mirror of https://github.com/grpc/grpc.git
Richard Belleville
6 years ago
parent
42b2fe154a
commit
7fa7f932e3
3 changed files with 180 additions and 146 deletions
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# Copyright the 2019 gRPC authors. |
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# |
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# Licensed under the Apache License, Version 2.0 (the "License"); |
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# you may not use this file except in compliance with the License. |
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# You may obtain a copy of the License at |
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# |
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# http://www.apache.org/licenses/LICENSE-2.0 |
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# |
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# Unless required by applicable law or agreed to in writing, software |
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# distributed under the License is distributed on an "AS IS" BASIS, |
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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# See the License for the specific language governing permissions and |
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# limitations under the License. |
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"""A search algorithm over the space of all bytestrings.""" |
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from __future__ import absolute_import |
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from __future__ import division |
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from __future__ import print_function |
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import base64 |
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import hashlib |
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import logging |
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import struct |
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from examples.python.cancellation import hash_name_pb2 |
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_LOGGER = logging.getLogger(__name__) |
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_BYTE_MAX = 255 |
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def _get_hamming_distance(a, b): |
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"""Calculates hamming distance between strings of equal length.""" |
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distance = 0 |
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for char_a, char_b in zip(a, b): |
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if char_a.lower() != char_b.lower(): |
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distance += 1 |
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return distance |
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def _get_substring_hamming_distance(candidate, target): |
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"""Calculates the minimum hamming distance between between the target |
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and any substring of the candidate. |
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Args: |
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candidate: The string whose substrings will be tested. |
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target: The target string. |
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Returns: |
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The minimum Hamming distance between candidate and target. |
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""" |
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min_distance = None |
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for i in range(len(candidate) - len(target) + 1): |
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distance = _get_hamming_distance(candidate[i:i + len(target)], target) |
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if min_distance is None or distance < min_distance: |
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min_distance = distance |
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return min_distance |
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def _get_hash(secret): |
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hasher = hashlib.sha1() |
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hasher.update(secret) |
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return base64.b64encode(hasher.digest()).decode('ascii') |
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class ResourceLimitExceededError(Exception): |
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"""Signifies the request has exceeded configured limits.""" |
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def _bytestrings_of_length(length): |
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"""Generates a stream containing all bytestrings of a given length. |
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Args: |
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length: A positive integer length. |
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Yields: |
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All bytestrings of length `length`. |
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""" |
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digits = [0] * length |
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while True: |
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yield b''.join(struct.pack('B', i) for i in digits) |
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digits[-1] += 1 |
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i = length - 1 |
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while digits[i] == _BYTE_MAX + 1: |
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digits[i] = 0 |
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i -= 1 |
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if i == -1: |
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# Terminate the generator since we've run out of strings of |
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# `length` bytes. |
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raise StopIteration() # pylint: disable=stop-iteration-return |
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else: |
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digits[i] += 1 |
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def _all_bytestrings(): |
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"""Generates a stream containing all possible bytestrings. |
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This generator does not terminate. |
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Yields: |
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All bytestrings in ascending order of length. |
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""" |
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length = 1 |
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while True: |
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for bytestring in _bytestrings_of_length(length): |
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yield bytestring |
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length += 1 |
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def search(target, |
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ideal_distance, |
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stop_event, |
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maximum_hashes, |
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interesting_hamming_distance=None): |
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"""Find candidate strings. |
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Search through the space of all bytestrings, in order of increasing length, |
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indefinitely, until a hash with a Hamming distance of `maximum_distance` or |
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less has been found. |
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Args: |
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target: The search string. |
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ideal_distance: The desired Hamming distance. |
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stop_event: An event indicating whether the RPC should terminate. |
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maximum_hashes: The maximum number of hashes to check before stopping. |
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interesting_hamming_distance: If specified, strings with a Hamming |
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distance from the target below this value will be yielded. |
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Yields: |
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Instances of HashNameResponse. The final entry in the stream will be of |
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`maximum_distance` Hamming distance or less from the target string, |
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while all others will be of less than `interesting_hamming_distance`. |
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Raises: |
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ResourceLimitExceededError: If the computation exceeds `maximum_hashes` |
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iterations. |
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""" |
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hashes_computed = 0 |
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for secret in _all_bytestrings(): |
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if stop_event.is_set(): |
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raise StopIteration() # pylint: disable=stop-iteration-return |
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candidate_hash = _get_hash(secret) |
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distance = _get_substring_hamming_distance(candidate_hash, target) |
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if interesting_hamming_distance is not None and distance <= interesting_hamming_distance: |
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# Surface interesting candidates, but don't stop. |
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yield hash_name_pb2.HashNameResponse( |
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secret=base64.b64encode(secret), |
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hashed_name=candidate_hash, |
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hamming_distance=distance) |
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elif distance <= ideal_distance: |
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# Yield ideal candidate and end the stream. |
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yield hash_name_pb2.HashNameResponse( |
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secret=base64.b64encode(secret), |
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hashed_name=candidate_hash, |
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hamming_distance=distance) |
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raise StopIteration() # pylint: disable=stop-iteration-return |
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hashes_computed += 1 |
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if hashes_computed == maximum_hashes: |
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raise ResourceLimitExceededError() |
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