"Untrusted packages could compromise your system's security" appears while trying to install anything

I've freshly installed Ubuntu 10.04 on a new computer. I'm trying to install an application that I need onto it (my old computer is broken and I have to send it for service). I've managed to install texlive, but then I can't install anything else. All of the software I want installed is the same software that I had successfully installed on my old computer previously (using the same version of Ubuntu). I don't understand why the terminal gives this warning (sorry, the terminal speaks half English, half Polish, but I hope it's enough):

maria@marysia-ubuntu:~$ sudo aptitude install emacs
Czytanie list pakietów... Gotowe
Budowanie drzewa zależności      
Odczyt informacji o stanie... Gotowe
Reading extended state information     
Initializing package states... Gotowe
The following NEW packages will be installed:
  emacs emacs23{a} emacs23-bin-common{a} emacs23-common{a}
  emacsen-common{a}
0 packages upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
Need to get 23,9MB of archives. After unpacking 73,8MB will be used.
Do you want to continue? [Y/n/?] Y
WARNING: untrusted versions of the following packages will be installed!

Untrusted packages could compromise your system's security.
You should only proceed with the installation if you are certain that
this is what you want to do.

  emacs emacs23-bin-common emacsen-common emacs23-common emacs23

Do you want to ignore this warning and proceed anyway?
To continue, enter "Yes"; to abort, enter "No"

I was trying to install other editors as well, with the same result. As I decided that I might be sure that I know the package I want to install is secure, I finally entered "Yes". The installation ended successfully, but the editor doesn't understand .tex files (and the .tex files themselves are known to be good):

this is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian)

restricted \write18 enabled.

entering extended mode

(./Szarfi.tex

! Undefined control sequence.

l.2 \documentclass

{book}

?

What's more, I've realised that in Synaptic Manager there aren't any packages which are marked as supported by Canonical....

Any tips? Thanks in advance.

P.S.

apt sources before using update:

maria@marysia-ubuntu:~$ cat /etc/apt/sources.list
#deb cdrom:[Ubuntu 10.04.2 LTS _Lucid Lynx_ - Release i386 (20110211.1)]/ lucid main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://pl.archive.ubuntu.com/ubuntu/ lucid main restricted
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://pl.archive.ubuntu.com/ubuntu/ lucid-updates main restricted
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://pl.archive.ubuntu.com/ubuntu/ lucid universe
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid universe
deb http://pl.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://pl.archive.ubuntu.com/ubuntu/ lucid multiverse
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid multiverse
deb http://pl.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://pl.archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse
# deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu lucid partner
# deb-src http://archive.canonical.com/ubuntu lucid partner

deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted
deb http://security.ubuntu.com/ubuntu lucid-security universe
deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse
maria@marysia-ubuntu:~$ 

After using update, it's almost fine. I've managed to install 3 applications (texlive, texworks and ekg), and Synaptic shows icons for "supported by Cannonical". But problems with connection persist.

I'm connected to Internet, I can use chat, but sometimes I can't open any web pages. I'm not sure if it this is part of the same problem, or if one is resolved and for the other one I should write a separate post.

List of apt sources after using update:

maria@marysia-ubuntu:~$ cat /etc/apt/sources.list
#deb cdrom:[Ubuntu 10.04.2 LTS _Lucid Lynx_ - Release i386 (20110211.1)]/ lucid main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://pl.archive.ubuntu.com/ubuntu/ lucid main restricted
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://pl.archive.ubuntu.com/ubuntu/ lucid-updates main restricted
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://pl.archive.ubuntu.com/ubuntu/ lucid universe
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid universe
deb http://pl.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://pl.archive.ubuntu.com/ubuntu/ lucid multiverse
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid multiverse
deb http://pl.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://pl.archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse
# deb-src http://pl.archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu lucid partner
# deb-src http://archive.canonical.com/ubuntu lucid partner

deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted
deb http://security.ubuntu.com/ubuntu lucid-security universe
deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse
maria@marysia-ubuntu:~$ 

Seems changed, but it's the only thing I can understand.

Thanks.


Try updating the database

sudo apt-get update

If you're still seeing warning messages after that, provide the list of your repositories

grep -IRH '^deb ' /etc/apt/

If you've just installed Ubuntu, and not added any repositories, update the package list and upgrade the packages:

 sudo apt-get update
 sudo apt-get upgrade

It's recommended to update the system first before installing other packages (at least, after the first install). The contents of the CD could be outdated.


I'm not a 100% sure but it looks like you are missing a bunch of gpg keys. To solve this problem I would install launchpad-getkeys which will import all of the missing keys on your system.

To install launchpad-getkeys you need to first add a ppa - What are ppa's and how do I use them The ppa line is ppa:nilarimogard/webupd8

then you can install launchpad-get keys first type this

sudo apt-get update

then this

sudo apt-get install launchpad-getkeys

and finally run with this command

sudo launchpad-getkeys

finally I would run another update after the keys have been imported.

sudo apt-get update

hope this helps