How to: Change the Cryptographic Provider for an X.509 Certificate's Private Key

This topic shows how to change the cryptographic provider used to provide an X.509 certificate's private key and how to integrate the provider into the Windows Communication Foundation (WCF) security framework. For more information about using certificates, see Working with Certificates.

The WCF security framework provides a way to introduce new security token types as described in How to: Create a Custom Token. It is also possible to use a custom token to replace existing system-provided token types.

In this topic, the system-provided X.509 security token is replaced by a custom X.509 token that provides a different implementation for the certificate private key. This is useful in scenarios where the actual private key is provided by a different cryptographic provider than the default Windows cryptographic provider. One example of an alternative cryptographic provider is a hardware security module that performs all private key related cryptographic operations, and does not store the private keys in memory, thus improving security of the system.

The following example is for demonstration purposes only. It does not replace the default Windows cryptographic provider, but it shows where such a provider could be integrated.

Procedures

Every security token that has an associated security key or keys must implement the SecurityKeys property, which returns a collection of keys from the security token instance. If the token is an X.509 security token, the collection contains a single instance of the X509AsymmetricSecurityKey class that represents both public and private keys associated with the certificate. To replace the default cryptographic provider used to provide the certificate's keys, create a new implementation of this class.

To create a custom X.509 asymmetric key

  1. Define a new class derived from the X509AsymmetricSecurityKey class.

  2. Override the KeySize read-only property. This property returns the actual key size of the certificate's public/private key pair.

  3. Override the DecryptKey method. This method is called by the WCF security framework to decrypt a symmetric key with the certificate's private key. (The key was previously encrypted with the certificate's public key.)

  4. Override the GetAsymmetricAlgorithm method. This method is called by the WCF security framework to obtain an instance of the AsymmetricAlgorithm class that represents the cryptographic provider for either the certificate's private or public key, depending on the parameters passed to the method.

  5. Optional. Override the GetHashAlgorithmForSignature method. Override this method if a different implementation of the HashAlgorithm class is required.

  6. Override the GetSignatureFormatter method. This method returns an instance of the AsymmetricSignatureFormatter class that is associated with the certificate's private key.

  7. Override the IsSupportedAlgorithm method. This method is used to indicate whether a particular cryptographic algorithm is supported by the security key implementation.

    class CustomX509AsymmetricSecurityKey : X509AsymmetricSecurityKey
    {
        X509Certificate2 certificate;
        object thisLock = new Object();
        bool privateKeyAvailabilityDetermined;
        AsymmetricAlgorithm privateKey;
        PublicKey publicKey;
    
        public CustomX509AsymmetricSecurityKey(X509Certificate2 certificate)
            : base(certificate)
        {
            this.certificate = certificate;
        }
    
        public override int KeySize
        {
            get { return this.PublicKey.Key.KeySize; }
        }
    
        AsymmetricAlgorithm PrivateKey
        {
            // You need to modify this to obtain the private key using a different cryptographic
            // provider if you do not want to use the default provider.
            get
            {
                if (!this.privateKeyAvailabilityDetermined)
                {
                    lock (ThisLock)
                    {
                        if (!this.privateKeyAvailabilityDetermined)
                        {
                            this.privateKey = this.certificate.PrivateKey;
                            this.privateKeyAvailabilityDetermined = true;
                        }
                    }
                }
                return this.privateKey;
            }
        }
    
        PublicKey PublicKey
        {
            get
            {
                if (this.publicKey == null)
                {
                    lock (ThisLock)
                    {
                        if (this.publicKey == null)
                        {
                            this.publicKey = this.certificate.PublicKey;
                        }
                    }
                }
                return this.publicKey;
            }
        }
    
        Object ThisLock
        {
            get
            {
                return thisLock;
            }
        }
    
        public override byte[] DecryptKey(string algorithm, byte[] keyData)
        {
            // You can decrypt the key only if you have the private key in the certificate.
            if (this.PrivateKey == null)
            {
                throw new NotSupportedException("Missing private key");
            }
    
