401 lines
11 KiB
Python
401 lines
11 KiB
Python
########################################################################
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# File name: hashes.py
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# This file is part of: aioxmpp
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#
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# LICENSE
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Lesser General Public License as
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# published by the Free Software Foundation, either version 3 of the
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# License, or (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this program. If not, see
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# <http://www.gnu.org/licenses/>.
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#
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########################################################################
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"""
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:mod:`~aioxmpp.hashes` --- Hash Functions for use with XMPP (:xep:`300`)
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########################################################################
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:xep:`300` consolidates the use of hash functions and their digests in XMPP.
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Identifiers (usually called `algo`) are defined to refer to specific
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implementations and parametrisations of hashes (:func:`hash_from_algo`,
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:func:`algo_of_hash`) and there is a defined XML format for carrying hash
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digests (:class:`Hash`) and hash algorithms to be used (:class:`HashUsed`).
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This allows other extensions to easily embed hash digests in their protocols
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(:class:`HashesParent`, :class:`HashesUsedParent`).
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The service :class:`HashService` registers the disco features for the
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supported hash functions and allows querying hash functions supported by
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you and another entity on the Jabber network supporting :xep:`300`.
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.. note::
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Compliance with :xep:`300` depends on your build of Python and possibly
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OpenSSL. Version 0.5.1 of :xep:`300` requires support of SHA3 and BLAKE2b,
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which was only introduced in Python 3.6.
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Utilities for Working with Hash Algorithm Identifiers
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=====================================================
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.. autofunction:: hash_from_algo
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.. autofunction:: algo_of_hash
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.. data:: default_hash_algorithms
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A set of `algo` values which consists of hash functions matching the
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following criteria:
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* They are specified as ``MUST`` or ``SHOULD`` in the supported version of
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:xep:`300`.
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* They are supported by :mod:`hashlib`.
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* Only one function from each matching family is selected. If multiple
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functions apply, ``MUST`` is preferred over ``SHOULD``.
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The set thus varies based on the build of Python and possibly OpenSSL. The
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algorithms in the set are guaranteed to return a valid hash implementation
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when passed to :func:`~aioxmpp.misc.hash_from_algo`.
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In a fully compliant build, this set consists of ``sha-256``, ``sha3-256``
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and ``blake2b-256``.
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Service
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=======
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.. autoclass:: HashService
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XSOs
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====
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.. autoclass:: Hash
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.. autoclass:: HashesParent()
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.. autoclass:: HashUsed
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.. autoclass:: HashesUsedParent()
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"""
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import asyncio
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import hashlib
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import aioxmpp.disco as disco
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import aioxmpp.service as service
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import aioxmpp.xso as xso
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from aioxmpp.utils import namespaces
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namespaces.xep0300_hashes2 = "urn:xmpp:hashes:2"
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namespaces.xep0300_hash_name_prefix = "urn:xmpp:hash-function-text-names:"
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_HASH_ALGO_MAPPING = [
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("md2", (False, ("md2", (), {}))),
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("md4", (False, ("md4", (), {}))),
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("md5", (False, ("md5", (), {}))),
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("sha-1", (True, ("sha1", (), {}))),
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("sha-224", (True, ("sha224", (), {}))),
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("sha-256", (True, ("sha256", (), {}))),
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("sha-384", (True, ("sha384", (), {}))),
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("sha-512", (True, ("sha512", (), {}))),
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("sha3-256", (True, ("sha3_256", (), {}))),
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("sha3-512", (True, ("sha3_512", (), {}))),
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("blake2b-256", (True, ("blake2b", (), {"digest_size": 32}))),
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("blake2b-512", (True, ("blake2b", (), {"digest_size": 64}))),
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]
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_HASH_ALGO_MAP = dict(_HASH_ALGO_MAPPING)
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_HASH_ALGO_REVERSE_MAP = {
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fun_name: (enabled, algo)
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for algo, (enabled, (fun_name, fun_args, fun_kwargs)) in _HASH_ALGO_MAPPING
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if not fun_args and not fun_kwargs
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}
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def is_algo_supported(algo):
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try:
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enabled, (fun_name, _, _) = _HASH_ALGO_MAP[algo]
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except KeyError:
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return False
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return enabled and hasattr(hashlib, fun_name)
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SUPPORTED_HASH_FEATURES = set()
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for _hash in _HASH_ALGO_MAP:
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if is_algo_supported(_hash):
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SUPPORTED_HASH_FEATURES.add(
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namespaces.xep0300_hash_name_prefix + _hash
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)
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del _hash
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def hash_from_algo(algo):
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"""
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Return a :mod:`hashlib` hash given the :xep:`300` `algo`.
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:param algo: The algorithm identifier as defined in :xep:`300`.
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:type algo: :class:`str`
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:raises NotImplementedError: if the hash algorithm is not supported by
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:mod:`hashlib`.
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:raises ValueError: if the hash algorithm MUST NOT be supported.
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:return: A hash object from :mod:`hashlib` or compatible.
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If the `algo` is not supported by the :mod:`hashlib` module,
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:class:`NotImplementedError` is raised.
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"""
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try:
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enabled, (fun_name, fun_args, fun_kwargs) = _HASH_ALGO_MAP[algo]
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except KeyError:
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raise NotImplementedError(
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"hash algorithm {!r} unknown".format(algo)
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) from None
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if not enabled:
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raise ValueError(
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"support of {} in XMPP is forbidden".format(algo)
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)
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try:
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fun = getattr(hashlib, fun_name)
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except AttributeError as exc:
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raise NotImplementedError(
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"{} not supported by hashlib".format(algo)
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) from exc
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return fun(*fun_args, **fun_kwargs)
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def algo_of_hash(h):
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"""
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Return a :xep:`300` `algo` from a given :mod:`hashlib` hash.
