unable to do apt-update

Question

I am running kali linux (debian) with root privileges. I do a update with sudo apt-get update and I get the error below, how do I sign the ubuntu's official website in this case ? I looked for other threads, they don't provide a solution for my own platform.

Output of unsigned

┌──(root㉿kali)-[/home/kali/Desktop]
└─# sudo apt-get update
Hit:1 http://kali.download/kali kali-rolling InRelease                                        
Get:2 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]                     
Err:2 http://security.ubuntu.com/ubuntu focal-security InRelease                                         
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
Hit:3 https://cli-assets.heroku.com/channels/stable/apt ./ InRelease    
Hit:4 https://packagecloud.io/AtomEditor/atom/any any InRelease
Reading package lists... Done                                 
W: GPG error: http://security.ubuntu.com/ubuntu focal-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
E: The repository 'http://security.ubuntu.com/ubuntu focal-security InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: https://cli-assets.heroku.com/channels/stable/apt/./InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.

The error is specifically this line:

E: The repository 'http://security.ubuntu.com/ubuntu focal-security InRelease' is not signed.

Answer 1

Simple answer is you, or some application you tried to install, decided to add ubuntu's repositories to your kali system.

The issue in question ought to have broken apt the moment you added ubuntu repositories to your kali system, and one dosen't generally mix repos. Even when they're downstream, or different forks of the same base distro, there's enough specific package naming conventions that things can break.

Basically, you just inadvertantly got saved from breaking your distro. As a side note - Kali isn't meant for day to day use. If you need ubuntu packages, run ubuntu, and use kali as a pentesting and security distro ONLY, not a general purpose or development one.

A quick/sane fix would simply be to comment out or remove the ubuntu lines.

In theory a less sane fix would be to find and install the key for the repos - you can find up to date instructions here -but this is a very bad idea.