Документация по криптоалгоритмам / CRYPTO30 / asn

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

#include "pch.h"
#include "asn.h"
#include "misc.h"

NAMESPACE_BEGIN(CryptoPP)

unsigned int DERLengthEncode(unsigned int length, byte *output)
{
	unsigned int i=0;
	if (length <= 0x7f)
	{
		output[i++] = byte(length);
	}
	else
	{
		output[i++] = byte(BytePrecision(length) | 0x80);
		for (int j=BytePrecision(length); j; --j)
		{
			output[i++] = byte (length >> (j-1)*8);
		}
	}
	return i;
}

unsigned int DERLengthEncode(unsigned int length, BufferedTransformation &bt)
{
	byte buf[10];   // should be more than enough
	unsigned int i = DERLengthEncode(length, buf);
	assert(i <= 10);
	bt.Put(buf, i);
	return i;
}

bool BERLengthDecode(BufferedTransformation &bt, unsigned int &length)
{
	byte b;

	if (!bt.Get(b))
		BERDecodeError();

	if (!(b & 0x80))
		length = b;
	else
	{
		unsigned int lengthBytes = b & 0x7f;
		if (bt.MaxRetrieveable() < lengthBytes)
			BERDecodeError();

		bt.Get(b);
		while (!b && lengthBytes>1)
		{
			bt.Get(b);
			lengthBytes--;
		}

		switch (lengthBytes)
		{
		case 0:
			return false;   // indefinite length
		case 1:
			length = b;
			break;
		case 2:
			length = b << 8;
			length |= (bt.Get(b), b);
			break;
		default:
			BERDecodeError();
		}
	}
	return true;
}

BERSequenceDecoder::BERSequenceDecoder(BufferedTransformation &inQueue)
	: inQueue(inQueue)
{
	byte b;
	if (!inQueue.Get(b) || b != (SEQUENCE | CONSTRUCTED))
		BERDecodeError();

	definiteLength = BERLengthDecode(inQueue, length);
}

BERSequenceDecoder::~BERSequenceDecoder()
{
	if (!definiteLength)
	{   // remove end-of-content octects
		word16 i;
		if (!inQueue.GetShort(i) || (i!=0))
			BERDecodeError();
	}
}

DERSequenceEncoder::DERSequenceEncoder(BufferedTransformation &outQueue)
	: outQueue(outQueue)
{
}

DERSequenceEncoder::~DERSequenceEncoder()
{
	unsigned int length = (unsigned int)CurrentSize();
	outQueue.Put(SEQUENCE | CONSTRUCTED);
	DERLengthEncode(length, outQueue);
	TransferTo(outQueue);
}

NAMESPACE_END