^{[7]
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2
Find the row of the first letter of the keyword. Look along it to find the first letter of the ciphered text in that row. Follow the column up to find the first letter of the encoded phrase at the top of the chart.^{[8]
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3
Continue on in this manner until you completely decipher the text.

Community Q&A

Question

What kind of secret texting uses double letters, capital and lowercase?

MePedro

Community Answer

Playfair uses pairs of capital letters. If you want to have lower case letters too, the alphabet of the classic ciphers could be enhanced. All modern ciphers support all kind of characters.
Question

How does W and L equal L? I didn't get that as my answer.

Community Answer

It's not W + L = L, but L + L = W. You take the written L, check with your keyword letter written under (L), and on your board you will find W.
Question

Can Vignere be used in combination with other ciphers (e.g. at-bash or a1z26)?

Community Answer

Yes, for instance: (your message), and if that was z gfxr cvd (not real message) you could just go: z=a, g=t, and so on.

Warnings

This cipher is not fool-proof (no cipher is) and can be quickly cracked. By current standards, the Vigenère cipher is extremely weak. Do not use this for anything truly top-secret. For stronger encryption research AES and RSA. This cipher can, however, be used with a one-time pad as a key (a truly random sequence with the same length as the text that is only used once) to produce a ciphertext that, as long as the key is secure, cannot be cracked faster than just doing a brute-force attack.

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