Encryption Explained: AES, RSA, and When to Use Each

Two Types of Encryption

All modern encryption falls into two categories:

In practice, most systems use both: RSA to securely exchange an AES key, then AES for the actual data encryption.

AES: The Workhorse

AES (Advanced Encryption Standard) is the most widely used encryption algorithm. It's what protects your HTTPS connections, encrypted drives, and password vaults.

const crypto = require('crypto');

// Generate a random 256-bit key
const key = crypto.randomBytes(32);  // 32 bytes = 256 bits
const iv = crypto.randomBytes(16);   // Initialization vector

// Encrypt
const cipher = crypto.createCipheriv('aes-256-gcm', key, iv);
let encrypted = cipher.update('secret data', 'utf8', 'hex');
encrypted += cipher.final('hex');
const authTag = cipher.getAuthTag();

// Decrypt
const decipher = crypto.createDecipheriv('aes-256-gcm', key, iv);
decipher.setAuthTag(authTag);
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');

RSA: For Key Exchange and Signatures

RSA uses a key pair: share your public key with everyone, keep your private key secret. Anyone can encrypt a message with your public key, but only you can decrypt it.

RSA is too slow for encrypting large amounts of data. Instead, it's used to:

• * Key exchange - Securely send an AES key to someone
• * Digital signatures - Prove a message came from you
• * Authentication - SSH keys, code signing

Hybrid Encryption in Practice

Here's how HTTPS, email encryption, and most secure systems actually work:

This gives you the best of both worlds: RSA's secure key exchange and AES's speed for bulk encryption.

Quick Decision Guide

Common Mistakes to Avoid