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114 lines
3.9 KiB
114 lines
3.9 KiB
// eprecomp.cpp - originally 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 "integer.h" |
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#include "algebra.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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CRYPTOPP_ASSERT(m_bases.size() > 0); |
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CRYPTOPP_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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