113 lines
3.7 KiB
C++
113 lines
3.7 KiB
C++
// eprecomp.cpp - written and placed in the public domain by Wei Dai
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#include "pch.h"
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#ifndef CRYPTOPP_IMPORTS
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#include "eprecomp.h"
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#include "asn.h"
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NAMESPACE_BEGIN(CryptoPP)
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template <class T> void DL_FixedBasePrecomputationImpl<T>::SetBase(const DL_GroupPrecomputation<Element> &group, const Element &i_base)
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{
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m_base = group.NeedConversions() ? group.ConvertIn(i_base) : i_base;
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if (m_bases.empty() || !(m_base == m_bases[0]))
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{
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m_bases.resize(1);
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m_bases[0] = m_base;
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}
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if (group.NeedConversions())
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m_base = i_base;
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}
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template <class T> void DL_FixedBasePrecomputationImpl<T>::Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage)
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{
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assert(m_bases.size() > 0);
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assert(storage <= maxExpBits);
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if (storage > 1)
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{
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m_windowSize = (maxExpBits+storage-1)/storage;
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m_exponentBase = Integer::Power2(m_windowSize);
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}
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m_bases.resize(storage);
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for (unsigned i=1; i<storage; i++)
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m_bases[i] = group.GetGroup().ScalarMultiply(m_bases[i-1], m_exponentBase);
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}
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template <class T> void DL_FixedBasePrecomputationImpl<T>::Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &bt)
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{
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BERSequenceDecoder seq(bt);
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word32 version;
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BERDecodeUnsigned<word32>(seq, version, INTEGER, 1, 1);
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m_exponentBase.BERDecode(seq);
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m_windowSize = m_exponentBase.BitCount() - 1;
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m_bases.clear();
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while (!seq.EndReached())
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m_bases.push_back(group.BERDecodeElement(seq));
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if (!m_bases.empty() && group.NeedConversions())
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m_base = group.ConvertOut(m_bases[0]);
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seq.MessageEnd();
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}
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template <class T> void DL_FixedBasePrecomputationImpl<T>::Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &bt) const
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{
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DERSequenceEncoder seq(bt);
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DEREncodeUnsigned<word32>(seq, 1); // version
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m_exponentBase.DEREncode(seq);
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for (unsigned i=0; i<m_bases.size(); i++)
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group.DEREncodeElement(seq, m_bases[i]);
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seq.MessageEnd();
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}
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template <class T> void DL_FixedBasePrecomputationImpl<T>::PrepareCascade(const DL_GroupPrecomputation<Element> &i_group, std::vector<BaseAndExponent<Element> > &eb, const Integer &exponent) const
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{
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const AbstractGroup<T> &group = i_group.GetGroup();
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Integer r, q, e = exponent;
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bool fastNegate = group.InversionIsFast() && m_windowSize > 1;
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unsigned int i;
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for (i=0; i+1<m_bases.size(); i++)
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{
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Integer::DivideByPowerOf2(r, q, e, m_windowSize);
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std::swap(q, e);
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if (fastNegate && r.GetBit(m_windowSize-1))
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{
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++e;
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eb.push_back(BaseAndExponent<Element>(group.Inverse(m_bases[i]), m_exponentBase - r));
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}
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else
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eb.push_back(BaseAndExponent<Element>(m_bases[i], r));
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}
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eb.push_back(BaseAndExponent<Element>(m_bases[i], e));
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}
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template <class T> T DL_FixedBasePrecomputationImpl<T>::Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const
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{
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std::vector<BaseAndExponent<Element> > eb; // array of segments of the exponent and precalculated bases
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eb.reserve(m_bases.size());
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PrepareCascade(group, eb, exponent);
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return group.ConvertOut(GeneralCascadeMultiplication<Element>(group.GetGroup(), eb.begin(), eb.end()));
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}
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template <class T> T
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DL_FixedBasePrecomputationImpl<T>::CascadeExponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent,
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const DL_FixedBasePrecomputation<T> &i_pc2, const Integer &exponent2) const
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{
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std::vector<BaseAndExponent<Element> > eb; // array of segments of the exponent and precalculated bases
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const DL_FixedBasePrecomputationImpl<T> &pc2 = static_cast<const DL_FixedBasePrecomputationImpl<T> &>(i_pc2);
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eb.reserve(m_bases.size() + pc2.m_bases.size());
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PrepareCascade(group, eb, exponent);
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pc2.PrepareCascade(group, eb, exponent2);
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return group.ConvertOut(GeneralCascadeMultiplication<Element>(group.GetGroup(), eb.begin(), eb.end()));
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}
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NAMESPACE_END
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#endif
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