esign.cpp

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

#include "pch.h"
#include "esign.h"
#include "asn.h"
#include "modarith.h"
#include "nbtheory.h"
#include "sha.h"
#include "algparam.h"

NAMESPACE_BEGIN(CryptoPP)

void ESIGN_TestInstantiations()
{
        ESIGN<SHA>::Verifier x1(1, 1);
        ESIGN<SHA>::Signer x2(NullRNG(), 1);
        ESIGN<SHA>::Verifier x3(x2);
        ESIGN<SHA>::Verifier x4(x2.GetKey());
        ESIGN<SHA>::Verifier x5(x3);
        ESIGN<SHA>::Signer x6 = x2;

        x6 = x2;
        x3 = ESIGN<SHA>::Verifier(x2);
        x4 = x2.GetKey();
}

void ESIGNFunction::BERDecode(BufferedTransformation &bt)
{
        BERSequenceDecoder seq(bt);
                m_n.BERDecode(seq);
                m_e.BERDecode(seq);
        seq.MessageEnd();
}

void ESIGNFunction::DEREncode(BufferedTransformation &bt) const
{
        DERSequenceEncoder seq(bt);
                m_n.DEREncode(seq);
                m_e.DEREncode(seq);
        seq.MessageEnd();
}

Integer ESIGNFunction::ApplyFunction(const Integer &x) const
{
        DoQuickSanityCheck();
        return STDMIN(a_exp_b_mod_c(x, m_e, m_n) >> (2*GetK()+2), MaxImage());
}

bool ESIGNFunction::Validate(RandomNumberGenerator &rng, unsigned int level) const
{
        bool pass = true;
        pass = pass && m_n > Integer::One() && m_n.IsOdd();
        pass = pass && m_e >= 8 && m_e < m_n;
        return pass;
}

bool ESIGNFunction::GetVoidValue(const char *name, const std::type_info &valueType, void *pValue) const
{
        return GetValueHelper(this, name, valueType, pValue).Assignable()
                CRYPTOPP_GET_FUNCTION_ENTRY(Modulus)
                CRYPTOPP_GET_FUNCTION_ENTRY(PublicExponent)
                ;
}

void ESIGNFunction::AssignFrom(const NameValuePairs &source)
{
        AssignFromHelper(this, source)
                CRYPTOPP_SET_FUNCTION_ENTRY(Modulus)
                CRYPTOPP_SET_FUNCTION_ENTRY(PublicExponent)
                ;
}

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

void InvertibleESIGNFunction::GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &param)
{
        int modulusSize = 1023*2;
        param.GetIntValue("ModulusSize", modulusSize) || param.GetIntValue("KeySize", modulusSize);

        if (modulusSize < 24)
                throw InvalidArgument("InvertibleESIGNFunction: specified modulus size is too small");

        if (modulusSize % 3 != 0)
                throw InvalidArgument("InvertibleESIGNFunction: modulus size must be divisible by 3");

        m_e = param.GetValueWithDefault("PublicExponent", Integer(32));

        if (m_e < 8)
                throw InvalidArgument("InvertibleESIGNFunction: public exponents less than 8 may not be secure");

        // VC70 workaround: putting these after primeParam causes overlapped stack allocation
        ConstByteArrayParameter seedParam;
        SecByteBlock seed;

        const Integer minP = Integer(204) << (modulusSize/3-8);
        const Integer maxP = Integer::Power2(modulusSize/3)-1;
        const NameValuePairs &primeParam = MakeParameters("Min", minP)("Max", maxP)("RandomNumberType", Integer::PRIME);

        if (param.GetValue("Seed", seedParam))
        {
                seed.resize(seedParam.size() + 4);
                memcpy(seed + 4, seedParam.begin(), seedParam.size());

