dsa.cpp

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

#include "pch.h"

#ifndef CRYPTOPP_IMPORTS

#include "dsa.h"
#include "nbtheory.h"

NAMESPACE_BEGIN(CryptoPP)

size_t DSAConvertSignatureFormat(byte *buffer, size_t bufferSize, DSASignatureFormat toFormat, const byte *signature, size_t signatureLen, DSASignatureFormat fromFormat)
{
        Integer r, s;
        StringStore store(signature, signatureLen);
        ArraySink sink(buffer, bufferSize);

        switch (fromFormat)
        {
        case DSA_P1363:
                r.Decode(store, signatureLen/2);
                s.Decode(store, signatureLen/2);
                break;
        case DSA_DER:
        {
                BERSequenceDecoder seq(store);
                r.BERDecode(seq);
                s.BERDecode(seq);
                seq.MessageEnd();
                break;
        }
        case DSA_OPENPGP:
                r.OpenPGPDecode(store);
                s.OpenPGPDecode(store);
                break;
        }

        switch (toFormat)
        {
        case DSA_P1363:
                r.Encode(sink, bufferSize/2);
                s.Encode(sink, bufferSize/2);
                break;
        case DSA_DER:
        {
                DERSequenceEncoder seq(sink);
                r.DEREncode(seq);
                s.DEREncode(seq);
                seq.MessageEnd();
                break;
        }
        case DSA_OPENPGP:
                r.OpenPGPEncode(sink);
                s.OpenPGPEncode(sink);
                break;
        }

        return (size_t)sink.TotalPutLength();
}

bool DSA::GeneratePrimes(const byte *seedIn, unsigned int g, int &counter,
                                                  Integer &p, unsigned int L, Integer &q, bool useInputCounterValue)
{
        assert(g%8 == 0);

        SHA sha;
        SecByteBlock seed(seedIn, g/8);
        SecByteBlock U(SHA::DIGESTSIZE);
        SecByteBlock temp(SHA::DIGESTSIZE);
        SecByteBlock W(((L-1)/160+1) * SHA::DIGESTSIZE);
        const int n = (L-1) / 160;
        const int b = (L-1) % 160;
        Integer X;

        sha.CalculateDigest(U, seed, g/8);

        for (int i=g/8-1, carry=true; i>=0 && carry; i--)
                carry=!++seed[i];

        sha.CalculateDigest(temp, seed, g/8);
        xorbuf(U, temp, SHA::DIGESTSIZE);

        U[0] |= 0x80;
        U[SHA::DIGESTSIZE-1] |= 1;
        q.Decode(U, SHA::DIGESTSIZE);

        if (!IsPrime(q))
                return false;

        int counterEnd = useInputCounterValue ? counter+1 : 4096;

        for (int c = 0; c < counterEnd; c++)
        {
                for (int k=0; k<=n; k++)
                {
                        for (int i=g/8-1, carry=true; i>=0 && carry; i--)
                                carry=!++seed[i];
                        if (!useInputCounterValue || c == counter)
                                sha.CalculateDigest(W+(n-k)*SHA::DIGESTSIZE, seed, g/8);
                }
                if (!useInputCounterValue || c == counter)
                {
                        W[SHA::DIGESTSIZE - 1 - b/8] |= 0x80;
                        X.Decode(W + SHA::DIGESTSIZE - 1 - b/8, L/8);
                        p = X-((X % (2*q))-1);

                        if (p.GetBit(L-1) && IsPrime(p))
                        {
                                counter = c;
                                return true;
                        }
                }
        }
        return false;
}

NAMESPACE_END

#endif

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