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Decryption of document data

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This commit is contained in:
Jakub Melka
2019-08-13 11:45:36 +02:00
parent cfc9593d14
commit 2623ef6825
5 changed files with 428 additions and 5 deletions
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35
PdfForQtLib/sources/pdfdocumentreader.cpp
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@ -268,6 +268,12 @@ PDFDocument PDFDocumentReader::readFromBuffer(const QByteArray& buffer)
// Now, we are ready to scan all objects
std::for_each(std::execution::parallel_policy(), occupiedEntries.cbegin(), occupiedEntries.cend(), processEntry);
if (m_result != Result::OK)
{
// Do not proceed further, if document loading failed
return PDFDocument();
}
// ------------------------------------------------------------------------------------------
// SECURITY - handle encrypted documents
// ------------------------------------------------------------------------------------------
@ -304,9 +310,11 @@ PDFDocument PDFDocumentReader::readFromBuffer(const QByteArray& buffer)
}
}
PDFObjectReference encryptObjectReference;
PDFObject encryptObject = trailerDictionary->get("Encrypt");
if (encryptObject.isReference())
{
encryptObjectReference = encryptObject.getReference();
PDFObjectReference encryptObjectReference = encryptObject.getReference();
if (static_cast<size_t>(encryptObjectReference.objectNumber) < objects.size() && objects[encryptObjectReference.objectNumber].generation == encryptObjectReference.generation)
{
@ -330,6 +338,33 @@ PDFDocument PDFDocumentReader::readFromBuffer(const QByteArray& buffer)
throw PDFParserException(PDFTranslationContext::tr("Authorization failed. Bad password provided."));
}
// Now, decrypt the document, if we are authorized. We must also check, if we have to decrypt the object.
// According to the PDF specification, following items are ommited from encryption:
// 1) Values for ID entry in the trailer dictionary
// 2) Any strings in Encrypt dictionary
// 3) String/streams in object streams (entire object streams are encrypted)
// 4) Hexadecimal strings in Content key in signature dictionary
//
// Trailer dictionary is not decrypted, because PDF specification provides no algorithm to decrypt it,
// because it needs object number and generation for generating the decrypt key. So 1) is handled
// automatically. 2) is handled in the code below. 3) is handled also automatically, because we do not
// decipher object streams here. 4) must be handled in the security handler.
if (securityHandler->getMode() != EncryptionMode::None)
{
auto decryptEntry = [encryptObjectReference, &securityHandler, &objects](const PDFXRefTable::Entry& entry)
{
if (encryptObjectReference.objectNumber != 0 && encryptObjectReference == entry.reference)
{
// 2) - Encrypt dictionary
return;
}
objects[entry.reference.objectNumber].object = securityHandler->decryptObject(objects[entry.reference.objectNumber].object, entry.reference);
};
std::for_each(std::execution::parallel_policy(), occupiedEntries.cbegin(), occupiedEntries.cend(), decryptEntry);
}
// ------------------------------------------------------------------------------------------
// SECURITY - security handler created
// ------------------------------------------------------------------------------------------