Public Key Cryptography: How SSL/TLS Protects Your Website
Securing your website with SSL encryption is essential. SSL (Secure Socket Layer), now commonly known as TLS (Transport Layer Security), defines how secure communication happens between clients and services on the internet. Below is an easy‑to‑understand explanation using a familiar analogy related to Public Key Cryptography.
How SSL/TLS Encryption Works
Alice and Bob are two friends who like to share secrets. They often send fun, secret letters to each other through the mail. One day, Alice discovered that Eve the Eavesdropper at the postal service would sometimes read their messages.
To secure their communication, they create a plan using padlocks and keys—an analogy for public key cryptography.
Public Keys and Private Keys Explained
Both Alice and Bob get padlocks with keys. When Alice wants to send Bob a message, she first sends him a letter saying she wants to communicate. Bob mails her his padlock.
Alice writes her message, places it in a box along with her padlock, locks it with Bob’s padlock (his public key), and sends it. Once locked, not even Alice can open it—and neither can Eve.
Bob unlocks it using his private key, finds Alice’s secret message and padlock, writes his response, and locks it with Alice’s padlock. This back‑and‑forth continues securely.
This mirrors how SSL/TLS encryption works:
- Public Key = padlock you give away
- Private Key = key only you hold
Why Public Key Infrastructure (PKI) Matters
SSL doesn't require sending padlocks repeatedly. Instead, public keys can be registered with outside services, known as the Public Key Infrastructure (PKI).
These organizations verify that a public key truly belongs to its owner. This prevents attackers like Eve from sending fake keys pretending to be someone else.
When Bob checks Alice’s padlock against PKI records, he can confirm its authenticity.
Self-Signed Certificates and Browser Warnings
If you use a self‑signed SSL certificate, your browser cannot verify the public key against trusted PKI records. This causes the warning message you likely saw when accessing the Plesk Panel. Visitors to your website will also receive this warning.
Self‑signed certificates are acceptable only when you are the sole user and already trust the key.
Certificate Authorities and Trust Chains
The PKI is not a single organization—it’s a network of trusted Certificate Authorities (CAs). Some are highly trusted “root” CAs; others are intermediate authorities.
When a CA issues an SSL certificate, it signs it using higher‑level CA keys. This creates a Certificate Authority Chain, which allows browsers to trust your SSL certificate automatically.
Most SSL certificates include this trust chain so that all systems can validate them consistently.