What is TLS?
TLS is the encryption layer that puts the S in HTTPS, protecting data between your browser and a server.
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TLS (Transport Layer Security) encrypts the connection between two programs so nobody in between can read or change the traffic. It is the envelope around a letter: the postal service can see the address but not the content. TLS also proves to your browser that the server really is who it claims to be, using a certificate.
You use TLS every time you see the padlock in the address bar. Web servers, mail servers, databases and APIs all speak it. People still say SSL, which is the older name for the same idea; modern systems should use TLS 1.2 or 1.3 only. Setting it up means obtaining a certificate, often free from Let’s Encrypt, and pointing the server at it.
openssl s_client -connect example.com:443 -briefSee also: What is a certificate? and What is encryption?
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See also
- 0278 What is a certificate? A certificate is a digital ID card that proves a website or server is genuine, issued by a trusted authority. Beginner · Explains an idea · Any system Article TLS & certificates 15 Oct 2026
- 0307 What is encryption? Encryption scrambles data with a key so only someone with the right key can read it again. Beginner · Explains an idea · Any system Article TLS & certificates 15 Oct 2026
- 0325 Fix: SSL certificate problem: unable to get local issuer certificate curl, git, pip or npm cannot chain the server's certificate to a root they trust. Usual causes: a corporate proxy that re-signs… Intermediate · Fixes an error · Linux, macOS, Windows Article Common errors · Making requests · TLS & certificates 15 Oct 2026
- 0355 TLS certificates explained What a certificate proves, who signs it, what the chain and expiry mean, and how to read any site's certificate from the… Beginner · Explains an idea · Any system Article TLS & certificates 15 Oct 2026
- 0356 Free HTTPS with Let’s Encrypt and certbot Install certbot, get a trusted certificate for your domain and let it configure nginx or Apache, or just obtain the files for… Beginner · Step by step · Linux Article TLS & certificates 15 Oct 2026
Repos in the wild
- certbot: the Let’s Encrypt client certbot/certbot The EFF's ACME client that obtains free TLS certificates from Let's Encrypt, can configure nginx and Apache for HTTPS automatically and renews everything on a timer. GitHub
- step-ca: run your own certificate authority for internal TLS and SSH smallstep/certificates step-ca from Smallstep is an open source certificate authority that issues TLS and SSH certificates for your own infrastructure, with ACME support so internal services get certificates the way public ones do. GitHub
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- Dominik +781 chars