Python HMAC hashed value encoding to base64

Question

I am trying to make a twitter auth with the help of django middleware, where I calculate the signature of a request like this (https://dev.twitter.com/oauth/overview/creating-signatures):

    key = b"MY_KEY&"
    raw_init = "POST" + "&" + quote("https://api.twitter.com/1.1/oauth/request_token", safe='')

    raw_params = <some_params>
    raw_params = quote(raw_params, safe='')

    #byte encoding for HMAC, otherwise it returns "expected bytes or bytearray, but got 'str'"
    raw_final = bytes(raw_init + "&" + raw_params, encoding='utf-8')

    hashed = hmac.new(key, raw_final, sha1)

    request.raw_final = hashed

    # here are my problems: I need a base64 encoded string, but get the error "'bytes' object has no attribute 'encode'"
    request.auth_header = hashed.digest().encode("base64").rstrip('\n')

As you can see, there is no way to base64 encode a 'bytes' object.

The proposed solution was here: Implementaion HMAC-SHA1 in python

@Jean-FrançoisFabre why would I encode raw_final? I need a HMAC object converted to base64 string... All of this according to twitter documentation - dev.twitter.com/oauth/overview/creating-signatures at the very bottom of the page — massive_dynamic
– massive_dynamic, Commented Aug 26, 2016 at 9:54

Jean-François Fabre · Accepted Answer · 2021-04-20 21:26:17Z

The trick is to use base64 module directly instead of str/byte encoding, which supports binary.

You can fit it like this (untested in your context, should work):

import base64
#byte encoding for HMAC, otherwise it returns "expected bytes or bytearray, but got 'str'"
raw_final = bytes(raw_init + "&" + raw_params, encoding='utf-8')

hashed = hmac.new(key, raw_final, sha1)

request.raw_final = hashed

# here directly use base64 module, and since it returns bytes, just decode it
request.auth_header = base64.b64encode(hashed.digest()).decode()

For test purposes, find below a standalone, working example (python 3 compatible, Python 2.x users have to remove the "ascii" parameter when creating the bytes string.):

from hashlib import sha1
import hmac
import base64

# key = CONSUMER_SECRET& #If you dont have a token yet
key = bytes("CONSUMER_SECRET&TOKEN_SECRET","ascii")


# The Base String as specified here:
raw = bytes("BASE_STRING","ascii") # as specified by oauth

hashed = hmac.new(key, raw, sha1)

print(base64.b64encode(hashed.digest()).decode())

result:

Rh3xUffks487KzXXTc3n7+Hna6o=

PS: the answer you linked to does not work anymore with Python 3. It's python 2 only.

Sahil · Accepted Answer · 2021-04-20 20:27:08Z

1

Just thought I'd adjust the answer for Python3.

from hashlib import sha512
import hmac
import base64


key = b"KEY"
path = b"WHAT YOU WANT TO BE SIGNED"

hashed = hmac.new(key, path, sha512).digest()

print(base64.b64encode(hashed))

answered Apr 20, 2021 at 20:27

Sahil

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