TLS

TLS, Transport Layer Security, is the protocol that secures most communication on the internet. It encrypts data in transit, verifies the identity of servers, and detects tampering. TLS is the successor to SSL, and it is what puts the S in HTTPS.

How It Works

TLS sits between the transport layer and the application. A connection begins with a handshake in which the parties agree on a protocol version and cipher suite, the server presents a digital certificate proving its identity, and the two sides establish shared session keys. The certificate is signed by a trusted certificate authority, which the client validates against its trust store.

Once the handshake completes, TLS provides three guarantees: confidentiality through symmetric encryption, integrity through message authentication codes, and authentication through certificates. TLS 1.3, the current version, streamlined the handshake to a single round trip and removed legacy, insecure options.

Why It Matters

TLS protects passwords, payment data, and private messages from eavesdropping and manipulation on untrusted networks. It is now expected by default; browsers warn on plain HTTP, and HTTP/2 and HTTP/3 effectively require it. Beyond the web, TLS secures email, APIs, database connections, and service-to-service traffic.

Operationally, TLS introduces certificate management: certificates expire and must be renewed, which automation such as ACME and Let's Encrypt has made routine. Strong configuration, including modern protocol versions and cipher suites, is essential, since weak settings undermine the protection TLS is meant to provide.

Related Terms

TLS runs over TCP and within QUIC for HTTP/3, secures HTTP/2 traffic, and follows the DNS lookup that locates a server.