cryptopp-cmake/ec2n.cpp at master · 0Knowledge/cryptopp-cmake · GitHub

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// ec2n.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"

#ifndef CRYPTOPP_IMPORTS

#include "ec2n.h"

#include "asn.h"

#include "algebra.cpp"

#include "eprecomp.cpp"

NAMESPACE_BEGIN(CryptoPP)

EC2N::EC2N(BufferedTransformation &bt)

: m_field(BERDecodeGF2NP(bt))

{

BERSequenceDecoder seq(bt);

m_field->BERDecodeElement(seq, m_a);

m_field->BERDecodeElement(seq, m_b);

// skip optional seed

if (!seq.EndReached())

{

SecByteBlock seed;

unsigned int unused;

BERDecodeBitString(seq, seed, unused);

}

seq.MessageEnd();

}

void EC2N::DEREncode(BufferedTransformation &bt) const

{

m_field->DEREncode(bt);

DERSequenceEncoder seq(bt);

m_field->DEREncodeElement(seq, m_a);

m_field->DEREncodeElement(seq, m_b);

seq.MessageEnd();

}

bool EC2N::DecodePoint(EC2N::Point &P, const byte *encodedPoint, size_t encodedPointLen) const

{

StringStore store(encodedPoint, encodedPointLen);

return DecodePoint(P, store, encodedPointLen);

}

bool EC2N::DecodePoint(EC2N::Point &P, BufferedTransformation &bt, size_t encodedPointLen) const

{

byte type;

if (encodedPointLen < 1 || !bt.Get(type))

return false;

switch (type)

{

case 0:

P.identity = true;

return true;

case 2:

case 3:

{

if (encodedPointLen != EncodedPointSize(true))

return false;

P.identity = false;

P.x.Decode(bt, m_field->MaxElementByteLength());

if (P.x.IsZero())

{

P.y = m_field->SquareRoot(m_b);

return true;

}

FieldElement z = m_field->Square(P.x);

assert(P.x == m_field->SquareRoot(z));

P.y = m_field->Divide(m_field->Add(m_field->Multiply(z, m_field->Add(P.x, m_a)), m_b), z);

assert(P.x == m_field->Subtract(m_field->Divide(m_field->Subtract(m_field->Multiply(P.y, z), m_b), z), m_a));

z = m_field->SolveQuadraticEquation(P.y);

assert(m_field->Add(m_field->Square(z), z) == P.y);

z.SetCoefficient(0, type & 1);

P.y = m_field->Multiply(z, P.x);

return true;

}

case 4:

{

if (encodedPointLen != EncodedPointSize(false))

return false;

unsigned int len = m_field->MaxElementByteLength();

P.identity = false;

P.x.Decode(bt, len);

P.y.Decode(bt, len);

return true;

}

default:

return false;

}

void EC2N::EncodePoint(BufferedTransformation &bt, const Point &P, bool compressed) const

{

if (P.identity)

NullStore().TransferTo(bt, EncodedPointSize(compressed));

else if (compressed)

{

bt.Put(2 + (!P.x ? 0 : m_field->Divide(P.y, P.x).GetBit(0)));

P.x.Encode(bt, m_field->MaxElementByteLength());

}

else

{

unsigned int len = m_field->MaxElementByteLength();

bt.Put(4); // uncompressed

P.x.Encode(bt, len);

P.y.Encode(bt, len);

}

void EC2N::EncodePoint(byte *encodedPoint, const Point &P, bool compressed) const

{

ArraySink sink(encodedPoint, EncodedPointSize(compressed));

EncodePoint(sink, P, compressed);

assert(sink.TotalPutLength() == EncodedPointSize(compressed));

}

EC2N::Point EC2N::BERDecodePoint(BufferedTransformation &bt) const

{

SecByteBlock str;

BERDecodeOctetString(bt, str);

Point P;

if (!DecodePoint(P, str, str.size()))

BERDecodeError();

return P;

}

void EC2N::DEREncodePoint(BufferedTransformation &bt, const Point &P, bool compressed) const

{

SecByteBlock str(EncodedPointSize(compressed));

EncodePoint(str, P, compressed);

DEREncodeOctetString(bt, str);

}

bool EC2N::ValidateParameters(RandomNumberGenerator &rng, unsigned int level) const

{

bool pass = !!m_b;

pass = pass && m_a.CoefficientCount() <= m_field->MaxElementBitLength();

pass = pass && m_b.CoefficientCount() <= m_field->MaxElementBitLength();

if (level >= 1)

pass = pass && m_field->GetModulus().IsIrreducible();

return pass;

}

bool EC2N::VerifyPoint(const Point &P) const

{

const FieldElement &x = P.x, &y = P.y;

return P.identity ||

(x.CoefficientCount() <= m_field->MaxElementBitLength()

