Python3 and hmac . How to handle string not being binary
PythonStringPython 3.xEncodingHmacPython Problem Overview
I had a script in Python2 that was working great.
def _generate_signature(data):
return hmac.new('key', data, hashlib.sha256).hexdigest()
Where data was the output of json.dumps
.
Now, if I try to run the same kind of code in Python 3, I get the following:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.4/hmac.py", line 144, in new
return HMAC(key, msg, digestmod)
File "/usr/lib/python3.4/hmac.py", line 42, in __init__
raise TypeError("key: expected bytes or bytearray, but got %r" %type(key).__name__)
TypeError: key: expected bytes or bytearray, but got 'str'
If I try something like transforming the key to bytes like so:
bytes('key')
I get
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: string argument without an encoding
I'm still struggling to understand the encodings in Python 3.
Python Solutions
Solution 1 - Python
You can use bytes literal: b'key'
def _generate_signature(data):
return hmac.new(b'key', data, hashlib.sha256).hexdigest()
In addition to that, make sure data
is also bytes. For example, if it is read from file, you need to use binary
mode (rb
) when opening the file.
Solution 2 - Python
Not to resurrect an old question but I did want to add something I feel is missing from this answer, to which I had trouble finding an appropriate explanation/example of anywhere else:
Aquiles Carattino was pretty close with his attempt at converting the string to bytes, but was missing the second argument, the encoding of the string to be converted to bytes.
If someone would like to convert a string to bytes through some other means than static assignment (such as reading from a config file or a DB), the following should work:
(Python 3+ only, not compatible with Python 2)
import hmac, hashlib
def _generate_signature(data):
key = 'key' # Defined as a simple string.
key_bytes= bytes(key , 'latin-1') # Commonly 'latin-1' or 'ascii'
data_bytes = bytes(data, 'latin-1') # Assumes `data` is also an ascii string.
return hmac.new(key_bytes, data_bytes , hashlib.sha256).hexdigest()
print(
_generate_signature('this is my string of data')
)
Solution 3 - Python
try
> codecs.encode()
which can be used both in python2.7.12 and 3.5.2
import hashlib
import codecs
import hmac
a = "aaaaaaa"
b = "bbbbbbb"
hmac.new(codecs.encode(a), msg=codecs.encode(b), digestmod=hashlib.sha256).hexdigest()
Solution 4 - Python
for python3 this is how i solved it.
import codecs
import hmac
def _generate_signature(data):
return hmac.new(codecs.encode(key), codecs.encode(data), codecs.encode(hashlib.sha256)).hexdigest()