Procedimiento para usar diferentes certificados X.509 para la firma y el cifrado

  • Artículo

En este tema se muestra cómo configurar Windows Communication Foundation (WCF) a fin de usar certificados diferentes para la firma de mensajes y el cifrado tanto en el cliente como en el servicio.

A fin de poder utilizar certificados independientes para la firma y el cifrado, se debe crear un cliente personalizado o las credenciales de servicio (o ambos) porque WCF no proporciona una API para establecer varios clientes o certificados de servicio. Además, se debe proporcionar un administrador de tokens de seguridad para sacar el máximo partido a la información de varios certificados y crear un proveedor de tokens de seguridad adecuado para el uso de claves especificado y la dirección del mensaje.

El diagrama siguiente muestra las clases principales que se utilizan, las clases de las que se heredan (identificadas mediante una flecha que señala hacia arriba) y los tipos de valor devueltos de ciertos métodos y propiedades.

Chart showing how client credentials are used

Para obtener más información sobre las credenciales de cliente, vea Tutorial: Creación de credenciales de cliente y servicio personalizadas.

Además, debe crear un comprobador de identidad personalizado y vincularlo a un elemento de enlace de seguridad en un enlace personalizado. También debe utilizar las credenciales personalizadas en lugar de las credenciales predeterminadas.

En el diagrama siguiente, se muestran las clases implicadas en el enlace personalizado y cómo se vincula el comprobador de identidad personalizado. Hay varios elementos de enlace implicados. Todos ellos se heredan de BindingElement. AsymmetricSecurityBindingElement tiene la propiedad LocalClientSecuritySettings, que devuelve una instancia de IdentityVerifier, a partir de la cual se personaliza MyIdentityVerifier.

Chart showing a custom binding element

Para obtener más información sobre cómo crear un comprobador de identidad personalizado, vea Procedimientos para crear un comprobador de identidad de clientes personalizado.

Para utilizar certificados independientes para la firma y el cifrado

  1. Defina una nueva clase de credenciales de cliente que herede de la clase ClientCredentials. Implemente cuatro nuevas propiedades para permitir la especificación de múltiples certificados: ClientSigningCertificate, ClientEncryptingCertificate, ServiceSigningCertificate y ServiceEncryptingCertificate. Invalide también el método CreateSecurityTokenManager para devolver una instancia de la clase ClientCredentialsSecurityTokenManager personalizada que se define en el paso siguiente.

    public class MyClientCredentials : ClientCredentials
{
    X509Certificate2 clientSigningCert;
    X509Certificate2 clientEncryptingCert;
    X509Certificate2 serviceSigningCert;
    X509Certificate2 serviceEncryptingCert;

    public MyClientCredentials()
    {
    }

    protected MyClientCredentials(MyClientCredentials other)
        : base(other)
    {
        this.clientEncryptingCert = other.clientEncryptingCert;
        this.clientSigningCert = other.clientSigningCert;
        this.serviceEncryptingCert = other.serviceEncryptingCert;
        this.serviceSigningCert = other.serviceSigningCert;
    }

    public X509Certificate2 ClientSigningCertificate
    {
        get
        {
            return this.clientSigningCert;
        }
        set
        {
            this.clientSigningCert = value;
        }
    }

    public X509Certificate2 ClientEncryptingCertificate
    {
        get
        {
            return this.clientEncryptingCert;
        }
        set
        {
            this.clientEncryptingCert = value;
        }
    }

    public X509Certificate2 ServiceSigningCertificate
    {
        get
        {
            return this.serviceSigningCert;
        }
        set
        {
            this.serviceSigningCert = value;
        }
    }

    public X509Certificate2 ServiceEncryptingCertificate
    {
        get
        {
            return this.serviceEncryptingCert;
        }
        set
        {
            this.serviceEncryptingCert = value;
        }
    }

    public override SecurityTokenManager CreateSecurityTokenManager()
    {
        return new MyClientCredentialsSecurityTokenManager(this);
    }

    protected override ClientCredentials CloneCore()
    {
        return new MyClientCredentials(this);
    }
}

    Public Class MyClientCredentials
    Inherits ClientCredentials

    Private clientSigningCert As X509Certificate2
    Private clientEncryptingCert As X509Certificate2
    Private serviceSigningCert As X509Certificate2
    Private serviceEncryptingCert As X509Certificate2

