npm package discovery and stats viewer.

Discover Tips

  • General search

    [free text search, go nuts!]

  • Package details

    pkg:[package-name]

  • User packages

    @[username]

Sponsor

Optimize Toolset

I’ve always been into building performant and accessible sites, but lately I’ve been taking it extremely seriously. So much so that I’ve been building a tool to help me optimize and monitor the sites that I build to make sure that I’m making an attempt to offer the best experience to those who visit them. If you’re into performant, accessible and SEO friendly sites, you might like it too! You can check it out at Optimize Toolset.

About

Hi, 👋, I’m Ryan Hefner  and I built this site for me, and you! The goal of this site was to provide an easy way for me to check the stats on my npm packages, both for prioritizing issues and updates, and to give me a little kick in the pants to keep up on stuff.

As I was building it, I realized that I was actually using the tool to build the tool, and figured I might as well put this out there and hopefully others will find it to be a fast and useful way to search and browse npm packages as I have.

If you’re interested in other things I’m working on, follow me on Twitter or check out the open source projects I’ve been publishing on GitHub.

I am also working on a Twitter bot for this site to tweet the most popular, newest, random packages from npm. Please follow that account now and it will start sending out packages soon–ish.

Open Software & Tools

This site wouldn’t be possible without the immense generosity and tireless efforts from the people who make contributions to the world and share their work via open source initiatives. Thank you 🙏

© 2024 – Pkg Stats / Ryan Hefner

@cryptoolsorg/caesarcipher

v1.0.0

Published

Caesar Cipher implementation by CrypTools

Downloads

8

Readme

Caesar Cipher

History and usage

The Caesar Cipher was named after Julius Caesar (100 B.C. – 44 B.C). He would use the cipher for secret communication (protect messages of military significance). The Caesar Cipher is a substitution cipher. Originally, Julius Caesar would use a shift of three to encrypt/decrypt a message. The Caesar Cipher encrypts a message using an affine function : f(x) = 1x + b.

Detailed Explanations : How it works?

  1. Firstly, each character of the initial text (message to encrypt) is converted in a number from 0 to 25, corresponding to its position in the Latin alphabet which contains 26 letters --> (a = 0, b = 1 ... z = 25 ).

  2. Then, each number obtained is transformed by an affine function (f(x) = 1x + b). "x" is representing the number while "b" is defined during the encryption. "b" is the key used to decrypt the final message.

  3. If we take all the images and put them in a list, we obtain n numbers corresponding to n characters of the initial text. The next step consists in finding the values of modulo 26 of each number. (Modulo means remainder)

Example : Modulo 4 of 19 is 3 because 15 = 4 * 4 + 3 In the other hand, modulo 26 of 26 is 0 because 26 = 26 * 1 + 0

  1. Therefore, we obtain a new list with n element, each between 0 and 25 both included. All these numbers are converted in letters of the Latin Alphabet using the tables below.

  2. We finally create the final message by putting all the letters side by side.

Steps 1 and 4 can be done with these tables :

| A | B | C | D | E | F | G | H | I | J | K | L | M | |---|---|---|---|---|---|---|---|---|---|----|----|----| | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |

| N | O | P | Q | R | S | T | U | V | W | X | Y | Z | |----|----|----|----|----|----|----|----|----|----|----|----|----| | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |

Weaknesses

  • If an attacker knows that the message has been encrypted using Caesar Cipher, he can try all shifts (b values from 1 to 25) to decrypt the message. This is called the bruteforce method.

  • We can also use frequency analysis to decrypt the message as each letter is encrypted with the same algorithm and the most common letters in english are :

Example

Encrypting

  • Message to encrypt : ZATTACKZ
  • Shift used : 4 (f(x) = 1x + 4)
  • That means that b = 4

Using the above tables, ATTACK can be written as : 25 0 19 19 0 2 10 25 Images of each number :

  • f(25) = 29
  • f(0) = 4
  • f(19) = 23
  • f(2) = 6
  • f(10) = 14

The new list is : 29 4 23 23 4 6 14 29

Using the modulo 26 method, we obtain:

  • Mod(29,26) = 3
  • Mod(4,26) = 4
  • Mod(23,26) = 23
  • Mod(6,26) = 6
  • Mod(14,26) = 14

The final message is 3 4 23 23 4 6 14 3 and using the tables again, we convert them in the encrypted message :

DEXXEGOD

ZATTACKZ is encrypted with the function x + 4 and becomes DEXXEGOD.

Decrypting

First method : Knowing the key (value of the shift used)

  • Message to decrypt : DEXXEGOD
  • Shift used : 4 (f(x) = 1x - 4)
  • That means that b = -4

Using the above tables, DEXXEGOD can be written as : 3 4 23 23 4 6 14 3 Images of each number :

  • f(3) = -1
  • f(4) = 0
  • f(23) = 19
  • f(6) = 2
  • f(14) = 10

The new list is : -1 0 19 19 0 2 10 -1

Using the modulo 26 method, we obtain :

  • Mod(-1,26) = 25
  • Mod(0,26) = 0
  • Mod(19,26) = 19
  • Mod(2,26) = 2
  • Mod(10,26) = 10

The final message is 25 0 19 19 0 2 10 25 and using the tables again, we convert them in the encrypted message :

ZATTACKZ

DEXXEGOD is decrypted with the function 1x - 4 and becomes ZATTACKZ.

Second method : Not knowing the key (value of the shift used)

This is called the bruteforce method.

  • Message to decrypt : DEXXEGOD

Using the above tables, DEXXEGOD can be written as : 3 4 23 23 4 6 14 3

a is a number between 0 and 25. (a = 0 would mean the message is already decrypted)

Using the function f(x) = Mod(1x + a, 26) :

We can get all these results :

| a |Decrypted text| |----|---| | 1 |fgzzgiqf| | 2 |ghaahjrg| | 3 |hibbiksh| | 4 |ijccjlti| | 5 |jkddkmuj| | 6 |kleelnvk| | 7 |lmffmowl| | 8 |mnggnpxm| | 9 |nohhoqyn| | 10 |opiiprzo| | 11 |pqjjqsap| | 12 |qrkkrtbq| | 13 |rsllsucr| | 14 |stmmtvds| | 15 |tunnuwet| | 16 |uvoovxfu| | 17 |vwppwygv| | 18 |wxqqxzhw| | 19 |xyrryaix| | 20 |yzsszbjy| | 21 |zattackz| | 22 |abuubdla| | 23 |bcvvcemb| | 24 |cdwwdfnc| | 25 |dexxegod|

The only text that makes sense is zattackz so we can deduce that the key is 21 (25 - b = 21).

DEXXEGOD is decrypted with the function f(x) = 1x - 4 or f(x) = 1x + 21 and becomes ZATTACKZ.