AES RSA Encryption

 

🌍 Step 1: Understand the Two Types of Encryption

Type	Example Algo	Key Used	Speed	Use Case
Symmetric Encryption	AES	Same key for encrypt + decrypt	⚡ Fast	Encrypt large data (like user info, PII)
Asymmetric Encryption	RSA	Public key ↔ Private key	🐢 Slower	Securely share / protect AES key

🔹 Step 2: Why We Use AES + RSA Together

Think of this like a locker system 🏦:

• AES → is the locker key (small, secret key used to lock data fast)

• RSA → is the safe where you store that AES key securely

Why?
Because:

• AES is fast, but if someone steals the AES key → they can read all data ❌

• So we protect the AES key using RSA public/private key pair.

👉 This technique is called Hybrid Encryption.

🧠 Step 3: Flow Overview (Very Simple Version)

PII Data (phone, email, account)

   ↓

Encrypt using AES key → (Fast)

   ↓

AES key itself encrypted using RSA Public Key → (Secure)

   ↓

Store both in DB:

  - Encrypted PII

  - RSA-encrypted AES key

When reading data:

Fetch encrypted PII + AES key

   ↓

Use RSA Private Key → Decrypt AES key

   ↓

Use AES key → Decrypt PII

🧩 Step 4: AES Key Generation (One-Time per Transaction or Session)

AES key is a random secret key (e.g., 128-bit or 256-bit).

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

KeyGenerator keyGen = KeyGenerator.getInstance("AES");

keyGen.init(256); // 128, 192, or 256 bits

SecretKey aesKey = keyGen.generateKey();

🔹 Step 6: Now Protect the AES Key using RSA (Key Wrapping)

You can’t store aesKey directly in DB — it’s secret!
So you encrypt that AES key using RSA public key.

🔧 Generate RSA Key Pair (one time, store safely).

import java.security.*;

KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");

generator.initialize(2048);

KeyPair keyPair = generator.generateKeyPair();

PublicKey publicKey = keyPair.getPublic();

PrivateKey privateKey = keyPair.getPrivate();