source: git/src-cryptopp/dsa.cpp

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

#include "pch.h"

#ifndef CRYPTOPP_IMPORTS

#include "dsa.h"
#include "asn.h"
#include "integer.h"
#include "filters.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();
}

NAMESPACE_END

#endif