env_dec.c

老外写的加密库cryptlib(版本3.1)

			envelopeInfoPtr->bufPos <= envelopeInfoPtr->bufSize );
	assert( ( envelopeInfoPtr->blockSize == 0 ) || \
			( envelopeInfoPtr->blockBufferPos >= 0 && \
			  envelopeInfoPtr->blockBufferPos < envelopeInfoPtr->blockSize ) );

	/* Figure out how much we can copy across.  First we calculate the
	   minimum of the amount of data passed in and the amount remaining in
	   the current segment.  If it's unknown-length data (which can only
	   happen for compressed data), it ends wherever the caller tells us it 
	   ends and we use it all */
	bytesToCopy = ( envelopeInfoPtr->segmentSize == CRYPT_UNUSED ) ? \
				  length : ( int ) min( envelopeInfoPtr->segmentSize, length );

	/* Now we check if this is affected by the total free space remaining in
	   the buffer.  If we're processing data blocks we can have two cases,
	   one in which the limit is the amount of buffer space available and the
	   other in which the limit is the amount of data available.  If the
	   limit is set by the available data, we don't have to worry about
	   flushing extra data out of the block buffer into the main buffer, but
	   if the limit is set by the available buffer space we have to reduce
	   the amount we can copy in based on any extra data that will be
	   flushed out of the block buffer.

	   There are two possible approaches that can be used when the block
	   buffer is involved.  The first one copies as much as we can into the
	   buffer and, if that isn't enough, maxes out the block buffer with as
	   much remaining data as possible.  The second only copies in as much as
	   can fit into the buffer, even if there's room in the block buffer for
	   a few more bytes.  The second approach is preferable because although
	   either will give the impression of a not-quite-full buffer into which
	   no more data can be copied, the second minimizes the amount of data
	   which is moved into and out of the block buffer.

	   The first approach may seem slightly more logical, but will only
	   cause confusion in the long run.  Consider copying (say) 43 bytes to
	   a 43-byte buffer.  The first time this will succeed, after which there
	   will be 40 bytes in the buffer (reported to the caller) and 3 in the
	   block buffer.  If the caller tries to copy in 3 more bytes to "fill"
	   the main buffer, they'll again vanish into the block buffer.  A second
	   call with three more bytes will copy 2 bytes and return with 1
	   uncopied.  In effect this method of using the block buffer extends the
	   blocksize-quantized main buffer by the size of the block buffer, which
	   will only cause confusion when data appears to vanish when copied in */
	bytesToCopy = min( bytesToCopy, \
					   ( envelopeInfoPtr->bufSize - envelopeInfoPtr->bufPos ) - \
						 envelopeInfoPtr->blockBufferPos );
	if( bytesToCopy < 0 || envelopeInfoPtr->blockBufferPos < 0 )
		{
		/* Safety check that verifies segmentSize, length, bufPos, and
		   blockBufferPos before we start into the following code */
		assert( NOTREACHED );
		return( CRYPT_ERROR_BADDATA );
		}

	/* If we're given a zero length, return now.  This can happen if all
	   input is consumed in processing the headers (we're passed a zero
	   length) */
	if( bytesToCopy <= 0 )
		return( 0 );

	/* If its a block encryption mode we need to provide special handling for
	   odd data lengths that don't match the block size */
	if( envelopeInfoPtr->blockSize > 1 )
		{
		int bytesCopied = 0, quantizedBytesToCopy;

		/* If the new data will fit into the block buffer, copy it in now and
		   return */
		if( envelopeInfoPtr->blockBufferPos + bytesToCopy < \
			envelopeInfoPtr->blockSize )
			{
			memcpy( envelopeInfoPtr->blockBuffer + envelopeInfoPtr->blockBufferPos,
					buffer, bytesToCopy );
			envelopeInfoPtr->blockBufferPos += bytesToCopy;

			/* Adjust the segment size based on what we've consumed */
			envelopeInfoPtr->segmentSize -= bytesToCopy;

			return( bytesToCopy );
			}

		/* If there isn't room in the main buffer for even one more block,
		   exit without doing anything.  This leads to slightly anomalous
		   behaviour where, with no room for a complete block in the main
		   buffer, copying in a data length smaller than the block buffer
		   will lead to the data being absorbed by the block buffer due to
		   the previous section of code, but copying in a length larger than
		   the block buffer will result in no data at all being absorbed,
		   even if there is still room in the block buffer */
		if( envelopeInfoPtr->bufSize - envelopeInfoPtr->bufPos < \
			envelopeInfoPtr->blockSize )
			return( 0 );	/* No room for even one more block */

		/* There's room for at least one more block in the buffer.  First,
		   if there are leftover bytes in the block buffer, move them into
		   the main buffer */
		if( envelopeInfoPtr->blockBufferPos > 0 )
			{
			memcpy( bufPtr, envelopeInfoPtr->blockBuffer,
					envelopeInfoPtr->blockBufferPos );
			bytesCopied = envelopeInfoPtr->blockBufferPos;
			}
		envelopeInfoPtr->blockBufferPos = 0;

