Assembly security

Hi,

I have written a class library and i don't want unauthorized access to
some (or all) methods in this library. With some research , i found that
i can use strongly named assemblies for this purpose

Here is what i did:
1- I created a consumer assembly signed with myKeyFile.snk
2- I get public key of this assembly with secutil.exe
3- I added StrongNameIdentityPermissionAttribute to the methods of class
library with LinkDemand option and the public key of consumer assembly
4- I signed my class library with a key file also,otherwise i cannot
reference it to consumer assembly.

Now i get it work, but i got a question. With this method all the
consumers of class library should be signed with same key file.
What if consumer assembly has some other references that have
StrongNameIdentityPermissionAttribute with different public keys ?
as far as i know ,we cannot sign an assembly with more than one key file.

and is there any other method to get same functionality?

thanks so much
Yener