What is a Assembly?
• Assembly is unit of deployment like EXE or a DLL.
• An assembly consists of one or more files (dlls, exe’s, html files etc.), and
represents a group of resources, type definitions, and implementations of those
types. An assembly may also contain references to other assemblies. These
resources, types and references are described in a block of data called a manifest.
The manifest is part of the assembly, thus making the assembly self-describing.
• An assembly is completely self-describing. An assembly contains metadata
information, which is used by the CLR for everything from type checking an
security to actually invoking the components methods. As all information is in
the assembly itself, it is independent of registry. This is the basic advantage as
compared to COM where the version was stored in registry.
• Multiple versions can be deployed side by side in different folders. These different
versions can execute at the same time without interfering with each other.
Assemblies can be private or shared. For private assembly deployment, the
assembly is copied to the same directory as the client program that references it. No
registration is needed, and no fancy installation program is required. When the
component is removed, no registry cleanup is needed, and no uninstall program is
required. Just delete it from the hard drive.
• In shared assembly deployment, an assembly is installed in the Global Assembly
Cache (or GAC). The GAC contains shared assemblies that are globally accessible
to all .NET applications on the machine.
different types of Assembly
There are two types of assembly Private and Public assembly. A private assembly is normally
used by a single application, and is stored in the application's directory, or a sub-directory
beneath. A shared assembly is normally stored in the global assembly cache, which is a repository
of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code,
which many applications will find useful, e.g. Crystal report classes that will be used by all
application for Reports.
NameSpace
Namespace has two basic functionality:-
• NameSpace Logically group types, example System.Web.UI logically groups UI
related features.
• In Object Oriented world, many times it is possible that programmers will use the
same class name. Qualifying NameSpace with class name can avoid this collision.
Difference between NameSpace and Assembly?
Following are the differences between namespace and assembly:
• Assembly is physical grouping of logical units, Namespace, logically groups
classes.
• Namespace can span multiple assembly.
View an Assembly :
Twist: What is ILDASM?
When it comes to understanding of internals, nothing can beat ILDASM. ILDASM converts the
whole ‘exe’ or ‘dll’ in to IL code. To run ILDASM you have to go to ‘C:\Program
Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Bin’. Note that we had v1.1 you have to
probably change it depending on the type of framework version you have.
If you run IDASM.EXE from the path you will be popped with the IDASM exe program as
shown in figure ILDASM. Click on file and browse to the respective directory for the DLL whose
assembly you want to view. After you select the DLL you will be popped with a tree view details
of the DLL as shown in figure ILDASM. On double clicking on manifest, you will be able to
view details of assembly, internal IL code etc as shown in Figure ‘Manifest View’.
Note : The version number are in the manifest itself which is defined
with the DLL or EXE thus making deployment much easier as compared to
COM where the information was stored in registry. Note the version
information in Figure Manifest view.
You can expand the tree for detail information regarding the DLL like methods, properties,
functions etc.
Figure: - 1.1 ILDASM
Figure: - 1.2 Manifest View
Manifest:
Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the
following things (See Figure Manifest View for more details):
• Version of assembly.
• Security identity.
• Scope of the assembly.
• Resolve references to resources and classes.
The assembly manifest can be stored in a PE file either (an .exe or) .dll with Microsoft
intermediate language (MSIL code with Microsoft intermediate language (MSIL) code or in a
stand-alone PE file, that contains only assembly manifest information.
Version information stored of an assembly
Version information is stored in assembly inside the manifest.
Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in
their individual folders. This does not mean versioning is not needed , you can still version it to
have better version control on the project.
GAC
situations will you register .NET assembly in GAC
GAC (Global Assembly Cache) is where all shared .NET assembly reside. GAC is used in the
following situations:-
• If the application has to be shared among several application.
• If the assembly has some special security, requirements like only administrators can
remove the assembly. If the assembly is private then a simple delete of assembly
the assembly file will remove the assembly.
Note:- Registering .NET assembly in GAC can lead to the old problem of
DLL hell, where COM version was stored in central registry. So GAC
should be used when absolutely necessary.
Concept of strong names
Strong name is similar to GUID (It is supposed to be unique in space and time) in COM
components. Strong Name is only needed when we need to deploy assembly in GAC. Strong
Names helps GAC to differentiate between two versions. Strong names use public key
cryptography (PKC) to ensure that no one can spoof it.PKC use public key and private key
concept.
Following are the step to generate a strong name and sign a assembly:-
• Go to “Visual Studio Command Prompt”. “Visual studio Command
prompt”. Same type of command prompt will be seen in 2003 also.
• Once you are in command, prompt type sn.exe -k “c:\test.snk”.
