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The Gnu Pricacy Guard seems to have the default option of setting an expiry date when the signed key has such a date. My gpg key used to have such an expiry day when I went to the first keysigning parties (LinuxTag, DebConf 3). I have removed the expiry date later, but still a lot of signatures are now no longer valid: While I have signed 310 keys, my key is currently (pre-DebConf 7) only has 170 valid signatures.

Tonight I wanted to find out what keys are these exactly, and after quite some trial and error I found a way to get that data, using only “real old unix tools” such as awk, sort, join:

gpg  --list-options show-sig-expire --fixed-list-mode --with-colons --list-sigs nomeata > my-sigs-col
cat my-sigs-col |awk -F: '$1 == "sig" && $7 != "" { print }' | sort -k 5,5 -t : -u > expired
cat my-sigs-col |awk -F: '$1 == "sig" && $7 == "" { print }' | sort -k 5,5 -t : -u > non-expired
join -v 1 -t : -j 5  expired non-expired > only-expired

Maybe I will use that list some time after DebConf7 to mail all these people, asking them to remove or update the expiry date from their signature.