What is Asymmetric Cryptography?

Asymmetric cryptography (also called public-key cryptography) is a type of encryption that uses two different but mathematically related keys:

• Public key → shared with everyone
• Private key → kept secret by the owner

What one key encrypts, only the other key can decrypt.

How it works (simple idea)

1. You generate a key pair: public + private
2. You share your public key
3. Someone encrypts data using your public key
4. Only your private key can decrypt that data

So even if attackers intercept the encrypted message, they cannot read it without the private key.

Why asymmetric cryptography is useful

It solves a major problem of symmetric cryptography:

How do we securely share a secret key in the first place?

With asymmetric cryptography:

• No secret needs to be exchanged ahead of time
• Trust can be established over insecure networks (like the internet)

Common use cases

1. Secure communication (HTTPS / TLS)

• Your browser uses the server’s public key
• A secure connection is established without sharing secrets openly

2. Digital signatures

• Sender signs data with their private key

• Anyone can verify it using the public key

• Ensures:

  • Authenticity
  • Integrity
  • Non-repudiation

3. Key exchange

• Asymmetric crypto is often used to safely exchange a symmetric key
• After that, faster symmetric encryption is used for data transfer

Popular asymmetric algorithms

Asymmetric vs Symmetric (quick comparison)

👉 In practice: both are used together.

Real-world analogy

🔐 Mailbox example

• Public key = mailbox slot (anyone can drop a letter)
• Private key = mailbox key (only you can open it)