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

SEC-C0007 · Cryptography & Encoding

Choosing Key Sizes

Write one key size as a note. Do not generate a production key during the reading, and a short size is not the choice.

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

Choosing Key Sizes names the purpose, the algorithm family, and the size you would refuse. You do not create the key. You do not lower the size to make an old client connect.

Write the system you administer, the name of this change, and the time. A second change waits until this line has been read back.

The browser tool drafts text or reads a paste you already hold. It does not log in, it does not scan, and it does not apply.

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.

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. Write the purpose in one sentence.
  2. Name the family.
  3. Write the size you would refuse.
  4. Do not generate a key.
  5. Stop.

Mistakes that outlive the statement

Choosing Key Sizes 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 Choosing Key Sizes: The purpose is one sentence. Nothing is generated. A short size is refused in the note. This is not a certificate. And one purpose is the window.

Checks before you call it done

Confirm this before you call the change done: The purpose is written. Nothing was generated. The refused size is written. The page is not called a certificate. And a second person can say the family. If one of those fails, stop.

# Key-size note. Do not generate a key during the reading.

Before you leave the system

Choosing Key Sizes 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.