293 lines
7.0 KiB
C++
293 lines
7.0 KiB
C++
// ec2n.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 "ec2n.h"
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#include "asn.h"
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#include "algebra.cpp"
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#include "eprecomp.cpp"
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NAMESPACE_BEGIN(CryptoPP)
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EC2N::EC2N(BufferedTransformation &bt)
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: m_field(BERDecodeGF2NP(bt))
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{
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BERSequenceDecoder seq(bt);
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m_field->BERDecodeElement(seq, m_a);
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m_field->BERDecodeElement(seq, m_b);
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// skip optional seed
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if (!seq.EndReached())
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{
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SecByteBlock seed;
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unsigned int unused;
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BERDecodeBitString(seq, seed, unused);
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}
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seq.MessageEnd();
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}
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void EC2N::DEREncode(BufferedTransformation &bt) const
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{
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m_field->DEREncode(bt);
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DERSequenceEncoder seq(bt);
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m_field->DEREncodeElement(seq, m_a);
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m_field->DEREncodeElement(seq, m_b);
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seq.MessageEnd();
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}
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bool EC2N::DecodePoint(EC2N::Point &P, const byte *encodedPoint, size_t encodedPointLen) const
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{
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StringStore store(encodedPoint, encodedPointLen);
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return DecodePoint(P, store, encodedPointLen);
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}
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bool EC2N::DecodePoint(EC2N::Point &P, BufferedTransformation &bt, size_t encodedPointLen) const
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{
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byte type;
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if (encodedPointLen < 1 || !bt.Get(type))
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return false;
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switch (type)
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{
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case 0:
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P.identity = true;
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return true;
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case 2:
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case 3:
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{
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if (encodedPointLen != EncodedPointSize(true))
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return false;
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P.identity = false;
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P.x.Decode(bt, m_field->MaxElementByteLength());
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if (P.x.IsZero())
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{
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P.y = m_field->SquareRoot(m_b);
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return true;
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}
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FieldElement z = m_field->Square(P.x);
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assert(P.x == m_field->SquareRoot(z));
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P.y = m_field->Divide(m_field->Add(m_field->Multiply(z, m_field->Add(P.x, m_a)), m_b), z);
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assert(P.x == m_field->Subtract(m_field->Divide(m_field->Subtract(m_field->Multiply(P.y, z), m_b), z), m_a));
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z = m_field->SolveQuadraticEquation(P.y);
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assert(m_field->Add(m_field->Square(z), z) == P.y);
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z.SetCoefficient(0, type & 1);
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P.y = m_field->Multiply(z, P.x);
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return true;
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}
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case 4:
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{
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if (encodedPointLen != EncodedPointSize(false))
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return false;
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unsigned int len = m_field->MaxElementByteLength();
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P.identity = false;
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P.x.Decode(bt, len);
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P.y.Decode(bt, len);
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return true;
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}
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default:
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return false;
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}
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}
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void EC2N::EncodePoint(BufferedTransformation &bt, const Point &P, bool compressed) const
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{
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if (P.identity)
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NullStore().TransferTo(bt, EncodedPointSize(compressed));
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else if (compressed)
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{
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bt.Put(2 + (!P.x ? 0 : m_field->Divide(P.y, P.x).GetBit(0)));
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P.x.Encode(bt, m_field->MaxElementByteLength());
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}
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else
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{
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unsigned int len = m_field->MaxElementByteLength();
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bt.Put(4); // uncompressed
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P.x.Encode(bt, len);
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P.y.Encode(bt, len);
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}
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}
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void EC2N::EncodePoint(byte *encodedPoint, const Point &P, bool compressed) const
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{
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ArraySink sink(encodedPoint, EncodedPointSize(compressed));
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EncodePoint(sink, P, compressed);
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assert(sink.TotalPutLength() == EncodedPointSize(compressed));
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}
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EC2N::Point EC2N::BERDecodePoint(BufferedTransformation &bt) const
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{
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SecByteBlock str;
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BERDecodeOctetString(bt, str);
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Point P;
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if (!DecodePoint(P, str, str.size()))
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BERDecodeError();
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return P;
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}
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void EC2N::DEREncodePoint(BufferedTransformation &bt, const Point &P, bool compressed) const
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{
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SecByteBlock str(EncodedPointSize(compressed));
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EncodePoint(str, P, compressed);
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DEREncodeOctetString(bt, str);
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}
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bool EC2N::ValidateParameters(RandomNumberGenerator &rng, unsigned int level) const
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{
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bool pass = !!m_b;
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pass = pass && m_a.CoefficientCount() <= m_field->MaxElementBitLength();
