SSL/TLS (Secure Sockets Layer/Transport Layer Security) is a cryptographic protocol that encrypts data in transit and authenticates the identity of servers, protecting confidentiality and integrity of network communications.
SSL, developed by Netscape in the 1990s, was the original protocol (versions 2.0 and 3.0). Both are now obsolete and insecure. TLS replaced SSL as the modern standard, beginning with TLS 1.0 (a refinement of SSL 3.0) and continuing through TLS 1.2 and TLS 1.3 (the current recommended version). The name "SSL/TLS" persists in common usage, though TLS is the accurate current term.
When you visit a website over HTTPS, TLS runs beneath the HTTP layer. The server presents a digital certificate (issued by a Certificate Authority) that proves its identity; your browser verifies the certificate and establishes an encrypted tunnel. All subsequent data—passwords, form submissions, API tokens—is encrypted so only the client and server can read it.
Key capabilities:
- Encryption: Data becomes unreadable to eavesdroppers
- Authentication: Verifies the server is who it claims to be
- Integrity: Detects tampering with transmitted data
TipAlways use TLS 1.2 or TLS 1.3. SSL 2.0, SSL 3.0, TLS 1.0, and TLS 1.1 have known vulnerabilities and should be disabled on production systems.
For email, TLS secures SMTP, IMAP, and POP3 connections. For APIs and microservices, TLS protects data between clients and backend systems. Use /tools/ssl-check to audit your TLS configuration.