OOXML Crypto Stream

Create, open and save password-protected Microsoft Office 2007 files.

Works with Office 2007 files and encryption scheme only (.docx, .xlsx, .pptx). No support for older formats.

Includes slightly modified ExcelPackage for accessing Excel 2007 .xlsx files.

Download the binary release (68k).

Written in C# / .Net 3.0

Sample Code

using (OfficeCryptoStream stream = OfficeCryptoStream.Open("a.xlsx", "password"))
{
    // Do stuff (e.g. create System.IO.Packaging.Package or 
    // ExcelPackage from the stream, make changes and save)

    // Change the password (optional)
    stream.Password = "newPassword";

    // Encrypt and save the file
    stream.Save();
}

Details

Office 2007 files (Word 2007 .docx, Excel 2007 .xlsx, Power Point 2007 .pptx) are zip files containing XML. They are relatively easy read and modify.

Microsoft's Package class provides access to plaintext Office 2007 files. This project adds support for password-protected files (OLE compound files with Microsoft's proprietary encryption applied).

Pieces

This project does little or no heavy lifting. It wraps together several open-source pieces in a single, easy-to-use package.

• ExcelPackage for accessing .xlsx spreadsheets. Modified to accept stream in the constructor.
• Lyquidity OoxmlCrypto open source sample code for encrypting/decrypting the files. Based on info from David LeBlanc from Microsoft.
• NPOI project for access to OLE2 Compount Container files (those are legacy Office format, used to wrap encrypted Office 2007 stream). This replaces Lyquidity's properietary container access library.