Encryption Middleware for NestJS 🚀🔒 Overview This module implements Hybrid Encryption in a NestJS middleware, ensuring that all incoming requests are decrypted and outgoing responses are encrypted using a combination of RSA and AES encryption.

🔹 Features ✅ Hybrid Encryption (RSA + AES-256-GCM) for speed and security ✅ Seamless Middleware Integration in NestJS ✅ Automatic Encryption & Decryption of request/response payloads ✅ Prevents Recursive Encryption for multiple middleware layers ✅ Tamper-proof Authentication Tag (authTag) for AES encryption

1️⃣ Installation First, install the required dependencies:

sh Copy Edit npm install crypto 2️⃣ How It Works 🔹 Hybrid Encryption (RSA + AES) Flow 1️⃣ Client-Side Encryption

Generates a random AES key & IV (Initialization Vector) Encrypts the data using AES-256-GCM Encrypts the AES key using RSA Public Key Sends { encryptedData, iv, authTag, encryptedAESKey } in the request 2️⃣ Middleware Decryption (Server-Side)

Decrypts the AES key using RSA Private Key Uses the AES key to decrypt encryptedData Ensures integrity using authTag Processes the decrypted request 3️⃣ Server-Side Response Encryption

Generates a new AES key & IV Encrypts the response with AES-256-GCM Encrypts the AES key using RSA Public Key Sends { encryptedData, iv, authTag, encryptedAESKey } back to the client 3️⃣ Middleware Usage 📌 Step 1: Register Middleware In your app.module.ts, apply the middleware globally:

ts Copy Edit import { MiddlewareConsumer, Module, NestModule } from '@nestjs/common'; import { EncryptionMiddleware } from './encryption.middleware';

@Module({}) export class AppModule implements NestModule { configure(consumer: MiddlewareConsumer) { consumer.apply(EncryptionMiddleware).forRoutes('*'); // Apply to all routes } } 4️⃣ Configuration 📌 Step 2: Provide RSA Keys Your RSA keys must be stored securely. Configure them in an environment file or pass them dynamically:

ts Copy Edit { rsaConfig: { privateKey: process.env.RSA_PRIVATE_KEY, // Keep this secret publicKey: process.env.RSA_PUBLIC_KEY // Used for encryption } } 5️⃣ Encryption & Decryption Logic 📌 Encrypting Data (AES + RSA) ts Copy Edit encryptData(data: string): { encryptedData: string; iv: string; authTag: string; encryptedAESKey: string } { const aesKey = crypto.randomBytes(32); // AES-256 key const iv = crypto.randomBytes(16); // IV for AES-GCM

const cipher = crypto.createCipheriv('aes-256-gcm', aesKey, iv); let encrypted = cipher.update(data, 'utf8', 'base64'); encrypted += cipher.final('base64');

const encryptedAESKey = crypto.publicEncrypt( { key: this.publicKey, padding: crypto.constants.RSA_PKCS1_OAEP_PADDING, }, aesKey );

return { encryptedData: encrypted, iv: iv.toString('base64'), authTag: cipher.getAuthTag().toString('base64'), encryptedAESKey: encryptedAESKey.toString('base64') }; } 📌 Decrypting Data (RSA + AES) ts Copy Edit decryptData(encryptedPayload: { encryptedData: string; iv: string; authTag: string; encryptedAESKey: string }): string { const { encryptedData, iv, authTag, encryptedAESKey } = encryptedPayload;

const decryptedAESKey = crypto.privateDecrypt( { key: this.privateKey, padding: crypto.constants.RSA_PKCS1_OAEP_PADDING, }, Buffer.from(encryptedAESKey, 'base64') );

const decipher = crypto.createDecipheriv('aes-256-gcm', decryptedAESKey, Buffer.from(iv, 'base64')); decipher.setAuthTag(Buffer.from(authTag, 'base64'));

let decrypted = decipher.update(encryptedData, 'base64', 'utf8'); decrypted += decipher.final('utf8');

return decrypted; } 6️⃣ Example Request & Response Format 📌 Encrypted Request (Client to Server) json Copy Edit { "encryptedData": "mYF83Vh+...", "iv": "sdfu8JKo...", "authTag": "0gA6X9ft...", "encryptedAESKey": "L2mp5JTo..." } 📌 Encrypted Response (Server to Client) json Copy Edit { "encryptedData": "mR4T3Dd+...", "iv": "Kjs73Dpd...", "authTag": "1qX9H2ba...", "encryptedAESKey": "R2nd7LPo..." } 7️⃣ Security Best Practices ✅ 🔐 Keep the RSA private key secure (never expose it in frontend or logs). 🔑 Rotate AES keys periodically to enhance security. ⚠️ Validate decrypted data before processing to avoid attacks. 📌 Store encryption logs securely to debug potential failures.