While we are at it - anyone knows how to verify PGP signature with just the public key and withuot creating the keyring file? All the libraries I have seen verify signatures against keyrings - but I want to store the keys in a database and making a temporary keyring with just one signature to do the verification sounds like an ugly hack.

Here is my question at stackoverflow: http://stackoverflow.com/questions/19683880/pgp-signature-ch...

Just another example of how unnecessary coupling is thwarting new uses.

Not exactly what you want, but perhaps something like this might help?

    export GNUPGHOME=/tmp/something
    gpg --verify ...
    rm -rf $GNUPGHOME
    unset GNUPGHOME