On 21/08/15 11:00, Peter Lebbing wrote: > Does GnuPG (or GPG-Agent in 2.1) actually check that the challenge sent > by the server is not a validly formatted OpenPGP signature or certification?
I should note that it is not possible for an SSH server to evoke a data signature from gpg-agent running as an SSH agent like this. The server only controls a minor part of the hashed data. Quickly browsing through the source code of the SSH agent code in gpg-agent, it seems it will actually sign whatever it is sent, if I read it correctly. I still don't think that's a problem because that is no different than gpg-agent itself which will also happily sign with unlocked keys, since this is actually its task. What gets sent to the agent is still under the control of the SSH client, running as the user themself. But an SSH agent is only a possible application, it seems to me the system with OpenPGP subkeys having the Authenticate flag is set up to be more broad than that. Other applications might be built in a way that the server controls all the data to be signed. Am I seeing ghosts here or should the system be more careful of sharing Authenticate with Sign/Certify? Oh, and by the way, I quickly realised after my previous message that authentication is probably always handled by the agent, not just in GnuPG v2.1. It just didn't seem to be worth a message on its own ;). Peter. -- I use the GNU Privacy Guard (GnuPG) in combination with Enigmail. You can send me encrypted mail if you want some privacy. My key is available at <http://digitalbrains.com/2012/openpgp-key-peter> _______________________________________________ Gnupg-users mailing list [email protected] http://lists.gnupg.org/mailman/listinfo/gnupg-users