    Public Sub New()
    End Sub

    Protected Sub New(ByVal other As MyClientCredentials)
        MyBase.New(other)
        Me.clientEncryptingCert = other.clientEncryptingCert
        Me.clientSigningCert = other.clientSigningCert
        Me.serviceEncryptingCert = other.serviceEncryptingCert
        Me.serviceSigningCert = other.serviceSigningCert
    End Sub

    Public Property ClientSigningCertificate() As X509Certificate2
        Get
            Return Me.clientSigningCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.clientSigningCert = value
        End Set
    End Property

    Public Property ClientEncryptingCertificate() As X509Certificate2
        Get
            Return Me.clientEncryptingCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.clientEncryptingCert = value
        End Set
    End Property

    Public Property ServiceSigningCertificate() As X509Certificate2
        Get
            Return Me.serviceSigningCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.serviceSigningCert = value
        End Set
    End Property

    Public Property ServiceEncryptingCertificate() As X509Certificate2
        Get
            Return Me.serviceEncryptingCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.serviceEncryptingCert = value
        End Set
    End Property

    Public Overrides Function CreateSecurityTokenManager() As SecurityTokenManager
        Return New MyClientCredentialsSecurityTokenManager(Me)
    End Function

    Protected Overrides Function CloneCore() As ClientCredentials
        Return New MyClientCredentials(Me)
    End Function

End Class

  2. Defina un nuevo administrador de tokens de seguridad del cliente que herede de la clase ClientCredentialsSecurityTokenManager. Invalide el método CreateSecurityTokenProvider para crear un proveedor de tokens de seguridad adecuado. El parámetro requirement (un SecurityTokenRequirement) proporciona la dirección del mensaje y el uso de las claves.

    internal class MyClientCredentialsSecurityTokenManager :
    ClientCredentialsSecurityTokenManager
{
    MyClientCredentials credentials;

    public MyClientCredentialsSecurityTokenManager(
        MyClientCredentials credentials): base(credentials)
    {
        this.credentials = credentials;
    }

    public override SecurityTokenProvider CreateSecurityTokenProvider(
        SecurityTokenRequirement requirement)
    {
        SecurityTokenProvider result = null;
        if (requirement.TokenType == SecurityTokenTypes.X509Certificate)
        {
            MessageDirection direction = requirement.GetProperty
                <MessageDirection>(ServiceModelSecurityTokenRequirement.
                MessageDirectionProperty);
            if (direction == MessageDirection.Output)
            {
                if (requirement.KeyUsage == SecurityKeyUsage.Signature)
                {
                    result = new X509SecurityTokenProvider(
                        this.credentials.ClientSigningCertificate);
                }
                else
                {
                    result = new X509SecurityTokenProvider(this.credentials.
                        ServiceEncryptingCertificate);
                }
            }
            else
            {
                if (requirement.KeyUsage == SecurityKeyUsage.Signature)
                {
                    result = new X509SecurityTokenProvider(this.
                        credentials.ServiceSigningCertificate);
                }
                else
                {
                    result = new X509SecurityTokenProvider(credentials.
                        ClientEncryptingCertificate);
                }
            }
        }
        else
        {
            result = base.CreateSecurityTokenProvider(requirement);
        }

        return result;
    }

    public override SecurityTokenAuthenticator
        CreateSecurityTokenAuthenticator(SecurityTokenRequirement
        tokenRequirement, out SecurityTokenResolver outOfBandTokenResolver)
    {
        return base.CreateSecurityTokenAuthenticator(tokenRequirement,
            out outOfBandTokenResolver);
    }
}

    Friend Class MyClientCredentialsSecurityTokenManager
    Inherits ClientCredentialsSecurityTokenManager

    Private credentials As MyClientCredentials

    Public Sub New(ByVal credentials As MyClientCredentials)
        MyBase.New(credentials)
        Me.credentials = credentials
    End Sub