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pass = pass && m_b.CoefficientCount() <= m_field->MaxElementBitLength();
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if (level >= 1)
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pass = pass && m_field->GetModulus().IsIrreducible();
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return pass;
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}
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bool EC2N::VerifyPoint(const Point &P) const
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{
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const FieldElement &x = P.x, &y = P.y;
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return P.identity ||
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(x.CoefficientCount() <= m_field->MaxElementBitLength()
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&& y.CoefficientCount() <= m_field->MaxElementBitLength()
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&& !(((x+m_a)*x*x+m_b-(x+y)*y)%m_field->GetModulus()));
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}
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bool EC2N::Equal(const Point &P, const Point &Q) const
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{
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if (P.identity && Q.identity)
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return true;
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if (P.identity && !Q.identity)
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return false;
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if (!P.identity && Q.identity)
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return false;
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return (m_field->Equal(P.x,Q.x) && m_field->Equal(P.y,Q.y));
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}
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const EC2N::Point& EC2N::Identity() const
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{
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return Singleton<Point>().Ref();
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}
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const EC2N::Point& EC2N::Inverse(const Point &P) const
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{
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if (P.identity)
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return P;
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else
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{
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m_R.identity = false;
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m_R.y = m_field->Add(P.x, P.y);
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m_R.x = P.x;
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return m_R;
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}
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}
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const EC2N::Point& EC2N::Add(const Point &P, const Point &Q) const
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{
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if (P.identity) return Q;
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if (Q.identity) return P;
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if (Equal(P, Q)) return Double(P);
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if (m_field->Equal(P.x, Q.x) && m_field->Equal(P.y, m_field->Add(Q.x, Q.y))) return Identity();
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FieldElement t = m_field->Add(P.y, Q.y);
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t = m_field->Divide(t, m_field->Add(P.x, Q.x));
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FieldElement x = m_field->Square(t);
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m_field->Accumulate(x, t);
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m_field->Accumulate(x, Q.x);
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m_field->Accumulate(x, m_a);
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m_R.y = m_field->Add(P.y, m_field->Multiply(t, x));
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m_field->Accumulate(x, P.x);
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m_field->Accumulate(m_R.y, x);
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m_R.x.swap(x);
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m_R.identity = false;
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return m_R;
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}
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const EC2N::Point& EC2N::Double(const Point &P) const
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{
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if (P.identity) return P;
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if (!m_field->IsUnit(P.x)) return Identity();
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FieldElement t = m_field->Divide(P.y, P.x);
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m_field->Accumulate(t, P.x);
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m_R.y = m_field->Square(P.x);
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m_R.x = m_field->Square(t);
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m_field->Accumulate(m_R.x, t);
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m_field->Accumulate(m_R.x, m_a);
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m_field->Accumulate(m_R.y, m_field->Multiply(t, m_R.x));
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m_field->Accumulate(m_R.y, m_R.x);
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m_R.identity = false;
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return m_R;
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}
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// ********************************************************
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/*
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EcPrecomputation<EC2N>& EcPrecomputation<EC2N>::operator=(const EcPrecomputation<EC2N> &rhs)
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{
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m_ec = rhs.m_ec;
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m_ep = rhs.m_ep;
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m_ep.m_group = m_ec.get();
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return *this;
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}
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void EcPrecomputation<EC2N>::SetCurveAndBase(const EC2N &ec, const EC2N::Point &base)
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{
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m_ec.reset(new EC2N(ec));
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m_ep.SetGroupAndBase(*m_ec, base);
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}
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void EcPrecomputation<EC2N>::Precompute(unsigned int maxExpBits, unsigned int storage)
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{
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m_ep.Precompute(maxExpBits, storage);
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}
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void EcPrecomputation<EC2N>::Load(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_ep.m_exponentBase.BERDecode(seq);
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m_ep.m_windowSize = m_ep.m_exponentBase.BitCount() - 1;
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m_ep.m_bases.clear();
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while (!seq.EndReached())
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m_ep.m_bases.push_back(m_ec->BERDecodePoint(seq));
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seq.MessageEnd();
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}
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void EcPrecomputation<EC2N>::Save(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_ep.m_exponentBase.DEREncode(seq);
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for (unsigned i=0; i<m_ep.m_bases.size(); i++)
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m_ec->DEREncodePoint(seq, m_ep.m_bases[i]);
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seq.MessageEnd();
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}
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EC2N::Point EcPrecomputation<EC2N>::Exponentiate(const Integer &exponent) const
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{
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return m_ep.Exponentiate(exponent);
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}
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EC2N::Point EcPrecomputation<EC2N>::CascadeExponentiate(const Integer &exponent, const DL_FixedBasePrecomputation<Element> &pc2, const Integer &exponent2) const
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{
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return m_ep.CascadeExponentiate(exponent, static_cast<const EcPrecomputation<EC2N> &>(pc2).m_ep, exponent2);
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}
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*/
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NAMESPACE_END
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#endif
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