This post originated from an RSS feed registered with .NET Buzz by Tim Sneath. Original Post: Limiting Callers to a .NET Assembly Feed Title: Tim Sneath's Blog Feed URL: /msdnerror.htm?aspxerrorpath=/tims/Rss.aspx Feed Description: Random mumblings on Microsoft, .NET, and other topics. Latest .NET Buzz Posts Latest .NET Buzz Posts by Tim Sneath Latest Posts From Tim Sneath's Blog

I've been asked the same question several times over the last couple of months, which suggests that possibly the answer isn't as well known as I presumed. Since I have to remind myself of the specifics of the answer each time, I figured I'd post both question and answer to save us all time in the long run!

Q. How can I limit access to a .NET assembly that I've created? I've got two separate assemblies A and B. A references B and uses a number of instance methods on B, but I don't want any other assembly to be able to access B. In effect, I'd like to make B "private" to my application. Is there any way to achieve that with .NET?

A. There are probably a number of ways to achieve this, but the simplest involves signing your calling assembly A with a unique public / private key pair (use sn -k to achieve this). Once it's signed, you can use the StrongNameIdentityPermission attribute on the callee assembly B to demand that any callers are signed with a matching public key. If any other assembly tries to call B that isn't signed with the same key, a SecurityException will be thrown.

For more information on the StrongNameIdentityPermission attribute, see the appropriate topic in the MSDN Library. There's also a good walkthrough here.