    Public Overrides Function CreateSecurityTokenProvider(ByVal requirement As SecurityTokenRequirement) As SecurityTokenProvider
        Dim result As SecurityTokenProvider = Nothing
        If requirement.TokenType = SecurityTokenTypes.X509Certificate Then
            Dim direction = requirement.GetProperty(Of MessageDirection)(ServiceModelSecurityTokenRequirement.MessageDirectionProperty)
            If direction = MessageDirection.Output Then
                If requirement.KeyUsage = SecurityKeyUsage.Signature Then
                    result = New X509SecurityTokenProvider(Me.credentials.ClientSigningCertificate)
                Else
                    result = New X509SecurityTokenProvider(Me.credentials.ServiceEncryptingCertificate)
                End If
            Else
                If requirement.KeyUsage = SecurityKeyUsage.Signature Then
                    result = New X509SecurityTokenProvider(Me.credentials.ServiceSigningCertificate)
                Else
                    result = New X509SecurityTokenProvider(credentials.ClientEncryptingCertificate)
                End If
            End If
        Else
            result = MyBase.CreateSecurityTokenProvider(requirement)
        End If

        Return result
    End Function

    Public Overrides Function CreateSecurityTokenAuthenticator(ByVal tokenRequirement As SecurityTokenRequirement, _
                                                               <System.Runtime.InteropServices.Out()> ByRef outOfBandTokenResolver As SecurityTokenResolver) As SecurityTokenAuthenticator
        Return MyBase.CreateSecurityTokenAuthenticator(tokenRequirement, _
                                                       outOfBandTokenResolver)
    End Function

End Class

  3. Defina una nueva clase de credenciales de servicio que hereda de la clase ServiceCredentials. Implemente cuatro nuevas propiedades para permitir la especificación de múltiples certificados: ClientSigningCertificate, ClientEncryptingCertificate, ServiceSigningCertificate y ServiceEncryptingCertificate. Invalide también el método CreateSecurityTokenManager para devolver una instancia de la clase ServiceCredentialsSecurityTokenManager personalizada que se define en el paso siguiente.

    public class MyServiceCredentials : ServiceCredentials
{
    X509Certificate2 clientSigningCert;
    X509Certificate2 clientEncryptingCert;
    X509Certificate2 serviceSigningCert;
    X509Certificate2 serviceEncryptingCert;

    public MyServiceCredentials()
    {
    }

    protected MyServiceCredentials(MyServiceCredentials other)
        : base(other)
    {
        this.clientEncryptingCert = other.clientEncryptingCert;
        this.clientSigningCert = other.clientSigningCert;
        this.serviceEncryptingCert = other.serviceEncryptingCert;
        this.serviceSigningCert = other.serviceSigningCert;
    }

    public X509Certificate2 ClientSigningCertificate
    {
        get
        {
            return this.clientSigningCert;
        }
        set
        {
            this.clientSigningCert = value;
        }
    }

    public X509Certificate2 ClientEncryptingCertificate
    {
        get
        {
            return this.clientEncryptingCert;
        }
        set
        {
            this.clientEncryptingCert = value;
        }
    }

    public X509Certificate2 ServiceSigningCertificate
    {
        get
        {
            return this.serviceSigningCert;
        }
        set
        {
            this.serviceSigningCert = value;
        }
    }

    public X509Certificate2 ServiceEncryptingCertificate
    {
        get
        {
            return this.serviceEncryptingCert;
        }
        set
        {
            this.serviceEncryptingCert = value;
        }
    }

    public override SecurityTokenManager CreateSecurityTokenManager()
    {
        return new MyServiceCredentialsSecurityTokenManager(this);
    }

    protected override ServiceCredentials CloneCore()
    {
        return new MyServiceCredentials(this);
    }
}

    Public Class MyServiceCredentials
    Inherits ServiceCredentials

    Private clientSigningCert As X509Certificate2
    Private clientEncryptingCert As X509Certificate2
    Private serviceSigningCert As X509Certificate2
    Private serviceEncryptingCert As X509Certificate2

    Public Sub New()
    End Sub

    Protected Sub New(ByVal other As MyServiceCredentials)
        MyBase.New(other)
        Me.clientEncryptingCert = other.clientEncryptingCert
        Me.clientSigningCert = other.clientSigningCert
        Me.serviceEncryptingCert = other.serviceEncryptingCert
        Me.serviceSigningCert = other.serviceSigningCert
    End Sub

