00001
00002
00003 #include "pch.h"
00004 #include "eprecomp.h"
00005 #include "asn.h"
00006
00007 NAMESPACE_BEGIN(CryptoPP)
00008
00009 template <class T> void DL_FixedBasePrecomputationImpl<T>::SetBase(const DL_GroupPrecomputation<Element> &group, const Element &i_base)
00010 {
00011 m_base = group.NeedConversions() ? group.ConvertIn(i_base) : i_base;
00012
00013 if (m_bases.empty() || !(m_base == m_bases[0]))
00014 {
00015 m_bases.resize(1);
00016 m_bases[0] = m_base;
00017 }
00018
00019 if (group.NeedConversions())
00020 m_base = i_base;
00021 }
00022
00023 template <class T> void DL_FixedBasePrecomputationImpl<T>::Precompute(const DL_GroupPrecomputation<Element> &group, unsigned int maxExpBits, unsigned int storage)
00024 {
00025 assert(m_bases.size() > 0);
00026 assert(storage <= maxExpBits);
00027
00028 if (storage > 1)
00029 {
00030 m_windowSize = (maxExpBits+storage-1)/storage;
00031 m_exponentBase = Integer::Power2(m_windowSize);
00032 }
00033
00034 m_bases.resize(storage);
00035 for (unsigned i=1; i<storage; i++)
00036 m_bases[i] = group.GetGroup().ScalarMultiply(m_bases[i-1], m_exponentBase);
00037 }
00038
00039 template <class T> void DL_FixedBasePrecomputationImpl<T>::Load(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &bt)
00040 {
00041 BERSequenceDecoder seq(bt);
00042 word32 version;
00043 BERDecodeUnsigned<word32>(seq, version, INTEGER, 1, 1);
00044 m_exponentBase.BERDecode(seq);
00045 m_windowSize = m_exponentBase.BitCount() - 1;
00046 m_bases.clear();
00047 while (!seq.EndReached())
00048 m_bases.push_back(group.BERDecodeElement(seq));
00049 if (!m_bases.empty() && group.NeedConversions())
00050 m_base = group.ConvertOut(m_bases[0]);
00051 seq.MessageEnd();
00052 }
00053
00054 template <class T> void DL_FixedBasePrecomputationImpl<T>::Save(const DL_GroupPrecomputation<Element> &group, BufferedTransformation &bt) const
00055 {
00056 DERSequenceEncoder seq(bt);
00057 DEREncodeUnsigned<word32>(seq, 1);
00058 m_exponentBase.DEREncode(seq);
00059 for (unsigned i=0; i<m_bases.size(); i++)
00060 group.DEREncodeElement(seq, m_bases[i]);
00061 seq.MessageEnd();
00062 }
00063
00064 template <class T> void DL_FixedBasePrecomputationImpl<T>::PrepareCascade(const DL_GroupPrecomputation<Element> &i_group, std::vector<BaseAndExponent<Element> > &eb, const Integer &exponent) const
00065 {
00066 const AbstractGroup<T> &group = i_group.GetGroup();
00067
00068 Integer r, q, e = exponent;
00069 bool fastNegate = group.InversionIsFast() && m_windowSize > 1;
00070 unsigned int i;
00071
00072 for (i=0; i+1<m_bases.size(); i++)
00073 {
00074 Integer::DivideByPowerOf2(r, q, e, m_windowSize);
00075 std::swap(q, e);
00076 if (fastNegate && r.GetBit(m_windowSize-1))
00077 {
00078 ++e;
00079 eb.push_back(BaseAndExponent<Element>(group.Inverse(m_bases[i]), m_exponentBase - r));
00080 }
00081 else
00082 eb.push_back(BaseAndExponent<Element>(m_bases[i], r));
00083 }
00084 eb.push_back(BaseAndExponent<Element>(m_bases[i], e));
00085 }
00086
00087 template <class T> T DL_FixedBasePrecomputationImpl<T>::Exponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent) const
00088 {
00089 std::vector<BaseAndExponent<Element> > eb;
00090 eb.reserve(m_bases.size());
00091 PrepareCascade(group, eb, exponent);
00092 return group.ConvertOut(GeneralCascadeMultiplication<Element>(group.GetGroup(), eb.begin(), eb.end()));
00093 }
00094
00095 template <class T> T
00096 DL_FixedBasePrecomputationImpl<T>::CascadeExponentiate(const DL_GroupPrecomputation<Element> &group, const Integer &exponent,
00097 const DL_FixedBasePrecomputation<T> &i_pc2, const Integer &exponent2) const
00098 {
00099 std::vector<BaseAndExponent<Element> > eb;
00100 const DL_FixedBasePrecomputationImpl<T> &pc2 = static_cast<const DL_FixedBasePrecomputationImpl<T> &>(i_pc2);
00101 eb.reserve(m_bases.size() + pc2.m_bases.size());
00102 PrepareCascade(group, eb, exponent);
00103 pc2.PrepareCascade(group, eb, exponent2);
00104 return group.ConvertOut(GeneralCascadeMultiplication<Element>(group.GetGroup(), eb.begin(), eb.end()));
00105 }
00106
00107 NAMESPACE_END