            RSA rsa = this.PrivateKey as RSA;
            if (rsa == null)
            {
                throw new NotSupportedException("Private key cannot be used with RSA algorithm");
            }
    
            // Support exchange keySpec, AT_EXCHANGE ?
            if (rsa.KeyExchangeAlgorithm == null)
            {
                throw new NotSupportedException("Private key does not support key exchange");
            }
    
            switch (algorithm)
            {
                case EncryptedXml.XmlEncRSA15Url:
                    return EncryptedXml.DecryptKey(keyData, rsa, false);
    
                case EncryptedXml.XmlEncRSAOAEPUrl:
                    return EncryptedXml.DecryptKey(keyData, rsa, true);
    
                default:
                    throw new NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm));
            }
        }
    
        public override AsymmetricAlgorithm GetAsymmetricAlgorithm(string algorithm, bool privateKey)
        {
            if (privateKey)
            {
                if (this.PrivateKey == null)
                {
                    throw new NotSupportedException("Missing private key");
                }
    
                switch (algorithm)
                {
                    case SignedXml.XmlDsigDSAUrl:
                        if ((this.PrivateKey as DSA) != null)
                        {
                            return (this.PrivateKey as DSA);
                        }
                        throw new NotSupportedException("Private key cannot be used with DSA");
    
                    case SignedXml.XmlDsigRSASHA1Url:
                    case EncryptedXml.XmlEncRSA15Url:
                    case EncryptedXml.XmlEncRSAOAEPUrl:
                        if ((this.PrivateKey as RSA) != null)
                        {
                            return (this.PrivateKey as RSA);
                        }
                        throw new NotSupportedException("Private key cannot be used with RSA");
                    default:
                        throw new NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm));
                }
            }
            else
            {
                switch (algorithm)
                {
                    case SignedXml.XmlDsigDSAUrl:
                        if ((this.PublicKey.Key as DSA) != null)
                        {
                            return (this.PublicKey.Key as DSA);
                        }
                        throw new NotSupportedException("Public key cannot be used with DSA");
                    case SignedXml.XmlDsigRSASHA1Url:
                    case EncryptedXml.XmlEncRSA15Url:
                    case EncryptedXml.XmlEncRSAOAEPUrl:
                        if ((this.PublicKey.Key as RSA) != null)
                        {
                            return (this.PublicKey.Key as RSA);
                        }
                        throw new NotSupportedException("Public key cannot be used with RSA");
                    default:
                        throw new NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm));
                }
            }
        }
    
        public override HashAlgorithm GetHashAlgorithmForSignature(string algorithm)
        {
            if (!this.IsSupportedAlgorithm(algorithm))
            {
                throw new NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm));
            }
    
            switch (algorithm)
            {
                case SignedXml.XmlDsigDSAUrl:
                case SignedXml.XmlDsigRSASHA1Url:
                    return new SHA1Managed();
                default:
                    throw new NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm));
            }
        }
    
        public override AsymmetricSignatureFormatter GetSignatureFormatter(string algorithm)
        {
            // The signature can be created only if the private key is present.
            if (this.PrivateKey == null)
            {
                throw new NotSupportedException("Private key is missing");
            }
    
            // Only one of the two algorithms is supported, not both.
            //     XmlDsigDSAUrl = "http://www.w3.org/2000/09/xmldsig#dsa-sha1";
            //     XmlDsigRSASHA1Url = "http://www.w3.org/2000/09/xmldsig#rsa-sha1";
            switch (algorithm)
            {
                case SignedXml.XmlDsigDSAUrl:
    
