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I N T R O D U C I N G   . N E T  A S S E M B L I E S

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The GAC is located under a subdirectory of your Windows directory named Assembly (e.g.,

C:\Windows\Assembly), as shown in Figure 15-17.

Figure 15-17.

The global assembly cache

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Note

You cannot install executable assemblies (

*.exe

) into the GAC. Only assemblies that take the 

*.dll

file

extension can be deployed as a shared assembly.

Understanding Strong Names

Before you can deploy an assembly to the GAC, you must assign it a strong name, which is used to

uniquely identify the publisher of a given .NET binary. Understand that a “publisher” could be an

individual programmer, a department within a given company, or an entire company at large.

In some ways, a strong name is the modern day .NET equivalent of the COM globally unique

identifier (GUID) identification scheme. If you have a COM background, you may recall that AppIDs

are GUIDs that identify a particular COM application. Unlike COM GUID values (which are nothing

more than 128-bit numbers), strong names are based (in part) on two cryptographically related keys

(termed the 

public key and the private key), which are much more unique and resistant to tamper-

ing than a simple GUID.

Formally, a strong name is composed of a set of related data, much of which is specified using

assembly-level attributes:

• The friendly name of the assembly (which you recall is the name of the assembly minus the

file extension)

• The version number of the assembly (assigned using the [AssemblyVersion] attribute)

• The public key value (assigned using the [AssemblyKeyFile] attribute)

• An optional culture identity value for localization purposes (assigned using the

[AssemblyCulture] attribute)

• An embedded 

digital signature created using a hash of the assembly’s contents and the

private key value

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