cipher.js

A javascript decryption libary.

This library is an attempt at not cheating the UK National Cipher Challenge, whilst also serving a purpose to the open source community. (That was a joke; I would only ever think about myself)

(Have a play-a-round on Codepen)

Wanna learn how to use it?

I've coded it into three categories: encrypt, decrypt and tools. These are all stored in the object cipher. So, if I wanted to get to the tools section, I would do: cipher.tools.BLAH.

The encrypt section.

As you can probably tell, the encrypt section is all about encrypting things. Although not the primary idea of the library, I've included these anyway.

caesar(str, amount)

This takes two arguments - str and amount. str is the phrase that you want to be encrypted, and amount is a number of letters to shift. Example:

  cipher.encrypt.caesar('abc', 1) // Returns 'bcd'

  var secretMessage = cipher.encrypt.caesar('Momma, I just killed a man-', 13);
  console.log(secretMessage) // Logs 'Zbzzn, V whfg xvyyrq n zna-'

reverseString(str, spaces)

This too takes two arguments - str and spaces. str is the phrase you want to be reversed, whilst spaces is a boolean. If true, the str will be reversed including spaces. If false, it will disregard all spaces and reverse it that way. Example:

  cipher.encrypt.reverseString('abc def', true); // returns 'def abc'
  cipher.encrypt.reverseString('abc def', false); // returns 'defabc'

The decrypt section.

This section is the primary focus of the library – allowing you to easily decipher text. This section references cipher.tools a lot.

caesar(str, amount)

However visually symmetrical to the cipher.encrypt.caesar, it has one difference. Instead of moving the letters forward by the amount, it moves them backwards. Example:

  cipher.decrypt.caesar('abc', 1) // returns 'zab'
  var decodedMessage = cipher.decrypt.caesar('Zbzzn, V whfg xvyyrq n zna-', 13);
  console.log(decodedMessage) // Logs 'Momma, I just killed a man-'

caesarGuess(str, letter)

This is my favourite bit of the library. It can take any string (the second argument isn't required) and guess a shift, then decode it into English.

To understand its use, you need to know how it works. These are the steps it follows:

• Find the most common letter, using a call to the cipher.tools.frequency().
• Work out the difference between it and the most common letters in English (e,a,t,o).
• Store these in an object.
• Decrypt the text using the cipher.decrypt.caesar() function using an amount of the chosen letter.
• Display result.

Usually it works when letter is 'e', because it's the mostest most common letter in English. Examples:

  var words = 'Hello! this is a very large piece of text containing a lot of vowels. Hey, look at that I\'m using e so much. I like e. Did you know that in mathematics e^n is a transcendental number?'
  var secretMessage = cipher.encrypt.caesar(words,18)
  cipher.decrypt.caesarGuess(secretMessage); // Returns what is the same as the words variable.

reverseString(str, spaces)

This is 100% the same as the cipher.encrypt.reverseString() function. Scroll up to read the documentation for that.

Tools

These do not encrypt or decrypt, but are common resuable bits of code.

alphabetNum(letter)

This function takes one argument - letter - and returns the number of that letter in the alphabet. Examples:

  cipher.tools.alphabetNum('a') // Returns 1.

stringNum(str)

This function does the same as the alphabetNum(), but instead turns a string into an array of numbers corresponding to the letters at that point. Examples:

  cipher.tools.stringNum('abc') // Returns ['1','2','3']

frequency(str)

This function returns an object of information about a given string. In total, it returns 5 things.

  cipher.tools.frequency(str)

  // Returns
  {
    consisency: // Equal to (range*str.length)/100 - the higher the number the more 'diverse' a string is. Used to check if                   // its been encrypted with a shift cipher.
    mostUsedLetter: // Funnily enough, the most used letter.
    maxAmountOfTimesALetterAppeared: // Have a guess.
    minAmountOfTimesALetterAppeared: // ""         ""
    range: // The range of the amount of times letters occured. If 'a' had been used 3 times and 'b' had been used once, the
           // range would be 2 (3-1).
  }