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Fixing Incus GPG Key Expiration Issues on Debian 12

ByPieter Bakker

When performing standard system updates on Debian 12 systems with Incus installed via the Zabbly repository, administrators may encounter the following error messages:

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://pkgs.zabbly.com/incus/stable bookworm InRelease: The following signatures were invalid: EXPKEYSIG 82CC8797C838DCFD Zabbly Kernel Builds <info@zabbly.com>

W: Failed to fetch https://pkgs.zabbly.com/incus/stable/dists/bookworm/InRelease The following signatures were invalid: EXPKEYSIG 82CC8797C838DCFD Zabbly Kernel Builds <info@zabbly.com>

W: Some index files failed to download. They have been ignored, or old ones used instead.

The EXPKEYSIG designation indicates that the repository’s GPG signing key has reached its expiration date, preventing APT from validating package authenticity.

Technical Analysis

Third-party repositories utilize GPG key expiration as a security mechanism to ensure ongoing key management and limit the potential impact of compromised signing keys. When a key expires, APT’s security protocols prevent repository updates until a valid key is obtained.

This behavior serves several security purposes:

  • Enforces regular key rotation practices
  • Limits exposure from potentially compromised keys
  • Ensures administrators maintain awareness of their repository sources
  • Provides an opportunity to verify continued trust in third-party sources

Resolution Procedure

The resolution involves updating the expired GPG key from the repository maintainer’s authoritative source:

wget -O /etc/apt/keyrings/zabbly.asc https://pkgs.zabbly.com/key.asc

Following key installation, standard package management operations can resume:

apt update && apt upgrade -y

Implementation Details

The wget command retrieves the current GPG key from the official Zabbly server and places it in the standardized keyring directory (/etc/apt/keyrings/). This location follows Debian’s recommended practices for third-party repository key management and ensures proper integration with APT’s security framework.

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