    Public Property ClientSigningCertificate() As X509Certificate2
        Get
            Return Me.clientSigningCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.clientSigningCert = value
        End Set
    End Property

    Public Property ClientEncryptingCertificate() As X509Certificate2
        Get
            Return Me.clientEncryptingCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.clientEncryptingCert = value
        End Set
    End Property

    Public Property ServiceSigningCertificate() As X509Certificate2
        Get
            Return Me.serviceSigningCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.serviceSigningCert = value
        End Set
    End Property

    Public Property ServiceEncryptingCertificate() As X509Certificate2
        Get
            Return Me.serviceEncryptingCert
        End Get
        Set(ByVal value As X509Certificate2)
            Me.serviceEncryptingCert = value
        End Set
    End Property

    Public Overrides Function CreateSecurityTokenManager() As SecurityTokenManager
        Return New MyServiceCredentialsSecurityTokenManager(Me)
    End Function

    Protected Overrides Function CloneCore() As ServiceCredentials
        Return New MyServiceCredentials(Me)
    End Function

End Class

  4. Defina un nuevo administrador de tokens de seguridad de servicio que herede de la clase ServiceCredentialsSecurityTokenManager. Invalide el método CreateSecurityTokenProvider para crear un proveedor de tokens de seguridad adecuado dada la dirección del mensaje pasada y el uso de las claves.

    internal class MyServiceCredentialsSecurityTokenManager :
    ServiceCredentialsSecurityTokenManager
{
    MyServiceCredentials credentials;

    public MyServiceCredentialsSecurityTokenManager(
        MyServiceCredentials credentials)
        : base(credentials)
    {
        this.credentials = credentials;
    }

    public override SecurityTokenProvider CreateSecurityTokenProvider(
        SecurityTokenRequirement requirement)
    {
        SecurityTokenProvider result = null;
        if (requirement.TokenType == SecurityTokenTypes.X509Certificate)
        {
            MessageDirection direction = requirement.
                GetProperty<MessageDirection>(
                ServiceModelSecurityTokenRequirement.
                MessageDirectionProperty);
            if (direction == MessageDirection.Input)
            {
                if (requirement.KeyUsage == SecurityKeyUsage.Exchange)
                {
                    result = new X509SecurityTokenProvider(
                        credentials.ServiceEncryptingCertificate);
                }
                else
                {
                    result = new X509SecurityTokenProvider(
                        credentials.ClientSigningCertificate);
                }
            }
            else
            {
                if (requirement.KeyUsage == SecurityKeyUsage.Signature)
                {
                    result = new X509SecurityTokenProvider(
                        credentials.ServiceSigningCertificate);
                }
                else
                {
                    result = new X509SecurityTokenProvider(
                        credentials.ClientEncryptingCertificate);
                }
            }
        }
        else
        {
            result = base.CreateSecurityTokenProvider(requirement);
        }
        return result;
    }
}

    Friend Class MyServiceCredentialsSecurityTokenManager
    Inherits ServiceCredentialsSecurityTokenManager

    Private credentials As MyServiceCredentials

    Public Sub New(ByVal credentials As MyServiceCredentials)
        MyBase.New(credentials)
        Me.credentials = credentials
    End Sub

    Public Overrides Function CreateSecurityTokenProvider(ByVal requirement As SecurityTokenRequirement) As SecurityTokenProvider
        Dim result As SecurityTokenProvider = Nothing
        If requirement.TokenType = SecurityTokenTypes.X509Certificate Then
            Dim direction = requirement.GetProperty(Of MessageDirection)(ServiceModelSecurityTokenRequirement.MessageDirectionProperty)
            If direction = MessageDirection.Input Then
                If requirement.KeyUsage = SecurityKeyUsage.Exchange Then
                    result = New X509SecurityTokenProvider(credentials.ServiceEncryptingCertificate)
                Else
                    result = New X509SecurityTokenProvider(credentials.ClientSigningCertificate)
                End If
            Else
                If requirement.KeyUsage = SecurityKeyUsage.Signature Then
                    result = New X509SecurityTokenProvider(credentials.ServiceSigningCertificate)
                Else
                    result = New X509SecurityTokenProvider(credentials.ClientEncryptingCertificate)
                End If
            End If
        Else
            result = MyBase.CreateSecurityTokenProvider(requirement)
        End If
        Return result
    End Function

