django/contrib/auth/hashers.py
import base64
import binascii
import functools
import hashlib
import importlib
import math
import warnings
from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.core.signals import setting_changed
from django.dispatch import receiver
from django.utils.crypto import (
RANDOM_STRING_CHARS,
constant_time_compare,
get_random_string,
pbkdf2,
)
from django.utils.module_loading import import_string
from django.utils.translation import gettext_noop as _
UNUSABLE_PASSWORD_PREFIX = "!" # This will never be a valid encoded hash
UNUSABLE_PASSWORD_SUFFIX_LENGTH = (
40 # number of random chars to add after UNUSABLE_PASSWORD_PREFIX
)
def is_password_usable(encoded):
"""
Return True if this password wasn't generated by
User.set_unusable_password(), i.e. make_password(None).
"""
return encoded is None or not encoded.startswith(UNUSABLE_PASSWORD_PREFIX)
def verify_password(password, encoded, preferred="default"):
"""
Return two booleans. The first is whether the raw password matches the
three part encoded digest, and the second whether to regenerate the
password.
"""
if password is None or not is_password_usable(encoded):
return False, False
preferred = get_hasher(preferred)
try:
hasher = identify_hasher(encoded)
except ValueError:
# encoded is gibberish or uses a hasher that's no longer installed.
return False, False
hasher_changed = hasher.algorithm != preferred.algorithm
must_update = hasher_changed or preferred.must_update(encoded)
is_correct = hasher.verify(password, encoded)
# If the hasher didn't change (we don't protect against enumeration if it
# does) and the password should get updated, try to close the timing gap
# between the work factor of the current encoded password and the default
# work factor.
if not is_correct and not hasher_changed and must_update:
hasher.harden_runtime(password, encoded)
return is_correct, must_update
def check_password(password, encoded, setter=None, preferred="default"):
"""
Return a boolean of whether the raw password matches the three part encoded
digest.
If setter is specified, it'll be called when you need to regenerate the
password.
"""
is_correct, must_update = verify_password(password, encoded, preferred=preferred)
if setter and is_correct and must_update:
setter(password)
return is_correct
async def acheck_password(password, encoded, setter=None, preferred="default"):
"""See check_password()."""
is_correct, must_update = verify_password(password, encoded, preferred=preferred)
if setter and is_correct and must_update:
await setter(password)
return is_correct
def make_password(password, salt=None, hasher="default"):
"""
Turn a plain-text password into a hash for database storage
Same as encode() but generate a new random salt. If password is None then
return a concatenation of UNUSABLE_PASSWORD_PREFIX and a random string,
which disallows logins. Additional random string reduces chances of gaining
access to staff or superuser accounts. See ticket #20079 for more info.
"""
if password is None:
return UNUSABLE_PASSWORD_PREFIX + get_random_string(
UNUSABLE_PASSWORD_SUFFIX_LENGTH
)
if not isinstance(password, (bytes, str)):
raise TypeError(
"Password must be a string or bytes, got %s." % type(password).__qualname__
)
hasher = get_hasher(hasher)
salt = salt or hasher.salt()
return hasher.encode(password, salt)
@functools.lru_cache
def get_hashers():
hashers = []
for hasher_path in settings.PASSWORD_HASHERS:
hasher_cls = import_string(hasher_path)
hasher = hasher_cls()
if not getattr(hasher, "algorithm"):
raise ImproperlyConfigured(
"hasher doesn't specify an algorithm name: %s" % hasher_path
)
hashers.append(hasher)
return hashers
@functools.lru_cache
def get_hashers_by_algorithm():
return {hasher.algorithm: hasher for hasher in get_hashers()}
@receiver(setting_changed)
def reset_hashers(*, setting, **kwargs):
if setting == "PASSWORD_HASHERS":
get_hashers.cache_clear()
get_hashers_by_algorithm.cache_clear()
def get_hasher(algorithm="default"):
"""
Return an instance of a loaded password hasher.
If algorithm is 'default', return the default hasher. Lazily import hashers
specified in the project's settings file if needed.
