gnupg: display digest of key How can I display what digest algorithm has a key? If I import a public key which has MD5 as digest, I get a warning about this weak algorith. But how can I check, what digest algorithms all my keys use in my keyring?
You can use gpg --list-packets [keyfile] to see a list of all packets and their contents. All hash algorithms have numbers which you can look up in section 9.4 of RFC 4880, "Hash Algorithms".

Alternatively, use pgpdump [keyfile] to create a similar output, but already containing the algorithm names instead of their numeric identifiers.