Text-Message-Encryption-and-Decryption

Shell script that does simple encryption/decryption algorithm for text messages with only alphabet characters. This encryption/decryption is based on the use of XOR logic gate.

Encryption process:

The process for the encryption algorithm can be summarized in the following steps:

Step 1 : Generate key. The key will be generated as following: Key = Max[(sum of characters index in the word) mod 256]

The character index is the order of the character in the English alphabet. I.e. The character index of “A” or “a” is 1, and the character index of “W” or “w” is 23. As an example for key generation, if the file contains the sentence “Welcome to Linux lab” then the key will be: Key = Max [ (23+5+12+3+15+13+5) mod 256 , (20+15) mod 256 , (12+9+14+21+24) mod 256 , (12+1+2) mod 256 ] = 80

Step 2: The key will then be represented as 8-bit binary number.

Step 3: for each character in the text file compute the XOR between the key generated and the ASCII code of the character. The result will be 8-binary digit.

Step 4: for each 8-bit binary result, swap the first 4-bit with the last four bit. For example: 10001100 become 11001000.

Step 5: at the end, swap the first 4-bit with the last four bit of the key and add it as the last character of the generated file.

Decryption process:

The process for the decryption algorithm can be summarized in the following steps:

Step 1: get key (the las character in the encryption file) and swap the first 4-bit with the last four bit

Step 2: for each character in the encrypted file, swap the first 4-bit with the last for bit.

Step 3: Do the XOR between the key and each character from the encrypted file.

⚙️ How to use it?

The usage of this script is pretty simple, just follow the below steps.

First of all clone this repository to your local machine using this command.

git clone https://github.com/NicolaLino/Text-Message-Encryption-and-Decryption.git

Now once you successfully cloned the repository now change your working directory and go to the project directory.
```
cd Text-Message-Encryption-and-Decryption
```
Now we are almost there, to run this use this command.
```
./SimpleEncryption.sh
```
This is the main shell script containing all the encryption and decryption functionalities
Enter the file name (if present in same directory) or enter the path of the file.
After that you will get an option to that what you want to do E to encrypt the file or D to decrypt the file.