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diff --git a/tools/pe_bliss/entropy.cpp b/tools/pe_bliss/entropy.cpp
new file mode 100644
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+++ b/tools/pe_bliss/entropy.cpp
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+/*************************************************************************/
+/* Copyright (c) 2015 dx, http://kaimi.ru                                */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person           */
+/* obtaining a copy of this software and associated documentation        */
+/* files (the "Software"), to deal in the Software without               */
+/* restriction, including without limitation the rights to use,          */
+/* copy, modify, merge, publish, distribute, sublicense, and/or          */
+/* sell copies of the Software, and to permit persons to whom the        */
+/* Software is furnished to do so, subject to the following conditions:  */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+#include <cmath>
+#include "entropy.h"
+#include "utils.h"
+
+namespace pe_bliss
+{
+//Calculates entropy for PE image section
+double entropy_calculator::calculate_entropy(const section& s)
+{
+	if(s.get_raw_data().empty()) //Don't count entropy for empty sections
+		throw pe_exception("Section is empty", pe_exception::section_is_empty);
+
+	return calculate_entropy(s.get_raw_data().data(), s.get_raw_data().length());
+}
+
+//Calculates entropy for istream (from current position of stream)
+double entropy_calculator::calculate_entropy(std::istream& file)
+{
+	uint32_t byte_count[256] = {0}; //Byte count for each of 255 bytes
+
+	if(file.bad())
+		throw pe_exception("Stream is bad", pe_exception::stream_is_bad);
+
+	std::streamoff pos = file.tellg();
+
+	std::streamoff length = pe_utils::get_file_size(file);
+	length -= file.tellg();
+
+	if(!length) //Don't calculate entropy for empty buffers
+		throw pe_exception("Data length is zero", pe_exception::data_is_empty);
+
+	//Count bytes
+	for(std::streamoff i = 0; i != length; ++i)
+		++byte_count[static_cast<unsigned char>(file.get())];
+
+	file.seekg(pos);
+
+	return calculate_entropy(byte_count, length);
+}
+
+//Calculates entropy for data block
+double entropy_calculator::calculate_entropy(const char* data, size_t length)
+{
+	uint32_t byte_count[256] = {0}; //Byte count for each of 255 bytes
+
+	if(!length) //Don't calculate entropy for empty buffers
+		throw pe_exception("Data length is zero", pe_exception::data_is_empty);
+
+	//Count bytes
+	for(size_t i = 0; i != length; ++i)
+		++byte_count[static_cast<unsigned char>(data[i])];
+
+	return calculate_entropy(byte_count, length);
+}
+
+//Calculates entropy for this PE file (only section data)
+double entropy_calculator::calculate_entropy(const pe_base& pe)
+{
+	uint32_t byte_count[256] = {0}; //Byte count for each of 255 bytes
+
+	size_t total_data_length = 0;
+
+	//Count bytes for each section
+	for(section_list::const_iterator it = pe.get_image_sections().begin(); it != pe.get_image_sections().end(); ++it)
+	{
+		const std::string& data = (*it).get_raw_data();
+		size_t length = data.length();
+		total_data_length += length;
+		for(size_t i = 0; i != length; ++i)
+			++byte_count[static_cast<unsigned char>(data[i])];
+	}
+
+	return calculate_entropy(byte_count, total_data_length);
+}
+
+//Calculates entropy from bytes count
+double entropy_calculator::calculate_entropy(const uint32_t byte_count[256], std::streamoff total_length)
+{
+	double entropy = 0.; //Entropy result value
+	//Calculate entropy
+	for(uint32_t i = 0; i < 256; ++i)
+	{
+		double temp = static_cast<double>(byte_count[i]) / total_length;
+		if(temp > 0.)
+			entropy += std::abs(temp * (std::log(temp) * pe_utils::log_2));
+	}
+
+	return entropy;
+}
+}