"""
if hasattr(algorithm, "algorithm"):
return algorithm
elif algorithm == "default":
return get_hashers()[0]
else:
hashers = get_hashers_by_algorithm()
try:
return hashers[algorithm]
except KeyError:
raise ValueError(
"Unknown password hashing algorithm '%s'. "
"Did you specify it in the PASSWORD_HASHERS "
"setting?" % algorithm
)
def identify_hasher(encoded):
"""
Return an instance of a loaded password hasher.
Identify hasher algorithm by examining encoded hash, and call
get_hasher() to return hasher. Raise ValueError if
algorithm cannot be identified, or if hasher is not loaded.
"""
# Ancient versions of Django created plain MD5 passwords and accepted
# MD5 passwords with an empty salt.
if (len(encoded) == 32 and "$" not in encoded) or (
len(encoded) == 37 and encoded.startswith("md5$$")
):
algorithm = "unsalted_md5"
# Ancient versions of Django accepted SHA1 passwords with an empty salt.
elif len(encoded) == 46 and encoded.startswith("sha1$$"):
algorithm = "unsalted_sha1"
else:
algorithm = encoded.split("$", 1)[0]
return get_hasher(algorithm)
def mask_hash(hash, show=6, char="*"):
"""
Return the given hash, with only the first ``show`` number shown. The
rest are masked with ``char`` for security reasons.
"""
masked = hash[:show]
masked += char * len(hash[show:])
return masked
def must_update_salt(salt, expected_entropy):
# Each character in the salt provides log_2(len(alphabet)) bits of entropy.
return len(salt) * math.log2(len(RANDOM_STRING_CHARS)) < expected_entropy
class BasePasswordHasher:
"""
Abstract base class for password hashers
When creating your own hasher, you need to override algorithm,
verify(), encode() and safe_summary().
PasswordHasher objects are immutable.
"""
algorithm = None
library = None
salt_entropy = 128
def _load_library(self):
if self.library is not None:
if isinstance(self.library, (tuple, list)):
name, mod_path = self.library
else:
mod_path = self.library
try:
module = importlib.import_module(mod_path)
except ImportError as e:
raise ValueError(
"Couldn't load %r algorithm library: %s"
% (self.__class__.__name__, e)
)
return module
raise ValueError(
"Hasher %r doesn't specify a library attribute" % self.__class__.__name__
)
def salt(self):
"""
Generate a cryptographically secure nonce salt in ASCII with an entropy
of at least `salt_entropy` bits.
"""
# Each character in the salt provides
# log_2(len(alphabet)) bits of entropy.
char_count = math.ceil(self.salt_entropy / math.log2(len(RANDOM_STRING_CHARS)))
return get_random_string(char_count, allowed_chars=RANDOM_STRING_CHARS)
def verify(self, password, encoded):
"""Check if the given password is correct."""
raise NotImplementedError(
"subclasses of BasePasswordHasher must provide a verify() method"
)
def _check_encode_args(self, password, salt):
if password is None:
raise TypeError("password must be provided.")
if not salt or "$" in salt:
raise ValueError("salt must be provided and cannot contain $.")
def encode(self, password, salt):
"""
Create an encoded database value.
The result is normally formatted as "algorithm$salt$hash" and
must be fewer than 128 characters.
"""
raise NotImplementedError(
"subclasses of BasePasswordHasher must provide an encode() method"
)
def decode(self, encoded):
"""
Return a decoded database value.
The result is a dictionary and should contain `algorithm`, `hash`, and
`salt`. Extra keys can be algorithm specific like `iterations` or
`work_factor`.
"""
raise NotImplementedError(
"subclasses of BasePasswordHasher must provide a decode() method."
)
def safe_summary(self, encoded):
"""
Return a summary of safe values.
The result is a dictionary and will be used where the password field
must be displayed to construct a safe representation of the password.
