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X509KeyUsageExtension Class

Defines the usage of a key contained within an X.509 certificate. This class cannot be inherited.

System.Object
  System.Security.Cryptography.AsnEncodedData
    System.Security.Cryptography.X509Certificates.X509Extension
      System.Security.Cryptography.X509Certificates.X509KeyUsageExtension

Namespace:  System.Security.Cryptography.X509Certificates
Assembly:  System (in System.dll)

'Declaration
Public NotInheritable Class X509KeyUsageExtension _
	Inherits X509Extension

The X509KeyUsageExtension type exposes the following members.

  NameDescription
Public methodX509KeyUsageExtensionInitializes a new instance of the X509KeyUsageExtension class.
Public methodX509KeyUsageExtension(AsnEncodedData, Boolean)Initializes a new instance of the X509KeyUsageExtension class using an AsnEncodedData object and a value that identifies whether the extension is critical.
Public methodX509KeyUsageExtension(X509KeyUsageFlags, Boolean)Initializes a new instance of the X509KeyUsageExtension class using the specified X509KeyUsageFlags value and a value that identifies whether the extension is critical.
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  NameDescription
Public propertyCriticalGets a Boolean value indicating whether the extension is critical. (Inherited from X509Extension.)
Public propertyKeyUsagesGets the key usage flag associated with the certificate.
Public propertyOidGets or sets the Oid value for an AsnEncodedData object. (Inherited from AsnEncodedData.)
Public propertyRawDataGets or sets the Abstract Syntax Notation One (ASN.1)-encoded data represented in a byte array. (Inherited from AsnEncodedData.)
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  NameDescription
Public methodCopyFromInitializes a new instance of the X509KeyUsageExtension class using an AsnEncodedData object. (Overrides X509Extension.CopyFrom(AsnEncodedData).)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodFormatReturns a formatted version of the Abstract Syntax Notation One (ASN.1)-encoded data as a string. (Inherited from AsnEncodedData.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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The X509KeyUsageExtension class uses the flags in the X509KeyUsageFlags enumeration to define or determine key usage.

The following code example demonstrates how to open a user’s personal certificate store and display information about each certificate in the store. This example uses the X509KeyUsageExtension class to display the information.


Imports System
Imports System.Security.Cryptography
Imports System.Security.Cryptography.X509Certificates



Module CertSelect

    Sub Main()
        Try
            Dim store As New X509Store("MY", StoreLocation.CurrentUser)
            store.Open(OpenFlags.ReadOnly Or OpenFlags.OpenExistingOnly)

            Dim collection As X509Certificate2Collection = CType(store.Certificates, X509Certificate2Collection)
            Dim i As Integer
            For i = 0 To collection.Count
                Dim extension As X509Extension
                For Each extension In collection(i).Extensions
                    Console.WriteLine(extension.Oid.FriendlyName + "(" + extension.Oid.Value + ")")


                    If extension.Oid.FriendlyName = "Key Usage" Then
                        Dim ext As X509KeyUsageExtension = CType(extension, X509KeyUsageExtension)
                        Console.WriteLine(ext.KeyUsages)
                    End If

                    If extension.Oid.FriendlyName = "Basic Constraints" Then
                        Dim ext As X509BasicConstraintsExtension = CType(extension, X509BasicConstraintsExtension)
                        Console.WriteLine(ext.CertificateAuthority)
                        Console.WriteLine(ext.HasPathLengthConstraint)
                        Console.WriteLine(ext.PathLengthConstraint)
                    End If

                    If extension.Oid.FriendlyName = "Subject Key Identifier" Then
                        Dim ext As X509SubjectKeyIdentifierExtension = CType(extension, X509SubjectKeyIdentifierExtension)
                        Console.WriteLine(ext.SubjectKeyIdentifier)
                    End If

                    If extension.Oid.FriendlyName = "Enhanced Key Usage" Then
                        Dim ext As X509EnhancedKeyUsageExtension = CType(extension, X509EnhancedKeyUsageExtension)
                        Dim oids As OidCollection = ext.EnhancedKeyUsages
                        Dim oid As Oid
                        For Each oid In oids
                            Console.WriteLine(oid.FriendlyName + "(" + oid.Value + ")")
                        Next oid
                    End If
                Next extension
            Next i
            store.Close()
        Catch
            Console.WriteLine("Information could not be written out for this certificate.")
        End Try

    End Sub
End Module


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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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