Transport Layer Security is the cryptographic protocol that provides encryption, authentication, and integrity for most internet traffic. TLS evolved from the earlier SSL protocol (Secure Sockets Layer) through a series of standardized versions: TLS 1.0 (1999), 1.1 (2006), 1.2 (2008), and 1.3 (2018). TLS 1.3 is the current default; earlier versions have known vulnerabilities and are being phased out.
TLS underlies HTTPS, secure email (SMTPS, IMAPS), VPN protocols, API authentication, and essentially every scenario where two networked parties need to communicate securely over an untrusted network. Certificate authorities (Let's Encrypt, DigiCert, Sectigo) are the trust anchors that let TLS clients verify server identities.
For enterprise deployment, TLS configuration is a specific security discipline. Weak cipher suites, outdated protocol versions, and certificate mismanagement remain common sources of production security incidents. Mutual TLS (mTLS) — where both client and server authenticate with certificates — has become the default for service-to-service communication in zero-trust architectures.