Limitations on Calling Strong Named Components

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In many cases, mobile code should be granted fewer permissions than full trust. However, this decision limits what libraries mobile code can call. The System.Security.AllowPartiallyTrustedCallersAttribute , nicknamed APTCA, is the cause of these restrictions. If code has been granted less than full trust, it cannot call into an assembly signed with a strong name unless that assembly is also marked with APTCA.

APTCA was created so that malicious semi-trusted code has fewer vectors of attack on a client. A given client will probably have many assemblies installed in the Global Assembly Cache, and each assembly could expose a vulnerability. Because the default behavior of strong named assemblies is to deny access to semi-trusted code, a developer will have to at least consider whether a given assembly should be used by partially trusted code.

Because APTCA is involved with the "contract" between managed code libraries and semi-trusted code, you should consider how security policy is involved with this. When you plan on giving trust to mobile code, you should look at what assemblies that mobile code will use. If any of those libraries have a strong name and do not contain APTCA, you have to grant full trust to the mobile code if you want it to run successfully. If this is too dangerous, your clients simply will not be able to run that particular mobile code.

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