Release top of distribution archive description and integrity information
Release.gpg top of distribution signature file for the "Release" file signed with the archive key
If all that fails, you can download and import the key manually:
curl 'http://pgp.surfnet.nl:11371/pks/lookup?op=get&search=0x38DBBDC86092693E' > gregkh.key
gpg --import gregkh.key