                    // Ensure that this is a DSA algorithm object.
                    DSA dsa = (this.PrivateKey as DSA);
                    if (dsa == null)
                    {
                        throw new NotSupportedException("Private key cannot be used DSA");
                    }
    
                    return new DSASignatureFormatter(dsa);
    
                case SignedXml.XmlDsigRSASHA1Url:
                    // Ensure that this is an RSA algorithm object.
                    RSA rsa = (this.PrivateKey as RSA);
                    if (rsa == null)
                    {
                        throw new NotSupportedException("Private key cannot be used RSA");
                    }
    
                    return new RSAPKCS1SignatureFormatter(rsa);
                default:
                    throw new NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm));
            }
        }
    
        public override bool IsSupportedAlgorithm(string algorithm)
        {
            switch (algorithm)
            {
                case SignedXml.XmlDsigDSAUrl:
                    return (this.PublicKey.Key is DSA);
    
                case SignedXml.XmlDsigRSASHA1Url:
                case EncryptedXml.XmlEncRSA15Url:
                case EncryptedXml.XmlEncRSAOAEPUrl:
                    return (this.PublicKey.Key is RSA);
    
                default:
                    return false;
            }
        }
    }
    
    Friend Class CustomX509AsymmetricSecurityKey
        Inherits X509AsymmetricSecurityKey
    
        Private _certificate As X509Certificate2
        Private _thisLock As New Object()
        Private _privateKeyAvailabilityDetermined As Boolean
        Private _privateKey As AsymmetricAlgorithm
        Private _publicKey As PublicKey
    
        Public Sub New(ByVal certificate As X509Certificate2)
            MyBase.New(certificate)
            Me._certificate = certificate
        End Sub
    
        Public Overrides ReadOnly Property KeySize() As Integer
            Get
                Return Me.PublicKey.Key.KeySize
            End Get
        End Property
    
        Private Overloads ReadOnly Property PrivateKey() As AsymmetricAlgorithm
            ' You need to modify this to obtain the private key using a different cryptographic
            ' provider if you do not want to use the default provider.
            Get
                If Not Me._privateKeyAvailabilityDetermined Then
                    SyncLock ThisLock
                        If Not Me._privateKeyAvailabilityDetermined Then
                            Me._privateKey = Me._certificate.PrivateKey
                            Me._privateKeyAvailabilityDetermined = True
                        End If
                    End SyncLock
                End If
                Return Me._privateKey
            End Get
        End Property
    
        Private Overloads ReadOnly Property PublicKey() As PublicKey
            Get
                If Me._publicKey Is Nothing Then
                    SyncLock ThisLock
                        If Me._publicKey Is Nothing Then
                            Me._publicKey = Me._certificate.PublicKey
                        End If
                    End SyncLock
                End If
                Return Me._publicKey
            End Get
        End Property
    
        Private Overloads ReadOnly Property ThisLock() As Object
            Get
                Return _thisLock
            End Get
        End Property
    
        Public Overrides Function DecryptKey(ByVal algorithm As String, _
                                             ByVal keyData() As Byte) As Byte()
            ' You can decrypt the key only if you have the private key in the certificate.
            If Me.PrivateKey Is Nothing Then
                Throw New NotSupportedException("Missing private key")
            End If
    
            Dim rsa = TryCast(Me.PrivateKey, RSA)
            If rsa Is Nothing Then
                Throw New NotSupportedException("Private key cannot be used with RSA algorithm")
            End If
    
            ' Support exchange keySpec, AT_EXCHANGE ?
            If rsa.KeyExchangeAlgorithm Is Nothing Then
                Throw New NotSupportedException("Private key does not support key exchange")
            End If
    
            Select Case algorithm
                Case EncryptedXml.XmlEncRSA15Url
                    Return EncryptedXml.DecryptKey(keyData, rsa, False)
    
                Case EncryptedXml.XmlEncRSAOAEPUrl
                    Return EncryptedXml.DecryptKey(keyData, rsa, True)
    
                Case Else
                    Throw New NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm))
            End Select
        End Function
    
