Replicating request to Chef with Python RSA

Question

Goal: I need a Python 3 wrapper for Chef's REST API. Because its Python-3, PyChef is out of the question.

Problem: I am trying to replicate the Chef request with Python RSA. But the wrapper results in an error message: "Invalid signature for user or client 'XXX'".

I approached the wrapper by trying to replicate the cURL script shown in Chef Authentication and Authorization with cURL using a Python RSA package: RSA Signing and verification.

Here's my rewrite. It could be simpler but I started getting paranoid about line breaks and headers order, so added a few unnecessary things:

import base64
import hashlib
import datetime
import rsa
import requests
import os
from collections import OrderedDict

body = ""
path = "/nodes"
client_name = "anton"
client_key = "/Users/velvetbaldmime/.chef/anton.pem"
# client_pub_key = "/Users/velvetbaldmime/.chef/anton.pub"

hashed_body = base64.b64encode(hashlib.sha1(body.encode()).digest()).decode("ASCII")
hashed_path = base64.b64encode(hashlib.sha1(path.encode()).digest()).decode("ASCII")
timestamp = datetime.datetime.now().strftime("%Y-%m-%dT%H:%M:%SZ")
canonical_request = 'Method:GET\\nHashed Path:{hashed_path}\\nX-Ops-Content-Hash:{hashed_body}\\nX-Ops-Timestamp:{timestamp}\\nX-Ops-UserId:{client_name}'
canonical_request = canonical_request.format(
    hashed_body=hashed_body, hashed_path=hashed_path, timestamp=timestamp, client_name=client_name)
headers = "X-Ops-Timestamp:{timestamp}\nX-Ops-Userid:{client_name}\nX-Chef-Version:0.10.4\nAccept:application/json\nX-Ops-Content-Hash:{hashed_body}\nX-Ops-Sign:version=1.0"
headers = headers.format(
    hashed_body=hashed_body, hashed_path=hashed_path, timestamp=timestamp, client_name=client_name)

headers = OrderedDict((a.split(":", 2)[0], a.split(":", 2)[1]) for a in headers.split("\n"))

headers["X-Ops-Timestamp"] = timestamp

with open(client_key, 'rb') as privatefile:
    keydata = privatefile.read()
    privkey = rsa.PrivateKey.load_pkcs1(keydata)

with open("pubkey.pem", 'rb') as pubfile:
    keydata = pubfile.read()
    pubkey = rsa.PublicKey.load_pkcs1_openssl_pem(keydata)

signed_request = base64.b64encode(rsa.sign(canonical_request.encode(), privkey, "SHA-1"))
dummy_sign = base64.b64encode(rsa.sign("hello".encode(), privkey, "SHA-1"))

print(dummy_sign)

def chunks(l, n):
    n = max(1, n)
    return [l[i:i + n] for i in range(0, len(l), n)]

auth_headers = OrderedDict(("X-Ops-Authorization-{0}".format(i+1), chunk) for i, chunk in enumerate(chunks(signed_request, 60)))

all_headers = OrderedDict(headers)
all_headers.update(auth_headers)

# print('curl '+' \\\n'.join("-H {0}: {1}".format(i[0], i[1]) for i in all_headers.items())+" \\\nhttps://chef.local/nodes")

print(requests.get("https://chef.local"+path, headers=all_headers).text)

At each step I tried to check if the variables have the same result as their counterparts in the curl script.

The problem seems to be at signing stage - there's an obvious discrepancy between the output of python's packages and my mac's openssl tools. Due to this discrepancy, Chef returns {"error":["Invalid signature for user or client 'anton'"]}. Curl script with the same values and keys works fine.

dummy_sign = base64.b64encode(rsa.sign("hello".encode(), privkey, "SHA-1")) from Python has the value of

N7QSZRD495vV9cC35vQsDyxfOvbMN3TcnU78in911R54IwhzPUKnJTdFZ4D/KpzyTVmVBPoR4nY5um9QVcihhqTJQKy+oPF+8w61HyR7YyXZRqmx6sjiJRffC4uOGb5Wjot8csAuRSeUuHaNTl6HCcfRKnwUZnB7SctKoK6fXv0skWN2CzV9CjfHByct3oiy/xAdTz6IB+fLIwSQUf1k7lJ4/CmLJLP/Gu/qALkvWOYDAKxmavv3vYX/kNhzApKgTYPMw6l5k1aDJGRVm9Ch/BNQbg1WfZiT6LK+m4KAMFbTORfEH45KGWBCj9zsyETyMCAtUycebjqMujMqEwzv7w==

while the output of echo -n "hello" | openssl rsautl -sign -inkey ~/.chef/anton.pem | openssl enc -base64 is

WfoASF1f5DPT3CVPlWDrIiTwuEnjr5yCV+WIlbQLFmwm3nfhIqfTPLyTM56SwTSg
CKdboVU4EBFxC3RsU2aPpELqRH6+Fnl2Tl273vo6kLzvC/8+tUBTdNZdzSPhx6S8
x+6wzVFXsd3QeGAWoHkEgTKodSByFzARnZFxO2JzUe4dnygijwruHdf9S4ldrRo6
eaShwaxuNzM0cIl+Umz5iym3cCD6GFL13njmXZs3cHRLesBtLKA7pNxJ1UDf2WN2
OK09aK+bHaM4jl5HeQ2SdNzBQIKvyDcxX4Divnf2I/0tzD16J6BEMGCfTfsI2f3K
TVGulq81+sH9zo8lGnpDrw==

I couldn't find the information on default hashing algorithm in openssl for rsautl, but I guess it's SHA-1.