End Class

Para utilizar varios certificados en el cliente

  1. Cree un enlace personalizado. El elemento de enlace de seguridad debe funcionar en modo dúplex para permitir que distintos proveedores de tokens de seguridad estén presentes para las solicitudes y respuestas. Una manera de hacerlo es utilizar un transporte de tipo dúplex o utilizar CompositeDuplexBindingElement tal y como se muestra en el código siguiente. Vincule el objeto IdentityVerifier personalizado que se define en el paso siguiente al elemento de enlace de seguridad. Reemplace las credenciales de cliente predeterminadas con las credenciales de cliente personalizadas creadas previamente.

                EndpointAddress serviceEndpoint =
                new EndpointAddress(new Uri("http://localhost:6060/service"));

            CustomBinding binding = new CustomBinding();

            AsymmetricSecurityBindingElement securityBE =
                SecurityBindingElement.CreateMutualCertificateDuplexBindingElement(
                MessageSecurityVersion.
WSSecurity10WSTrustFebruary2005WSSecureConversationFebruary2005WSSecurityPolicy11BasicSecurityProfile10);
            // Add a custom IdentityVerifier because the service uses two certificates
            // (one for signing and one for encryption) and an endpoint identity that
            // contains a single identity claim.
            securityBE.LocalClientSettings.IdentityVerifier = new MyIdentityVerifier();
            binding.Elements.Add(securityBE);

            CompositeDuplexBindingElement compositeDuplex =
                new CompositeDuplexBindingElement();
            compositeDuplex.ClientBaseAddress = new Uri("http://localhost:6061/client");
            binding.Elements.Add(compositeDuplex);

            binding.Elements.Add(new OneWayBindingElement());

            binding.Elements.Add(new HttpTransportBindingElement());

            using (ChannelFactory<IMyServiceChannel> factory =
                new ChannelFactory<IMyServiceChannel>(binding, serviceEndpoint))
            {
                MyClientCredentials credentials = new MyClientCredentials();
                SetupCertificates(credentials);
                factory.Endpoint.Behaviors.Remove(typeof(ClientCredentials));
                factory.Endpoint.Behaviors.Add(credentials);

                IMyServiceChannel channel = factory.CreateChannel();
                Console.WriteLine(channel.Hello("world"));
                channel.Close();
            }

    Dim serviceEndpoint As New EndpointAddress(New Uri("http://localhost:6060/service"))

Dim binding As New CustomBinding()

Dim securityBE = SecurityBindingElement.CreateMutualCertificateDuplexBindingElement(MessageSecurityVersion.WSSecurity10WSTrustFebruary2005WSSecureConversationFebruary2005WSSecurityPolicy11BasicSecurityProfile10)
' Add a custom IdentityVerifier because the service uses two certificates 
' (one for signing and one for encryption) and an endpoint identity that 
' contains a single identity claim.
securityBE.LocalClientSettings.IdentityVerifier = New MyIdentityVerifier()
binding.Elements.Add(securityBE)

Dim compositeDuplex As New CompositeDuplexBindingElement()

compositeDuplex.ClientBaseAddress = New Uri("http://localhost:6061/client")

With binding.Elements
    .Add(compositeDuplex)
    .Add(New OneWayBindingElement())
    .Add(New HttpTransportBindingElement())
End With

Using factory As New ChannelFactory(Of IMyServiceChannel)(binding, serviceEndpoint)
    Dim credentials As New MyClientCredentials()
    SetupCertificates(credentials)

    With factory.Endpoint.Behaviors
        .Remove(GetType(ClientCredentials))
        .Add(credentials)
    End With

    Dim channel = factory.CreateChannel()
    Console.WriteLine(channel.Hello("world"))
    channel.Close()
End Using

  2. Defina un objeto IdentityVerifier personalizado. El servicio tiene varias identidades porque se usan certificados diferentes para cifrar la solicitud y firmar la respuesta.

