_fastmath error in python: HAVE_DECL_MPZ_POWM_SEC

Question

I am running python 2.6 on Red Hat 6.4

I had a script running on one machine using paramiko sftp. When I transferred it to another machine I got an exception: SFTP file has no attribute __exit__ (something along those lines).

I decided to upgrade paramiko (thought it would solve the problem) with pip. Now I am getting this the moment I run a python script:

  ...
  File "/usr/lib/python2.6/site-packages/paramiko/__init__.py", line 64, in <module>
    from transport import SecurityOptions, Transport
  File "/usr/lib/python2.6/site-packages/paramiko/transport.py", line 33, in <module>
    from paramiko import util
  File "/usr/lib/python2.6/site-packages/paramiko/util.py", line 33, in <module>
    from paramiko.common import *
  File "/usr/lib/python2.6/site-packages/paramiko/common.py", line 98, in <module>
    from Crypto import Random
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/__init__.py", line 29, in <module>
    from Crypto.Random import _UserFriendlyRNG
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/_UserFriendlyRNG.py", line 38, in <module>
    from Crypto.Random.Fortuna import FortunaAccumulator
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/Fortuna/FortunaAccumulator.py", line 39, in <module>
    import FortunaGenerator
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/Fortuna/FortunaGenerator.py", line 34, in <module>
    from Crypto.Util.number import ceil_shift, exact_log2, exact_div
  File "/usr/lib64/python2.6/site-packages/Crypto/Util/number.py", line 56, in <module>
    if _fastmath is not None and not _fastmath.HAVE_DECL_MPZ_POWM_SEC:
AttributeError: 'module' object has no attribute 'HAVE_DECL_MPZ_POWM_SEC'

So help!!

Answer 1

It seems you have a mix of PyCrypto libraries installed in your system. This bug report on the PyCrypto trackiong system seems related:

My guess is that you have the python-crypto-2.0.1 RPM installed system-wide, and you didn't have gmp-devel installed when you built & installed a later version of PyCrypto, so you'reusing a newer version of PyCrypto with an older version of _fastmath.

You may try to do as suggested: install the gmp-devel package and then PyCrypto with pip.

Answer 2

For me, the issue was that I had the python-crypto package installed via yum, and then had also installed the pycrypto module via pip.

yum remove python-crypto

worked for me.

Answer 3

This one gives better insight into the error itself.

Some developer thought it a good idea to provide a user-friendly warning about a potential security threat, but botched up the code that prints that warning.

I just replaced this:

# You need libgmp v5 or later to get mpz_powm_sec.  Warn if it's not available.
if _fastmath is not None and not _fastmath.HAVE_DECL_MPZ_POWM_SEC:
    _warn("Not using mpz_powm_sec.  You should rebuild using libgmp >= 5 to avoid timing attack vulnerability.", PowmInsecureWarning)

with this:

# You need libgmp v5 or later to get mpz_powm_sec.  Warn if it's not available.
if _fastmath is not None and not hasattr(_fastmath, 'HAVE_DECL_MPZ_POWM_SEC'):
    _warn("Not using mpz_powm_sec.  You should rebuild using libgmp >= 5 to avoid timing attack vulnerability.", PowmInsecureWarning)

in my /usr/lib64/python2.6/site-packages/Crypto/Util/number.py

It still can be done better, but if you don't care for the security threat, this will get you going.

Answer 4

If (like me) you don't have access to number.py, the following may help:

import Crypto.PublicKey._fastmath
Crypto.PublicKey._fastmath.HAVE_DECL_MPZ_POWM_SEC=False

add before to ignore the warning:

import warnings
from Crypto.pct_warnings import PowmInsecureWarning
warnings.simplefilter("ignore", PowmInsecureWarning)

Answer 5

you can find file: /usr/lib/python2.7/site-packages/Crypto/Util/number.py with content:

if _fastmath is not None and not _fastmath.HAVE_DECL_MPZ_POWM_SEC:

Then, you can annotate this line like

#if _fastmath is not None and not _fastmath.HAVE_DECL_MPZ_POWM_SEC:

and you can import paramiko