Python OpenSSL libraries' private key signing vs. OpenSSL's rsautl

punnel.py

#!/usr/bin/env python
from __future__ import print_function


import base64
import sys


PEM = ("""-----BEGIN RSA PRIVATE KEY-----
MIIEogIBAAKCAQEAgK1Q6Ydi8UUheJLvnTYJE65NOZtAtjDdDSxS+6b4x9EakjIylljSzs5uLEJn
kCe4f/vvQKrAKQiQdcjTM8Ea/wiS/Mj+xSGD3Sfk0BuRuYat9gpwCFY9mzyruesp6WAE5hXmsDNQ
I1sY3b2xJePnP4YWV+2oUaXn11vpOOTk7XVwnP7VfQu8PIIRHVJbZfV2C6rkCIhJrzBfa3jIe6F/
KY+dTwu5CZHiopuPsjbbSKfqhLf4f3zUBcdgUsdZCB21LoBNWvGpPZlQJ1VvXWHkwYNo1r5L35H0
7KarS8Y6D3gL29YKvtkY/UHvyuNDcwM02IUewdrHDaGiOEiUsarmyQIDAQABAoH/VPIVeBToPF5m
ujJF/IKve06VrHHRRnT7eLbKEVco5MAlyl1ZB+ebQusD0DQGKiQOqG6ogwg10uDUfO0WgBP6vmHq
pvYJOhnl8xli8/8/NDq0nLhHPTmxccmblCCqimXY1gufPrKhNLXutHOFfn31KvpZxbIea8gaRRFn
5Sc1+YueD4Bq6P/XRnQjAvAGmMTuNMbvHwX8K6JKNh6JNpPkJQ5+dXpd16ahAwYMsWaCLjTikoOb
NEhviVz22rJMw/KWCQYyIWHDaQd7QMhXdP2BUwbans7U1d+Igw6/dXf9BufM5d2IB02idTB/jFRE
6QtCb3kmBVBZdEwmPCUkqHRlAoGBALrmZGMxcY94rd922/H94hPmUlJPG1fxG+lnMAALdC7tpC73
dmlEYDdsEQW5Y9C9wSraIawxd0xtxOG90ZbZ/yMqpFZ9+5FVr3zpGrMxngDV92KLrJ2AElD/CeLB
NatNJoO+mqKuW6vX3XEZA2KqX3oTm0zhhS5nazZixmt1dAYbAoGBALBAROTLulzSh9SLFWiY3A1a
zoK7ATusesUFLeY6/K6SV4dQDT6fTDiZh2qXMir88UDCOBxCEjGGIw+sMh3iAUHBzHdi5xtAFesN
WyjfhddTQwtfRgO93P+/RgvssrhsItWqnTfAdNkO7+woSjC0eQ7fEdWsIYhWdqSW9LZowKTrAoGB
AIbUGettCc1Ec7pXlofWbTeJ2i1CoCkq6MXSCNCfcqtACEdRgfyitP6GWSlV+mnl2eo9/jioXrWm
InfvZbl7fhEye+dhbxADTlvAFeDblG5p7NMMi/P7JjuEIO+SDlOLjpNP92IQglVPnpIuR0DwQ3xf
lJM7xcYaGT/cteNjkdWtAoGBAKk5S+yRXyH4UcpUr/15pu57nYQPoSN2e3nneyZuxGWoxLl6tvzF
Xh2J62cAPH7h1ZFj6RPYrDc4nzlRD915PdOxC2wlXdfgNCs266vW0V7o5ppoo4S8KxCyycJxRTel
O90Cr2j0NDykBuAr3u/cl88bhrgtSRTqT4fAGL163lx5AoGAWiWgczL19PAIzv2WxnRmlwIexPBG
6A+KURg4/APfZOxa5rA91lKU2cQoGqgHErWhSdfZrdyNSqppAFtdB8Sgy1irkKGLBBiWOq4hfX2V
pCGks4zzBYQJ27/GnY2gbv6U6bBx2JW2zDvZZSU6ckv6eoJ2YEVMn63uzdpdwXlsTzE=
-----END RSA PRIVATE KEY-----""")


def via_cryptography(message):
    from cryptography.hazmat.primitives import serialization
    from cryptography.hazmat.backends import default_backend
    private_key = serialization.load_pem_private_key(
	PEM, password=None, backend=default_backend())
    from cryptography.hazmat.primitives import hashes
    from cryptography.hazmat.primitives.asymmetric import padding
    return private_key.sign(message, padding.PKCS1v15(), hashes.SHA1())


def via_openssl(message):
    import subprocess
    import tempfile
    with open("my-pem", "wb+") as f:
        f.write(PEM)
        f.flush()
	p = subprocess.Popen(
            "openssl rsautl -sign -inkey " + f.name,
            shell=True,
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)
    stdout, stderr = p.communicate(input=message)
    if stderr or p.returncode != 0:
        print(stderr)
    return stdout


def via_pycrypto(message):
    from Crypto.PublicKey import RSA
    from Crypto.Hash import SHA
    from Crypto.Signature import PKCS1_PSS
    rsakey = RSA.importKey(PEM)
    return rsakey.encrypt(message, None)[0]


def via_pyopenssl(message, digest="sha1"):
    import OpenSSL
    key = OpenSSL.crypto.load_privatekey(OpenSSL.crypto.FILETYPE_PEM, PEM)
    return OpenSSL.crypto.sign(key, message, digest)


def via_rsa(message):
    import rsa
    privkey = rsa.PrivateKey.load_pkcs1(PEM)
    return rsa.sign(message, privkey, "SHA-1")


def via_ruby(message):
    import subprocess
    syntax = (
        "require 'openssl'; key = OpenSSL::PKey::RSA.new('%s'); "
        "print key.private_encrypt('asdf')"
    ) % PEM
    return subprocess.check_output('ruby -e "%s"' % syntax, shell=True)


if __name__ == "__main__":
    message = "asdf"
    for each in (via_cryptography, via_openssl, via_pycrypto, via_pyopenssl,
                 via_rsa, via_ruby):
        print("Using %s:" % each.__name__)
        print(base64.b64encode(each(message)))
        print()

You're right about pycrypto. I tried using private key encryption rather than signing, and didn't revert the function back. The end result for me must authenticate against Chef, which I've managed using none of the Python libraries (my lack of any expertise is probably why): https://docs.chef.io/api_chef_server.html

Where I tried encrypt among the Python libraries, the resulting signature appears to be different each time around (e.g., rsa.encrypt(message, rsa.PrivateKey.load_pkcs1(PEM))).

I used Ruby's private_encrypt rather than sign (stolen from https://gist.github.com/gmcmillan/3184964) because it generates the same signature as openssl rsautl, which is what Chef's curl example uses: https://docs.chef.io/auth.html

Where I tried encrypt among the Python libraries, the resulting signature appears to be different each time around (e.g., rsa.encrypt(message, rsa.PrivateKey.load_pkcs1(PEM))).

That's because it uses random padding :)

To get consistent results change the openssl command to:
openssl dgst -sha1 -sign

However it seems you are looking for a way to encrypt using the python modules available