Practical tools for system, network, security, and operations administrators.

SEC-C0014 · PKI & Certificates

How SSL/TLS Works

Read a certificate you are allowed to look at. A green result is not a verdict that the site is safe.

Updated 25 October 2026 · Explainer

This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.

What this hour is for

TLS is a certificate, a name, and a date. The checker reads the certificate facts. It does not log in, and it does not make an untrusted certificate trusted.

You do not disable verification to make a check pass. You do not point the page at a host you do not administer just to browse it.

192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. A sample password is replaced. It is not a password you keep.

The change you can finish

Apply nothing while you are writing the note. When the lab window opens, it is one change on the system named in the ticket. Read the draft, then the system, then decide.

Rollback is the file, the record, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.

  1. Name the host you administer.
  2. Read the name and the date.
  3. Write the mismatch, if there is one.
  4. Do not disable verification.
  5. Stop.

Mistakes that outlive the statement

How SSL/TLS Works goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.

Decisions to write down

One decision for How SSL/TLS Works: The host is yours. The name and date are written. And verification stayed on.

Checks before you call it done

Confirm this before you call the change done: The host is written. The certificate was read. Verification is still on. No secret is in the note. And nothing was installed. If one of those fails, stop.

# Read the certificate. Do not disable verification.
# 192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. A sample password is replaced. It is not a password you keep.

Before you leave the system

How SSL/TLS Works ends when the system in the note is the system in the ticket. If it is not, stop.

The draft stays a draft until a person has read the names in it. A generator does not log in, does not scan, and does not send mail.

192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you publish because a draft included them.

prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save. A sample password is replaced. It is not a password you keep.

One change is the window. If two things move and the result is wrong, you will not know which one did it.

If the same step fails twice, stop for the day. Restore the copy you took first.

A second person reads the scope aloud. If they cannot find it in the ticket, the note is not done.

This page is a planning guide. It is not legal advice, not an audit opinion, not a vendor manual, and not the text of a standard. You do not disable a security control to make a check pass. You do not use the page against a system you do not administer.

Tools for this guide

These tools run in the browser on this site. They do not log into your machines.

More in this cluster

The pillar for this page, and the next published pages filed with it.

Companion: Network: How to Check TLS Versions and Ciphers.