Add Encrypted File Relationship to encrypted parts and models

[feliperoos]

As stated by Secure Content spec item 3.3,

"OPC parts that are encrypted MUST be associated with the package root through a Encrypted File relationship, and each SHOULD have an entry in the Key Store. If a custom OPC part is not referenced by a Encrypted File relationship it is assumed they are not encrypted and MUST NOT be any entry in the Key store associated to the file"

@martinweismann and @jordig100 I think this is one left over we forgot to add. Just have a question: the text mention package root. I just want to make sure that the relationship to be added is not on the package root model rels, rather at 'package root' rels (the sample provided makes it a bit confusing as external models aren't referenced from the package root rels).

If that's the case, we've the ability to add this relationship to the root model when we detect a part must be wrapped for encryption,

lib3mf/Source/Model/Writer/NMR_KeyStoreOpcPackageWriter.cpp

Lines 140 to 145 in 8d4a912

	auto pPart = m_pPackageWriter->addPart(sPath);
	NMR::PKeyStoreResourceData rd = keyStore->findResourceData(sPath);
	if (nullptr != rd) {
	if (secureContext->hasDekCtx()) {
	return wrapPartStream(rd, pPart);
	} else {

Another option would be to have it right before we finish writing the package

lib3mf/Source/Model/Writer/NMR_KeyStoreOpcPackageWriter.cpp

Lines 162 to 168 in 8d4a912

	if (!keyStore->empty()) {
	POpcPackagePart pKeyStorePart = m_pPackageWriter->addPart(PACKAGE_3D_KEYSTORE_URI);
	m_pPackageWriter->addContentType(pKeyStorePart, PACKAGE_KEYSTORE_CONTENT_TYPE);
	m_pPackageWriter->addRootRelationship(PACKAGE_KEYSTORE_RELATIONSHIP_TYPE, pKeyStorePart.get());
	m_pPackageWriter->addRootRelationship(PACKAGE_MUST_PRESERVE_RELATIONSHIP_TYPE, pKeyStorePart.get());
	PXmlWriter_Native pXMLWriter4KeyStore = std::make_shared<CXmlWriter_Native>(pKeyStorePart->getExportStream());

Let me now what you think.

[jordig100]

Hi @feliperoos, this is already captured in the issue: 3MFConsortium/spec_securecontent#12

I think the asnwer is just to remove the "root" word from that sentence.

In the following link you an find the proposed change: https://github.com/3MFConsortium/spec_securecontent/blob/dev/3MF%20Secure%20Content.md#33-encrypted-file-relationship