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X509Extension Class

Represents an X509 extension.

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

'Declaration
Public Class X509Extension _
	Inherits AsnEncodedData

The X509Extension type exposes the following members.

  NameDescription
Protected methodX509ExtensionInitializes a new instance of the X509Extension class.
Public methodX509Extension(AsnEncodedData, Boolean)Initializes a new instance of the X509Extension class.
Public methodX509Extension(Oid, Byte(), Boolean)Initializes a new instance of the X509Extension class.
Public methodX509Extension(String, Byte(), Boolean)Initializes a new instance of the X509Extension class.
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  NameDescription
Public propertyCriticalGets a Boolean value indicating whether the extension is critical.
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 methodCopyFromCopies the extension properties of the specified AsnEncodedData object. (Overrides AsnEncodedData.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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X509 extensions are dynamic, extended properties that can be added to an X509 certificate and changed. The X509Extension class can be used to create extensions that are associated with a certificate but are not part of a certificate as issued by a certification authority (CA).

In its most basic form, an X509 extension has an object identifier (OID), a Boolean value describing whether the extension is considered critical or not, and ASN-encoded data. Custom extensions can be registered in a CryptoConfig file.

The.NET Framework includes implementations of several common X509 extensions:

The following code example demonstrates using the X509Extension class.


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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