Figure: - 1.4 Running SN.EXE
Figure: - 1.5 Successful output of SN.EXE
Figure: - 1.6 Sample view of test.snk file
• After generation of the file you can view the SNK file in a simple notepad
• After the SNK file is generated its time to sign the project with this SNK file.
Figure: - 1.7 Click on project & then click on “classlibrary1 properties” menu to sign the assembly
• Click on project -- properties and the browse the SNK file from the respective folder
and compile the project.
Figure: - 1.8 Click on ‘Use a key file’ to sign the assembly with strong name
(I) How to add and remove an assembly from GAC?
There are two ways to install .NET assembly in GAC:-
• Using Microsoft Installer Package. You can get download of installer from
http://www.microsoft.com.
• Using Gacutil. Go to “Visual Studio Command Prompt” and type “gacutil –i
(assembly name)”, where (assembly name) is the DLL name of the project.
(B) What is Delay signing?
During development process you will need strong name keys to be exposed to developer which is
not a good practice from security aspect point of view.In such situations you can assign the key
later on and during development you an use delay signing
Following is process to delay sign an assembly:
• First obtain your string name keys using SN.EXE.
• Annotate the source code for the assembly with two custom attributes from
System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file
containing the public key as a parameter to its constructor.
AssemblyDelaySignAttribute, which indicates that delay signing, is being used by
passing true as a parameter to its constructor. For example as shown below:
[Visual Basic]
<Assembly: AssemblyKeyFileAttribute ("myKey.snk")>
<Assembly: AssemblyDelaySignAttribute (true)>
[C#]
[Assembly: AssemblyKeyFileAttribute ("myKey.snk")]
[Assembly: AssemblyDelaySignAttribute (true)]
The compiler inserts the public key into the assembly manifest and reserves space in the PE file
for the full strong name signature. The real public key must be stored while the assembly is built
so that other assemblies that reference this assembly can obtain the key to store in their own
assembly reference.
• Because the assembly does not have a valid strong name signature, the verification of
that signature must be turned off. You can do this by using the –Vr option with the
Strong Name tool. The following example turns off verification for an assembly called
myAssembly.dll.
Sn –Vr myAssembly.dll
• Just before shipping, you submit the assembly to your organization signing authority
for the actual strong name signing using the –R option with the Strong Name tool. The
following example signs an assembly called myAssembly.dll with a strong name using the
sgKey.snk key pair.
Sn -R myAssembly.dll sgKey.snk
• Assembly is unit of deployment like EXE or a DLL.
• An assembly consists of one or more files (dlls, exe’s, html files etc.), and
represents a group of resources, type definitions, and implementations of those
types. An assembly may also contain references to other assemblies. These
resources, types and references are described in a block of data called a manifest.
The manifest is part of the assembly, thus making the assembly self-describing.
• An assembly is completely self-describing. An assembly contains metadata
information, which is used by the CLR for everything from type checking an
security to actually invoking the components methods. As all information is in
the assembly itself, it is independent of registry. This is the basic advantage as
compared to COM where the version was stored in registry.
• Multiple versions can be deployed side by side in different folders. These different
versions can execute at the same time without interfering with each other.
Assemblies can be private or shared. For private assembly deployment, the
assembly is copied to the same directory as the client program that references it. No
registration is needed, and no fancy installation program is required. When the
component is removed, no registry cleanup is needed, and no uninstall program is
required. Just delete it from the hard drive.
• In shared assembly deployment, an assembly is installed in the Global Assembly
Cache (or GAC). The GAC contains shared assemblies that are globally accessible
to all .NET applications on the machine.
different types of Assembly
There are two types of assembly Private and Public assembly. A private assembly is normally
used by a single application, and is stored in the application's directory, or a sub-directory
beneath. A shared assembly is normally stored in the global assembly cache, which is a repository
of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code,
which many applications will find useful, e.g. Crystal report classes that will be used by all
application for Reports.
NameSpace
Namespace has two basic functionality:-
• NameSpace Logically group types, example System.Web.UI logically groups UI
related features.
• In Object Oriented world, many times it is possible that programmers will use the
same class name. Qualifying NameSpace with class name can avoid this collision.
Difference between NameSpace and Assembly?
Following are the differences between namespace and assembly:
• Assembly is physical grouping of logical units, Namespace, logically groups
classes.
• Namespace can span multiple assembly.
View an Assembly :
Twist: What is ILDASM?
When it comes to understanding of internals, nothing can beat ILDASM. ILDASM converts the
whole ‘exe’ or ‘dll’ in to IL code. To run ILDASM you have to go to ‘C:\Program
Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Bin’. Note that we had v1.1 you have to
probably change it depending on the type of framework version you have.
