imports System
imports System.Security.Cryptography

Namespace Contoso
    Public Class ContosoDeformatter
        Inherits AsymmetricKeyExchangeDeformatter

        Private rsaKey As RSA

        ' Default constructor.
        Public Sub New()

        End Sub

        ' Constructor with the public key to use for decryption.
        Public Sub New(ByVal key As AsymmetricAlgorithm)
            SetKey(key)
        End Sub

        ' Set the public key for encyption operations.
        Public Overrides Sub SetKey(ByVal key As AsymmetricAlgorithm)
            If (Not key Is Nothing) Then
                rsaKey = CType(key, RSA)
            Else
                Throw New ArgumentNullException("key")
            End If
        End Sub

        ' Disallow access to the parameters of the formatter.
        Public Overrides Property Parameters() As String
            Get
                Return Nothing
            End Get
            Set(ByVal Value As String)

            End Set
        End Property

        ' Create the encrypted key exchange data from the specified input
        ' data. This method uses the RSACryptoServiceProvider only. To
        ' support additional providers or provide custom decryption logic,
        ' add logic to this member.
        Public Overrides Function DecryptKeyExchange( _
            ByVal rgbData() As Byte) As Byte()

            Dim decryptedBytes() As Byte

            If (Not rsaKey Is Nothing) Then
                If (TypeOf (rsaKey) Is RSACryptoServiceProvider) Then
                    Dim rsaProvider As RSACryptoServiceProvider
                    rsaProvider = CType(rsaKey, RSACryptoServiceProvider)

                    decryptedBytes = rsaProvider.Decrypt(rgbData, True)
                End If

                ' Add custom decryption logic here.

            Else
                Throw New CryptographicUnexpectedOperationException( _
                    "Cryptography_MissingKey")
            End If

            Return decryptedBytes
        End Function
    End Class
End Namespace
'
' This code example produces the following output:
'
' Data to encrypt : Sample Contoso encryption application.
' Encrypted data: Kh34dfg-(*&834d+3
' Data decrypted : Sample Contoso encryption application.
' 
' This sample completed successfully; press Exit to continue.

using System;
using System.Security.Cryptography;

namespace Contoso
{
    public class ContosoDeformatter : AsymmetricKeyExchangeDeformatter 
    {
        private RSA rsaKey;

        // Default constructor.
        public ContosoDeformatter(){}

        // Constructor with the public key to use for decryption.
        public ContosoDeformatter(AsymmetricAlgorithm key) 
        {
            SetKey(key);
        }

        // Set the public key for encyption operations.
        public override void SetKey(AsymmetricAlgorithm key) 
        {
            if (key != null) 
            {
                rsaKey = (RSA) key;            }
            else 
            {
                throw new ArgumentNullException("key");
            }
        }

        // Disallow access to the parameters of the formatter.
        public override String Parameters 
        {
            get { return null; }
            set { ; }
        }

        // Create the encrypted key exchange data from the specified input
        // data. This method uses the RSACryptoServiceProvider only. To
        // support additional providers or provide custom decryption logic,
        // add logic to this member.
        public override byte[] DecryptKeyExchange(byte[] rgbData) 
        {
            byte[] decryptedBytes = null;

            if (rsaKey != null)
            {
                if (rsaKey is RSACryptoServiceProvider) 
                {
                    RSACryptoServiceProvider serviceProvder = 
                        (RSACryptoServiceProvider) rsaKey;

                    decryptedBytes = serviceProvder.Decrypt(rgbData, true);
                } 
                // Add custom decryption logic here.
            }
            else 
            {
                throw new CryptographicUnexpectedOperationException(
                    "Cryptography_MissingKey");
            }

            return decryptedBytes;
        }
    }
}
//
// This code example produces the following output:
//
// Data to encrypt : Sample Contoso encryption application.
// Encrypted data: Khasdf-3248&$%23
// Data decrypted : Sample Contoso encryption application.
// 
// This sample completed successfully; press Enter to exit.