Many managed applications start up slower than they really need to because of time spent verifying their strong name signatures.  For most of these applications, the strong name verification isn't buying the application anything - especially fully trusted desktop applications that are using C# as a better C++.

Since these applications were paying the cost of verifying their assemblies at load time, but were not receiving any benefit from that cost, we've made a change in .NET 3.5 SP1 which lets these applications bypass strong name signature verification.

Specifically, for any assembly which is:

  1. Fully signed (delay signed assemblies still require a skip verification entry)
  2. Fully trusted (without considering its strong name evidence)
  3. Loaded into a Fully trusted AppDomain
  4. Loaded from a location under the AppDomain's ApplicationBase

The CLR will no longer verify the assembly's strong name when it is loaded.

This provides an assembly load performance win for most full trust applications, however not all applications will want to have their fully trusted assemblies skip strong name verification.  If your application wants to re-enable strong name verification, it can add a .exe.config file with the following setting:

<configuration>
    <runtime>
        <bypassTrustedAppStrongNames enabled="false"/>
    </runtime>
</configuration>

Also, if a machine administrator wants to disable strong name bypass for all assemblies loaded on a particular computer, they can set the DWORD registry value named AllowStrongNameBypass to 0 under the HKLM\Software\Microsoft\.NETFramework key:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework]
"AllowStrongNameBypass"=dword:00000000

(The usual disclaimers apply about modifying the registry only if you know what you're doing)

As with other strong name configuration, on a 64 bit machine this registry setting will need to be set in both the 32 and 64 bit HKLM\Software keys.

For users who have the SDK installed, SN.exe also adds an option to query and update this key for you.  You can run SN -Pb [y|n] to allow or disable assemblies from bypassing strong name verification on your machine. (Again, using both a 32 and 64 bit SN.exe on 64 bit machines).  SN -Pb with no argument will display the current value of the setting.