"""
raise NotImplementedError(
"subclasses of BasePasswordHasher must provide a safe_summary() method"
)
def must_update(self, encoded):
return False
def harden_runtime(self, password, encoded):
"""
Bridge the runtime gap between the work factor supplied in `encoded`
and the work factor suggested by this hasher.
Taking PBKDF2 as an example, if `encoded` contains 20000 iterations and
`self.iterations` is 30000, this method should run password through
another 10000 iterations of PBKDF2. Similar approaches should exist
for any hasher that has a work factor. If not, this method should be
defined as a no-op to silence the warning.
"""
warnings.warn(
"subclasses of BasePasswordHasher should provide a harden_runtime() method"
)
class PBKDF2PasswordHasher(BasePasswordHasher):
"""
Secure password hashing using the PBKDF2 algorithm (recommended)
Configured to use PBKDF2 + HMAC + SHA256.
The result is a 64 byte binary string. Iterations may be changed
safely but you must rename the algorithm if you change SHA256.
"""
algorithm = "pbkdf2_sha256"
iterations = 870000
digest = hashlib.sha256
def encode(self, password, salt, iterations=None):
self._check_encode_args(password, salt)
iterations = iterations or self.iterations
hash = pbkdf2(password, salt, iterations, digest=self.digest)
hash = base64.b64encode(hash).decode("ascii").strip()
return "%s$%d$%s$%s" % (self.algorithm, iterations, salt, hash)
def decode(self, encoded):
algorithm, iterations, salt, hash = encoded.split("$", 3)
assert algorithm == self.algorithm
return {
"algorithm": algorithm,
"hash": hash,
"iterations": int(iterations),
"salt": salt,
}
def verify(self, password, encoded):
decoded = self.decode(encoded)
encoded_2 = self.encode(password, decoded["salt"], decoded["iterations"])
return constant_time_compare(encoded, encoded_2)
def safe_summary(self, encoded):
decoded = self.decode(encoded)
return {
_("algorithm"): decoded["algorithm"],
_("iterations"): decoded["iterations"],
_("salt"): mask_hash(decoded["salt"]),
_("hash"): mask_hash(decoded["hash"]),
}
def must_update(self, encoded):
decoded = self.decode(encoded)
update_salt = must_update_salt(decoded["salt"], self.salt_entropy)
return (decoded["iterations"] != self.iterations) or update_salt
def harden_runtime(self, password, encoded):
decoded = self.decode(encoded)
extra_iterations = self.iterations - decoded["iterations"]
if extra_iterations > 0:
self.encode(password, decoded["salt"], extra_iterations)
class PBKDF2SHA1PasswordHasher(PBKDF2PasswordHasher):
"""
Alternate PBKDF2 hasher which uses SHA1, the default PRF
recommended by PKCS #5. This is compatible with other
implementations of PBKDF2, such as openssl's
PKCS5_PBKDF2_HMAC_SHA1().
"""
algorithm = "pbkdf2_sha1"
digest = hashlib.sha1
class Argon2PasswordHasher(BasePasswordHasher):
"""
Secure password hashing using the argon2 algorithm.
This is the winner of the Password Hashing Competition 2013-2015
(https://password-hashing.net). It requires the argon2-cffi library which
depends on native C code and might cause portability issues.
"""
algorithm = "argon2"
library = "argon2"
time_cost = 2
memory_cost = 102400
parallelism = 8
def encode(self, password, salt):
argon2 = self._load_library()
params = self.params()
data = argon2.low_level.hash_secret(
password.encode(),
salt.encode(),
time_cost=params.time_cost,
memory_cost=params.memory_cost,
parallelism=params.parallelism,
hash_len=params.hash_len,
type=params.type,
)
return self.algorithm + data.decode("ascii")
def decode(self, encoded):
argon2 = self._load_library()
algorithm, rest = encoded.split("$", 1)
assert algorithm == self.algorithm
params = argon2.extract_parameters("$" + rest)
variety, *_, b64salt, hash = rest.split("$")
