copy a secret key from GnuPG's gpg-agent to OpenSSH's ssh-agent

 agent-transfer is a simple utility to extract a secret key from
 GnuPG's gpg-agent and send it to a running ssh-agent. This is useful
 for those who prefer the runtime semantics and behavior of OpenSSH's
 ssh-agent, but whose secret keys are held in long-term storage by
 GnuPG's gpg-agent.
 .
 This tool comes from the monkeysphere project.