		/* Determine how many bytes we can copy into the buffer to fill it
		   to the nearest available block size */
		quantizedBytesToCopy = ( bytesToCopy + bytesCopied ) & \
							   envelopeInfoPtr->blockSizeMask;
		quantizedBytesToCopy -= bytesCopied;
		if( bytesToCopy < 0 || quantizedBytesToCopy <= 0 || \
			quantizedBytesToCopy > bytesToCopy )
			{
			/* Safety check */
			assert( NOTREACHED );
			return( CRYPT_ERROR_BADDATA );
			}

		/* Now copy across a number of bytes which is a multiple of the block
		   size and decrypt them.  Note that we have to use memmove() rather
		   than memcpy() because if we're sync'ing data in the buffer we're
		   doing a copy within the buffer rather than copying in external 
		   data */
		memmove( bufPtr + bytesCopied, buffer, quantizedBytesToCopy );
		envelopeInfoPtr->bufPos += bytesCopied + quantizedBytesToCopy;
		envelopeInfoPtr->segmentSize -= bytesToCopy;
		status = krnlSendMessage( envelopeInfoPtr->iCryptContext, 
								  IMESSAGE_CTX_DECRYPT, bufPtr, 
								  bytesCopied + quantizedBytesToCopy );
		if( cryptStatusError( status ) )
			return( status );
		assert( envelopeInfoPtr->bufPos >=0 && \
				envelopeInfoPtr->bufPos <= envelopeInfoPtr->bufSize );
		assert( envelopeInfoPtr->segmentSize >= 0 );

		/* If the payload has a definite length and we've reached its end,
		   set the EOC flag to make sure that we don't go any further */
		if( envelopeInfoPtr->payloadSize != CRYPT_UNUSED && \
			envelopeInfoPtr->segmentSize <= 0 )
			{
			status = processEOC( envelopeInfoPtr );
			if( cryptStatusError( status ) )
				return( status );
			}
		else
			{
			const int blockBufferBToC = bytesToCopy - quantizedBytesToCopy;

			/* Copy any remainder (the difference between the amount to copy
			   and the blocksize-quantized amount) into the block buffer */
			if( blockBufferBToC > 0 )
				memcpy( envelopeInfoPtr->blockBuffer, buffer + quantizedBytesToCopy,
						blockBufferBToC );
			envelopeInfoPtr->blockBufferPos = blockBufferBToC;
			}

		return( bytesToCopy );
		}

	/* It's unencrypted or encrypted with a stream cipher, just copy over as
	   much of the segment as we can and decrypt it if necessary */
	memcpy( envelopeInfoPtr->buffer + envelopeInfoPtr->bufPos, buffer,
			bytesToCopy );
	envelopeInfoPtr->bufPos += bytesToCopy;
	if( envelopeInfoPtr->segmentSize != CRYPT_UNUSED )
		envelopeInfoPtr->segmentSize -= bytesToCopy;
	if( envelopeInfoPtr->iCryptContext != CRYPT_ERROR )
		{
		status = krnlSendMessage( envelopeInfoPtr->iCryptContext, 
								  IMESSAGE_CTX_DECRYPT, bufPtr, 
								  bytesToCopy );
		if( cryptStatusError( status ) )
			return( status );
		}

	/* If the payload has a definite length and we've reached its end, set
	   the EOC flag to make sure that we don't go any further */
	if( envelopeInfoPtr->payloadSize != CRYPT_UNUSED && \
		envelopeInfoPtr->segmentSize <= 0 )
		{
		status = processEOC( envelopeInfoPtr );
		if( cryptStatusError( status ) )
			return( status );
		}

	return( bytesToCopy );
	}

/* Copy data into the de-enveloping envelope.  Returns the number of bytes
   copied */

static int copyToDeenvelope( ENVELOPE_INFO *envelopeInfoPtr, 
							 const BYTE *buffer, const int length )
	{
	BYTE *bufPtr = ( BYTE * ) buffer;
	int currentLength = length, bytesCopied;

	assert( isWritePtr( envelopeInfoPtr, sizeof( ENVELOPE_INFO ) ) );
	assert( length > 0 );
	assert( isReadPtr( buffer, length ) );
	assert( envelopeInfoPtr->bufPos >=0 && \
			envelopeInfoPtr->bufPos <= envelopeInfoPtr->bufSize );

	/* If we're trying to copy into a full buffer, return a count of 0 bytes
	   (the calling routine may convert this to an overflow error if
	   necessary) */
	if( envelopeInfoPtr->bufPos >= envelopeInfoPtr->bufSize )
		return( 0 );

