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MS-Offcrypto Examples

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In response to some questions I've gotten about details of MS-OFFCRYPTO, I've created a CodePlex project to contain sample code demonstrating the documentation. You can find it at https://www.codeplex.com/offcrypto. I had originally wanted to include sample code in MS-OFFCRYPTO itself, but we couldn't do that. Instead, we can put sample code on CodePlex. To keep it real, I did the work from my home system where I don't have access to the original source, and wrote it in C# instead of the original C++ to shake out library differences.

Please note that the sample code is not intended to replace proper documentation. In the course of helping a customer with their attempt to implement the AES encryption, we figured out a problem with the CryptDeriveKey documentation, and got that updated. If there are any nuances of the approach that are in the sample, but not the documentation, we'll update the document to match. The sample code is there to verify that the documentation is complete, and to help anyone who wants to do this.

Currently, there are 2 projects – the first is ExtractStream. I'd needed a way to get streams out of structured storage so that the rest of the sample code could be a lot simpler, and I'm also not too good at managed-unmanaged interop. You use this app to extract the stream you'd like to parse – the rest of the examples will use this. It may turn out to be a good thing having this as a stand-alone project – there's some other features we can build on this that might be helpful.

The second project is OoxmlEncrypt – it demonstrates parsing and validating an EncryptionInfo stream, as well as validating the password.

I have a third project that I need to post which does the same for the CAPI RC4 encryption, which is default for encrypted PowerPoint files, and can show up as a format for Word and Excel files. That's done – I just need to post it.

A fourth project that I'm working on (hindered by the fact that .NET has no RC4) is to demonstrate the legacy 40-bit RC4.

After that, as I find time, I'll move on to signatures. BTW, if someone else would like to contribute to the project, that's certainly possible – just let me know, and sign a release, then we can add other people as devs.

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