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/*
* EntropySource
* (C) 2008-2009 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#ifndef BOTAN_ENTROPY_SOURCE_BASE_H__
#define BOTAN_ENTROPY_SOURCE_BASE_H__
#include <botan/buf_comp.h>
#include <string>
#include <utility>
namespace Botan {
/**
* Class used to accumulate the poll results of EntropySources
*/
class BOTAN_DLL Entropy_Accumulator
{
public:
/**
* Initialize an Entropy_Accumulator
* @param goal is how many bits we would like to collect
*/
Entropy_Accumulator(size_t goal) :
entropy_goal(goal), collected_bits(0) {}
virtual ~Entropy_Accumulator() {}
/**
* Get a cached I/O buffer (purely for minimizing allocation
* overhead to polls)
*
* @param size requested size for the I/O buffer
* @return cached I/O buffer for repeated polls
*/
MemoryRegion<byte>& get_io_buffer(size_t size)
{ io_buffer.resize(size); return io_buffer; }
/**
* @return number of bits collected so far
*/
size_t bits_collected() const
{ return static_cast<size_t>(collected_bits); }
/**
* @return if our polling goal has been achieved
*/
bool polling_goal_achieved() const
{ return (collected_bits >= entropy_goal); }
/**
* @return how many bits we need to reach our polling goal
*/
size_t desired_remaining_bits() const
{
if(collected_bits >= entropy_goal)
return 0;
return static_cast<size_t>(entropy_goal - collected_bits);
}
/**
* Add entropy to the accumulator
* @param bytes the input bytes
* @param length specifies how many bytes the input is
* @param entropy_bits_per_byte is a best guess at how much
* entropy per byte is in this input
*/
void add(const void* bytes, size_t length, double entropy_bits_per_byte)
{
add_bytes(reinterpret_cast<const byte*>(bytes), length);
collected_bits += entropy_bits_per_byte * length;
}
/**
* Add entropy to the accumulator
* @param v is some value
* @param entropy_bits_per_byte is a best guess at how much
* entropy per byte is in this input
*/
template<typename T>
void add(const T& v, double entropy_bits_per_byte)
{
add(&v, sizeof(T), entropy_bits_per_byte);
}
private:
virtual void add_bytes(const byte bytes[], size_t length) = 0;
SecureVector<byte> io_buffer;
size_t entropy_goal;
double collected_bits;
};
/**
* Entropy accumulator that puts the input into a BufferedComputation
*/
class BOTAN_DLL Entropy_Accumulator_BufferedComputation : public Entropy_Accumulator
{
public:
/**
* @param sink the hash or MAC we are feeding the poll data into
* @param goal is how many bits we want to collect in this poll
*/
Entropy_Accumulator_BufferedComputation(BufferedComputation& sink,
size_t goal) :
Entropy_Accumulator(goal), entropy_sink(sink) {}
private:
virtual void add_bytes(const byte bytes[], size_t length)
{
entropy_sink.update(bytes, length);
}
BufferedComputation& entropy_sink;
};
/**
* Abstract interface to a source of (hopefully unpredictable) system entropy
*/
class BOTAN_DLL EntropySource
{
public:
/**
* @return name identifying this entropy source
*/
virtual std::string name() const = 0;
/**
* Perform an entropy gathering poll
* @param accum is an accumulator object that will be given entropy
*/
virtual void poll(Entropy_Accumulator& accum) = 0;
virtual ~EntropySource() {}
};
}
#endif
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