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pythongh-94199: Remove hashlib.pbkdf2_hmac() Python implementation (p…
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…ythonGH-94200)

Remove the pure Python implementation of hashlib.pbkdf2_hmac(),
deprecated in Python 3.10. Python 3.10 and newer requires OpenSSL
1.1.1 or newer (PEP 644), this OpenSSL version provides a C
implementation of pbkdf2_hmac() which is faster.
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vstinner authored and gvanrossum committed Jun 30, 2022
1 parent 4c130ea commit 8603119
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Showing 5 changed files with 22 additions and 87 deletions.
18 changes: 6 additions & 12 deletions Doc/library/hashlib.rst
Original file line number Diff line number Diff line change
Expand Up @@ -300,23 +300,17 @@ include a `salt <https://en.wikipedia.org/wiki/Salt_%28cryptography%29>`_.

>>> from hashlib import pbkdf2_hmac
>>> our_app_iters = 500_000 # Application specific, read above.
>>> dk = pbkdf2_hmac('sha256', b'password', b'bad salt'*2, our_app_iters)
>>> dk = pbkdf2_hmac('sha256', b'password', b'bad salt' * 2, our_app_iters)
>>> dk.hex()
'15530bba69924174860db778f2c6f8104d3aaf9d26241840c8c4a641c8d000a9'

.. versionadded:: 3.4

.. note::
Function only available when Python is compiled with OpenSSL.

A fast implementation of *pbkdf2_hmac* is available with OpenSSL. The
Python implementation uses an inline version of :mod:`hmac`. It is about
three times slower and doesn't release the GIL.

.. deprecated:: 3.10
.. versionadded:: 3.4

Slow Python implementation of *pbkdf2_hmac* is deprecated. In the
future the function will only be available when Python is compiled
with OpenSSL.
.. versionchanged:: 3.12
Function now only available when Python is built with OpenSSL. The slow
pure Python implementation has been removed.

.. function:: scrypt(password, *, salt, n, r, p, maxmem=0, dklen=64)

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6 changes: 6 additions & 0 deletions Doc/whatsnew/3.12.rst
Original file line number Diff line number Diff line change
Expand Up @@ -273,6 +273,12 @@ Removed
use :func:`locale.format_string` instead.
(Contributed by Victor Stinner in :gh:`94226`.)

* :mod:`hashlib`: Remove the pure Python implementation of
:func:`hashlib.pbkdf2_hmac()`, deprecated in Python 3.10. Python 3.10 and
newer requires OpenSSL 1.1.1 (:pep:`644`): this OpenSSL version provides
a C implementation of :func:`~hashlib.pbkdf2_hmac()` which is faster.
(Contributed by Victor Stinner in :gh:`94199`.)


Porting to Python 3.12
======================
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70 changes: 4 additions & 66 deletions Lib/hashlib.py
Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,7 @@
algorithms_available = set(__always_supported)

__all__ = __always_supported + ('new', 'algorithms_guaranteed',
'algorithms_available', 'pbkdf2_hmac', 'file_digest')
'algorithms_available', 'file_digest')


__builtin_constructor_cache = {}
Expand Down Expand Up @@ -180,72 +180,10 @@ def __hash_new(name, data=b'', **kwargs):
try:
# OpenSSL's PKCS5_PBKDF2_HMAC requires OpenSSL 1.0+ with HMAC and SHA
from _hashlib import pbkdf2_hmac
__all__ += ('pbkdf2_hmac',)
except ImportError:
from warnings import warn as _warn
_trans_5C = bytes((x ^ 0x5C) for x in range(256))
_trans_36 = bytes((x ^ 0x36) for x in range(256))

def pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None):
"""Password based key derivation function 2 (PKCS #5 v2.0)
This Python implementations based on the hmac module about as fast
as OpenSSL's PKCS5_PBKDF2_HMAC for short passwords and much faster
for long passwords.
"""
_warn(
"Python implementation of pbkdf2_hmac() is deprecated.",
category=DeprecationWarning,
stacklevel=2
)
if not isinstance(hash_name, str):
raise TypeError(hash_name)

if not isinstance(password, (bytes, bytearray)):
password = bytes(memoryview(password))
if not isinstance(salt, (bytes, bytearray)):
salt = bytes(memoryview(salt))

# Fast inline HMAC implementation
inner = new(hash_name)
outer = new(hash_name)
blocksize = getattr(inner, 'block_size', 64)
if len(password) > blocksize:
password = new(hash_name, password).digest()
password = password + b'\x00' * (blocksize - len(password))
inner.update(password.translate(_trans_36))
outer.update(password.translate(_trans_5C))

def prf(msg, inner=inner, outer=outer):
# PBKDF2_HMAC uses the password as key. We can re-use the same
# digest objects and just update copies to skip initialization.
icpy = inner.copy()
ocpy = outer.copy()
icpy.update(msg)
ocpy.update(icpy.digest())
return ocpy.digest()

if iterations < 1:
raise ValueError(iterations)
if dklen is None:
dklen = outer.digest_size
if dklen < 1:
raise ValueError(dklen)

dkey = b''
loop = 1
from_bytes = int.from_bytes
while len(dkey) < dklen:
prev = prf(salt + loop.to_bytes(4))
# endianness doesn't matter here as long to / from use the same
rkey = from_bytes(prev)
for i in range(iterations - 1):
prev = prf(prev)
# rkey = rkey ^ prev
rkey ^= from_bytes(prev)
loop += 1
dkey += rkey.to_bytes(inner.digest_size)

return dkey[:dklen]
pass


try:
# OpenSSL's scrypt requires OpenSSL 1.1+
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10 changes: 1 addition & 9 deletions Lib/test/test_hashlib.py
Original file line number Diff line number Diff line change
Expand Up @@ -1096,15 +1096,7 @@ def _test_pbkdf2_hmac(self, pbkdf2, supported):
iterations=1, dklen=None)
self.assertEqual(out, self.pbkdf2_results['sha1'][0][0])

@unittest.skipIf(builtin_hashlib is None, "test requires builtin_hashlib")
def test_pbkdf2_hmac_py(self):
with warnings_helper.check_warnings():
self._test_pbkdf2_hmac(
builtin_hashlib.pbkdf2_hmac, builtin_hashes
)

@unittest.skipUnless(hasattr(openssl_hashlib, 'pbkdf2_hmac'),
' test requires OpenSSL > 1.0')
@unittest.skipIf(openssl_hashlib is None, "requires OpenSSL bindings")
def test_pbkdf2_hmac_c(self):
self._test_pbkdf2_hmac(openssl_hashlib.pbkdf2_hmac, openssl_md_meth_names)

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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
:mod:`hashlib`: Remove the pure Python implementation of
:func:`hashlib.pbkdf2_hmac()`, deprecated in Python 3.10. Python 3.10 and
newer requires OpenSSL 1.1.1 (:pep:`644`): this OpenSSL version provides
a C implementation of :func:`~hashlib.pbkdf2_hmac()` which is faster. Patch
by Victor Stinner.

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