When running apt update on Debian systems with Google Cloud SDK repository configured, you might encounter this signature verification error:

Err:19 https://packages.cloud.google.com/apt cloud-sdk InRelease
  The following signatures couldn't be verified because the public key is not available: 
  NO_PUBKEY B53DC80D13EDEF05 NO_PUBKEY FEEA9169307EA071

This occurs because your system lacks the GPG keys required to verify packages from Google's repository.

The most straightforward fix is to import the missing GPG keys:

sudo apt-get install -y apt-transport-https ca-certificates gnupg
curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -

After this, run sudo apt update again and the error should be resolved.

If the above doesn't work, try manually importing each missing key:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B53DC80D13EDEF05 FEEA9169307EA071

Check that the keys are properly installed with:

apt-key list | grep -A1 Google

You should see output similar to:

pub   rsa4096 2016-04-12 [SCEA]
      EB4C 1BFD 4F04 2F6D DDCC  EC91 7721 F63B D38B 4796
uid           [ unknown] Google Inc. (Linux Packages Signing Authority) 

For new Google Cloud SDK installations, always include the key import step:

echo "deb [signed-by=/usr/share/keyrings/cloud.google.gpg] https://packages.cloud.google.com/apt cloud-sdk main" | sudo tee -a /etc/apt/sources.list.d/google-cloud-sdk.list
curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/cloud.google.gpg

---

When running apt update on Debian systems with Google Cloud SDK repository configured, you might encounter this signature verification error:

Err:19 https://packages.cloud.google.com/apt cloud-sdk InRelease
  The following signatures couldn't be verified because the public key is not available: 
  NO_PUBKEY B53DC80D13EDEF05 NO_PUBKEY FEEA9169307EA071

The error occurs because your system doesn't have the GPG keys needed to verify packages from Google's repository. Package managers like APT use cryptographic signatures to ensure package authenticity.

The most straightforward solution is to import the missing keys manually:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B53DC80D13EDEF05 FEEA9169307EA071

After importing, run:

sudo apt update

For systems where apt-key might be deprecated (Debian 11+), use this approach:

curl -fsSL https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/cloud.google.gpg

Then ensure your repository definition in /etc/apt/sources.list.d/google-cloud-sdk.list uses the keyring:

deb [signed-by=/usr/share/keyrings/cloud.google.gpg] https://packages.cloud.google.com/apt cloud-sdk main

After applying either solution, verify the keys are properly installed:

apt-key list | grep -A1 "Google Cloud"

Or for newer systems:

gpg --list-keys --keyring /usr/share/keyrings/cloud.google.gpg

If problems persist, try these additional steps:

# Clear the package cache
sudo apt clean
sudo rm -rf /var/lib/apt/lists/*

# Reinstall Google Cloud SDK repository
sudo rm /etc/apt/sources.list.d/google-cloud-sdk.list
sudo apt-add-repository "deb https://packages.cloud.google.com/apt cloud-sdk main"

# Full system update
sudo apt update && sudo apt upgrade -y

To avoid similar issues in the future:

• Regularly update your keyring: sudo apt-key update
• Consider using keyring files instead of global key storage
• Always verify repository URLs before adding them