&& y.CoefficientCount() <= m_field->MaxElementBitLength()

&& !(((x+m_a)*x*x+m_b-(x+y)*y)%m_field->GetModulus()));

}

bool EC2N::Equal(const Point &P, const Point &Q) const

{

if (P.identity && Q.identity)

return true;

if (P.identity && !Q.identity)

return false;

if (!P.identity && Q.identity)

return false;

return (m_field->Equal(P.x,Q.x) && m_field->Equal(P.y,Q.y));

}

const EC2N::Point& EC2N::Identity() const

{

return Singleton<Point>().Ref();

}

const EC2N::Point& EC2N::Inverse(const Point &P) const

{

if (P.identity)

return P;

else

{

m_R.identity = false;

m_R.y = m_field->Add(P.x, P.y);

m_R.x = P.x;

return m_R;

}

const EC2N::Point& EC2N::Add(const Point &P, const Point &Q) const

{

if (P.identity) return Q;

if (Q.identity) return P;

if (Equal(P, Q)) return Double(P);

if (m_field->Equal(P.x, Q.x) && m_field->Equal(P.y, m_field->Add(Q.x, Q.y))) return Identity();

FieldElement t = m_field->Add(P.y, Q.y);

t = m_field->Divide(t, m_field->Add(P.x, Q.x));

FieldElement x = m_field->Square(t);

m_field->Accumulate(x, t);

m_field->Accumulate(x, Q.x);

m_field->Accumulate(x, m_a);

m_R.y = m_field->Add(P.y, m_field->Multiply(t, x));

m_field->Accumulate(x, P.x);

m_field->Accumulate(m_R.y, x);

m_R.x.swap(x);

m_R.identity = false;

return m_R;

}

const EC2N::Point& EC2N::Double(const Point &P) const

{

if (P.identity) return P;

if (!m_field->IsUnit(P.x)) return Identity();

FieldElement t = m_field->Divide(P.y, P.x);

m_field->Accumulate(t, P.x);

m_R.y = m_field->Square(P.x);

m_R.x = m_field->Square(t);

m_field->Accumulate(m_R.x, t);

m_field->Accumulate(m_R.x, m_a);

m_field->Accumulate(m_R.y, m_field->Multiply(t, m_R.x));

m_field->Accumulate(m_R.y, m_R.x);

m_R.identity = false;

return m_R;

}

// ********************************************************

EcPrecomputation<EC2N>& EcPrecomputation<EC2N>::operator=(const EcPrecomputation<EC2N> &rhs)

{

m_ec = rhs.m_ec;

m_ep = rhs.m_ep;

m_ep.m_group = m_ec.get();

return *this;

}

void EcPrecomputation<EC2N>::SetCurveAndBase(const EC2N &ec, const EC2N::Point &base)

{

m_ec.reset(new EC2N(ec));

m_ep.SetGroupAndBase(*m_ec, base);

}

void EcPrecomputation<EC2N>::Precompute(unsigned int maxExpBits, unsigned int storage)

{

m_ep.Precompute(maxExpBits, storage);

}

void EcPrecomputation<EC2N>::Load(BufferedTransformation &bt)

{

BERSequenceDecoder seq(bt);

word32 version;

BERDecodeUnsigned<word32>(seq, version, INTEGER, 1, 1);

m_ep.m_exponentBase.BERDecode(seq);

m_ep.m_windowSize = m_ep.m_exponentBase.BitCount() - 1;

m_ep.m_bases.clear();

while (!seq.EndReached())

m_ep.m_bases.push_back(m_ec->BERDecodePoint(seq));

seq.MessageEnd();

}

void EcPrecomputation<EC2N>::Save(BufferedTransformation &bt) const

{

DERSequenceEncoder seq(bt);

DEREncodeUnsigned<word32>(seq, 1); // version

m_ep.m_exponentBase.DEREncode(seq);

for (unsigned i=0; i<m_ep.m_bases.size(); i++)

m_ec->DEREncodePoint(seq, m_ep.m_bases[i]);

seq.MessageEnd();

}

EC2N::Point EcPrecomputation<EC2N>::Exponentiate(const Integer &exponent) const

{

return m_ep.Exponentiate(exponent);

}

EC2N::Point EcPrecomputation<EC2N>::CascadeExponentiate(const Integer &exponent, const DL_FixedBasePrecomputation<Element> &pc2, const Integer &exponent2) const

{

return m_ep.CascadeExponentiate(exponent, static_cast<const EcPrecomputation<EC2N> &>(pc2).m_ep, exponent2);

}

NAMESPACE_END

#endif

cryptopp-cmake/ec2n.cpp at master · 0Knowledge/cryptopp-cmake · GitHub

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