HMAC using SHA-1: Can't concat int to bytes

Question

I need to implement hmac with sha1 using haslib.sha1.

I defined a sha1 function which instantiates a sha1object for using it for the hmac function.

Goal is a correct padding of the Key and using it for HMAC Function with SHA-1. I get an Type error when i want to concat bytes with the int to bytes.

Input Signature for hmac_sha1 should be like:

key = bytes('Test Key', 'UTF-8')

data = bytes("Test Message", 'UTF-8')

Error - Message : 

TypeError                                 Traceback (most recent call last)
Cell In[13], line 8
      4 digester = hmac.new(key, message, hashlib.sha1)
      5 signature1 = digester.digest()
      7 assert (
----> 8     hmac_sha1(b'Test Nachricht', b'Test Key')
      9     == signature1
     10 )
     12 print(f"Die Signatur ist {signature1}")

Cell In[12], line 29, in hmac_sha1(data, key)
     25 else:
     26     K_exp = key + b'\x00' * (B-len(key))
---> 29 return sha1(bxor(K_exp,OPAD) + sha1(bxor(K_exp, IPAD)+ data))

TypeError: can't concat _hashlib.HASH to bytes
  

def sha1(data):
    encoded_message = base64.b64encode(data) # Kodiere Binär-message in Base64
    sha1_object = hashlib.sha1() #Init Hash object
    sha1_object.update(encoded_message)
    print(sha1_object.hexdigest())

    return sha1_object

def hmac_sha1(data, key):
    IPAD = b'\x36'*64
    OPAD = b'\x5C'*64

    B, L = B,L = hashlib.sha1().block_size, hashlib.sha1().digest_size
    
    
    if(len(key) == B):
        K_exp = key
    
    elif len(key)> B:
        K_exp = sha1(key) + b'\x00' *(B-L)  #TODO Error wegen concat int and bytes
    
    else:
        K_exp = key + b'\x00' *(B-len(key))


    return sha1(bxor(K_exp,OPAD) + sha1(bxor(K_exp, IPAD)+ data))

I already thought of editing the sha1 function, but i think i have to change the format for concatting.

Answer 1

You need to zip your data when concatting it

import base64
import hashlib

def sha1(data):
    sha1_object = hashlib.sha1()  # Init Hash object
    sha1_object.update(data)
    return sha1_object.hexdigest()

def hmac_sha1(data, key):
    IPAD = b'\x36' * 64
    OPAD = b'\x5C' * 64
    B, L = hashlib.sha1().block_size, hashlib.sha1().digest_size
    if len(key) == B:
        K_exp = key
    elif len(key) > B:
        K_exp = sha1(key.encode()) + b'\x00' * (B - L)
    else:
        K_exp = key.encode() + b'\x00' * (B - len(key))
    return sha1(
        bytes([a ^ b for a, b in zip(K_exp, OPAD)]) + sha1(
            bytes([a ^ b for a, b in zip(K_exp, IPAD)]) + data.encode()
        )
    )