	/* If we're verifying a detached signature, just hash the data and exit.
	   We don't have to check for problems with the context at this point
	   since they'll be detected when we complete the hashing, and we don't 
	   have to check whether hashing is active or not since it'll always be 
	   active for detached data, which is hashed and discarded */
	if( envelopeInfoPtr->flags & ENVELOPE_DETACHED_SIG )
		{
		ACTION_LIST *hashActionPtr;

		assert( envelopeInfoPtr->dataFlags & ENVDATA_HASHACTIONSACTIVE );
		assert( envelopeInfoPtr->actionList != NULL );

		for( hashActionPtr = envelopeInfoPtr->actionList;
			 hashActionPtr != NULL && hashActionPtr->action == ACTION_HASH; 
			 hashActionPtr = hashActionPtr->next )
			krnlSendMessage( hashActionPtr->iCryptHandle, IMESSAGE_CTX_HASH, 
							 ( void * ) buffer, currentLength );
		return( currentLength );
		}

	/* Keep processing data until either we run out of input or we can't copy
	   in any more data.  The code sequence within this loop acts as a simple
	   FSM so that if we exit at any point then the next call to this
	   function will resume where we left off */
	do
		{
		int segmentCount, status;

		/* If there's no segment information currently available, we need to
		   process a segment header before we can handle any data.  The use 
		   of a loop is necessary to handle some broken implementations that
		   emit zero-length sub-segments.  We limit the segment count to 10
		   sub-segments to make sure that we don't spend forever trying to 
		   process extremely broken data */
		for( segmentCount = 0; \
			 segmentCount < 10 && envelopeInfoPtr->segmentSize <= 0; \
			 segmentCount++ )
			{
			status = getNextSegment( envelopeInfoPtr, bufPtr, currentLength );
			if( status == OK_SPECIAL )
				/* We got the length via some other mechanism because it's a 
				   definite-length or non-segmenting encoding, no input was
				   consumed and we can exit */
				break;
			if( cryptStatusError( status ) )
				return( status );
			bufPtr += status;
			currentLength -= status;

			/* If we've reached the EOC or consumed all of the input data, 
			   exit */
			if( ( envelopeInfoPtr->dataFlags & ENVDATA_ENDOFCONTENTS ) || \
				currentLength <= 0 )
				return( length - currentLength );
			}
		if( segmentCount >= 10 )
			/* We've processed ten consecutive sub-segments in a row, there's 
			   something wrong with the input data */
			return( CRYPT_ERROR_BADDATA );

		/* Copy the data into the envelope, decrypting it as we go if 
		   necessary */
		bytesCopied = copyData( envelopeInfoPtr, bufPtr, currentLength );
		if( cryptStatusError( bytesCopied ) )
			return( bytesCopied );
		bufPtr += bytesCopied;
		currentLength -= bytesCopied;

		/* Sanity check to catch copying errors */
		assert( envelopeInfoPtr->bufPos >= 0 && \
				envelopeInfoPtr->bufPos <= envelopeInfoPtr->bufSize );
		assert( currentLength >= 0 );
		assert( ( envelopeInfoPtr->segmentSize >= 0 ) || \
				( ( envelopeInfoPtr->dataFlags & ENVDATA_NOSEGMENT ) && \
				  ( envelopeInfoPtr->payloadSize == CRYPT_UNUSED ) && \
				  ( envelopeInfoPtr->segmentSize == CRYPT_UNUSED ) ) );
		}
	while( currentLength > 0 && bytesCopied > 0 );

	return( length - currentLength );
	}

/****************************************************************************
*																			*
*								Copy from Envelope							*
*																			*
****************************************************************************/

/* Copy data from the envelope.  Returns the number of bytes copied */

static int copyFromDeenvelope( ENVELOPE_INFO *envelopeInfoPtr, BYTE *buffer,
							   int length )
	{
	BYTE *bufPtr = envelopeInfoPtr->buffer;
	const BOOLEAN isLookaheadRead = ( length < 0 ) ? TRUE : FALSE;
	int bytesToCopy, bytesCopied, remainder;
	int oobBytesCopied = 0;

	assert( isWritePtr( envelopeInfoPtr, sizeof( ENVELOPE_INFO ) ) );
	assert( envelopeInfoPtr->bufPos >=0 && \
			envelopeInfoPtr->bufPos <= envelopeInfoPtr->bufSize );
	assert( envelopeInfoPtr->oobBufPos >= 0 && \
			envelopeInfoPtr->oobBufPos <= OOB_BUFFER_SIZE );

	/* Remember how much data we need to copy.  A negative length specifies 
	   that this is a speculative/lookahead read, so we turn it into a 
	   positive value if necessary */
	bytesToCopy = length = ( length < 0 ) ? -length : length;
	if( bytesToCopy < 0 )
		{
		/* Safety checks, also covers some later operations like the OOB 
		   copy */