        Public Overrides Function GetAsymmetricAlgorithm(ByVal algorithm As String, _
                                                         ByVal privateKey As Boolean) As AsymmetricAlgorithm
            If privateKey Then
                If Me.PrivateKey Is Nothing Then
                    Throw New NotSupportedException("Missing private key")
                End If
    
                Select Case algorithm
                    Case SignedXml.XmlDsigDSAUrl
                        If TryCast(Me.PrivateKey, DSA) IsNot Nothing Then
                            Return (TryCast(Me.PrivateKey, DSA))
                        End If
                        Throw New NotSupportedException("Private key cannot be used with DSA")
    
                    Case SignedXml.XmlDsigRSASHA1Url, EncryptedXml.XmlEncRSA15Url, EncryptedXml.XmlEncRSAOAEPUrl
                        If TryCast(Me.PrivateKey, RSA) IsNot Nothing Then
                            Return (TryCast(Me.PrivateKey, RSA))
                        End If
                        Throw New NotSupportedException("Private key cannot be used with RSA")
                    Case Else
                        Throw New NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm))
                End Select
            Else
                Select Case algorithm
                    Case SignedXml.XmlDsigDSAUrl
                        If TryCast(Me.PublicKey.Key, DSA) IsNot Nothing Then
                            Return (TryCast(Me.PublicKey.Key, DSA))
                        End If
                        Throw New NotSupportedException("Public key cannot be used with DSA")
                    Case SignedXml.XmlDsigRSASHA1Url, EncryptedXml.XmlEncRSA15Url, EncryptedXml.XmlEncRSAOAEPUrl
                        If TryCast(Me.PublicKey.Key, RSA) IsNot Nothing Then
                            Return (TryCast(Me.PublicKey.Key, RSA))
                        End If
                        Throw New NotSupportedException("Public key cannot be used with RSA")
                    Case Else
                        Throw New NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm))
                End Select
            End If
        End Function
    
        Public Overrides Function GetHashAlgorithmForSignature(ByVal algorithm As String) As HashAlgorithm
            If Not Me.IsSupportedAlgorithm(algorithm) Then
                Throw New NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm))
            End If
    
            Select Case algorithm
                Case SignedXml.XmlDsigDSAUrl, SignedXml.XmlDsigRSASHA1Url
                    Return New SHA1Managed()
                Case Else
                    Throw New NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm))
            End Select
        End Function
    
        Public Overrides Function GetSignatureFormatter(ByVal algorithm As String) As AsymmetricSignatureFormatter
            ' The signature can be created only if the private key is present.
            If Me.PrivateKey Is Nothing Then
                Throw New NotSupportedException("Private key is missing")
            End If
    
            ' Only one of the two algorithms is supported, not both.
            '     XmlDsigDSAUrl = "http://www.w3.org/2000/09/xmldsig#dsa-sha1";
            '     XmlDsigRSASHA1Url = "http://www.w3.org/2000/09/xmldsig#rsa-sha1";
            Select Case algorithm
                Case SignedXml.XmlDsigDSAUrl
    
                    ' Ensure that this is a DSA algorithm object.
                    Dim dsa = (TryCast(Me.PrivateKey, DSA))
                    If dsa Is Nothing Then
                        Throw New NotSupportedException("Private key cannot be used DSA")
                    End If
    
                    Return New DSASignatureFormatter(dsa)
    
                Case SignedXml.XmlDsigRSASHA1Url
                    ' Ensure that this is an RSA algorithm object.
                    Dim rsa = (TryCast(Me.PrivateKey, RSA))
                    If rsa Is Nothing Then
                        Throw New NotSupportedException("Private key cannot be used RSA")
                    End If
    
                    Return New RSAPKCS1SignatureFormatter(rsa)
                Case Else
                    Throw New NotSupportedException(String.Format("Algorithm {0} is not supported", algorithm))
            End Select
        End Function
    
        Public Overrides Function IsSupportedAlgorithm(ByVal algorithm As String) As Boolean
            Select Case algorithm
                Case SignedXml.XmlDsigDSAUrl
                    Return (TypeOf Me.PublicKey.Key Is DSA)
    
