Working with Isolated Storage in .NET

While it is challenging to develop software to meet the user requirements, it is also equally vital to protect the data handled in the software application with the right level of security requirements. This is even more important for internet- based applications.

Most of the time, the data saved during the application instance is about its state and sometimes other key essential data like the user credentials, code, application-specific complex data, etc. This can be highly vulnerable to corruption and lead to unauthorized access to harmful programs like viruses. To prevent such events and provide a lucid way of granting access to store information with limited security and high reliability, .Net framework has introduced the concept of Isolated Storage.

Isolated Storage is mainly designed to improve the security of application data in a secure way such that the storing and retrieval method by the application is not on adhoc basis. It provides a standard system for storage and retrieval of data without any conflict among the applications executing in the computer system. It enables the application to run under partial, limited or full trust. With this, there is no need for granting access rights to the User or the application for storing data in a specific file or folder in the hard disk. It also provides an easy alternate solution to avoid storing such data in a database which can bring an overhead in maintenance and cost.

Overview of Isolated Storage

Isolated Storage allocates compartments for storing information related to the application like application state, temporary data, etc. with/without user-specific data. These compartments represent the Isolated Storage and contain the actual location of directories/files in which this data is maintained. These files can reside on a client or server based on the requirement.

The framework provides options to the Administrator of the system to control the file size of the Isolated Storage files based on the access level of the User who has been granted rights. While developing an application using Isolated Storage through code, the executing code has to possess the required access for operating with the Isolated Storage files. By default, the managed code executed by a .Net application has all access rights to work with the Isolated Storage files.

This can be denied in case access rights are impersonation based. If it is so, care should be taken to ensure that the impersonated user executing the application using Isolated Storage files has proper operating system rights. Isolated Storage facilitates storing information along with user’s roaming profile in the server which will make information available always for a roaming user.

Working with Isolated Storage

.Net framework has implemented this concept of Isolated Storage in the form of rich classes which are included in the System.IO.IsolatedStorage namespace. Following are the different steps involved in executing the Isolated Storage concept in an application.

Creating a File store

Before creating a file store, it is necessary to plan for the scope of the data in the store. The scope of information can be restricted to either assembly calling the method and to the specific machine executing the application OR to calling assembly and the current user. In the former method, application-specific data can be stored while the user-specific data can be stored in the latter method. The IsolatedStorageFile class is used to access safe areas to store data for assemblies and users.

Writing and reading data

Before using Isolated Storage, the assembly has to ensure that it has sufficient permissions for which it has to be demanded. For this, IsolatedStorageFilepermission class is used. The two important properties of this class which has to be set for permissions are as below:

UsageAllowed - Gets or sets the types of usage allowed

UserQuota - Gets or sets the overall size of storage allowed per user
By specifying these values, the way the code intends to use Isolated Storage is specified to the security system.

The IsolatedStorageFileStream class is used to read and write data into the safe file stores. Since this class is derived from FileStream class, its usage is similar to that of FileStream class. Object of this class type is created by passing the relative path of the filename, modes of opening the file (create or read or write) and the file store object to include within it. Hence, at the instant of creation of this object, the file is created or opened for reading / writing.

For reading the data, the file has to be opened in Read mode which will fetch the file contents. Before opening the file for reading it, the file existence has to be checked by calling the method, GetFileNames() of the class IsolatedStorageFile with the filename as parameter.
Best practices while using Isolated Storage

• Some of the typical usage of Isolated Storage is as below:

o When a restricted access needs to be given for components that need to be shared amongst applications

o At the server side, when the user specific data has to be maintained for different users who request the server application, data is isolated based on the identity that is used for impersonation by the server while making request.

o Web applications which need to execute file handling operations for storing/retrieving application-specific data, can use Isolated Storage instead of File I/O classes which do not allow them to do so.

• Since the data stored through Isolated Storage is accessible to unmanaged code and any trusted user of the system, it is advisable to avoid storing sensitive information like unencrypted passwords, user credentials, configuration and deployment details, etc.

• It is also suggested not to store code or complex data unless if it is really necessary.

• Although application-specific data can be stored in Isolated Storage in the form of database, it becomes an overhead if the data slowly becomes voluminous, especially when the number of users becomes more. Hence, it has to be carefully decided.

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