    Nota:

    En el ejemplo siguiente, el comprobador de identidad personalizado proporcionado no realiza ninguna comprobación de identidad del punto de conexión con fines de demostración. No se trata de una práctica recomendada para el código de producción.

    class MyIdentityVerifier : IdentityVerifier
{
    IdentityVerifier defaultVerifier;

    public MyIdentityVerifier()
    {
        this.defaultVerifier = IdentityVerifier.CreateDefault();
    }

    public override bool CheckAccess(EndpointIdentity identity,
        AuthorizationContext authContext)
    {
        // The following implementation is for demonstration only, and
        // does not perform any checks regarding EndpointIdentity.
        // Do not use this for production code.
        return true;
    }

    public override bool TryGetIdentity(EndpointAddress reference,
        out EndpointIdentity identity)
    {
        return this.defaultVerifier.TryGetIdentity(reference, out identity);
    }
}


    Friend Class MyIdentityVerifier
    Inherits IdentityVerifier

    Private defaultVerifier As IdentityVerifier

    Public Sub New()
        Me.defaultVerifier = IdentityVerifier.CreateDefault()
    End Sub

    Public Overrides Function CheckAccess(ByVal identity As EndpointIdentity, ByVal authContext As AuthorizationContext) As Boolean
        ' The following implementation is for demonstration only, and
        ' does not perform any checks regarding EndpointIdentity.
        ' Do not use this for production code.
        Return True
    End Function

    Public Overrides Function TryGetIdentity(ByVal reference As EndpointAddress, <System.Runtime.InteropServices.Out()> ByRef identity As EndpointIdentity) As Boolean
        Return Me.defaultVerifier.TryGetIdentity(reference, identity)
    End Function

End Class

Para utilizar varios certificados en el servicio

  1. Cree un enlace personalizado. El elemento de enlace de seguridad debe funcionar en modo dúplex para permitir que distintos proveedores de tokens de seguridad estén presentes para las solicitudes y respuestas. Tal y como ocurre con el cliente, utilice un transporte de tipo dúplex o use CompositeDuplexBindingElement tal y como se muestra en el código siguiente. Reemplace las credenciales de servicio predeterminadas con las credenciales de servicio personalizadas creadas previamente.

                Uri serviceEndpoint = new Uri("http://localhost:6060/service");
            using (ServiceHost host = new ServiceHost(typeof(Service), serviceEndpoint))
            {
                CustomBinding binding = new CustomBinding();
                binding.Elements.Add(SecurityBindingElement.
                    CreateMutualCertificateDuplexBindingElement(
MessageSecurityVersion.WSSecurity10WSTrustFebruary2005WSSecureConversationFebruary2005WSSecurityPolicy11BasicSecurityProfile10));
                binding.Elements.Add(new CompositeDuplexBindingElement());
                binding.Elements.Add(new OneWayBindingElement());
                binding.Elements.Add(new HttpTransportBindingElement());

                MyServiceCredentials credentials = new MyServiceCredentials();
                SetupCertificates(credentials);
                host.Description.Behaviors.Remove(typeof(ServiceCredentials));
                host.Description.Behaviors.Add(credentials);

                ServiceEndpoint endpoint = host.AddServiceEndpoint(
                    typeof(IMyService), binding, "");
                host.Open();

                Console.WriteLine("Service started, press ENTER to stop...");
                Console.ReadLine();
            }

    Dim serviceEndpoint As New Uri("http://localhost:6060/service")
Using host As New ServiceHost(GetType(Service), serviceEndpoint)
    Dim binding As New CustomBinding()

    With binding.Elements
        .Add(SecurityBindingElement.CreateMutualCertificateDuplexBindingElement(MessageSecurityVersion.WSSecurity10WSTrustFebruary2005WSSecureConversationFebruary2005WSSecurityPolicy11BasicSecurityProfile10))
        .Add(New CompositeDuplexBindingElement())
        .Add(New OneWayBindingElement())
        .Add(New HttpTransportBindingElement())
    End With

    Dim credentials As New MyServiceCredentials()
    SetupCertificates(credentials)
    With host.Description.Behaviors
        .Remove(GetType(ServiceCredentials))
        .Add(credentials)
    End With

    Dim endpoint = host.AddServiceEndpoint(GetType(IMyService), binding, "")
    host.Open()

    Console.WriteLine("Service started, press ENTER to stop...")
    Console.ReadLine()
End Using

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