Encrypting Excel Files with C++

Microsoft Excel (97 - 365) enables you to encrypt and password protect your spreadsheets. It uses algorithms provided by a cryptographic service provider, or CSP, a set of cryptographic algorithms with different properties. The default CSP is ‘Office 97/2000 Compatible’ or ‘Weak Encryption (XOR)’. It’s important to choose the proper encryption key length. Some CSPs don’t support more than 40 or 56 bits. That’s considered to be weak encryption. For strong encryption, a minimum key length of 128 bits is required. Microsoft Windows contains CSPs that offer strong encryption types as well, for example the ‘Microsoft Strong Cryptographic Provider’. To give you an idea, 128 bits encryption is what banks use to encrypt the connection with their Internet Banking systems.

Aspose.Cells allows you to encrypt and password protect Microsoft Excel files with your desired encryption type.

Using Microsoft Excel

To set file encryption settings in Microsoft Excel (here Microsoft Excel 2003):

From the Tools menu, select Options. A dialog will appear.
Select the Security tab.
Input a password and click Advanced
Choose the encryption type and confirm the password.

Encryption with Aspose.Cells

The following example shows how to encrypt and password protect an Excel file using the Aspose.Cells API.

#include <iostream>
#include "Aspose.Cells.h"
using namespace Aspose::Cells;

int main()
{
    Aspose::Cells::Startup();

    // For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-C

    // Source directory path
    U16String srcDir(u"..\\Data\\01_SourceDirectory\\");

    // Output directory path
    U16String outDir(u"..\\Data\\02_OutputDirectory\\");

    // Path of input excel file
    U16String inputFilePath = srcDir + u"Book1.xls";

    // Path of output excel file
    U16String outputFilePath = outDir + u"encryptedBook1.out.xls";

    // Instantiate a Workbook object and open the excel file
    Workbook workbook(inputFilePath);

    // Specify XOR encryption type
    workbook.SetEncryptionOptions(EncryptionType::XOR, 40);

    // Specify Strong Encryption type (RC4, Microsoft Strong Cryptographic Provider)
    workbook.SetEncryptionOptions(EncryptionType::StrongCryptographicProvider, 128);

    // Password protect the file
    workbook.GetSettings().SetPassword(u"1234");

    // Save the encrypted excel file
    workbook.Save(outputFilePath);

    std::cout << "File encrypted and saved successfully!" << std::endl;

    Aspose::Cells::Cleanup();
}

Specifying Password to modify Option

The following example shows how to set the Password to modify Microsoft Excel option for an existing file using the Aspose.Cells API.

#include <iostream>
#include "Aspose.Cells.h"
using namespace Aspose::Cells;

int main()
{
    Aspose::Cells::Startup();

    // For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-C

    // Source directory path
    U16String srcDir(u"..\\Data\\01_SourceDirectory\\");

    // Output directory path
    U16String outDir(u"..\\Data\\02_OutputDirectory\\");

    // Path of input excel file
    U16String inputFilePath = srcDir + u"Book1.xls";

    // Path of output excel file
    U16String outputFilePath = outDir + u"SpecifyPasswordToModifyOption.out.xls";

    // Create workbook
    Workbook workbook(inputFilePath);

    // Set the password for modification
    workbook.GetSettings().GetWriteProtection().SetPassword(u"1234");

    // Save the excel file
    workbook.Save(outputFilePath);

    std::cout << "Password for modification set successfully!" << std::endl;

    Aspose::Cells::Cleanup();
}

Verify the password of the encrypted file

To verify the password of the encrypted file, Aspose.Cells for C++ provides the VerifyPassword method. This method accepts two parameters, the file stream and the password that needs to be verified. The following code snippet demonstrates the use of the VerifyPassword method to verify whether the provided password is valid or not.

#include <iostream>
#include <fstream>
#include <vector>
#include "Aspose.Cells.h"
using namespace Aspose::Cells;

int main()
{
    Aspose::Cells::Startup();

    U16String srcDir(u"..\\Data\\01_SourceDirectory\\");
    U16String inputPath = srcDir + u"EncryptedBook1.xlsx";
    std::vector<uint8_t> fileData;

    std::ifstream file(inputPath.ToUtf8(), std::ios::binary);
    if (file)
    {
        file.seekg(0, std::ios::end);
        fileData.resize(file.tellg());
        file.seekg(0, std::ios::beg);
        file.read(reinterpret_cast<char*>(fileData.data()), fileData.size());
    }
    Vector<uint8_t> data(fileData.data(), static_cast<int32_t>(fileData.size()));
    bool isPasswordValid = FileFormatUtil::VerifyPassword(data, u"123456");
    std::cout << "Password is Valid: " << std::boolalpha << isPasswordValid << std::endl;

    Aspose::Cells::Cleanup();
}

Encryption/Decryption of ODS file with Aspose.Cells

Aspose.Cells allows you to encrypt and decrypt ODS files. Decrypted ODS files can be opened both in Excel and OpenOffice, however encrypted ODS files can only be opened by OpenOffice after providing the password. Excel cannot open the encrypted ODS file and may raise a warning message. The encryption options are not applicable for ODS files unlike other file types. For encrypting an ODS file, load the file and set the WorkbookSettings.GetPassword() value to the actual password before saving it. The output encrypted ODS file can be opened in OpenOffice only.

#include <iostream>
#include "Aspose.Cells.h"
using namespace Aspose::Cells;

int main()
{
    Aspose::Cells::Startup();

    // For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-C++

    // Source directory path
    U16String sourceDir = u"..\\Data\\01_SourceDirectory\\";

    // Output directory path
    U16String outputDir = u"..\\Data\\02_OutputDirectory\\";

    // Open an ODS file
    Workbook workbook(sourceDir + u"sampleODSFile.ods");

    // Password protect the file
    workbook.GetSettings().SetPassword(u"1234");

    // Save the ODS file
    workbook.Save(outputDir + u"outputEncryptedODSFile.ods");

    std::cout << "ODS file password protected and saved successfully!" << std::endl;

    Aspose::Cells::Cleanup();
    return 0;
}

For decrypting an ODS file, load the file by providing a password in the LoadOptions.GetPassword(). Once the file is loaded, set the WorkbookSettings.GetPassword() string to null.

#include <iostream>
#include "Aspose.Cells.h"
using namespace Aspose::Cells;

int main()
{
    Aspose::Cells::Startup();

    // Path to the source directory
    U16String sourceDir = u"..\\Data\\01_SourceDirectory\\";

    // Output directory
    U16String outputDir = u"..\\Data\\02_OutputDirectory\\";

    // Open an encrypted ODS file
    LoadOptions loadOptions(LoadFormat::Ods);
    
    // Set original password
    loadOptions.SetPassword(u"1234");

    // Load the encrypted ODS file with the appropriate load options
    Workbook workbook(sourceDir + u"sampleEncryptedODSFile.ods", loadOptions);

    // Set the password to null
    workbook.GetSettings().SetPassword(nullptr);

    // Save the decrypted ODS file
    workbook.Save(outputDir + u"outputDecryptedODSFile.ods");

    std::cout << "Decrypted ODS file saved successfully!" << std::endl;

    Aspose::Cells::Cleanup();
}

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