$ ls /etc/apt/keyrings/
crio.gpg  kubernetes.gpg  ...

$ cat /etc/apt/sources.list.d/crio.list
deb [signed-by=/etc/apt/keyrings/crio.gpg] https://download.opensuse.org/repositories/isv:/cri-o:/stable:/v1.33/deb/ /

$ gpg --show-keys /etc/apt/keyrings/crio.gpg
pub   rsa4096 2025-02-11 [SC] [expires: 2027-04-22]
      85B67D5C50100B1AC8CEFE49CBA9C85640A2B579
uid                      isv:cri-o OBS Project <isv:cri-o@build.opensuse.org>

$ sudo apt update
Hit:1 https://prod-cdn.packages.k8s.io/repositories/isv:/kubernetes:/core:/stable:/v1.33/deb  InRelease
Hit:2 http://security.ubuntu.com/ubuntu noble-security InRelease
Hit:3 https://packages.broadcom.com/artifactory/saltproject-deb stable InRelease
Hit:4 http://us.archive.ubuntu.com/ubuntu noble InRelease
Hit:5 http://us.archive.ubuntu.com/ubuntu noble-updates InRelease
Hit:6 http://us.archive.ubuntu.com/ubuntu noble-backports InRelease
Get:7 https://download.opensuse.org/repositories/isv:/cri-o:/stable:/v1.33/deb  InRelease [1,504 B]
Err:7 https://download.opensuse.org/repositories/isv:/cri-o:/stable:/v1.33/deb  InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY CBA9C85640A2B579
Reading package lists... Done
W: GPG error: https://download.opensuse.org/repositories/isv:/cri-o:/stable:/v1.33/deb  InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY CBA9C85640A2B579
E: The repository 'https://download.opensuse.org/repositories/isv:/cri-o:/stable:/v1.33/deb  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.

$ cat /etc/os-release
PRETTY_NAME="Ubuntu 24.04.2 LTS"
NAME="Ubuntu"
VERSION_ID="24.04"
VERSION="24.04.2 LTS (Noble Numbat)"
VERSION_CODENAME=noble
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=noble
LOGO=ubuntu-logo