eprecomp.cpp

300中加密方法

#include "pch.h"
#include "eprecomp.h"
#include "algebra.h"

#include <vector>

NAMESPACE_BEGIN(CryptoPP)

template <class T> void ExponentiationPrecomputation<T>::Precompute(const Element &base, unsigned int maxExpBits)
{
	assert(storage <= maxExpBits);
	exponentBase = Integer::Power2((maxExpBits+storage-1)/storage);

	g[0] = base;
	for (unsigned i=1; i<storage; i++)
		g[i] = group.IntMultiply(g[i-1], exponentBase);
}

template <class T> ExponentiationPrecomputation<T>::Element ExponentiationPrecomputation<T>::Exponentiate(const Integer &exponent) const
{
	std::vector<std::pair<Integer, Element> > eb(storage);	// array of segments of the exponent and precalculated bases
	Integer temp, e = exponent;
	unsigned i;

	for (i=0; i+1<storage; i++)
	{
		Integer::Divide(eb[i].first, temp, e, exponentBase);
		std::swap(temp, e);
		eb[i].second = g[i];
	}
	eb[i].first = e;
	eb[i].second = g[i];

	return GeneralCascadeMultiplication<Element>(group, eb.begin(), eb.end());
}

template <class T> ExponentiationPrecomputation<T>::Element 
	ExponentiationPrecomputation<T>::CascadeExponentiate(const Integer &exponent, 
		const ExponentiationPrecomputation<T> &pc2, const Integer &exponent2) const
{
	std::vector<std::pair<Integer, Element> > eb(storage+pc2.storage);	// array of segments of the exponent and precalculated bases
	Integer temp, e = exponent;
	unsigned i;

	for (i=0; i+1<storage; i++)
	{
		Integer::Divide(eb[i].first, temp, e, exponentBase);
		std::swap(temp, e);
		eb[i].second = g[i];
	}
	eb[i].first = e;
	eb[i].second = g[i];

	e = exponent2;
	for (i=storage; i+1<storage+pc2.storage; i++)
	{
		Integer::Divide(eb[i].first, temp, e, exponentBase);
		std::swap(temp, e);
		eb[i].second = pc2.g[i-storage];
	}
	eb[i].first = e;
	eb[i].second = pc2.g[i-storage];

	return GeneralCascadeMultiplication<Element>(group, eb.begin(), eb.end());
}

NAMESPACE_END