Cryptography Algorithms App Documentation

Table of Contents

1. Project Overview
2. Installation
3. Usage
4. Encryption Algorithms
5. Examples

Project Overview 📝

The Cryptography Algorithms App is a web-based application that provides text encryption and decryption capabilities using two industry-standard encryption algorithms: AES (Advanced Encryption Standard) for symmetric encryption and RSA (Rivest-Shamir-Adleman) for asymmetric encryption. The application features a clean, user-friendly interface for secure text processing.

Installation ⚙️

To install and run the Cryptography Algorithms App, follow these steps:

1. Install the required dependencies:

npm install

2. Launch the application:

node app.js

The server will start running on port 3000 (default) or your specified port.

Usage 📖

1. Access the application through your web browser at http://localhost:3000

2. The interface provides two main sections:

   • Encryption Form
     • Enter the text you want to encrypt
     • Select encryption method (AES or RSA)
     • Click "Encrypt" button
   • Decryption Form
     • Enter the encrypted text
     • Select the same method used for encryption
     • Click "Decrypt" button

3. The application will display:

   • The encryption/decryption result in the output area
   • Any error messages in a separate error output area

Encryption Algorithms 🔐

AES Implementation

The application uses AES-256-CBC (Advanced Encryption Standard with Cipher Block Chaining), one of the most secure symmetric encryption algorithms available.

Algorithm Details

• Block Size: 128 bits (16 bytes)
• Key Size: 256 bits (32 bytes)
• Mode: Cipher Block Chaining (CBC)
• Rounds: 14 transformation rounds

Key Security

• 32-byte encryption key (stored in environment variables)
• 16-byte random salt for each encryption
• PBKDF2 key derivation with:
  • 100,000 iterations
  • SHA-256 hash function
  • 32-byte derived key length

Core Operations (per round -> 14)

1. SubBytes Transformation

   • Each byte is replaced using a substitution table (S-box)
   • Provides non-linearity in the cipher
   • Helps prevent differential cryptanalysis

2. ShiftRows Operation

   • Bytes in each row are cyclically shifted left
   • Row 0: No shift
   • Row 1: Shift 1 position left
   • Row 2: Shift 2 positions left
   • Row 3: Shift 3 positions left

3. MixColumns Transformation

   • Each column is multiplied by a fixed polynomial
   • Provides diffusion in the cipher
   • Mixes data within columns for better security
   • It's not maintained for the last round

4. AddRoundKey

   • Round key is XORed with current block
   • Combines subkey with data block
   • Different key used in each round

RSA Implementation

Key Features

• 2048-bit key size
• Generated on server start
• Base64 encoded output

Mathematical Foundation

1. Key Generation

   1. Select two prime numbers: p and q
   2. Calculate n = p × q
   3. Calculate φ(n) = (p-1) × (q-1)
   4. Choose e where 1 < e < φ(n) and gcd(e, φ(n)) = 1
   5. Calculate d where d × e ≡ 1 (mod φ(n))
   

2. Public Key

   • Consists of (n, e)
   • Typically e = 65537 (2¹⁶ + 1)
   • n is the modulus (2048 bits)

3. Private Key

   • Consists of (n, d)
   • d is kept secret
   • Used for decryption

Encryption Process

For message M:
Ciphertext = M^e mod n

Decryption Process

For ciphertext C:
Message = C^d mod n

Examples 📌

AES Encryption/Decryption

Input:

Hello World

Encrypted Output (format):

a5a870f83f41c76b172d29484816bdf8:8fbcf9a5ae55e236d222f6c2877ad7c8:caec2245c5bd4077d722ff656ee6bf09

Example 1: AES Encryption

Example 2: AES Decryption

RSA Encryption/Decryption

Input:

Hello World

Encrypted Output:

P0nbRS0XhFnce6dPjzpLYDTmoggFigp5381xBzQOFgfcVziLx2lz5q345uyYCXZj2gjnhtryOlR0pr3jO2AbublAo5YqlJ1kW/MzJICVDLpy44YIzMkFSUc8HdL36xJ9VhDxKrFltpxReh3RjUGs7dHlmm0fzCSyIXAKCVImXNmcxFvJfuiZNbO2JHWMNAVCvIuVIQ0mDk4NYlOHUjhvroJwvABUzXyO5aoKSXHOmOl22gouA+tRjnWKygYStD/wV3uUiqmoAsCDNal7f7yMgWFR8Fz4iY0QraPzRue8blV1lmZzqhuquXdqwmnjSnZH3Y5pq4FCZxS3oYYyGImaYg==

Example 3: RSA Encryption

Example 4: RSA Decryption

Error Handling Examples

The application handles various error scenarios:

1. Missing Input:

{
    "error": "Text is required."
}

2. Invalid Encryption Method:

{
    "error": "Invalid encryption method."
}

3. Invalid AES Format:

{
    "error": "AES decryption error: Invalid encrypted text format."
}

4. Invalid RSA Data:

{
    "error": "RSA decryption error: Invalid RSA encrypted text."
}

Current Security Measures:

• HTTP security headers via Helmet
• Input validation
• Secure key derivation
• Random IV and salt generation
• Error messages that don't expose internal details
• Environment variable for sensitive data

Note: This documentation reflects the current implementation. Some features mentioned in the original documentation (like GCM mode, rate limiting, and request size limits) are not currently implemented in the codebase.