I install debian 8.5 system from dvd. I accept most default settings. I store software repository in /mnt. I avoid changing most system settings. I do not allow internet to adjust my system. I do not setup sudo.

Remove package ats-lang-anairiats.
Will keyring fix this? Can keyring be setup offline?

No.

I asked in your other thread (which may be why we're 'here'?) if you had modified
anything at or below /etc/apt/ ?

Handbook.

I think that you have to expect to use the Internet to finish installation from a DVD, because whatever's on that DVD is likely to be stale and that might conceivably include a problem with a package's signature-key or even contents. Certainly, you should never install a package that does not verify. Search the vendor's support site for a trouble-ticket referencing it.

Don't allow the interweb, allow Debian... plus, try:
https://cdimage.debian.org/cdimage/u...y-live-builds/

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I manually do this after install.This was all done automatically.I have not modified anything else.

debian-handbook/html/en-US/sect.package-authentication.html
The Debian Administrator's Handbook. 6.5. Checking Package Authenticity.
Says to run this command.But how do I make key.asc?

You are aware for security updates you need to connect or download a full (at lest) netinst over and over?

From the internet... https://wiki.debian.org/SecureApt

Is the computer connected to the internet or it it not?
If it is then you can just download the various updates.
If not then just choose not to have any internet mirror during install and forget about it.
If you did choose not to use an internet mirror during install then please elaborate on how exactly you are installing, which options you chose and the exact errors.

to Habitual, LQ Addict.
You say keyring will not fix this. Can anything fix it? Other than allowing internet to automatically adjust my system.

to sundialsvcs, LQ Guru.
Thank you, that is a good opinion. Slightly outdated, or stale, is ok with me. And to be more updated, I simply get a new official debian repository dvd set. That sounds like a good way to find the answer. I assume you mean the place where I get the dvd set from. And I also guess that the product is always the same, no matter who the dvd vendor is. They are all made from the iso file on the debian website.

to jamison20000e, Senior Member.
I do not understand. You say I should download a cd image, then install my system from that? But I like my current system. To fix the problem, is that what I need, a security update? I thought a new dvd set would have a security update. And I remember debian 6 had the same problem.

to 273, LQ Addict.
Is the computer connected to the internet or it it not?
Yes, the computer is connected to the internet.

If it is then you can just download the various updates.
When I want an update, I simply get an updated dvd set. I have done that many times.

If not then just choose not to have any internet mirror during install and forget about it.
But apt-get still says WARNING: The following packages cannot be authenticated!

If you did choose not to use an internet mirror during install then please elaborate on how exactly you are installing, which options you chose and the exact errors.
I installed my system from debian 8.5 dvd set, with internet off, when the dvd set was first released. That was a long time ago. But as I recall, I chose most of the default answers.

I think you are forgetting the title of this post. How to authenticate packages offline?

You use a public key (from online) to authenticate packages...