                Case SignedXml.XmlDsigRSASHA1Url, EncryptedXml.XmlEncRSA15Url, EncryptedXml.XmlEncRSAOAEPUrl
                    Return (TypeOf Me.PublicKey.Key Is RSA)
    
                Case Else
                    Return False
            End Select
        End Function
    
    End Class
    

The following procedure shows how to integrate the custom X.509 asymmetric security key implementation created in the preceding procedure with the WCF security framework in order to replace the system-provided X.509 security token.

To replace the system-provided X.509 security token with a custom X.509 asymmetric security key token

  1. Create a custom X.509 security token that returns the custom X.509 asymmetric security key instead of the system-provided security key, as shown in the following example. For more information about custom security tokens, see How to: Create a Custom Token.

    class CustomX509SecurityToken : X509SecurityToken
    {
        ReadOnlyCollection<SecurityKey> securityKeys;
        public CustomX509SecurityToken(X509Certificate2 certificate)
            : base(certificate)
        {
        }
    
        public override ReadOnlyCollection<SecurityKey> SecurityKeys
        {
            get
            {
                if (this.securityKeys == null)
                {
                    List<SecurityKey> temp = new List<SecurityKey>(1);
                    temp.Add(new CustomX509AsymmetricSecurityKey(this.Certificate));
                    this.securityKeys = temp.AsReadOnly();
                }
                return this.securityKeys;
            }
        }
    }
    
    Friend Class CustomX509SecurityToken
        Inherits X509SecurityToken
    
        Private _securityKeys As ReadOnlyCollection(Of SecurityKey)
    
        Public Sub New(ByVal certificate As X509Certificate2)
            MyBase.New(certificate)
        End Sub
    
        Public Overrides ReadOnly Property SecurityKeys() As ReadOnlyCollection(Of SecurityKey)
            Get
                If Me._securityKeys Is Nothing Then
                    Dim temp As New List(Of SecurityKey)(1)
                    temp.Add(New CustomX509AsymmetricSecurityKey(Me.Certificate))
                    Me._securityKeys = temp.AsReadOnly()
                End If
                Return Me._securityKeys
            End Get
        End Property
    
    End Class
    
  2. Create a custom security token provider that returns a custom X.509 security token, as shown in the example. For more information about custom security token providers, see How to: Create a Custom Security Token Provider.

    class CustomX509SecurityTokenProvider : SecurityTokenProvider
    {
        X509Certificate2 certificate;
    
        public CustomX509SecurityTokenProvider(X509Certificate2 certificate)
        {
            this.certificate = certificate;
        }
    
        protected override SecurityToken GetTokenCore(TimeSpan timeout)
        {
            return new CustomX509SecurityToken(certificate);
        }
    }
    
    Friend Class CustomX509SecurityTokenProvider
        Inherits SecurityTokenProvider
    
        Private _certificate As X509Certificate2
    
        Public Sub New(ByVal certificate As X509Certificate2)
            Me._certificate = certificate
        End Sub
    
        Protected Overrides Function GetTokenCore(ByVal timeout As TimeSpan) As SecurityToken
            Return New CustomX509SecurityToken(_certificate)
        End Function
    End Class
    
  3. If the custom security key needs to be used on the initiator side, create a custom client security token manager and custom client credentials classes, as shown in the following example. For more information about custom client credentials and client security token managers, see Walkthrough: Creating Custom Client and Service Credentials.

