What it is
Transport Layer Security (TLS) is a cryptographic protocol designed to provide secure communication over a computer network. It's the successor to SSL (Secure Sockets Layer) and is widely used to secure web traffic, email, and other network communications.
TLS operates at the transport layer of the OSI model, sitting between the application layer (HTTP, SMTP, etc.) and the network layer (TCP/IP). When you see "https://" in your browser, you're using TLS to encrypt the connection between your browser and the web server.
Why it matters
TLS provides three critical security properties:
- Confidentiality: Data is encrypted so that only the intended recipient can read it.
- Integrity: Data cannot be modified in transit without detection.
- Authentication: The server (and optionally the client) can verify each other's identity using certificates.
Without TLS, anyone on the network path between you and the server could intercept, read, or modify your data. This is especially critical for sensitive information like passwords, credit card numbers, and personal data.
In practice
Best practices for TLS deployment:
- Use TLS 1.2 or TLS 1.3 (avoid older versions like TLS 1.0 and 1.1)
- Keep certificates up to date and monitor expiration dates
- Use strong cipher suites and disable weak ones
- Enable HSTS (HTTP Strict Transport Security) to force HTTPS
- Regularly audit your TLS configuration for vulnerabilities
- Use certificate pinning for high-security applications
- Monitor certificate expiration and set up automated renewal
Further reading
- RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3
- RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
- OWASP TLS Cheat Sheet
- Mozilla SSL Configuration Generator
Put the theory to work: run a domain through the TLS tester, or read Cipher suites next.
Related guides
- Cipher suites
- Certificate lifecycle
- Visual TLS handshake
- SSL Studio — check whether a certificate is valid and when it expires.