Source code for plaso.analyzers.hashers.entropy

# -*- coding: utf-8 -*-
"""The entropy calculation implementation."""

import collections
import math

from plaso.analyzers.hashers import interface
from plaso.analyzers.hashers import manager

[docs] class EntropyHasher(interface.BaseHasher): """Calculates the byte entropy of input files.""" NAME = 'entropy' ATTRIBUTE_NAME = 'file_entropy' DESCRIPTION = 'Calculates the byte entropy of input data.'
[docs] def __init__(self): """Initializes the entropy hasher.""" super(EntropyHasher, self).__init__() self._byte_frequency_counter = collections.Counter() self._file_length = 0
[docs] def GetStringDigest(self): """Calculates the byte entropy value. Byte entropy is a value between 0.0 and 8.0, and is returned as a string to match the Plaso analyzer and storage APIs. Returns: str: byte entropy formatted as a floating point number with 6 decimal places calculated over the data blocks passed to Update(). """ if self._file_length == 0: return '0.000000' entropy = 0.0 for byte_frequency in self._byte_frequency_counter.values(): byte_probability = byte_frequency / self._file_length if byte_probability: entropy += - byte_probability * math.log(byte_probability, 2) return f'{entropy:.6f}'
[docs] def Update(self, data): """Updates the state of the entropy calculator with a new block of data. Repeated calls to update are equivalent to one single call with the concatenation of the arguments. Args: data(bytes): block of data with which to update the context of the entropy calculator. """ # The call to update() determines the number of occurrences of a byte value # within data. self._byte_frequency_counter.update(data) self._file_length += len(data)