Unable to use specific EC_KEY operations from 'cryptography' packages openssl backend

Question

I am trying to use the EC arithmetic operations in OpenSSL by using the cryptography python package's default_backend.

I need to perform point multiplication, addition, etc. on the public keys that cryptography uses. I am not familiar with the OpenSSL API at all, so I found this old repository which tries to do exactly what I need to do: https://github.com/tuxxy/hazmat-math

Unfortunately, the repo above is dead and the author inactive so I don't expect an answer from them, hence my question.

Unfortunately, when I try to execute the following code

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric import ec, utils
from hazmat_math import operations as ops

nist256 = ec.SECP256R1()
priv = ec.generate_private_key(nist256, default_backend())
pub = priv.public_key()

pub2 = ops.EC_POINT_MUL(pub, priv)

I get the following error:

Traceback (most recent call last):
  File "/home/gidavid/Documents/eVoting/test_bench/test_arithmetic.py", line 11, in <module>
    pub2 = ops.EC_POINT_MUL(pub, priv)
  File "/home/gidavid/Documents/eVoting/test_bench/venv/lib/python3.8/site-packages/hazmat_math/operations.py", line 190, in EC_POINT_MUL
    return _point_to_public_key(backend, group, prod)
  File "/home/gidavid/Documents/eVoting/test_bench/venv/lib/python3.8/site-packages/hazmat_math/utils.py", line 53, in _point_to_public_key
    res = backend._lib.EC_KEY_set_group(ec_key, group)
AttributeError: module 'lib' has no attribute 'EC_KEY_set_group'

I suspected this might be to do with OpenSSL version as the EC_KEY_set_group function was deprecated in v3.0.0 as per the documentation https://www.openssl.org/docs/man3.0/man3/EC_KEY_set_public_key.html However, opening a Python shell and getting the OpenSSL version number returns:

>>> import ssl
>>> ssl.OPENSSL_VERSION
'OpenSSL 1.1.1f  31 Mar 2020'

Attempting to discern if the cryptography library is somehow using a different version of OpenSSL than my Python installation:

>>> from cryptography.hazmat.backends import default_backend
>>> d = default_backend()
>>> d._binding.lib.CRYPTOGRAPHY_OPENSSL_300_OR_GREATER
1

which implies it is in fact 3.0.0 or greater, and therefore the function is deprecated.

This leaves me with two options by my reckoning:

Try and track down the OpenSSL installation used by the cryptography package and mess with it so that I can use deprecated functions
Try and revert it to an earlier openssl version
Take a completely different approach to getting constant time point multiplication on EC curves

Any input is greatly appreciated

Unable to use specific EC_KEY operations from 'cryptography' packages openssl backend

0 Answers0