gfpcrypt.cpp

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

#include "pch.h"

#ifndef CRYPTOPP_IMPORTS

#include "gfpcrypt.h"
#include "asn.h"
#include "oids.h"
#include "nbtheory.h"

NAMESPACE_BEGIN(CryptoPP)

void TestInstantiations_gfpcrypt()
{
        GDSA<SHA>::Signer test;
        GDSA<SHA>::Verifier test1;
        DSA::Signer test5(NullRNG(), 100);
        DSA::Signer test2(test5);
        NR<SHA>::Signer test3;
        NR<SHA>::Verifier test4;
        DLIES<>::Encryptor test6;
        DLIES<>::Decryptor test7;
}

void DL_GroupParameters_DSA::GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &alg)
{
        Integer p, q, g;

        if (alg.GetValue("Modulus", p) && alg.GetValue("SubgroupGenerator", g))
        {
                q = alg.GetValueWithDefault("SubgroupOrder", ComputeGroupOrder(p)/2);
        }
        else
        {
                int modulusSize = 1024;
                alg.GetIntValue("ModulusSize", modulusSize) || alg.GetIntValue("KeySize", modulusSize);

                if (!DSA::IsValidPrimeLength(modulusSize))
                        throw InvalidArgument("DSA: not a valid prime length");

                SecByteBlock seed(SHA::DIGESTSIZE);
                Integer h;
                int c;

                do
                {
                        rng.GenerateBlock(seed, SHA::DIGESTSIZE);
                } while (!DSA::GeneratePrimes(seed, SHA::DIGESTSIZE*8, c, p, modulusSize, q));

                do
                {
                        h.Randomize(rng, 2, p-2);
                        g = a_exp_b_mod_c(h, (p-1)/q, p);
                } while (g <= 1);
        }

        Initialize(p, q, g);
}

bool DL_GroupParameters_DSA::ValidateGroup(RandomNumberGenerator &rng, unsigned int level) const
{
        bool pass = DL_GroupParameters_GFP::ValidateGroup(rng, level);
        pass = pass && DSA::IsValidPrimeLength(GetModulus().BitCount());
        pass = pass && GetSubgroupOrder().BitCount() == 160;
        return pass;
}

void DL_SignatureMessageEncodingMethod_DSA::ComputeMessageRepresentative(RandomNumberGenerator &rng, 
        const byte *recoverableMessage, size_t recoverableMessageLength,
        HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
        byte *representative, size_t representativeBitLength) const
{
        assert(recoverableMessageLength == 0);
        assert(hashIdentifier.second == 0);
        const size_t representativeByteLength = BitsToBytes(representativeBitLength);
        const size_t digestSize = hash.DigestSize();
        const size_t paddingLength = SaturatingSubtract(representativeByteLength, digestSize);

        memset(representative, 0, paddingLength);
        hash.TruncatedFinal(representative+paddingLength, STDMIN(representativeByteLength, digestSize));

        if (digestSize*8 > representativeBitLength)
        {
                Integer h(representative, representativeByteLength);
                h >>= representativeByteLength*8 - representativeBitLength;
                h.Encode(representative, representativeByteLength);
        }
}

void DL_SignatureMessageEncodingMethod_NR::ComputeMessageRepresentative(RandomNumberGenerator &rng, 
        const byte *recoverableMessage, size_t recoverableMessageLength,
        HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
        byte *representative, size_t representativeBitLength) const
{
        assert(recoverableMessageLength == 0);
        assert(hashIdentifier.second == 0);
        const size_t representativeByteLength = BitsToBytes(representativeBitLength);
        const size_t digestSize = hash.DigestSize();
        const size_t paddingLength = SaturatingSubtract(representativeByteLength, digestSize);

        memset(representative, 0, paddingLength);
        hash.TruncatedFinal(representative+paddingLength, STDMIN(representativeByteLength, digestSize));

        if (digestSize*8 >= representativeBitLength)
        {
                Integer h(representative, representativeByteLength);
                h >>= representativeByteLength*8 - representativeBitLength + 1;
                h.Encode(representative, representativeByteLength);
        }
}

bool DL_GroupParameters_IntegerBased::ValidateGroup(RandomNumberGenerator &rng, unsigned int level) const
{
        const Integer &p = GetModulus(), &q = GetSubgroupOrder();

        bool pass = true;
        pass = pass && p > Integer::One() && p.IsOdd();
        pass = pass && q > Integer::One() && q.IsOdd();

        if (level >= 1)
                pass = pass && GetCofactor() > Integer::One() && GetGroupOrder() % q == Integer::Zero();
        if (level >= 2)
                pass = pass && VerifyPrime(rng, q, level-2) && VerifyPrime(rng, p, level-2);

        return pass;
}

bool DL_GroupParameters_IntegerBased::ValidateElement(unsigned int level, const Integer &g, const DL_FixedBasePrecomputation<Integer> *gpc) const
{
        const Integer &p = GetModulus(), &q = GetSubgroupOrder();

        bool pass = true;
        pass = pass && GetFieldType() == 1 ? g.IsPositive() : g.NotNegative();
        pass = pass && g < p && !IsIdentity(g);

        if (level >= 1)
        {
                if (gpc)
                        pass = pass && gpc->Exponentiate(GetGroupPrecomputation(), Integer::One()) == g;
        }
        if (level >= 2)
        {
                if (GetFieldType() == 2)
                        pass = pass && Jacobi(g*g-4, p)==-1;

