Microsoft introduces improvements for ZIP file handling in .NET 4.5 in the System.IO.Compression namespace. Namely the classes ZipArchive and ZipFile.
However, I have not yet seen a way to use native .NET ZIP file handling for password protected files. Is there a way to achieve this? (I am aware that there are pretty good 3rd party zip file libraries, that is not the question.)
Unfortunately not. There is no support within the .Net Framework 4.5 for password protected zip files. In this case you have to switch to one of the well known 3rd party libraries.