NuGet does not currently support code signing for package or nuspec files, so the author of the package cannot truly be identified. This issue was raised as a feature request in 2010, but it didn’t get much attention and hasn’t been implemented. See http://nuget.codeplex.com/workitem/79.
Currently an already existing package NuGet can only be upgraded by the same account that it was originally uploaded by but this does not verify the actual author of the code which I believe is what you are getting at.
Outside of NuGet, code signing for assemblies still exists. Based on this I would suggest that you ideally:
- Only use signed assemblies from a trusted publisher.
- Use strong name references in your projects (which binds the project/assemblies to a specific public key).
- Verify the signature for each assembly you download.
Possibly another concern is that a NuGet packages can have PowerShell install/uninstall scripts attached to it which are automatically run when using the NuGet package command-line. NuGet 1.4+ does support code signing for PowerShell scripts so I would suggest leaving PowerShell execution policy to RemoteSigned.
Alternatively don’t use NuGet and download the .msi/.exe from an official release and verify the signature on the file.