Question 1

What is a Caesar cipher?

Accepted Answer

A Caesar cipher shifts each letter by a fixed number of positions in the alphabet. For example, with a shift of 3, A becomes D, B becomes E, and so on. It is one of the simplest and oldest encryption techniques.

Question 2

What is ROT13 and why is it special?

Accepted Answer

ROT13 is a Caesar cipher with a shift of 13. Since the English alphabet has 26 letters, applying ROT13 twice returns the original text. This makes it its own inverse, useful for hiding spoilers or simple obfuscation.

Question 3

How does the Vigenere cipher work?

Accepted Answer

Vigenere uses a keyword to shift each letter by a different amount. Each letter of the keyword determines the shift for the corresponding letter of the plaintext. The keyword repeats cyclically over the message.

Question 4

How do I break a Caesar cipher?

Accepted Answer

Try all 26 possible shifts and look for readable text. This tool provides a brute-force matrix that shows all 26 decodes at once, sorted by how "English-like" each result is.

Question 5

What is the difference between Caesar and Vigenere?

Accepted Answer

Caesar uses a single fixed shift for every letter, while Vigenere uses a repeating keyword where each letter applies a different shift. Vigenere is significantly harder to break by brute force.

Question 6

What is the Index of Coincidence?

Accepted Answer

The Index of Coincidence (IC) measures how likely it is that two randomly selected letters from a text are the same. English text has an IC around 0.067, while random text is around 0.038. It helps estimate Vigenere keyword length.

Caesar & Vigenere Cipher Tool

Input

Output

Brute-Force Matrix

Frequency Analysis

Vigenere Square (key letter × plaintext letter)

How the Cipher Tool Works