Crypty

Crypty is a small tool for cryptographic encoding / decoding of images.

Before usage

First of all, you need to set up environment variables for the programme. The first environment variable is CRYPTY_SECRET_KEY, and it can be used in the following way:

CRYPTY_SECRET_KEY=<your value goes here>

You can think about CRYPTY_SECRET_KEY as a passphrase that is used for encryption and decryption of images. Let's say you encrypt your image with CRYPTY_SECRET_KEY=4b0c51cfcc09816d60d1c711af56502005eb8a0237dac905f8cc9c5972d5340c. It will mean that to decrypt the image we should use the same value for CRYPTY_SECRET_KEY. In our case it's 4b0c51cfcc09816d60d1c711af56502005eb8a0237dac905f8cc9c5972d5340c. These random characters are just the hex representation of random byte array with length 32 bytes.

The second environment variable is CRYPTY_INIT_VECTOR. It's used similarly to the previous parameter, and it's utilized for additional security while encrypting the image:

CRYPTY_INIT_VECTOR=<your value goes here>

You need this initialization vector for decoding as well. So, the value of CRYPTY_SECRET_KEY and CRYPTY_INIT_VECTOR should be consistent both for encoding and decoding. The example of the value for CRYPTY_INIT_VECTOR is CRYPTY_INIT_VECTOR=3d5b5b14c0c641640218e8b1a03b3e3b. This is the hex representation of the random byte array with length 16 bytes.

In Linux and Mac you can set these values using export expression:

export CRYPTY_SECRET_KEY=4b0c51cfcc09816d60d1c711af56502005eb8a0237dac905f8cc9c5972d5340c
export CRYPTY_INIT_VECTOR=3d5b5b14c0c641640218e8b1a03b3e3b

How to get the value for CRYPTY_SECRET_KEY and ? In node-js you can get them like this:

const crypto = require('crypto')

const secret_key = crypto.randomBytes(32);
console.log(secret_key.toString('hex'));

const initialization_vector = crypto.randomBytes(16);
console.log(initialization_vector.toString('hex'));

Usage

When the environment variables are set. We can use the Crypty. Here are the instructions how to do it:

1. Navigate to src directory of the project:

cd ./src

2. use node command to run crypty and arguments of crypty to achieve the desired behaviour. For example, if I put the cat.png image into /src directory(next to crypty.js), and I want to encrypt cat.png then I execute the following command:

node crypty.js encrypt img="./cat.png" out="./cat-encrypted"

• encrypt argument - says Crypty that we want to encrypt the image.
• img argument - specifies the location of the image for Crypty.
• out argument - specifies the path where the encrypted image should be put.

To decrypt the cat image we can use the following command:

node crypty.js decrypt img="./cat-encrypted" out="cat_as_image.png"

We should specify the action we want to perform, in this case it's "decrypt". Then we specify where the encrypted image is located img="./cat-encrypted". And then we write the path where the decrypted image will be put.