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diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..fb94b77 --- /dev/null +++ b/.gitignore @@ -0,0 +1,5 @@ +# .gitignore for gpg-forward-agent -*- conf -*- + +# Editor backup files +*~ +.#* @@ -0,0 +1,425 @@ +Attribution-ShareAlike 4.0 International + +======================================================================= + +Creative Commons Corporation ("Creative Commons") is not a law firm and +does not provide legal services or legal advice. Distribution of +Creative Commons public licenses does not create a lawyer-client or +other relationship. Creative Commons makes its licenses and related +information available on an "as-is" basis. Creative Commons gives no +warranties regarding its licenses, any material licensed under their +terms and conditions, or any related information. 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See the License for more details. +# +# You should have received a copy of the License along with this program. If +# not, see <https://creativecommons.org/licenses/>. + + +# This program is based on the answers to +# <https://superuser.com/questions/161973>. + + +# This program connects a GnuPG executable on a remote machine with your local +# gpg-agent instance, thereby allowing you to sign, verify, encrypt, and +# decrypt data on the remote machine without your key being present there. +# +############################################################################### +# THIS PROGRAM DOES NOT ALLOW YOU TO WORK WITH GNUPG ON AN UNTRUSTED MACHINE! # +############################################################################### +# Only use this program when you trust both the local and remote machines! +# Although your key material will never be resident on the remote machine and +# your passphrase never transmitted over the wire, the gpg executable on the +# remote machine may still MitM your message. +# +# That said, the gpg-agent is tunneled using SSH, so it should be protected +# against attacks on the wire between the two machines. +# +# Graphically, the dataflow looks something like this: +# +# remote gpg +# <---------> gpg-agent socket on remote machine +# <-[socat]-> TCP port on remote machine +# <--[SSH]--> TCP port on local machine +# <-[socat]-> gpg-agent socket on local machine +# <---------> local gpg-agent + + +# Usage: +# gpg-forward-agent target_machine [ssh_args ...] +# Hit ^C when you're ready to terminate the connection. +# +# If your connection drops (e.g., because your wi-fi fails) while the +# connection is open, there will likely be a stale socat left on the remote +# machine. You can take care of this by running +# +# sudo netstat -antpl | grep $FORWARD_PORT +# +# where $FORWARD_PORT is set below, and killing the process that comes up. + + +# Configuration +# +# Pick a port, any port. Well, not /any/ port--it should be a port over 1024, +# lest you need to run this script as root. +readonly FORWARD_PORT=39973 + + +# You shouldn't need to touch anything below this line. + +if [ $# -lt 1 ]; then + echo "usage: $0 ssh_args ..." >&2 + exit 1 +fi + +readonly gpg_sock="`echo "$GPG_AGENT_INFO" | cut -d: -f1`" +if [ -z "$gpg_sock" ] ; then + echo "No GPG agent configured - this won't work out." >&2 + exit 2 +fi + +socat TCP-LISTEN:$FORWARD_PORT,bind=localhost,fork,reuseaddr UNIX-CONNECT:$gpg_sock & +readonly local_socat=$! +trap "kill $local_socat" EXIT + +ssh -R $FORWARD_PORT:localhost:$FORWARD_PORT "$@" -tt \ + socat UNIX-LISTEN:$HOME/.gnupg/S.gpg-agent,unlink-close,unlink-early,fork,reuseaddr TCP4:localhost:$FORWARD_PORT |