When trying `emerge --sync` on a box behind a Tor transparent proxy it tries to import some GPG keys from keyservers. However, this fails with an ambiguous error 'server indicated a failure'
I believe the error is caused by sks-keyservers.net blocking Tor exits. One solution would be that I manually import keys. I can't find an option to disable automatic refetching so it skips this step, uses manually imported keys and does GPG verification.
At the moment all I can do to update the system is turn off verification entirely. This is bad because, as pointed out, I am behind Tor exits which might be bad.
Maybe a duplicate of bug 648586.
For bug 648586, the underlying issue related to gnupg dirmngr interaction with DNS handling of SRV records is tracked by https://dev.gnupg.org/T3517. You need to verify the behavior of your DNS server, as discussed there.