How to extract the original data from a non detached binary gnupg signature with python?

Question

How do i get original data from a not detached binary signature?

import gnupg

gpg = gnupg.GPG(gnupghome='/tmp/testGPG')

params = {
 'Key-Type': 'DSA',
 'Key-Length': 1024,
 'Name-Real' : 'Real Name',
 'Expire-Date': 0,
}
cmd = gpg.gen_key_input(**params)
gpg.gen_key(cmd)

data = str.encode('To be signed')

sig = gpg.sign(data, detach=False, binary=True)

res = gpg.verify(sig.data)

print(res.data)

I'd expect res.data to be equal to orig_data but it is just b''

Answer 1

The easiest way is to "decrypt" that data. I just tried this in my ipython shell:

In [18]: gpg.import_keys(private_key).count
Out[18]: 1

In [19]: signature = gpg.sign("Some data to sign")

In [20]: gpg.decrypt(signature.data).data
Out[20]: b'Some data to sign\n'

---

Please note that the snippet you provided does not work for me. GPG complains that it can not generate a key:

[GNUPG:] PINENTRY_LAUNCHED 9678 curses:curses 1.0.0 ? ? ?
gpg: DBG: chan_3 -> END
gpg: DBG: chan_3 <- ERR 83918950 Inappropriate ioctl for device <Pinentry>
gpg: agent_genkey failed: Inappropriate ioctl for device
gpg: key generation failed: Inappropriate ioctl for device

This does not make your code fail and produces empty signature!

Maybe this is my local issue. But always make sure that your key generation / key import procedure succeed before you start signing/verifying your data! Otherwise you might get a weird state or expose sensitive information.