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AsymmetricKeyExchangeDeformatter Class

Represents the base class from which all asymmetric key exchange deformatters derive.

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

public abstract class AsymmetricKeyExchangeDeformatter

Asymmetric key exchange deformatters decrypt key exchange data.

Key exchange allows a sender to create secret information, such as random data that can be used as a key in a symmetric encryption algorithm, and use encryption to send it to the intended recipient.

Caution noteCaution:

It is highly recommended that you not attempt to create your own key exchange method from the basic functionality provided, because many details of the operation must be performed carefully in order for the key exchange to be successful.

The following example demonstrates how to extend the AsymmetricKeyExchangeDeformatter class.

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) 

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

            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.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5

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