GLOBAL ASSEMBLY CACHE

What is GAC?

The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer. You should share assemblies by installing them into the global assem...

What is Global Assembly Cache (GAC) and what is the purpose of it? (How to make an assembly to public? Steps) How more than one version of an assembly can keep in same place?

Each computer where the common language runtime is installed has a machine-wide code cache called the global assembly cache. The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer. You should share assemblies by installing them into the global assembly cache only when you need to.
Steps
- Create a strong name using sn.exe tool
eg: sn -k keyPair.snk
- with in AssemblyInfo.cs add the generated file name
eg: [assembly: AssemblyKeyFile("abc.snk")]
- recompile project, then install it to GAC by either
drag & drop it to assembly folder (C:\WINDOWS\assembly OR C:\WINNT\assembly) (shfusion.dll tool)
or
gacutil -i abc.dll

What is strong name?

A name that consists of an assembly's identity—its simple text name, version number, and culture information (if provided)—strengthened by a public key and a digital signature generated over the assembly.

9. What is portable executable (PE)?

The file format defining the structure that all executable files (EXE) and Dynamic Link Libraries (DLL) must use to allow them to be loaded and executed by Windows. PE is derived from the Microsoft Common Object File Format (COFF). The EXE and DLL files created using the .NET Framework obey the PE/COFF formats and also add additional header and data sections to the files that are only used by the CLR. The specification for the PE/COFF file formats is available at

http://www.microsoft.com/whdc/hwdev/hardware/pecoffdown.mspx

What is FullTrust? Do GAC’ed assemblies have FullTrust?

Before the .NET Framework existed, Windows had two levels of trust for downloaded code. This old model was a binary trust model. You only had two choices: Full Trust, and No Trust. The code could either do anything you could do, or it wouldn't run at all.

The permission sets in .NET include FullTrust, SkipVerification, Execution, Nothing, LocalIntranet, Internet and Everything. Full Trust Grants unrestricted permissions to system resources. Fully trusted code run by a normal, nonprivileged user cannot do administrative tasks, but can access any resources the user can access, and do anything the user can do. From a security standpoint, you can think of fully trusted code as being similar to native, unmanaged code, like a traditional ActiveX control.
GAC assemblies are granted FullTrust. In v1.0 and 1.1, the fact that assemblies in the GAC seem to always get a FullTrust grant is actually a side effect of the fact that the GAC lives on the local machine. If anyone were to lock down the security policy by changing the grant set of the local machine to something less than FullTrust, and if your assembly did not get extra permission from some other code group, it would no longer have FullTrust even though it lives in the GAC.

What does this do? gacutil /l | find /i "Corillian"

The Global Assembly Cache tool allows you to view and manipulate the contents of the global assembly cache and download cache.The tool comes with various optional params to do that.
""/l"" option Lists the contents of the global assembly cache. If you specify the assemblyName parameter(/l [assemblyName]), the tool lists only the assemblies matching that name.

Creating a Key Pair

You can create a key pair using the Strong Name tool (Sn.exe). Key pair files usually have an .snk extension.
To create a key pair

How's the DLL Hell problem solved in .NET?

Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.

What does this do .. sn -t foo.dll ?

Sn -t option displays the token for the public key stored in infile. The contents of infile must be previously generated using -p.
Sn.exe computes the token using a hash function from the public key. To save space, the common language runtime stores public key tokens in the manifest as part of a reference to another assembly when it records a dependency to an assembly that has a strong name. The -tp option displays the public key in addition to the token.

How do you create shared assemblies?.

Just look through the definition of Assemblies..
* An Assembly is a logical unit of code
* Assembly physically exist as DLLs or EXEs
* One assembly can contain one or more files
* The constituent files can include any file types like image files, text files etc. along with DLLs or EXEs
* When you compile your source code by default the exe/dll generated is actually an assembly
* Unless your code is bundled as assembly it can not be used in any other application
* When you talk about version of a component you are actually talking about version of the assembly to which the component belongs.
* Every assembly file contains information about itself. This information is called as Assembly Manifest.

Following steps are involved in creating shared assemblies :

* Create your DLL/EXE source code
* Generate unique assembly name using SN utility
* Sign your DLL/EXE with the private key by modifying AssemblyInfo file
* Compile your DLL/EXE
* Place the resultant DLL/EXE in global assembly cache using AL utility

What is global assembly cache?

Each computer where the common language runtime is installed has a machine-wide code cache called the global assembly cache. The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer.
There are several ways to deploy an assembly into the global assembly cache:
· Use an installer designed to work with the global assembly cache. This is the preferred option for installing assemblies into the global assembly cache.
· Use a developer tool called the Global Assembly Cache tool (Gacutil.exe), provided by the .NET Framework SDK.
· Use Windows Explorer to drag assemblies into the cache.

How do you generate a strong name?

.NET provides an utility called strong name tool. You can run this toolfrom the VS.NET command prompt to generate a strong name with an option "-k" and providing the strong key file name. i.e. sn- -k <>