    class CustomClientSecurityTokenManager : ClientCredentialsSecurityTokenManager
    {
        CustomClientCredentials credentials;
    
        public CustomClientSecurityTokenManager(CustomClientCredentials credentials)
            : base(credentials)
        {
            this.credentials = credentials;
        }
    
        public override SecurityTokenProvider CreateSecurityTokenProvider(SecurityTokenRequirement tokenRequirement)
        {
            SecurityTokenProvider result = null;
    
            if (tokenRequirement.TokenType == SecurityTokenTypes.X509Certificate)
            {
                MessageDirection direction = tokenRequirement.GetProperty<MessageDirection>(ServiceModelSecurityTokenRequirement.MessageDirectionProperty);
                if (direction == MessageDirection.Output)
                {
                    if (tokenRequirement.KeyUsage == SecurityKeyUsage.Signature)
                    {
                        result = new CustomX509SecurityTokenProvider(credentials.ClientCertificate.Certificate);
                    }
                }
                else
                {
                    if (tokenRequirement.KeyUsage == SecurityKeyUsage.Exchange)
                    {
                        result = new CustomX509SecurityTokenProvider(credentials.ClientCertificate.Certificate);
                    }
                }
            }
    
            if (result == null)
            {
                result = base.CreateSecurityTokenProvider(tokenRequirement);
            }
            return result;
        }
    }
    
    Friend Class CustomClientSecurityTokenManager
        Inherits ClientCredentialsSecurityTokenManager
    
        Private credentials As CustomClientCredentials
    
        Public Sub New(ByVal credentials As CustomClientCredentials)
            MyBase.New(credentials)
            Me.credentials = credentials
        End Sub
    
        Public Overrides Function CreateSecurityTokenProvider(ByVal tokenRequirement As SecurityTokenRequirement) _
        As SecurityTokenProvider
            Dim result As SecurityTokenProvider = Nothing
    
            If tokenRequirement.TokenType = SecurityTokenTypes.X509Certificate Then
                Dim direction = tokenRequirement.GetProperty(Of MessageDirection) _
                (ServiceModelSecurityTokenRequirement.MessageDirectionProperty)
                If direction = MessageDirection.Output Then
                    If tokenRequirement.KeyUsage = SecurityKeyUsage.Signature Then
                        result = New CustomX509SecurityTokenProvider(credentials.ClientCertificate.Certificate)
                    End If
                Else
                    If tokenRequirement.KeyUsage = SecurityKeyUsage.Exchange Then
                        result = New CustomX509SecurityTokenProvider(credentials.ClientCertificate.Certificate)
                    End If
                End If
            End If
    
            If result Is Nothing Then
                result = MyBase.CreateSecurityTokenProvider(tokenRequirement)
            End If
            Return result
        End Function
    End Class
    
    public class CustomClientCredentials : ClientCredentials
    {
        public CustomClientCredentials()
        {
        }
    
        protected CustomClientCredentials(CustomClientCredentials other)
            : base(other)
        {
        }
    
        protected override ClientCredentials CloneCore()
        {
            return new CustomClientCredentials(this);
        }
    
        public override SecurityTokenManager CreateSecurityTokenManager()
        {
            return new CustomClientSecurityTokenManager(this);
        }
    }
    
    Public Class CustomClientCredentials
        Inherits ClientCredentials
    
        Public Sub New()
        End Sub
    
        Protected Sub New(ByVal other As CustomClientCredentials)
            MyBase.New(other)
        End Sub
    
        Protected Overrides Function CloneCore() As ClientCredentials
            Return New CustomClientCredentials(Me)
        End Function
    
        Public Overrides Function CreateSecurityTokenManager() As SecurityTokenManager
            Return New CustomClientSecurityTokenManager(Me)
        End Function
    End Class
    
  4. If the custom security key needs to be used on the recipient side, create a custom service security token manager and custom service credentials, as shown in the following example. For more information about custom service credentials and service security token managers, see Walkthrough: Creating Custom Client and Service Credentials.