If you run IDASM.EXE from the path you will be popped with the IDASM exe program as
shown in figure ILDASM. Click on file and browse to the respective directory for the DLL whose
assembly you want to view. After you select the DLL you will be popped with a tree view details
of the DLL as shown in figure ILDASM. On double clicking on manifest, you will be able to
view details of assembly, internal IL code etc as shown in Figure ‘Manifest View’.
Note : The version number are in the manifest itself which is defined
with the DLL or EXE thus making deployment much easier as compared to
COM where the information was stored in registry. Note the version
information in Figure Manifest view.
You can expand the tree for detail information regarding the DLL like methods, properties,
functions etc.
Figure: - 1.1 ILDASM
Figure: - 1.2 Manifest View
Manifest:
Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the
following things (See Figure Manifest View for more details):
• Version of assembly.
• Security identity.
• Scope of the assembly.
• Resolve references to resources and classes.
The assembly manifest can be stored in a PE file either (an .exe or) .dll with Microsoft
intermediate language (MSIL code with Microsoft intermediate language (MSIL) code or in a
stand-alone PE file, that contains only assembly manifest information.
Version information stored of an assembly
Version information is stored in assembly inside the manifest.
Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in
their individual folders. This does not mean versioning is not needed , you can still version it to
have better version control on the project.
GAC
situations will you register .NET assembly in GAC
GAC (Global Assembly Cache) is where all shared .NET assembly reside. GAC is used in the
following situations:-
• If the application has to be shared among several application.
• If the assembly has some special security, requirements like only administrators can
remove the assembly. If the assembly is private then a simple delete of assembly
the assembly file will remove the assembly.
Note:- Registering .NET assembly in GAC can lead to the old problem of
DLL hell, where COM version was stored in central registry. So GAC
should be used when absolutely necessary.
Concept of strong names
Strong name is similar to GUID (It is supposed to be unique in space and time) in COM
components. Strong Name is only needed when we need to deploy assembly in GAC. Strong
Names helps GAC to differentiate between two versions. Strong names use public key
cryptography (PKC) to ensure that no one can spoof it.PKC use public key and private key
concept.
Following are the step to generate a strong name and sign a assembly:-
• Go to “Visual Studio Command Prompt”. “Visual studio Command
prompt”. Same type of command prompt will be seen in 2003 also.
• Once you are in command, prompt type sn.exe -k “c:\test.snk”.
Figure: - 1.4 Running SN.EXE
Figure: - 1.5 Successful output of SN.EXE
Figure: - 1.6 Sample view of test.snk file
• After generation of the file you can view the SNK file in a simple notepad
• After the SNK file is generated its time to sign the project with this SNK file.
Figure: - 1.7 Click on project & then click on “classlibrary1 properties” menu to sign the assembly
• Click on project -- properties and the browse the SNK file from the respective folder
and compile the project.
Figure: - 1.8 Click on ‘Use a key file’ to sign the assembly with strong name
(I) How to add and remove an assembly from GAC?
There are two ways to install .NET assembly in GAC:-
• Using Microsoft Installer Package. You can get download of installer from
http://www.microsoft.com.
• Using Gacutil. Go to “Visual Studio Command Prompt” and type “gacutil –i
(assembly name)”, where (assembly name) is the DLL name of the project.
(B) What is Delay signing?
During development process you will need strong name keys to be exposed to developer which is
not a good practice from security aspect point of view.In such situations you can assign the key
later on and during development you an use delay signing
Following is process to delay sign an assembly:
• First obtain your string name keys using SN.EXE.
• Annotate the source code for the assembly with two custom attributes from
System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file
containing the public key as a parameter to its constructor.
AssemblyDelaySignAttribute, which indicates that delay signing, is being used by
passing true as a parameter to its constructor. For example as shown below:
[Visual Basic]
<Assembly: AssemblyKeyFileAttribute ("myKey.snk")>
<Assembly: AssemblyDelaySignAttribute (true)>
[C#]
[Assembly: AssemblyKeyFileAttribute ("myKey.snk")]
[Assembly: AssemblyDelaySignAttribute (true)]
The compiler inserts the public key into the assembly manifest and reserves space in the PE file
for the full strong name signature. The real public key must be stored while the assembly is built
so that other assemblies that reference this assembly can obtain the key to store in their own
assembly reference.
• Because the assembly does not have a valid strong name signature, the verification of
that signature must be turned off. You can do this by using the –Vr option with the
Strong Name tool. The following example turns off verification for an assembly called
myAssembly.dll.
Sn –Vr myAssembly.dll
• Just before shipping, you submit the assembly to your organization signing authority
for the actual strong name signing using the –R option with the Strong Name tool. The
following example signs an assembly called myAssembly.dll with a strong name using the
sgKey.snk key pair.
Sn -R myAssembly.dll sgKey.snk
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