What Is Public Key Cryptography? Explained

What public key cryptography is

Public key cryptography, also called asymmetric cryptography, is a method of securing communication using a pair of mathematically linked keys: a public key that can be shared freely, and a private key kept secret. What one key locks, only the other can unlock. This clever arrangement solves a fundamental problem in securing communication, and it underpins much of modern online security, from secure websites to encrypted messaging to digital signatures. It is one of the most important ideas in all of computer security.

The problem it solves

Traditional encryption used a single shared secret key to both lock and unlock messages, which created a dilemma: how do two people securely share that secret key in the first place, especially over an insecure network? If you send the key, an eavesdropper could intercept it. Public key cryptography elegantly solves this. Because the public key can be shared openly without compromising security, two parties can establish secure communication without ever having to secretly exchange a shared key beforehand.

How the key pair works

Each person has a key pair: a public key they share with anyone, and a private key they keep secret. The keys are mathematically related such that something encrypted with the public key can only be decrypted with the matching private key. So if someone wants to send you a secret message, they encrypt it with your public key, and only you, with your private key, can read it. The public key locks; only the private key unlocks. The security relies on it being practically impossible to derive the private key from the public one.

Encryption and signatures

Public key cryptography enables two powerful capabilities. First, secure encryption: anyone can encrypt a message to you using your public key, and only you can decrypt it. Second, digital signatures: you can sign something with your private key, and anyone can verify it with your public key, proving it came from you and was not altered. This dual power, confidential encryption and verifiable signatures, is why public key cryptography is so central to online trust and security.

Where it is used

Public key cryptography is everywhere, usually invisibly. It secures the HTTPS connections behind the padlock in your browser, establishing a safe channel with websites. It underlies the digital certificates that verify website identities, secure messaging apps, software signing, and much more. Nearly every time you do something securely online, public key cryptography is working behind the scenes. It is a foundational technology that makes safe communication over the open internet possible.

Why it matters

Public key cryptography is one of the most important inventions in computer security, solving the fundamental challenge of secure communication between strangers over an insecure network. Understanding it clarifies how the padlock in your browser, encrypted messaging, and digital signatures actually work. Even at a conceptual level, grasping the two-key idea, public to lock, private to unlock, gives real insight into how trust and security are maintained across the entire internet.

Related on Skillo

See also: What are HTTPS and SSL certificates? Explained, What is a digital certificate? Explained.

Sources

• Public-key cryptography - Wikipedia

Published date reflects the original event date (2023-11-14). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.