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Diffstat (limited to '')
| -rw-r--r-- | CryptoPP/eprecomp.cpp | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/CryptoPP/eprecomp.cpp b/CryptoPP/eprecomp.cpp new file mode 100644 index 000000000..a061cf6cd --- /dev/null +++ b/CryptoPP/eprecomp.cpp @@ -0,0 +1,112 @@ +// eprecomp.cpp - written and placed in the public domain by Wei Dai + +#include "pch.h" + +#ifndef CRYPTOPP_IMPORTS + +#include "eprecomp.h" +#include "asn.h" + +NAMESPACE_BEGIN(CryptoPP) + +template <class T> void DL_FixedBasePrecomputationImpl<T>::SetBase(const DL_GroupPrecomputation<Element> &group, const Element &i_base) +{ + m_base = group.NeedConversions() ? group.ConvertIn(i_base) : i_base; + + if (m_bases.empty() || !(m_base == m_bases[0])) + { + m_bases.resize(1); + m_bases[0] = m_base; + } + + if (group.NeedConversions()) + m_base = i_base; +} + +template <class T> void DL_FixedBasePrecomputationImpl<T>::Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage) +{ + assert(m_bases.size() > 0); + assert(storage <= maxExpBits); + + if (storage > 1) + { + m_windowSize = (maxExpBits+storage-1)/storage; + m_exponentBase = Integer::Power2(m_windowSize); + } + + m_bases.resize(storage); + for (unsigned i=1; i<storage; i++) + m_bases[i] = group.GetGroup().ScalarMultiply(m_bases[i-1], m_exponentBase); +} + +template <class T> void DL_FixedBasePrecomputationImpl<T>::Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &bt) +{ + BERSequenceDecoder seq(bt); + word32 version; + BERDecodeUnsigned<word32>(seq, version, INTEGER, 1, 1); + m_exponentBase.BERDecode(seq); + m_windowSize = m_exponentBase.BitCount() - 1; + m_bases.clear(); + while (!seq.EndReached()) + m_bases.push_back(group.BERDecodeElement(seq)); + if (!m_bases.empty() && group.NeedConversions()) + m_base = group.ConvertOut(m_bases[0]); + seq.MessageEnd(); +} + +template <class T> void DL_FixedBasePrecomputationImpl<T>::Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &bt) const +{ + DERSequenceEncoder seq(bt); + DEREncodeUnsigned<word32>(seq, 1); // version + m_exponentBase.DEREncode(seq); + for (unsigned i=0; i<m_bases.size(); i++) + group.DEREncodeElement(seq, m_bases[i]); + seq.MessageEnd(); +} + +template <class T> void DL_FixedBasePrecomputationImpl<T>::PrepareCascade(const DL_GroupPrecomputation<Element> &i_group, std::vector<BaseAndExponent<Element> > &eb, const Integer &exponent) const +{ + const AbstractGroup<T> &group = i_group.GetGroup(); + + Integer r, q, e = exponent; + bool fastNegate = group.InversionIsFast() && m_windowSize > 1; + unsigned int i; + + for (i=0; i+1<m_bases.size(); i++) + { + Integer::DivideByPowerOf2(r, q, e, m_windowSize); + std::swap(q, e); + if (fastNegate && r.GetBit(m_windowSize-1)) + { + ++e; + eb.push_back(BaseAndExponent<Element>(group.Inverse(m_bases[i]), m_exponentBase - r)); + } + else + eb.push_back(BaseAndExponent<Element>(m_bases[i], r)); + } + eb.push_back(BaseAndExponent<Element>(m_bases[i], e)); +} + +template <class T> T DL_FixedBasePrecomputationImpl<T>::Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const +{ + std::vector<BaseAndExponent<Element> > eb; // array of segments of the exponent and precalculated bases + eb.reserve(m_bases.size()); + PrepareCascade(group, eb, exponent); + return group.ConvertOut(GeneralCascadeMultiplication<Element>(group.GetGroup(), eb.begin(), eb.end())); +} + +template <class T> T + DL_FixedBasePrecomputationImpl<T>::CascadeExponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent, + const DL_FixedBasePrecomputation<T> &i_pc2, const Integer &exponent2) const +{ + std::vector<BaseAndExponent<Element> > eb; // array of segments of the exponent and precalculated bases + const DL_FixedBasePrecomputationImpl<T> &pc2 = static_cast<const DL_FixedBasePrecomputationImpl<T> &>(i_pc2); + eb.reserve(m_bases.size() + pc2.m_bases.size()); + PrepareCascade(group, eb, exponent); + pc2.PrepareCascade(group, eb, exponent2); + return group.ConvertOut(GeneralCascadeMultiplication<Element>(group.GetGroup(), eb.begin(), eb.end())); +} + +NAMESPACE_END + +#endif |