Hash sums of plugin/extension files can be found here: https://sourceforge.net/p/keepass/wiki/Integrity/.
OpenPGP Public Key
Signatures are created with the following keys:
Current (since KeePass 1.32 and 2.34):
Old (up to KeePass 1.31 and 2.33):
OpenPGP File Signatures - KeePass 1.x
OpenPGP File Signatures - Official KeePass Releases
Signatures of official KeePass releases can be found here: KeePass Release Signatures.