    class CustomServiceSecurityTokenManager : ServiceCredentialsSecurityTokenManager
    {
        CustomServiceCredentials credentials;
    
        public CustomServiceSecurityTokenManager(CustomServiceCredentials credentials)
            : base(credentials)
        {
            this.credentials = credentials;
        }
    
        public override SecurityTokenProvider CreateSecurityTokenProvider(SecurityTokenRequirement tokenRequirement)
        {
            SecurityTokenProvider result = null;
    
            if (tokenRequirement.TokenType == SecurityTokenTypes.X509Certificate)
            {
                MessageDirection direction = tokenRequirement.GetProperty<MessageDirection>(ServiceModelSecurityTokenRequirement.MessageDirectionProperty);
                if (direction == MessageDirection.Input)
                {
                    if (tokenRequirement.KeyUsage == SecurityKeyUsage.Exchange)
                    {
                        result = new CustomX509SecurityTokenProvider(credentials.ServiceCertificate.Certificate);
                    }
                }
                else
                {
                    if (tokenRequirement.KeyUsage == SecurityKeyUsage.Signature)
                    {
                        result = new CustomX509SecurityTokenProvider(credentials.ServiceCertificate.Certificate);
                    }
                }
            }
    
            if (result == null)
            {
                result = base.CreateSecurityTokenProvider(tokenRequirement);
            }
            return result;
        }
    }
    
    Friend Class CustomServiceSecurityTokenManager
        Inherits ServiceCredentialsSecurityTokenManager
    
        Private credentials As CustomServiceCredentials
    
        Public Sub New(ByVal credentials As CustomServiceCredentials)
            MyBase.New(credentials)
            Me.credentials = credentials
        End Sub
    
        Public Overrides Function CreateSecurityTokenProvider(ByVal tokenRequirement As SecurityTokenRequirement) As SecurityTokenProvider
            Dim result As SecurityTokenProvider = Nothing
    
            If tokenRequirement.TokenType = SecurityTokenTypes.X509Certificate Then
                Dim direction = tokenRequirement.GetProperty(Of MessageDirection) _
                (ServiceModelSecurityTokenRequirement.MessageDirectionProperty)
                If direction = MessageDirection.Input Then
                    If tokenRequirement.KeyUsage = SecurityKeyUsage.Exchange Then
                        result = New CustomX509SecurityTokenProvider(credentials.ServiceCertificate.Certificate)
                    End If
                Else
                    If tokenRequirement.KeyUsage = SecurityKeyUsage.Signature Then
                        result = New CustomX509SecurityTokenProvider(credentials.ServiceCertificate.Certificate)
                    End If
                End If
            End If
    
            If result Is Nothing Then
                result = MyBase.CreateSecurityTokenProvider(tokenRequirement)
            End If
            Return result
        End Function
    End Class
    
    public class CustomServiceCredentials : ServiceCredentials
    {
        public CustomServiceCredentials()
        {
        }
    
        protected CustomServiceCredentials(CustomServiceCredentials other)
            : base(other)
        {
        }
    
        protected override ServiceCredentials CloneCore()
        {
            return new CustomServiceCredentials(this);
        }
    
        public override SecurityTokenManager CreateSecurityTokenManager()
        {
            return new CustomServiceSecurityTokenManager(this);
        }
    }
    
    Public Class CustomServiceCredentials
        Inherits ServiceCredentials
    
        Public Sub New()
        End Sub
    
        Protected Sub New(ByVal other As CustomServiceCredentials)
            MyBase.New(other)
        End Sub
    
        Protected Overrides Function CloneCore() As ServiceCredentials
            Return New CustomServiceCredentials(Me)
        End Function
    
        Public Overrides Function CreateSecurityTokenManager() As SecurityTokenManager
            Return New CustomServiceSecurityTokenManager(Me)
        End Function
    
    End Class
    

See Also

X509AsymmetricSecurityKey
AsymmetricSecurityKey
SecurityKey
AsymmetricAlgorithm
HashAlgorithm
AsymmetricSignatureFormatter
Walkthrough: Creating Custom Client and Service Credentials
How to: Create a Custom Security Token Authenticator
How to: Create a Custom Security Token Provider
How to: Create a Custom Token
Security Architecture