Running apt update on my Devuan machine today results in these:

# apt update
Get:1 https://deb.devuan.org/merged chimaera InRelease [33.9 kB]
Err:1 https://deb.devuan.org/merged chimaera InRelease
  The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
Get:2 https://deb.devuan.org/merged chimaera-security InRelease [26.5 kB]
Err:2 https://deb.devuan.org/merged chimaera-security InRelease
  The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
Get:3 https://deb.devuan.org/merged chimaera-updates InRelease [26.5 kB]
Err:3 https://deb.devuan.org/merged chimaera-updates InRelease
  The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
Fetched 86.9 kB in 1s (88.4 kB/s)
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://deb.devuan.org/merged chimaera InRelease: The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://deb.devuan.org/merged chimaera-security InRelease: The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://deb.devuan.org/merged chimaera-updates InRelease: The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
W: Failed to fetch https://deb.devuan.org/merged/dists/chimaera/InRelease  The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
W: Failed to fetch https://deb.devuan.org/merged/dists/chimaera-security/InRelease  The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
W: Failed to fetch https://deb.devuan.org/merged/dists/chimaera-updates/InRelease  The following signatures were invalid: EXPKEYSIG BB23C00C61FC752C Devuan Repository (Amprolla3 on Nemesis) <repository@devuan.org>
W: Some index files failed to download. They have been ignored, or old ones used instead.

It turns out that the keyring has been rebuilt (read post #7). More than one way to fix it - I choose this one:

rm -rf /var/lib/apt/lists/*
apt update --allow-insecure-repositories
apt install devuan-keyring --allow-unauthenticated

note: removing all in list may be overkill - maybe try removing just deb.devuan.org_merged_dists_chimaera_InRelease instead? keep in mind that some pc may still use pkgmaster.devuan.org

All is well now… and that is all I have to say about that.