How to perform symmetric encryption with gpgme in python?

Question

I'm trying to implement symmetric encryption using python's wrapper to gpgme, pygpgme. Unfortunately I'm using gpg 2.0.22 and gpg-agent 2.0.22. This mailing list post says that the passphrase callback is ignored in 2.0, which is the issue I'm running in to.

When I run the following code, I always get an error saying 'Bad passphrase', but I'm not even prompted for one. Ideally though I'd like to be able to supply the passphrase on behalf of the user:

import gpgme

def passphrase_cb(uid_hint, passphrase_info, prev_was_bad, fd):
    print "Entered passphrase_cb"
    print "uid_hint=%s passphrase_info=%s" % (uid_hint, passphrase_info)

def main():
    ctx = gpgme.Context()
    ctx.armor = False
    ctx.passphrase_cb = passphrase_cb
    ctx.set_engine_info(gpgme.PROTOCOL_OpenPGP, "/usr/local/bin/gpg",
                        "/Users/me/Library/Application Support/temp/test")

    input_path = "/tmp/input.pdf"
    enc_output_path = "/tmp/output.pdf.gpg"

    with open(input_path, 'rb') as input:
        with open(enc_output_path, 'wb') as enc_output:
            res = ctx.encrypt(None,
                              gpgme.ENCRYPT_ALWAYS_TRUST,
                              input,
                              enc_output)

passphrase_cb is never called.

How can I supply a passphrase so I can perform symmetric encryption?

Answer 1

Well it's not so important. I'll just shell out to the gpg binary for symmetric crypto. I found this answer useful.