                UnalignedPutWord(BIG_ENDIAN_ORDER, seed, (word32)0);
                m_p.GenerateRandom(rng, CombinedNameValuePairs(primeParam, MakeParameters("Seed", ConstByteArrayParameter(seed))));
                UnalignedPutWord(BIG_ENDIAN_ORDER, seed, (word32)1);
                m_q.GenerateRandom(rng, CombinedNameValuePairs(primeParam, MakeParameters("Seed", ConstByteArrayParameter(seed))));
        }
        else
        {
                m_p.GenerateRandom(rng, primeParam);
                m_q.GenerateRandom(rng, primeParam);
        }

        m_n = m_p * m_p * m_q;

        assert(m_n.BitCount() == modulusSize);
}

void InvertibleESIGNFunction::BERDecode(BufferedTransformation &bt)
{
        BERSequenceDecoder privateKey(bt);
                m_n.BERDecode(privateKey);
                m_e.BERDecode(privateKey);
                m_p.BERDecode(privateKey);
                m_q.BERDecode(privateKey);
        privateKey.MessageEnd();
}

void InvertibleESIGNFunction::DEREncode(BufferedTransformation &bt) const
{
        DERSequenceEncoder privateKey(bt);
                m_n.DEREncode(privateKey);
                m_e.DEREncode(privateKey);
                m_p.DEREncode(privateKey);
                m_q.DEREncode(privateKey);
        privateKey.MessageEnd();
}

Integer InvertibleESIGNFunction::CalculateRandomizedInverse(RandomNumberGenerator &rng, const Integer &x) const 
{
        DoQuickSanityCheck();

        Integer pq = m_p * m_q;
        Integer p2 = m_p * m_p;
        Integer r, z, re, a, w0, w1;

        do
        {
                r.Randomize(rng, Integer::Zero(), pq);
                z = x << (2*GetK()+2);
                re = a_exp_b_mod_c(r, m_e, m_n);
                a = (z - re) % m_n;
                Integer::Divide(w1, w0, a, pq);
                if (w1.NotZero())
                {
                        ++w0;
                        w1 = pq - w1;
                }
        }
        while ((w1 >> 2*GetK()+1).IsPositive());

        ModularArithmetic modp(m_p);
        Integer t = modp.Divide(w0 * r % m_p, m_e * re % m_p);
        Integer s = r + t*pq;
        assert(s < m_n);
/*
        using namespace std;
        cout << "f = " << x << endl;
        cout << "r = " << r << endl;
        cout << "z = " << z << endl;
        cout << "a = " << a << endl;
        cout << "w0 = " << w0 << endl;
        cout << "w1 = " << w1 << endl;
        cout << "t = " << t << endl;
        cout << "s = " << s << endl;
*/
        return s;
}

bool InvertibleESIGNFunction::Validate(RandomNumberGenerator &rng, unsigned int level) const
{
        bool pass = ESIGNFunction::Validate(rng, level);
        pass = pass && m_p > Integer::One() && m_p.IsOdd() && m_p < m_n;
        pass = pass && m_q > Integer::One() && m_q.IsOdd() && m_q < m_n;
        pass = pass && m_p.BitCount() == m_q.BitCount();
        if (level >= 1)
                pass = pass && m_p * m_p * m_q == m_n;
        if (level >= 2)
                pass = pass && VerifyPrime(rng, m_p, level-2) && VerifyPrime(rng, m_q, level-2);
        return pass;
}

bool InvertibleESIGNFunction::GetVoidValue(const char *name, const std::type_info &valueType, void *pValue) const
{
        return GetValueHelper<ESIGNFunction>(this, name, valueType, pValue).Assignable()
                CRYPTOPP_GET_FUNCTION_ENTRY(Prime1)
                CRYPTOPP_GET_FUNCTION_ENTRY(Prime2)
                ;
}

void InvertibleESIGNFunction::AssignFrom(const NameValuePairs &source)
{
        AssignFromHelper<ESIGNFunction>(this, source)
                CRYPTOPP_SET_FUNCTION_ENTRY(Prime1)
                CRYPTOPP_SET_FUNCTION_ENTRY(Prime2)
                ;
}

NAMESPACE_END

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