RSAPKCS1KeyExchangeDeformatter Class
Collapse the table of content
Expand the table of content

RSAPKCS1KeyExchangeDeformatter Class


Decrypts the PKCS #1 key exchange data.

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


public class RSAPKCS1KeyExchangeDeformatter : AsymmetricKeyExchangeDeformatter


Initializes a new instance of the RSAPKCS1KeyExchangeDeformatter class.


Initializes a new instance of the RSAPKCS1KeyExchangeDeformatter class with the specified key.


Gets the parameters for the PKCS #1 key exchange.(Overrides AsymmetricKeyExchangeDeformatter.Parameters.)


Gets or sets the random number generator algorithm to use in the creation of the key exchange.


Extracts secret information from the encrypted key exchange data.(Overrides AsymmetricKeyExchangeDeformatter.DecryptKeyExchange(Byte[]).)


Determines whether the specified object is equal to the current object.(Inherited from Object.)


Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)


Serves as the default hash function. (Inherited from Object.)


Gets the Type of the current instance.(Inherited from Object.)


Creates a shallow copy of the current Object.(Inherited from Object.)


Sets the private key to use for decrypting the secret information.(Overrides AsymmetricKeyExchangeDeformatter.SetKey(AsymmetricAlgorithm).)


Returns a string that represents the current object.(Inherited from Object.)

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.

Use RSAPKCS1KeyExchangeFormatter to create the key exchange message using the RSA algorithm.


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 shows how to use the RSAPKCS1KeyExchangeDeformatter class to recreate an exchange key to be used to decrypt a message.

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

class Alice
    public static void Main(string[] args)
        using (Bob bob = new Bob())
            using (RSACryptoServiceProvider rsaKey = new RSACryptoServiceProvider())
                // Get Bob's public key
                byte[] encryptedSessionKey = null;
                byte[] encryptedMessage = null;
                byte[] iv = null;
                Send(rsaKey, "Secret message", out iv, out encryptedSessionKey, out encryptedMessage);
                bob.Receive(iv, encryptedSessionKey, encryptedMessage);

    private static void Send(RSA key, string secretMessage, out byte[] iv, out byte[] encryptedSessionKey, out byte[] encryptedMessage)
        using (Aes aes = new AesCryptoServiceProvider())
            iv = aes.IV;

            // Encrypt the session key
            RSAPKCS1KeyExchangeFormatter keyFormatter = new RSAPKCS1KeyExchangeFormatter(key);
            encryptedSessionKey = keyFormatter.CreateKeyExchange(aes.Key, typeof(Aes));

            // Encrypt the message
            using (MemoryStream ciphertext = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ciphertext, aes.CreateEncryptor(), CryptoStreamMode.Write))
                byte[] plaintextMessage = Encoding.UTF8.GetBytes(secretMessage);
                cs.Write(plaintextMessage, 0, plaintextMessage.Length);

                encryptedMessage = ciphertext.ToArray();

public class Bob : IDisposable
    public byte[] key;
    private RSACryptoServiceProvider rsaKey = new RSACryptoServiceProvider();
    public Bob()
        key = rsaKey.ExportCspBlob(false);
    public void Receive(byte[] iv, byte[] encryptedSessionKey, byte[] encryptedMessage)

        using (Aes aes = new AesCryptoServiceProvider())
            aes.IV = iv;

            // Decrypt the session key
            RSAPKCS1KeyExchangeDeformatter keyDeformatter = new RSAPKCS1KeyExchangeDeformatter(rsaKey);
            aes.Key = keyDeformatter.DecryptKeyExchange(encryptedSessionKey);

            // Decrypt the message
            using (MemoryStream plaintext = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(plaintext, aes.CreateDecryptor(), CryptoStreamMode.Write))
                cs.Write(encryptedMessage, 0, encryptedMessage.Length);

                string message = Encoding.UTF8.GetString(plaintext.ToArray());
    public void Dispose()

.NET Framework
Available since 1.1
Windows Phone Silverlight
Available since 7.1

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

Return to top
© 2015 Microsoft