X509Extension Class
Represents an X509 extension.
Assembly: System (in System.dll)
System.Security.Cryptography.AsnEncodedData
System.Security.Cryptography.X509Certificates.X509Extension
System.Security.Cryptography.X509Certificates.X509BasicConstraintsExtension
System.Security.Cryptography.X509Certificates.X509EnhancedKeyUsageExtension
System.Security.Cryptography.X509Certificates.X509KeyUsageExtension
System.Security.Cryptography.X509Certificates.X509SubjectKeyIdentifierExtension
| Name | Description | |
|---|---|---|
![]() | X509Extension() | Initializes a new instance of the X509Extension class. |
![]() | X509Extension(AsnEncodedData, Boolean) | Initializes a new instance of the X509Extension class. |
![]() | X509Extension(Oid, Byte(), Boolean) | Initializes a new instance of the X509Extension class. |
![]() | X509Extension(String, Byte(), Boolean) | Initializes a new instance of the X509Extension class. |
| Name | Description | |
|---|---|---|
![]() | Critical | Gets a Boolean value indicating whether the extension is critical. |
![]() | Oid | Gets or sets the Oid value for an AsnEncodedData object.(Inherited from AsnEncodedData.) |
![]() | RawData | Gets or sets the Abstract Syntax Notation One (ASN.1)-encoded data represented in a byte array.(Inherited from AsnEncodedData.) |
| Name | Description | |
|---|---|---|
![]() | CopyFrom(AsnEncodedData) | Copies the extension properties of the specified AsnEncodedData object.(Overrides AsnEncodedData.CopyFrom(AsnEncodedData).) |
![]() | Equals(Object) | Determines whether the specified object is equal to the current object.(Inherited from Object.) |
![]() | Finalize() | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.) |
![]() | Format(Boolean) | Returns a formatted version of the Abstract Syntax Notation One (ASN.1)-encoded data as a string.(Inherited from AsnEncodedData.) |
![]() | GetHashCode() | Serves as the default hash function. (Inherited from Object.) |
![]() | GetType() | |
![]() | MemberwiseClone() | |
![]() | ToString() | Returns a string that represents the current object.(Inherited from Object.) |
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:
X509KeyUsageExtension. Describes the key usages of a certificate.
X509BasicConstraintsExtension. Describes the constraints for a certificate.
X509EnhancedKeyUsageExtension. Describes the enhanced key usages of a certificate.
X509SubjectKeyIdentifierExtension. Describes the key identifier. For example, used with XMLDSIG.
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
Available since 2.0
Any public static ( Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.


