How to enable passphrase callback (instead of prompt) in `pygpgme`?

Question

I am writing software to retrieve encrypted files, decrypt them and populate a data lake on AWS S3 with the information contained in them on a scheduled basis. The files are encrypted with a GPG key and we are using the pygpgme (https://launchpad.net/pygpgme) package for cryptography. I am on a Mac, I have GPG 2.2.16 and pygpgme 0.3 installed.

The private key we use to decrypt the files has a passphrase.

I've tried multiple techniques/suggestions I've found online, including:

• http://www.topdog.za.net/2012/05/23/python-modules-you-should-know:-pygpgme/
• trying to change the Context().pinentry_mode parameter, which seems to not exist in my version of pygpgme
• trying to add parameters to {GNUPGHOME}/gpg.conf:
  • batch
  • use-agent

None disable the prompt.

Here is the code I use for assigning the passphrase callback:

ctx.passphrase_cb = \
        lambda uid_hint, passphrase_info, prev_was_bad, fd: os.write(
            fd, b'{}\\n'.format(EQF_PASSPHRASE)
        )

Here is my gpg.conf:

# don't prompt for a password!
batch

# Try to use the GnuPG-Agent. With this option, GnuPG first tries to connect to
# the agent before it asks for a passphrase.
use-agent

Nonetheless, I get a prompt asking for a passphrase in the command line every time I run the service. How can I make the software use the callback I provide?

Answer 1

After hours of tinkering around, I've made it work using the following configuration at {GNUPGHOME}/gpg.conf:

batch
pinentry-mode loopback

I can the use passphrase_cb in the Python code as intended.

Hope this helps!