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// 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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