Handling encrypted documents - basics

PdfForQtLib/sources/pdfsecurityhandler.h

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+//    Copyright (C) 2019 Jakub Melka
+//
+//    This file is part of PdfForQt.
+//
+//    PdfForQt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    PdfForQt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef PDFSECURITYHANDLER_H
+#define PDFSECURITYHANDLER_H
+
+#include "pdfglobal.h"
+#include "pdfobject.h"
+
+#include <QByteArray>
+#include <QSharedPointer>
+
+#include <map>
+
+namespace pdf
+{
+
+enum class EncryptionMode
+{
+    None,       ///< Document is not encrypted
+    Standard,   ///< Document is encrypted and using standard security handler
+    Custom      ///< Document is encrypted and using custom security handler. Custom handlers must return this value.
+};
+
+enum class CryptFilterType
+{
+    None,       ///< The application shall decrypt the data using the security handler
+    V2,         ///< Use file encryption key for RC4 algorithm
+    AESV2,      ///< Use file encryption key for AES algorithm
+    AESV3,      ///< Use file encryption key for AES 256 bit algorithm
+    Identity,   ///< Don't decrypt anything, use identity function
+};
+
+enum class AuthEvent
+{
+    DocOpen,    ///< Authorize on document open
+    EFOpen      ///< Authorize when accessing embedded file stream
+};
+
+enum class CryptFilterApplication
+{
+    String,         ///< Apply filter to decrypt/encrypt strings
+    Stream,         ///< Apply filter to decrypt/encrypt streams
+    EmbeddedFile    ///< Apply filter to decrypt/encrypt embedded file streams
+};
+
+struct CryptFilter
+{
+    CryptFilterType type = CryptFilterType::None;
+    AuthEvent authEvent = AuthEvent::DocOpen;
+};
+
+class PDFSecurityHandler;
+using PDFSecurityHandlerPointer = QSharedPointer<PDFSecurityHandler>;
+
+class PDFSecurityHandler
+{
+public:
+    explicit PDFSecurityHandler() = default;
+    virtual ~PDFSecurityHandler() = default;
+
+    virtual EncryptionMode getMode() const = 0;
+
+    /// Creates a security handler from the object. If object is null, then
+    /// "None" security handler is created. If error occurs, then exception is thrown.
+    /// \param encryptionDictionaryObject Encryption dictionary object
+    static PDFSecurityHandlerPointer createSecurityHandler(const PDFObject& encryptionDictionaryObject);
+
+private:
+    /// Version of the encryption, shall be a number from 1 to 5, according the
+    /// PDF specification. Other values are invalid.
+    int m_V = 0;
+
+    /// Length of the key to encrypt/decrypt the document in bits. Only valid
+    /// for V = 2 or V = 3, otherwise it is invalid.
+    int m_keyLength = 40;
+
+    /// Map containing crypt filters.
+    std::map<QByteArray, CryptFilter> m_cryptFilters;
+
+    /// Crypt filter for decrypting strings
+    CryptFilter m_filterStrings;
+
+    /// Crypt filter for decrypting streams
+    CryptFilter m_filterStreams;
+
+    /// Crypt filter for decrypting embedded files
+    CryptFilter m_filterEmbeddedFiles;
+};
+
+/// Specifies the security of unencrypted document
+class PDFNoneSecurityHandler : public PDFSecurityHandler
+{
+public:
+    virtual EncryptionMode getMode() const { return EncryptionMode::None; }
+};
+
+/// Specifies the security using standard security handler (see PDF specification
+/// for details).
+class PDFStandardSecurityHandler : public PDFSecurityHandler
+{
+public:
+    virtual EncryptionMode getMode() const { return EncryptionMode::Standard; }
+
+private:
+
+};
+
+}   // namespace pdf
+
+
+#endif // PDFSECURITYHANDLER_H