Encryption is the process of transforming readable data into an unreadable format using a mathematical algorithm, so that only parties holding the correct key can decode and access the original information. In the context of web security, encryption is the foundational mechanism that protects sensitive data as it travels between a user's browser and a web server, preventing third parties from intercepting or tampering with it.
Symmetric vs. asymmetric encryption
There are two broad categories of encryption used in web security. Symmetric encryption uses a single shared key to both encrypt and decrypt data. It is computationally fast and efficient, making it well-suited for encrypting large volumes of data in transit. The challenge with symmetric encryption, however, is securely sharing that key between two parties in the first place.
Asymmetric encryption, also called public-key cryptography, solves this problem by using a mathematically linked key pair: a public key, which anyone can use to encrypt data, and a private key, which only the intended recipient holds and uses to decrypt it. Asymmetric encryption is slower than symmetric encryption but is essential for securely establishing a shared secret between two parties who have never communicated before.
How TLS and HTTPS use encryption
Modern web encryption is delivered through TLS (Transport Layer Security), the successor to the now-deprecated SSL (Secure Sockets Layer). When a browser connects to a website over HTTPS, TLS orchestrates a process called a handshake. During this handshake, asymmetric encryption is used to authenticate the server's identity via a digital certificate and to securely negotiate a shared session key. Once that key is established, the connection switches to symmetric encryption for the remainder of the session, combining the security strengths of both approaches.
The result is a secure channel where data in transit, whether a login credential, a payment detail, or a private message, is protected from eavesdropping and manipulation. A padlock icon in the browser's address bar indicates that this TLS-encrypted connection is active.
Encryption and broader web security
Encryption in transit is one layer of a broader security posture. HSTS (HTTP Strict Transport Security) complements it by instructing browsers to always use HTTPS for a given domain, preventing accidental unencrypted connections. Encryption also underpins newer authentication mechanisms: Passkeys, for example, rely on asymmetric cryptography to authenticate users without transmitting a password at all, using a private key stored securely on the user's device.
It is important to distinguish encryption in transit from encryption at rest, which protects stored data on servers and databases. Both are necessary in a complete security strategy, but HTTPS addresses the former, ensuring that data moving across the network cannot be read even if intercepted.