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"""
Django's standard crypto functions and utilities.
"""
from __future__ import unicode_literals
import binascii
import hashlib
import hmac
import random
import struct
import time
from django.conf import settings
from django.utils import six
from django.utils.encoding import force_bytes
from django.utils.six.moves import range
# Use the system PRNG if possible
try:
random = random.SystemRandom()
using_sysrandom = True
except NotImplementedError:
import warnings
warnings.warn('A secure pseudo-random number generator is not available '
'on your system. Falling back to Mersenne Twister.')
using_sysrandom = False
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
key_salt = force_bytes(key_salt)
secret = force_bytes(secret)
# 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 = hashlib.sha1(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=force_bytes(value), digestmod=hashlib.sha1)
def get_random_string(length=12,
allowed_chars='abcdefghijklmnopqrstuvwxyz'
'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'):
"""
Returns a securely generated random string.
The default length of 12 with the a-z, A-Z, 0-9 character set returns
a 71-bit value. log_2((26+26+10)^12) =~ 71 bits
"""
if not using_sysrandom:
# This is ugly, and a hack, but it makes things better than
# the alternative of predictability. This re-seeds the PRNG
# using a value that is hard for an attacker to predict, every
# time a random string is required. This may change the
# properties of the chosen random sequence slightly, but this
# is better than absolute predictability.
random.seed(
hashlib.sha256(
("%s%s%s" % (
random.getstate(),
time.time(),
settings.SECRET_KEY)).encode('utf-8')
).digest())
return ''.join(random.choice(allowed_chars) for i in range(length))
if hasattr(hmac, "compare_digest"):
# Prefer the stdlib implementation, when available.
def constant_time_compare(val1, val2):
return hmac.compare_digest(force_bytes(val1), force_bytes(val2))
else:
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.
For the sake of simplicity, this function executes in constant time only
when the two strings have the same length. It short-circuits when they
have different lengths. Since Django only uses it to compare hashes of
known expected length, this is acceptable.
"""
if len(val1) != len(val2):
return False
result = 0
if six.PY3 and isinstance(val1, bytes) and isinstance(val2, bytes):
for x, y in zip(val1, val2):
result |= x ^ y
else:
for x, y in zip(val1, val2):
result |= ord(x) ^ ord(y)
return result == 0
def _bin_to_long(x):
"""
Convert a binary string into a long integer
This is a clever optimization for fast xor vector math
"""
return int(binascii.hexlify(x), 16)
def _long_to_bin(x, hex_format_string):
"""
Convert a long integer into a binary string.
hex_format_string is like "%020x" for padding 10 characters.
"""
return binascii.unhexlify((hex_format_string % x).encode('ascii'))
if hasattr(hashlib, "pbkdf2_hmac"):
def pbkdf2(password, salt, iterations, dklen=0, digest=None):
"""
Implements PBKDF2 with the same API as Django's existing
implementation, using the stdlib.
This is used in Python 2.7.8+ and 3.4+.
"""
if digest is None:
digest = hashlib.sha256
if not dklen:
dklen = None
password = force_bytes(password)
salt = force_bytes(salt)
return hashlib.pbkdf2_hmac(
digest().name, password, salt, iterations, dklen)
else:
def pbkdf2(password, salt, iterations, dklen=0, digest=None):
"""
Implements PBKDF2 as defined in RFC 2898, section 5.2
HMAC+SHA256 is used as the default pseudo random function.
As of 2014, 100,000 iterations was the recommended default which took
100ms on a 2.7Ghz Intel i7 with an optimized implementation. This is
probably the bare minimum for security given 1000 iterations was
recommended in 2001. This code is very well optimized for CPython and
is about five times slower than OpenSSL's implementation. Look in
django.contrib.auth.hashers for the present default, it is lower than
the recommended 100,000 because of the performance difference between
this and an optimized implementation.
"""
assert iterations > 0
if not digest:
digest = hashlib.sha256
password = force_bytes(password)
salt = force_bytes(salt)
hlen = digest().digest_size
if not dklen:
dklen = hlen
if dklen > (2 ** 32 - 1) * hlen:
raise OverflowError('dklen too big')
l = -(-dklen // hlen)
r = dklen - (l - 1) * hlen
hex_format_string = "%%0%ix" % (hlen * 2)
inner, outer = digest(), digest()
if len(password) > inner.block_size:
password = digest(password).digest()
password += b'\x00' * (inner.block_size - len(password))
inner.update(password.translate(hmac.trans_36))
outer.update(password.translate(hmac.trans_5C))
def F(i):
u = salt + struct.pack(b'>I', i)
result = 0
for j in range(int(iterations)):
dig1, dig2 = inner.copy(), outer.copy()
dig1.update(u)
dig2.update(dig1.digest())
u = dig2.digest()
result ^= _bin_to_long(u)
return _long_to_bin(result, hex_format_string)
T = [F(x) for x in range(1, l)]
return b''.join(T) + F(l)[:r]
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