ProtectedData Class
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ProtectedData Class

 

Provides methods for encrypting and decrypting data. This class cannot be inherited.

Namespace:   System.Security.Cryptography
Assembly:  System.Security (in System.Security.dll)

System.Object
  System.Security.Cryptography.ProtectedData

<HostProtectionAttribute(SecurityAction.LinkDemand, MayLeakOnAbort := True)>
Public NotInheritable Class ProtectedData

NameDescription
System_CAPS_pubmethodSystem_CAPS_staticProtect(Byte(), Byte(), DataProtectionScope)

Encrypts the data in a specified byte array and returns a byte array that contains the encrypted data.

System_CAPS_pubmethodSystem_CAPS_staticUnprotect(Byte(), Byte(), DataProtectionScope)

Decrypts the data in a specified byte array and returns a byte array that contains the decrypted data.

This class provides access to the Data Protection API (DPAPI) available in Microsoft Windows 2000 and later operating systems. This is a service that is provided by the operating system and does not require additional libraries. It provides protection using the user or machine credentials to encrypt or decrypt data.

The class consists of two wrappers for the unmanaged DPAPI, Protect and Unprotect. These two methods can be used to encrypt and decrypt data such as passwords, keys, and connection strings.

If you use these methods during impersonation, you may receive the following error: "Key not valid for use in specified state." This occurs because the DPAPI stores the key data in user profiles. If the profile is not loaded, DPAPI won’t be able to perform the decryption. To prevent this error, load the profile of the user you want to impersonate before calling either method. Using DPAPI with impersonation can incur significant complication and requires careful design choices.

The following example shows how to use data protection.

Imports System
Imports System.Security.Cryptography



Public Class DataProtectionSample
    ' Create byte array for additional entropy when using Protect method.
    Private Shared s_aditionalEntropy As Byte() = {9, 8, 7, 6, 5}


    Public Shared Sub Main()
        ' Create a simple byte array containing data to be encrypted.
        Dim secret As Byte() = {0, 1, 2, 3, 4, 1, 2, 3, 4}

        'Encrypt the data.
        Dim encryptedSecret As Byte() = Protect(secret)
        Console.WriteLine("The encrypted byte array is:")
        PrintValues(encryptedSecret)

        ' Decrypt the data and store in a byte array.
        Dim originalData As Byte() = Unprotect(encryptedSecret)
        Console.WriteLine("{0}The original data is:", Environment.NewLine)
        PrintValues(originalData)

    End Sub


    Public Shared Function Protect(ByVal data() As Byte) As Byte()
        Try
            ' Encrypt the data using DataProtectionScope.CurrentUser. The result can be decrypted
            '  only by the same current user.
            Return ProtectedData.Protect(data, s_aditionalEntropy, DataProtectionScope.CurrentUser)
        Catch e As CryptographicException
            Console.WriteLine("Data was not encrypted. An error occurred.")
            Console.WriteLine(e.ToString())
            Return Nothing
        End Try

    End Function


    Public Shared Function Unprotect(ByVal data() As Byte) As Byte()
        Try
            'Decrypt the data using DataProtectionScope.CurrentUser.
            Return ProtectedData.Unprotect(data, s_aditionalEntropy, DataProtectionScope.CurrentUser)
        Catch e As CryptographicException
            Console.WriteLine("Data was not decrypted. An error occurred.")
            Console.WriteLine(e.ToString())
            Return Nothing
        End Try

    End Function


    Public Shared Sub PrintValues(ByVal myArr() As [Byte])
        Dim i As [Byte]
        For Each i In myArr
            Console.Write(vbTab + "{0}", i)
        Next i
        Console.WriteLine()

    End Sub
End Class

.NET Framework
Available since 2.0
Windows Phone Silverlight
Available since 7.1

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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