Encryption Fundamentals: The Difference Between AES and RSA

Keeping Secrets in the Digital World

We transfer money through internet banking, chat with friends on messengers, and make card payments at online shops. In all these moments, our sensitive information is transmitted to servers somewhere around the world. So how is it that hackers can't intercept this information in the middle? The answer lies in encryption.

Encryption is the process of converting readable data (plaintext) into an unreadable form (ciphertext). It's like when you exchanged secret letters with friends in childhood, substituting letters according to agreed-upon rules. However, modern encryption is mathematically far more complex - so much so that even with all the computers in existence working together, it's impossible to break.

There are two encryption methods most widely used today: AES (symmetric encryption) and RSA (asymmetric encryption). The names might seem intimidating, but once you understand the concepts, it becomes clear why two methods are needed and when to use each one.

Symmetric vs Asymmetric Keys: The Fundamental Difference

In the world of encryption, a 'key' is like a key that opens a lock. In symmetric encryption, you lock and unlock with the same key. Think of your front door - one key can lock and unlock it. Simple and fast, but there's a problem: how do you safely deliver the key to the other party?

Asymmetric encryption elegantly solves this problem. It uses two keys - one is the public key that can be shared with anyone, and the other is the private key that must never be disclosed. What's locked with the public key can only be opened with the private key. It's like a mailbox - anyone can drop in letters, but only the person with the key can open it and retrieve them.

AES: Fast and Powerful Symmetric Encryption

AES (Advanced Encryption Standard) is a standard encryption algorithm adopted by the US government in 2001. When the previously used DES became insecure due to advances in computing power, AES was selected through a worldwide competition among cryptographers. The winner was the Rijndael algorithm created by Belgian cryptographers.

AES's strength is speed. Modern processors have dedicated instructions for AES operations (AES-NI), enabling gigabytes of data to be encrypted in an instant. AES is used when encrypting files with passwords, protecting sensitive database information, or encrypting entire disks.

Depending on key length, there's AES-128, AES-192, and AES-256. The number represents the key's bit count. AES-256 has 2^256 possible key combinations - more than the number of atoms in the universe. With current technology, it's impossible to break through brute force attacks.

However, there's one important decision when using AES: choosing the operating mode. ECB mode should never be used because the same plaintext block always produces the same ciphertext, exposing patterns. The currently recommended mode is GCM (Galois/Counter Mode). GCM verifies data integrity along with encryption, allowing detection of whether ciphertext has been tampered with.

const crypto = require('crypto');

function encrypt(text, key) {
  const iv = crypto.randomBytes(12); // GCM recommends 12-byte IV
  const cipher = crypto.createCipheriv('aes-256-gcm', key, iv);

  let encrypted = cipher.update(text, 'utf8', 'hex');
  encrypted += cipher.final('hex');

  const authTag = cipher.getAuthTag();

  return {
    iv: iv.toString('hex'),
    encrypted,
    authTag: authTag.toString('hex')
  };
}

RSA: The Synonymous Name for Public Key Encryption

RSA is an algorithm named after three MIT professors from 1977: Rivest, Shamir, and Adleman. It's based on the mathematical principle that factoring large numbers is difficult. Multiplying two large prime numbers is easy, but finding the original two primes from the product is astronomically difficult.

RSA's biggest advantage is solving the key distribution problem. The public key can literally be made public. If someone wants to send you an encrypted message, they encrypt it with your public key. Only you can open it with your private key that only you possess.

RSA is also used for digital signatures. In this case, you sign with your private key and verify with your public key. Since only you have the private key, a valid signature proves the message really came from you. This is used to verify the authenticity of software update packages or legal documents.

However, RSA is slow. It's hundreds to thousands of times slower than AES, making it unsuitable for directly encrypting large amounts of data. That's why hybrid methods are used in practice.

Hybrid Encryption: Combining the Best of Both Worlds

Most real-world encryption systems use AES and RSA together. Here's a simplified version of what happens when you access a website with HTTPS:

First, when your browser connects to a server, the server sends a certificate containing its public key. The browser generates a random AES key (session key) and encrypts it with the server's RSA public key before sending it. The server decrypts this with its private key to obtain the AES key. Now both sides have the same AES key, and all subsequent communication is encrypted with this fast AES.

The beauty of this approach is that it takes advantage of RSA's key distribution benefits and AES's speed. RSA only encrypts small data (the AES key), so its slowness isn't a problem, and the actual bulk communication is handled by fast AES.

Cautions When Implementing Encryption

The encryption algorithms themselves are powerful, but they become useless if used incorrectly. There are several common mistakes to avoid.

Never hardcode keys in source code. You occasionally see news about AWS keys being exposed in code uploaded to GitHub, leading to hacking. Keys should be stored in environment variables or specialized key management services like AWS KMS or HashiCorp Vault.

AES's IV (Initialization Vector) must use a new random value each time. Reusing the same IV with the same key can break the encryption. The IV isn't secret, so it can be stored with the ciphertext. The important thing is not to reuse it.

Don't try to implement encryption algorithms yourself. Using verified libraries is much safer. Cryptography is a field where one subtle mistake can bring down the entire security.

Wrapping Up

Encryption is the foundation of the modern digital world. Understanding the principles of these two algorithms, AES and RSA, naturally leads to understanding how HTTPS works, why passwords should be stored as hashes, and what digital signatures are.

Try encrypting and decrypting text yourself with Toolypet's encryption tools. When abstract concepts turn into concrete experience, your understanding of security will deepen by one level.