cryptosign: reading private ssh key is broken

Using this example but replacing a call to cryptosign.SigningKey.from_raw_key with cryptosign.SigningKey.from_ssh_key (as I had my private ssh key as a text file) fails, as there is an apparent bug out there, I narrowed it down to a simple test case below.

>>> from autobahn.wamp.cryptosign import SigningKey
>>> SigningKey.from_ssh_key('/home/om26er/.ssh/id_ed25519')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.5/dist-packages/autobahn/wamp/cryptosign.py", line 561, in from_ssh_key
    keydata, comment = _read_ssh_ed25519_privkey(keydata)
  File "/usr/local/lib/python3.5/dist-packages/autobahn/wamp/cryptosign.py", line 244, in _read_ssh_ed25519_privkey
    raise Exception('invalid OpenSSH private key (padlen={}, actual_pad={}, expected_pad={})'.format(len(pad), pad, _makepad(len(pad))))
Exception: invalid OpenSSH private key (padlen=7, actual_pad=b'\x01\x02\x03\x04\x05\x06\x07', expected_pad=)

The hack was to comment out this condition. I believe we are making some assumptions there that may not be always correct.

[sethrh]

The autobahn.wamp.cryptosign._makepad function doesn’t work properly in Python 3.

_makepad(6) returns '\x01\x02\x03\x04\x05\x06' (a str) rather than b'\x01\x02\x03\x04\x05\x06' (bytes). The str/bytes type difference causes the pad != _makepad(len(pad)) the statement to fail.

My workaround is to monkey patch it:

import autobahn.wamp.cryptosign
def _makepad_py3(size):
    return bytes(range(1, size + 1))
autobahn.wamp.cryptosign._makepad = _makepad_py3

This solution unfortunately does not work in Python2. To make it compatible with both, you’d need to do something like this:

def _makepad_py23(size): 
    ''.join([chr(x) for x in range(1, size + 1)]).encode('ascii')

(I would hope there is a cleaner-looking solution, but that seems to work.)

[oberstet]

fixed via https://github.com/crossbario/autobahn-python/pull/1543

test:

(cpy39_1) (base) oberstet@intel-nuci7:~/scm/crossbario/autobahn-python$ ssh-keygen -t ed25519 -f /tmp/id_ed25519
Generating public/private ed25519 key pair.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /tmp/id_ed25519
Your public key has been saved in /tmp/id_ed25519.pub
The key fingerprint is:
SHA256:6ce5TX9KqKZAtEVk31ktodyrfbG0OPM8iZHtLh1ox7w oberstet@intel-nuci7
The key's randomart image is:
+--[ED25519 256]--+
|       .+     oo |
|       o . o =. .|
|      . . . = .. |
|     . o .     . |
|      o S     Bo |
|     . . . . Oo*+|
|      . . + =+Oo=|
|       . ..= ==E.|
|        .oo . =*.|
+----[SHA256]-----+
(cpy39_1) (base) oberstet@intel-nuci7:~/scm/crossbario/autobahn-python$ python -c "from autobahn.wamp.cryptosign import SigningKey; SigningKey.from_ssh_key('/tmp/id_ed25519')"
(cpy39_1) (base) oberstet@intel-nuci7:~/scm/crossbario/autobahn-python$ make test_cryptosign
USE_ASYNCIO=1 trial autobahn.wamp.test.test_wamp_cryptosign
autobahn.wamp.test.test_wamp_cryptosign
  TestAuth
    test_authenticator ...                                                 [OK]
    test_testvectors ...                                                   [OK]
    test_valid ...                                                         [OK]
  TestKey
    test_key ...                                                           [OK]
    test_pad ...                                                           [OK]
    test_pubkey ...                                                        [OK]

-------------------------------------------------------------------------------
Ran 6 tests in 0.087s

PASSED (successes=6)
USE_TWISTED=1 trial autobahn.wamp.test.test_wamp_cryptosign
autobahn.wamp.test.test_wamp_cryptosign
  TestAuth
    test_authenticator ...                                                 [OK]
    test_testvectors ...                                                   [OK]
    test_valid ...                                                         [OK]
  TestKey
    test_key ...                                                           [OK]
    test_pad ...                                                           [OK]
    test_pubkey ...                                                        [OK]

-------------------------------------------------------------------------------
Ran 6 tests in 0.089s

PASSED (successes=6)
(cpy39_1) (base) oberstet@intel-nuci7:~/scm/crossbario/autobahn-python$