[Bug 1758071] Re: Graphical prompt (pinentry-gnome3) invoked even when connected via ssh

[karlwilbur]

In the hope that this might help someone else...

When trying to sign over SSH I was getting `Operation cancelled`:
```bash
-> % echo "test" | gpg --clearsign
gpg: using "FD2073A7" as default secret key for signing
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

test
gpg: signing failed: Operation cancelled
gpg: [stdin]: clear-sign failed: Operation cancelled
```

I'd tried `pinentry-gtk-2` (from `pinentry-gtk2`) and it didn't work for
this situation:

```bash
-> % sudo apt install pinentry-gtk2
-> % sudo update-alternatives --config pinentry
# Select option for `/usr/bin/pinentry-gtk-2`
-> % echo "test" | gpg --clearsign             
gpg: using "FD2073A7" as default secret key for signing
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

test
gpg: signing failed: Inappropriate ioctl for device
gpg: [stdin]: clear-sign failed: Inappropriate ioctl for device
```

While it didn't work, it was progress. After running `GPG_TTY=$(tty);
export GPG_TTY` it worked! But each time I connect, I need to set the
`GPG_TTY` and `update-alternatives` for `pinentry` to `/usr/bin
/pinentry-tty` or `/usr/bin/pinentry-gtk-2`. Not a good solution, but at
least it works.

(Ref: https://unix.stackexchange.com/questions/257061/gentoo-linux-gpg-
encrypts-properly-a-file-passed-through-parameter-but-
throws-i/257065#257065)

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https://bugs.launchpad.net/bugs/1758071

Title:
  Graphical prompt (pinentry-gnome3) invoked even when connected via ssh

Status in gnupg2 package in Ubuntu:
  Confirmed

Bug description:
  When I'm connected to my desktop computer via ssh, with the desktop
  computer's desktop environment running and unlocked, trying to decrypt
  a gpg-encrypted file causes gpg-agent to invoke pinentry-gnome3 on the
  desktop. Assuming I'm physically elsewhere, I'm obviously unable to
  use the prompt on the desktop to enter the passphrase.

  This happens despite both pinentry-tty and pinentry-curses being
  present on the desktop (in addition to pinentry-gnome3), and having
  GPG_TTY point to the correct tty (export GPG_TTY=$(tty)). Under these
  circumstances I'd expect gpg-agent to gracefully fall back to non-
  graphical alternatives.

  Granted, I've so far only simulated being physically elsewhere by
  first ssh'ing out of the desktop, then back in again from the other
  end. If gpg-agent is using some kind of magic to detect that in
  reality I'm still physically on the desktop, then this report is
  invalid (although I'd still feel uneasy about such magic).

  == Steps to reproduce ==
  1. log in to desktop computer A
  2. use another computer B to ssh in to the desktop computer
  3. still physically on B, invoke `gpg -d encrypted.gpg` on A (over ssh)

  == What happens ==
  Graphical passphrase prompt pops up on A, while your ssh terminal on B waits

  == What I expect to happen ==
  For a non-graphical passphrase prompt (such as pinentry-tty or pinentry-curses) to appear on B's ssh terminal

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: gpg-agent 2.2.4-1ubuntu1
  ProcVersionSignature: Ubuntu 4.15.0-12.13-generic 4.15.7
  Uname: Linux 4.15.0-12-generic x86_64
  ApportVersion: 2.20.8-0ubuntu10
  Architecture: amd64
  CurrentDesktop: ubuntu:GNOME
  Date: Thu Mar 22 16:04:09 2018
  InstallationDate: Installed on 2016-10-13 (525 days ago)
  InstallationMedia: Ubuntu-Server 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=fi_FI.UTF-8
   SHELL=/bin/bash
  SourcePackage: gnupg2
  UpgradeStatus: No upgrade log present (probably fresh install)

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