# Add padding.
b64salt += "=" * (-len(b64salt) % 4)
salt = base64.b64decode(b64salt).decode("latin1")
return {
"algorithm": algorithm,
"hash": hash,
"memory_cost": params.memory_cost,
"parallelism": params.parallelism,
"salt": salt,
"time_cost": params.time_cost,
"variety": variety,
"version": params.version,
"params": params,
}
def verify(self, password, encoded):
argon2 = self._load_library()
algorithm, rest = encoded.split("$", 1)
assert algorithm == self.algorithm
try:
return argon2.PasswordHasher().verify("$" + rest, password)
except argon2.exceptions.VerificationError:
return False
def safe_summary(self, encoded):
decoded = self.decode(encoded)
return {
_("algorithm"): decoded["algorithm"],
_("variety"): decoded["variety"],
_("version"): decoded["version"],
_("memory cost"): decoded["memory_cost"],
_("time cost"): decoded["time_cost"],
_("parallelism"): decoded["parallelism"],
_("salt"): mask_hash(decoded["salt"]),
_("hash"): mask_hash(decoded["hash"]),
}
def must_update(self, encoded):
decoded = self.decode(encoded)
current_params = decoded["params"]
new_params = self.params()
# Set salt_len to the salt_len of the current parameters because salt
# is explicitly passed to argon2.
new_params.salt_len = current_params.salt_len
update_salt = must_update_salt(decoded["salt"], self.salt_entropy)
return (current_params != new_params) or update_salt
def harden_runtime(self, password, encoded):
# The runtime for Argon2 is too complicated to implement a sensible
# hardening algorithm.
pass
def params(self):
argon2 = self._load_library()
# salt_len is a noop, because we provide our own salt.
return argon2.Parameters(
type=argon2.low_level.Type.ID,
version=argon2.low_level.ARGON2_VERSION,
salt_len=argon2.DEFAULT_RANDOM_SALT_LENGTH,
hash_len=argon2.DEFAULT_HASH_LENGTH,
time_cost=self.time_cost,
memory_cost=self.memory_cost,
parallelism=self.parallelism,
)
class BCryptSHA256PasswordHasher(BasePasswordHasher):
"""
Secure password hashing using the bcrypt algorithm (recommended)
This is considered by many to be the most secure algorithm but you
must first install the bcrypt library. Please be warned that
this library depends on native C code and might cause portability
issues.
"""
algorithm = "bcrypt_sha256"
digest = hashlib.sha256
library = ("bcrypt", "bcrypt")
rounds = 12
def salt(self):
bcrypt = self._load_library()
return bcrypt.gensalt(self.rounds)
def encode(self, password, salt):
bcrypt = self._load_library()
password = password.encode()
# Hash the password prior to using bcrypt to prevent password
# truncation as described in #20138.
if self.digest is not None:
# Use binascii.hexlify() because a hex encoded bytestring is str.
password = binascii.hexlify(self.digest(password).digest())
data = bcrypt.hashpw(password, salt)
return "%s$%s" % (self.algorithm, data.decode("ascii"))
def decode(self, encoded):
algorithm, empty, algostr, work_factor, data = encoded.split("$", 4)
assert algorithm == self.algorithm
return {
"algorithm": algorithm,
"algostr": algostr,
"checksum": data[22:],
"salt": data[:22],
"work_factor": int(work_factor),
}
def verify(self, password, encoded):
algorithm, data = encoded.split("$", 1)
assert algorithm == self.algorithm
encoded_2 = self.encode(password, data.encode("ascii"))
return constant_time_compare(encoded, encoded_2)
def safe_summary(self, encoded):
decoded = self.decode(encoded)
return {
_("algorithm"): decoded["algorithm"],
_("work factor"): decoded["work_factor"],
_("salt"): mask_hash(decoded["salt"]),
_("checksum"): mask_hash(decoded["checksum"]),
}
def must_update(self, encoded):
decoded = self.decode(encoded)
return decoded["work_factor"] != self.rounds
def harden_runtime(self, password, encoded):
_, data = encoded.split("$", 1)
salt = data[:29] # Length of the salt in bcrypt.
rounds = data.split("$")[2]
# work factor is logarithmic, adding one doubles the load.
diff = 2 ** (self.rounds - int(rounds)) - 1
while diff > 0:
self.encode(password, salt.encode("ascii"))
diff -= 1
class BCryptPasswordHasher(BCryptSHA256PasswordHasher):
"""
Secure password hashing using the bcrypt algorithm
This is considered by many to be the most secure algorithm but you
must first install the bcrypt library. Please be warned that
this library depends on native C code and might cause portability
issues.
