91 lines
2.6 KiB
C++
91 lines
2.6 KiB
C++
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#include <cmath>
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#include "entropy.h"
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#include "utils.h"
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namespace pe_bliss
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{
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//Calculates entropy for PE image section
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double entropy_calculator::calculate_entropy(const section& s)
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{
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if(s.get_raw_data().empty()) //Don't count entropy for empty sections
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throw pe_exception("Section is empty", pe_exception::section_is_empty);
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return calculate_entropy(s.get_raw_data().data(), s.get_raw_data().length());
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}
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//Calculates entropy for istream (from current position of stream)
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double entropy_calculator::calculate_entropy(std::istream& file)
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{
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uint32_t byte_count[256] = {0}; //Byte count for each of 255 bytes
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if(file.bad())
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throw pe_exception("Stream is bad", pe_exception::stream_is_bad);
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std::streamoff pos = file.tellg();
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std::streamoff length = pe_utils::get_file_size(file);
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length -= file.tellg();
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if(!length) //Don't calculate entropy for empty buffers
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throw pe_exception("Data length is zero", pe_exception::data_is_empty);
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//Count bytes
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for(std::streamoff i = 0; i != length; ++i)
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++byte_count[static_cast<unsigned char>(file.get())];
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file.seekg(pos);
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return calculate_entropy(byte_count, length);
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}
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//Calculates entropy for data block
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double entropy_calculator::calculate_entropy(const char* data, size_t length)
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{
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uint32_t byte_count[256] = {0}; //Byte count for each of 255 bytes
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if(!length) //Don't calculate entropy for empty buffers
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throw pe_exception("Data length is zero", pe_exception::data_is_empty);
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//Count bytes
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for(size_t i = 0; i != length; ++i)
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++byte_count[static_cast<unsigned char>(data[i])];
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return calculate_entropy(byte_count, length);
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}
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//Calculates entropy for this PE file (only section data)
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double entropy_calculator::calculate_entropy(const pe_base& pe)
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{
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uint32_t byte_count[256] = {0}; //Byte count for each of 255 bytes
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size_t total_data_length = 0;
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//Count bytes for each section
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for(section_list::const_iterator it = pe.get_image_sections().begin(); it != pe.get_image_sections().end(); ++it)
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{
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const std::string& data = (*it).get_raw_data();
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size_t length = data.length();
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total_data_length += length;
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for(size_t i = 0; i != length; ++i)
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++byte_count[static_cast<unsigned char>(data[i])];
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}
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return calculate_entropy(byte_count, total_data_length);
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}
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//Calculates entropy from bytes count
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double entropy_calculator::calculate_entropy(const uint32_t byte_count[256], std::streamoff total_length)
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{
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double entropy = 0.; //Entropy result value
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//Calculate entropy
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for(uint32_t i = 0; i < 256; ++i)
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{
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double temp = static_cast<double>(byte_count[i]) / total_length;
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if(temp > 0.)
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entropy += std::abs(temp * (std::log(temp) * pe_utils::log_2));
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}
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return entropy;
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}
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}
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