GPG...an unsupported filetype?

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1) Remove the broken keyring:

Code:

sudo rm /etc/apt/trusted.gpg.d/ayufan.key.chroot.gpg

2) Try to update:

Code:

sudo apt-get update

You will receive an error "The following signatures couldn't be verified because the public key is not available: NO_PUBKEY XXXXXXXXXXXXXXXX"
(where XXXXXXXXXXXXXXXX is the public key)

3) Add missing key to keyring:

Code:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys XXXXXXXXXXXXXXXX

(where XXXXXXXXXXXXXXXX is the public key from the error above)

4) Update again :

Code:

sudo apt-get update

This is how I solved it; but anyone more knowledgeable than me is welcome to explain in more detail, or suggest a better solution.