This hasher does not first hash the password which means it is subject to
bcrypt's 72 bytes password truncation. Most use cases should prefer the
BCryptSHA256PasswordHasher.
"""
algorithm = "bcrypt"
digest = None
class ScryptPasswordHasher(BasePasswordHasher):
"""
Secure password hashing using the Scrypt algorithm.
"""
algorithm = "scrypt"
block_size = 8
maxmem = 0
parallelism = 1
work_factor = 2**14
def encode(self, password, salt, n=None, r=None, p=None):
self._check_encode_args(password, salt)
n = n or self.work_factor
r = r or self.block_size
p = p or self.parallelism
hash_ = hashlib.scrypt(
password.encode(),
salt=salt.encode(),
n=n,
r=r,
p=p,
maxmem=self.maxmem,
dklen=64,
)
hash_ = base64.b64encode(hash_).decode("ascii").strip()
return "%s$%d$%s$%d$%d$%s" % (self.algorithm, n, salt, r, p, hash_)
def decode(self, encoded):
algorithm, work_factor, salt, block_size, parallelism, hash_ = encoded.split(
"$", 6
)
assert algorithm == self.algorithm
return {
"algorithm": algorithm,
"work_factor": int(work_factor),
"salt": salt,
"block_size": int(block_size),
"parallelism": int(parallelism),
"hash": hash_,
}
def verify(self, password, encoded):
decoded = self.decode(encoded)
encoded_2 = self.encode(
password,
decoded["salt"],
decoded["work_factor"],
decoded["block_size"],
decoded["parallelism"],
)
return constant_time_compare(encoded, encoded_2)
def safe_summary(self, encoded):
decoded = self.decode(encoded)
return {
_("algorithm"): decoded["algorithm"],
_("work factor"): decoded["work_factor"],
_("block size"): decoded["block_size"],
_("parallelism"): decoded["parallelism"],
_("salt"): mask_hash(decoded["salt"]),
_("hash"): mask_hash(decoded["hash"]),
}
def must_update(self, encoded):
decoded = self.decode(encoded)
return (
decoded["work_factor"] != self.work_factor
or decoded["block_size"] != self.block_size
or decoded["parallelism"] != self.parallelism
)
def harden_runtime(self, password, encoded):
# The runtime for Scrypt is too complicated to implement a sensible
# hardening algorithm.
pass
class MD5PasswordHasher(BasePasswordHasher):
"""
The Salted MD5 password hashing algorithm (not recommended)
"""
algorithm = "md5"
def encode(self, password, salt):
self._check_encode_args(password, salt)
hash = hashlib.md5((salt + password).encode()).hexdigest()
return "%s$%s$%s" % (self.algorithm, salt, hash)
def decode(self, encoded):
algorithm, salt, hash = encoded.split("$", 2)
assert algorithm == self.algorithm
return {
"algorithm": algorithm,
"hash": hash,
"salt": salt,
}
def verify(self, password, encoded):
decoded = self.decode(encoded)
encoded_2 = self.encode(password, decoded["salt"])
return constant_time_compare(encoded, encoded_2)
def safe_summary(self, encoded):
decoded = self.decode(encoded)
return {
_("algorithm"): decoded["algorithm"],
_("salt"): mask_hash(decoded["salt"], show=2),
_("hash"): mask_hash(decoded["hash"]),
}
def must_update(self, encoded):
decoded = self.decode(encoded)
return must_update_salt(decoded["salt"], self.salt_entropy)
def harden_runtime(self, password, encoded):
pass