Some time ago I’ve noticed that Skype UI on my Ubuntu machine was insisting on the need to apply updates constantly, and required message was in place in spite of running sudo apt update / sudo apt upgrade. After looking more carefully at sudo apt update output it turned out to be an issue with repository signature:
Exact error message text was the following:
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://repo.skype.com/deb stable InRelease: The following signatures were invalid: EXPKEYSIG 1F3045A5DF7587C3 Skype Linux Client Repository <firstname.lastname@example.org> W: Failed to fetch https://repo.skype.com/deb/dists/stable/InRelease The following signatures were invalid: EXPKEYSIG 1F3045A5DF7587C3 Skype Linux Client Repository <email@example.com> W: Some index files failed to download. They have been ignored, or old ones used instead.
To resolve this problem it is necessary to perform the following steps:
1) Delete incorrect signature key:
sudo apt-key del 1F3045A5DF7587C3
2) Re-add new valid key:
curl https://repo.skype.com/data/SKYPE-GPG-KEY | sudo apt-key add -
3) Re-run apt update and apt upgrade:
sudo apt update && sudo apt upgrade
That should remove Skype update errors.