46 lines
1.4 KiB
Python
46 lines
1.4 KiB
Python
"""
|
|
Django's standard crypto functions and utilities.
|
|
"""
|
|
import hmac
|
|
|
|
from django.conf import settings
|
|
from django.utils.hashcompat import sha_constructor, sha_hmac
|
|
|
|
|
|
def salted_hmac(key_salt, value, secret=None):
|
|
"""
|
|
Returns the HMAC-SHA1 of 'value', using a key generated from key_salt and a
|
|
secret (which defaults to settings.SECRET_KEY).
|
|
|
|
A different key_salt should be passed in for every application of HMAC.
|
|
"""
|
|
if secret is None:
|
|
secret = settings.SECRET_KEY
|
|
|
|
# We need to generate a derived key from our base key. We can do this by
|
|
# passing the key_salt and our base key through a pseudo-random function and
|
|
# SHA1 works nicely.
|
|
|
|
key = sha_constructor(key_salt + secret).digest()
|
|
|
|
# If len(key_salt + secret) > sha_constructor().block_size, the above
|
|
# line is redundant and could be replaced by key = key_salt + secret, since
|
|
# the hmac module does the same thing for keys longer than the block size.
|
|
# However, we need to ensure that we *always* do this.
|
|
|
|
return hmac.new(key, msg=value, digestmod=sha_hmac)
|
|
|
|
|
|
def constant_time_compare(val1, val2):
|
|
"""
|
|
Returns True if the two strings are equal, False otherwise.
|
|
|
|
The time taken is independent of the number of characters that match.
|
|
"""
|
|
if len(val1) != len(val2):
|
|
return False
|
|
result = 0
|
|
for x, y in zip(val1, val2):
|
|
result |= ord(x) ^ ord(y)
|
|
return result == 0
|