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X509KeyUsageExtension Class

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

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

public sealed class X509KeyUsageExtension : X509Extension

The X509KeyUsageExtension type exposes the following members.

  NameDescription
Public methodX509KeyUsageExtension()Initializes 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.)
Public methodFormatReturns a formatted version of the Abstract Syntax Notation One (ASN.1)-encoded data as a string. (Inherited from AsnEncodedData.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (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.

using System;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

public class CertSelect
{
    public static void Main()
    {
        try
        {
            X509Store store = new X509Store("MY", StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);

            X509Certificate2Collection collection = (X509Certificate2Collection)store.Certificates;
            for (int i = 0; i < collection.Count; i++)
            {
                foreach (X509Extension extension in collection[i].Extensions)
                {
                    Console.WriteLine(extension.Oid.FriendlyName + "(" + extension.Oid.Value + ")");


                    if (extension.Oid.FriendlyName == "Key Usage")
                    {
                        X509KeyUsageExtension ext = (X509KeyUsageExtension)extension;
                        Console.WriteLine(ext.KeyUsages);
                    }

                    if (extension.Oid.FriendlyName == "Basic Constraints")
                    {
                        X509BasicConstraintsExtension ext = (X509BasicConstraintsExtension)extension;
                        Console.WriteLine(ext.CertificateAuthority);
                        Console.WriteLine(ext.HasPathLengthConstraint);
                        Console.WriteLine(ext.PathLengthConstraint);
                    }

                    if (extension.Oid.FriendlyName == "Subject Key Identifier")
                    {
                        X509SubjectKeyIdentifierExtension ext = (X509SubjectKeyIdentifierExtension)extension;
                        Console.WriteLine(ext.SubjectKeyIdentifier);
                    }

                    if (extension.Oid.FriendlyName == "Enhanced Key Usage")
                    {
                        X509EnhancedKeyUsageExtension ext = (X509EnhancedKeyUsageExtension)extension;
                        OidCollection oids = ext.EnhancedKeyUsages;
                        foreach (Oid oid in oids)
                        {
                            Console.WriteLine(oid.FriendlyName + "(" + oid.Value + ")");
                        }
                    }
                }
            }
            store.Close();
        }
        catch (CryptographicException)
        {
            Console.WriteLine("Information could not be written out for this certificate.");
        }
    }
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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