                // verifying that Lucas((p+1)/2, w, p)==2 is omitted because it's too costly
                // and at most 1 bit is leaked if it's false
                bool fullValidate = (GetFieldType() == 2 && level >= 3) || !FastSubgroupCheckAvailable();

                if (fullValidate && pass)
                {
                        Integer gp = gpc ? gpc->Exponentiate(GetGroupPrecomputation(), q) : ExponentiateElement(g, q);
                        pass = pass && IsIdentity(gp);
                }
                else if (GetFieldType() == 1)
                        pass = pass && Jacobi(g, p) == 1;
        }

        return pass;
}

void DL_GroupParameters_IntegerBased::GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &alg)
{
        Integer p, q, g;
        
        if (alg.GetValue("Modulus", p) && alg.GetValue("SubgroupGenerator", g))
        {
                q = alg.GetValueWithDefault("SubgroupOrder", ComputeGroupOrder(p)/2);
        }
        else
        {
                int modulusSize, subgroupOrderSize;

                if (!alg.GetIntValue("ModulusSize", modulusSize))
                        modulusSize = alg.GetIntValueWithDefault("KeySize", 2048);

                if (!alg.GetIntValue("SubgroupOrderSize", subgroupOrderSize))
                        subgroupOrderSize = GetDefaultSubgroupOrderSize(modulusSize);

                PrimeAndGenerator pg;
                pg.Generate(GetFieldType() == 1 ? 1 : -1, rng, modulusSize, subgroupOrderSize);
                p = pg.Prime();
                q = pg.SubPrime();
                g = pg.Generator();
        }

        Initialize(p, q, g);
}

Integer DL_GroupParameters_IntegerBased::DecodeElement(const byte *encoded, bool checkForGroupMembership) const
{
        Integer g(encoded, GetModulus().ByteCount());
        if (!ValidateElement(1, g, NULL))
                throw DL_BadElement();
        return g;
}

void DL_GroupParameters_IntegerBased::BERDecode(BufferedTransformation &bt)
{
        BERSequenceDecoder parameters(bt);
                Integer p(parameters);
                Integer q(parameters);
                Integer g;
                if (parameters.EndReached())
                {
                        g = q;
                        q = ComputeGroupOrder(p) / 2;
                }
                else
                        g.BERDecode(parameters);
        parameters.MessageEnd();

        SetModulusAndSubgroupGenerator(p, g);
        SetSubgroupOrder(q);
}

void DL_GroupParameters_IntegerBased::DEREncode(BufferedTransformation &bt) const
{
        DERSequenceEncoder parameters(bt);
                GetModulus().DEREncode(parameters);
                m_q.DEREncode(parameters);
                GetSubgroupGenerator().DEREncode(parameters);
        parameters.MessageEnd();
}

bool DL_GroupParameters_IntegerBased::GetVoidValue(const char *name, const std::type_info &valueType, void *pValue) const
{
        return GetValueHelper<DL_GroupParameters<Element> >(this, name, valueType, pValue)
                CRYPTOPP_GET_FUNCTION_ENTRY(Modulus);
}

void DL_GroupParameters_IntegerBased::AssignFrom(const NameValuePairs &source)
{
        AssignFromHelper(this, source)
                CRYPTOPP_SET_FUNCTION_ENTRY2(Modulus, SubgroupGenerator)
                CRYPTOPP_SET_FUNCTION_ENTRY(SubgroupOrder)
                ;
}

OID DL_GroupParameters_IntegerBased::GetAlgorithmID() const
{
        return ASN1::id_dsa();
}

void DL_GroupParameters_GFP::SimultaneousExponentiate(Element *results, const Element &base, const Integer *exponents, unsigned int exponentsCount) const
{
        ModularArithmetic ma(GetModulus());
        ma.SimultaneousExponentiate(results, base, exponents, exponentsCount);
}

DL_GroupParameters_GFP::Element DL_GroupParameters_GFP::MultiplyElements(const Element &a, const Element &b) const
{
        return a_times_b_mod_c(a, b, GetModulus());
}

DL_GroupParameters_GFP::Element DL_GroupParameters_GFP::CascadeExponentiate(const Element &element1, const Integer &exponent1, const Element &element2, const Integer &exponent2) const
{
        ModularArithmetic ma(GetModulus());
        return ma.CascadeExponentiate(element1, exponent1, element2, exponent2);
}

Integer DL_GroupParameters_IntegerBased::GetMaxExponent() const
{
        return STDMIN(GetSubgroupOrder()-1, Integer::Power2(2*DiscreteLogWorkFactor(GetFieldType()*GetModulus().BitCount())));
}

unsigned int DL_GroupParameters_IntegerBased::GetDefaultSubgroupOrderSize(unsigned int modulusSize) const
{
        return 2*DiscreteLogWorkFactor(GetFieldType()*modulusSize);
}

NAMESPACE_END

#endif

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