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Cipher

This is an ecnryption tool that implements Feistel Cipher and allows to encrypt and decrypt any text string - inluding all languages characters, symbols and emojis.

Links

Demo

Documentation

Motivation

This tool was created for the recruitment process and as a portfolio. As well to to learn and improve programming skills.

Password

Password : admin

As mentioned above, this tool was created for the recruitment process which required logging in, thus the password is made public.

Feistel Cipher implementation

You can read how Feistel Cipher works on Wikipedia

Diagram below shows basic usage:

enter image description here

Algorithm assumptions:

  • Encrypting function F defined as one of:
    • xor
    • or
    • and
    • signed right shift
  • Round-dependant key (sub-key) creation function:
    1. Define master key as hashed user provided key (string) with sh256 hash function truncated to 64bit hash
    2. Round subkey is defined as sha256 of master key + round number + round number to the power of 37 truncated to 64bit hash
  • Every character is represented in 16bit format
  • Every block size has size of 128bit
  • Key size is 64bit
  • Padding character is defined as Unicode End of Text (\u0003)
  • In order to provide user friendly encrypted text, result of algorithm is converted to Base64 on input and output.

Algorithm steps:

Encryption
  1. Divide input string into 128bit blocks
    • Due to asumptions every single block has 8 characters (block size 128bit / char size 16bit)
    • Last block is filled with padding character when necessary - less than 8 characters
  2. Every block is processed separately
  3. Each block input text is converted to binary represantation
  4. Core Feistel Cipher alhorithm is executed
    • Binary input is split into two equal pieces
    • In each round right halft of the block goes through unchanged and becomes new left
    • Left half is XOR-ed with output of encryption function F that takes right side and round key as parameters - result of that becomes new left
    • Once the last round is completed - right side is swapped with left.
  5. Concatenate results from each block converted back to UTF16 string as final cipher
Decryption
  1. Same as encryption process but order of applied keys is reversed.
  2. Possible padding characters (\u0003) are removed from final text.

Tests

Cipher app includes unit tests created with JEST.js

Documentation

Documentation created with JSDoc

Available at cipher.ovh/docs

Available Scripts

npm run start - Runs the app in the development mode
npm run test - Runs all tests
npm run build - Builds the app for production to the build folder
npm run docs - Generates docs in docs folder

© May 2021 Patryk Bura