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:param h: Hash object from :mod:`hashlib`.
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:raises ValueError: if `h` does not have a defined `algo` value.
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:raises ValueError: if the hash function MUST NOT be supported.
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:return: The `algo` value for the given hash.
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:rtype: :class:`str`
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.. warning::
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Use with caution for :func:`hashlib.blake2b` hashes.
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:func:`algo_of_hash` cannot safely determine whether blake2b was
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initialised with a salt, personality, key or other non-default
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:xep:`300` mode.
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In such a case, the return value will be the matching ``blake2b-*``
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`algo`, but the digest will not be compatible with the results of other
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implementations.
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"""
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try:
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enabled, algo = _HASH_ALGO_REVERSE_MAP[h.name]
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except KeyError:
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pass
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else:
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if not enabled:
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raise ValueError("support of {} in XMPP is forbidden".format(
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algo
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))
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return algo
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if h.name == "blake2b":
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return "blake2b-{}".format(h.digest_size * 8)
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raise ValueError(
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"unknown hash implementation: {!r}".format(h)
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)
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class Hash(xso.XSO):
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"""
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Represent a single hash digest.
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.. attribute:: algo
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The hash algorithm used. The name is as specified in :xep:`300`.
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.. attribute:: digest
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The digest as :class:`bytes`.
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"""
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TAG = namespaces.xep0300_hashes2, "hash"
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algo = xso.Attr(
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"algo",
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)
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digest = xso.Text(
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type_=xso.Base64Binary()
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)
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def __init__(self, algo, digest):
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super().__init__()
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self.algo = algo
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self.digest = digest
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def get_impl(self):
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"""
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Return a new :mod:`hashlib` hash for the :attr:`algo` set on this
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object.
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See :func:`hash_from_algo` for details and exceptions.
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"""
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return hash_from_algo(self.algo)
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class HashUsed(xso.XSO):
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"""
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Represent a single hash-used algorithm spec.
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.. attribute:: algo
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The hash algorithm used. The name is as specified in :xep:`300`.
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"""
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TAG = namespaces.xep0300_hashes2, "hash-used"
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algo = xso.Attr(
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"algo",
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)
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def __init__(self, algo):
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super().__init__()
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self.algo = algo
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def get_impl(self):
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"""
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Return a new :mod:`hashlib` hash for the :attr:`algo` set on this
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object.
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See :func:`hash_from_algo` for details and exceptions.
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"""
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return hash_from_algo(self.algo)
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class HashType(xso.AbstractElementType):
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@classmethod
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def get_xso_types(cls):
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return [Hash]
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def unpack(self, obj):
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return obj.algo, obj.digest
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def pack(self, pair):
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return Hash(*pair)
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class HashesParent(xso.XSO):
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"""
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Mix-in class for XSOs which use :class:`Hash` children.
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.. attribute:: digests
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A mapping which maps from the :attr:`Hash.algo` to the
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:attr:`Hash.digest`.
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"""
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digests = xso.ChildValueMap(
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type_=HashType(),
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)
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class HashUsedType(xso.AbstractElementType):
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@classmethod
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def get_xso_types(cls):
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return [HashUsed]
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def unpack(self, obj):
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return obj.algo
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def pack(self, item):
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return HashUsed(item)
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class HashesUsedParent(xso.XSO):
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"""
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Mix-in class for XSOs which use :class:`HashUsed` children.
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.. attribute:: algos
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A list of hash algorithms.
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"""
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algos = xso.ChildValueList(
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type_=HashUsedType(),
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)
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default_hash_algorithms = {
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algo
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for algo in ["sha-256", "sha3-256", "blake2b-256"]
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if is_algo_supported(algo)
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}
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class HashService(service.Service):
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"""
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The service component of the :xep:`300` support. This service registers
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the features and allows to query the hash functions supported by us and
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a remote entity:
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.. automethod:: select_common_hashes
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"""
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ORDER_AFTER = [
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disco.DiscoClient,
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disco.DiscoServer,
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]
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hashes_feature = disco.register_feature(namespaces.xep0300_hashes2)
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def __init__(self, client, **kwargs):
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super().__init__(client, **kwargs)
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self._disco_client = self.dependencies[disco.DiscoClient]
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self._disco_server = self.dependencies[disco.DiscoServer]
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for feature in SUPPORTED_HASH_FEATURES:
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self._disco_server.register_feature(feature)
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async def _shutdown(self):
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for feature in SUPPORTED_HASH_FEATURES:
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self._disco_server.unregister_feature(feature)
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await super()._shutdown()
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async def select_common_hashes(self, other_entity):
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"""
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Return the list of algos supported by us and `other_entity`. The
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algorithms are represented by their :xep:`300` URNs
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(`urn:xmpp:hash-function-text-names:...`).
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:param other_entity: the address of another entity
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:type other_entity: :class:`aioxmpp.JID`
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:returns: the identifiers of the hash algorithms supported by
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both us and the other entity
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:rtype: :class:`set`
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:raises RuntimeError: if the other entity does not support the
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:xep:`300` feature nor does not publish hash functions
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URNs we support.
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Note: This assumes the protocol is supported if valid hash
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function features are detected, even if `urn:xmpp:hashes:2` is
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not listed as a feature.
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"""
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disco_info = await self._disco_client.query_info(other_entity)
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intersection = disco_info.features & SUPPORTED_HASH_FEATURES
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if (not intersection and
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namespaces.xep0300_hashes2 not in disco_info.features):
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raise RuntimeError(
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"Remote does not support the urn:xmpp:hashes:2 feature.")
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return intersection
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