RSA module throws AttributeError

[mociepka]

I don't knew that error is because of Paramiko==1.16.0 but with PyCrypto it works. I am using pycryptodome==3.3.1.

Traceback (most recent call last):
  File "build/bdist.linux-x86_64/egg/paramiko/transport.py", line 1744, in run
    self.kex_engine.parse_next(ptype, m)
  File "build/bdist.linux-x86_64/egg/paramiko/kex_group1.py", line 75, in parse_next
    return self._parse_kexdh_reply(m)
  File "build/bdist.linux-x86_64/egg/paramiko/kex_group1.py", line 111, in _parse_kexdh_reply
    self.transport._verify_key(host_key, sig)
  File "build/bdist.linux-x86_64/egg/paramiko/transport.py", line 1604, in _verify_key
    if not key.verify_ssh_sig(self.H, Message(sig)):
  File "build/bdist.linux-x86_64/egg/paramiko/rsakey.py", line 113, in verify_ssh_sig
    return rsa.verify(hash_obj, (sig,))
  File "/path_to_env/local/lib/python2.7/site-packages/pycryptodome-3.3.1-py2.7-linux-x86_64.egg/Crypto/PublicKey/RSA.py", line 123, in __getattr__
    raise AttributeError(attrname)
AttributeError: verify

[Legrandin]

Paramiko verifies RSA signatures in an insecure way and it does that by means of some old, questionable parts of the PyCrypto API (specifically, the method verify of an RSA key object).

PyCryptodome is (fortunately or unfortunately, depending on how you look at it) not 100% compatible to PyCrypto: I explicitly removed or modified those few APIs that are inherently dangerous (like the verify method).

I was considering submitting a PR to paramiko so that safer and less-error prone APIs already offered by PyCrypto are used instead (i.e. the Crypto.Signature package, which are also available in PyCryptodome). Until now though, this was not high on my priority list.

[mociepka]

Many packages can use those "old, questionable parts", maybe adding them with DeprecationWarning will be more delicate way? Or at least more verbose error NotImplementedError('Some explanation')?

I got this error using fabric. Fabric highjacks logger so at the beginning I got AttributeError: verify with trace from logging 💢 . More verbose error message would have saved me a lot of time.

[Legrandin]

That is a good point, and raising NotImplementedError when appropriate the best solution.

[rockwelln]

Waiting for a cleaner solution, to make it work with paramiko, I had to make 2 things:
in lib/Crypto/PublicKey/RSA.py:

class RsaKey(object):
    ...
    def verify(self, m, sig):
        warnings.warn("verify is deprecated on RSA key", FutureWarning)
        s, = sig[:1]
        return self._encrypt(s) == m
    ...

and in paramiko: transport.py

    def _get_cipher(self, name, key, iv):
        ...
            return self._cipher_info[name]['class'].new(key, self._cipher_info[name]['mode'], iv, counter=counter)
        ...