Add support for encrypting XLSX files with a password

[modeverv]

Add support for encrypting XLSX files with a password

I've implemented this feature by studying Apache POI’s code base.
With this PR, NPOI can now create password-protected .xlsx files.

Basic usage

XSSFWorkbook wb = new();
ISheet sheet = wb.CreateSheet("Sheet1");
sheet.CreateRow(0).CreateCell(0).SetCellValue("Hello");
// do something to xlsx...

using PasswordXlsxOutputStream outputStream = new(outputPath, password);
wb.Write(outputStream);

Tests

Includes byte-level comparison with a file encrypted by Apache POI.
See: TestCases.POIFS.FileSystem.TestPasswordXlsxOutputStream.TestEncryptor

Notes

I’m relatively new to C#, POI and NPOI.
Please review the code and give feedback on design, naming, and integration with the existing NPOI style.

ref: #1641

Thank you!

[tonyqus]

Reference: https://poi.apache.org/encryption.html

XML-based formats - Encryption

try (POIFSFileSystem fs = new POIFSFileSystem()) {
    EncryptionInfo info = new EncryptionInfo(EncryptionMode.agile);
    // EncryptionInfo info = new EncryptionInfo(EncryptionMode.agile, CipherAlgorithm.aes192, HashAlgorithm.sha384, -1, -1, null);
    Encryptor enc = info.getEncryptor();
    enc.confirmPassword("foobaa");
    // Read in an existing OOXML file and write to encrypted output stream
    // don't forget to close the output stream otherwise the padding bytes aren't added
    try (OPCPackage opc = OPCPackage.open(new File("..."), PackageAccess.READ_WRITE);
        OutputStream os = enc.getDataStream(fs)) {
        opc.save(os);
    }
    // Write out the encrypted version
    try (FileOutputStream fos = new FileOutputStream("...")) {
        fs.writeFilesystem(fos);
    }
}

https://github.com/nissl-lab/npoi/blob/master/ooxml/POIFS/Crypt/Agile/AgileEncryptionInfoBuilder.cs

[tonyqus]

Although the code is working (as you mentioned), it's not the expected coding style of NPOI.

using PasswordXlsxOutputStream outputStream = new(outputPath, password);
wb.Write(outputStream);

One way is to add IWorkbook.Write(stream, password) as a new interface for OOXML Excel files

[modeverv]

thanks for review. I check your comment tommorow.
I now checking CI error.

Errors & Warnings
  [ERR] Test: Target Test has thrown an exception
​

I've write a "can not pass test" code?

[tonyqus]

windows-latest test always fails. Please ignore the error.

[modeverv]

@tonyqus

Thank you for your review! I've updated the implementation to follow the NPOI coding style as you suggested.

Changes

• Added IWorkbook.Write(stream, password) method for easier usage
• Kept the POI-compatible approach using EncryptionInfo and Encryptor

Usage Examples

Easy Way (New NPOI-style API)

XSSFWorkbook wb = new();
ISheet sheet = wb.CreateSheet("Sheet1");
sheet.CreateRow(0).CreateCell(0).SetCellValue("Hello");

using(FileStream fs = File.Create(outputPath))
{
    wb.Write(fs, password);
}

POI-Compatible Way

csharpXSSFWorkbook wb = new();
ISheet sheet = wb.CreateSheet("Sheet1");
sheet.CreateRow(0).CreateCell(0).SetCellValue("Hello");

using(POIFSFileSystem fs = new())
{
    EncryptionInfo info = new(EncryptionMode.AgileXlsx);
    Encryptor enc = info.Encryptor;
    enc.ConfirmPassword(password);
    
    using(OutputStream os = enc.GetDataStream(fs))
    {
        wb.Write(os);
    }
    
    using(FileStream fos = File.Create(outputPath))
    {
        fs.WriteFileSystem(fos);
    }
}

Please let me know if there are any other changes needed. Thank you!

[modeverv]

add encrypt options

• AES-256 + SHA-256
• AES-192 + SHA-384
• AES-256 + SHA-512
• AES-128 + MD5