Transport Layer Security (TLS)

What is TLS?

TLS encrypts network traffic so eavesdroppers cannot read or tamper with data in flight. When you visit https://, HTTP runs over TLS. The older name SSL is still used colloquially though SSL 3.0 is deprecated.

How a handshake works (simplified)

1. Client connects and advertises supported cipher suites
2. Server presents certificate proving domain identity
3. Keys are exchanged; symmetric encryption secures the session
4. Application data flows encrypted

Certificates

• Issued by Certificate Authorities (Let’s Encrypt, DigiCert, etc.)
• Bind a public key to a domain name
• Auto-renewal via ACME is standard on modern platforms

TLS termination

Encryption may end at a CDN, load balancer, or reverse proxy (termination), with optional re-encryption to backends (TLS passthrough or mTLS internally).

Best practices (informational)

• Enforce TLS 1.2+ (prefer 1.3)
• Use HSTS to force HTTPS in browsers
• Monitor certificate expiry
• Disable weak ciphers

Related terms

mTLS (mutual TLS) requires both client and server to present certificates — common in service meshes and zero-trust architectures.

What people get wrong

• Letting certificates expire. Still a top cause of self-inflicted outages; automate renewal (ACME) and alert two weeks out, not the morning of.
• Terminating TLS at the edge and forgetting the inside. Plaintext between the load balancer and backends undermines the whole model — re-encrypt or use mTLS internally where the network isn’t trusted.
• Testing HTTPS only in the browser. Older mobile clients, webhooks, and API consumers can fail on modern-only cipher configs; test with the clients you actually serve.

TLS Version History and Why It Matters

TLS 1.2, released in 2008, remained the dominant version in production for over a decade, but TLS 1.3, finalized in 2018, simplified the handshake process (reducing it from two round trips to typically one), removed support for older, cryptographically weaker cipher suites, and made forward secrecy mandatory rather than optional — meaning even if a server’s private key is later compromised, previously captured encrypted traffic can’t retroactively be decrypted. Major browsers and cloud platforms have progressively deprecated support for TLS 1.0 and 1.1 due to known vulnerabilities, and compliance frameworks like PCI DSS now require TLS 1.2 or higher, making TLS version support a genuine, auditable security and compliance consideration rather than a purely technical implementation detail.

This is why security scanners and compliance audits routinely check which TLS versions and cipher suites a server accepts, treating support for deprecated versions as a finding to remediate even if no active exploit has occurred against that specific server yet.