At this point I don't really know which way to look, hope anyone can help make it right.

Answer 1

From Chef Authentication and Authorization with cURL,

timestamp=$(date -u "+%Y-%m-%dT%H:%M:%SZ")  

time is in UTC, so in Python, it has to be

timestamp = datetime.datetime.now(datetime.timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")  

openssl equivalent of Python,

dummy_sign = base64.b64encode(rsa.sign("hello".encode(), privkey, "SHA-1"))  

is

echo -n hello|openssl dgst -sha1 -sign ~/.chef/anton.pem -keyform PEM|openssl enc -base64

In Python code, you're signing the message digest, SHA-1, of the message. That's called detached signature.

echo -n "hello" | openssl rsautl -sign -inkey ~/.chef/anton.pem | openssl enc -base64 but this one signs the whole message, without making digest.

Python rsa module has no equivalent of openssl rsautl -sign. So I defined a function to fill that space.

from rsa import common, transform, core, varblock
from rsa.pkcs1 import _pad_for_signing

def pure_sign(message, priv_key):
    '''Signs the message with the private key.

    :param message: the message to sign. Can be an 8-bit string or a file-like
        object. If ``message`` has a ``read()`` method, it is assumed to be a
        file-like object.
    :param priv_key: the :py:class:`rsa.PrivateKey` to sign with
    :return: a message signature block.
    :raise OverflowError: if the private key is too small to contain the
        requested hash.

    '''

    keylength = common.byte_size(priv_key.n)
    padded = _pad_for_signing(message, keylength)

    payload = transform.bytes2int(padded)
    encrypted = core.encrypt_int(payload, priv_key.d, priv_key.n)
    block = transform.int2bytes(encrypted, keylength)

    return block

Test;
openssl

echo -n hello|openssl rsautl -sign -inkey .chef/anton.pem |base64  

foIy6HVpfIpNk4hMYg8YWCEZwZ7w4Qexr6KXDbJ7/vr5Jym56joofkn1qUak57iSercqQ1xqBsIT
fo6bDs2suYUKu15nj3FRQ54+LcVKjDrUUEyl2kfJgVtXLsdhzYj1SBFJZnbz32irVMVytARWQusy
b2f2GQKLTogGhCywFFyhw5YpAHmKc2CQIHw+SsVngcPrmVAAtvCZQRNV5zR61ICipckNEXnya8/J
Ga34ntyELxWDradY74726OlJSgszpHbAOMK02C4yx7OU32GWlPlsZBUGAqS5Tu4MSjlD1f/eQBsF
x/pn8deP4yuR1294DTP7dsZ9ml64ZlcIlg==

Python

base64.b64encode(pure_sign.pure_sign(b'hello',prik)).decode()

'foIy6HVpfIpNk4hMYg8YWCEZwZ7w4Qexr6KXDbJ7/vr5Jym56joofkn1qUak57iSercqQ1xqBsITfo6bDs2suYUKu15nj3FRQ54+LcVKjDrUUEyl2kfJgVtXLsdhzYj1SBFJZnbz32irVMVytARWQusyb2f2GQKLTogGhCywFFyhw5YpAHmKc2CQIHw+SsVngcPrmVAAtvCZQRNV5zR61ICipckNEXnya8/JGa34ntyELxWDradY74726OlJSgszpHbAOMK02C4yx7OU32GWlPlsZBUGAqS5Tu4MSjlD1f/eQBsFx/pn8deP4yuR1294DTP7dsZ9ml64ZlcIlg=='

Change the line;

signed_request = base64.b64encode(rsa.sign(canonical_request.encode(), privkey, "SHA-1"))

to

signed_request = base64.b64encode(pure_sign(canonical_request.encode(), privkey))

Answer 2

I recently wrote a chef client library for python 2.7 & 3.x, built on top of pyca/cryptography and requests. It includes built-in support for Chef's authentication protocol:

https://github.com/samstav/okchef

>>> import chef
>>>
>>> client = chef.ChefClient('https://api.opscode.com')
>>> client.authenticate('chef-user', '~/chef-user.pem')
>>> response = client.get('/users/chef-user')
>>> print(response.json())
{'display_name': 'chef-user',
 'email': 'chef-user@example.com',
 'first_name': 'Chef',
 'last_name': 'User',
 'middle_name': '',
 'public_key': '-----BEGIN PUBLIC KEY-----\nMIIBIj...IDAQAB\n-----END PUBLIC KEY-----\n',
 'username': 'chef-user'}

I created a separate repository for the code which handles the rsa/authentication bits:

https://github.com/samstav/requests-chef

The nuts and bolts for the auth implementation are in this file:

https://github.com/samstav/requests-chef/blob/master/requests_chef/mixlib_auth.py

Answer 3

You may automate your interaction with Chef - using these tools:

• mechanize
• urllib2
• requests
• scrapy
• selenium

Note:

As jww commented, the OP mentioned that he doesn't want to use Selenium.
However, I wanted my answer to be complete (it may be used by others (including me) besides the OP), I included Selenium in the list.