RSAPKCS1KeyExchangeFormatter Class

Definition

Namespace:

System.Security.Cryptography

Assembly:

System.Security.Cryptography.dll

Source:

RSAPKCS1KeyExchangeFormatter.cs

Creates the PKCS#1 key exchange data using RSA.

public ref class RSAPKCS1KeyExchangeFormatter : System::Security::Cryptography::AsymmetricKeyExchangeFormatter

public class RSAPKCS1KeyExchangeFormatter : System.Security.Cryptography.AsymmetricKeyExchangeFormatter

type RSAPKCS1KeyExchangeFormatter = class
    inherit AsymmetricKeyExchangeFormatter

Public Class RSAPKCS1KeyExchangeFormatter
Inherits AsymmetricKeyExchangeFormatter

Inheritance

Object

AsymmetricKeyExchangeFormatter

RSAPKCS1KeyExchangeFormatter

Examples

The following example shows how to use the RSAPKCS1KeyExchangeFormatter class to create an exchange key for a message recipient.

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
                rsaKey.ImportCspBlob(bob.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);
                cs.Close();

                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);
                cs.Close();

                string message = Encoding.UTF8.GetString(plaintext.ToArray());
                Console.WriteLine(message);
            }
        }
    }
    public void Dispose()
    {
        rsaKey.Dispose();
    }
}

Imports System.IO
Imports System.Security.Cryptography
Imports System.Text




Class Alice

    Public Shared Sub Main(ByVal args() As String)
        Dim bob As New Bob()
        Try
            Dim rsaKey As New RSACryptoServiceProvider()
            Try
                ' Get Bob's public key
                rsaKey.ImportCspBlob(bob.key)
                Dim encryptedSessionKey As Byte() = Nothing
                Dim encryptedMessage As Byte() = Nothing
                Dim iv As Byte() = Nothing
                Send(rsaKey, "Secret message", iv, encryptedSessionKey, encryptedMessage)
                bob.Receive(iv, encryptedSessionKey, encryptedMessage)
            Finally
                rsaKey.Dispose()
            End Try
        Finally
            bob.Dispose()
        End Try

    End Sub


    Private Shared Sub Send(ByVal key As RSA, ByVal secretMessage As String, ByRef iv() As Byte, ByRef encryptedSessionKey() As Byte, ByRef encryptedMessage() As Byte)
        Dim aes = New AesCryptoServiceProvider()
        Try
            iv = aes.IV

            ' Encrypt the session key
            Dim keyFormatter As New RSAPKCS1KeyExchangeFormatter(key)
            encryptedSessionKey = keyFormatter.CreateKeyExchange(aes.Key, GetType(Aes))

            ' Encrypt the message
            Dim ciphertext As New MemoryStream()
            Try
                Dim cs As New CryptoStream(ciphertext, aes.CreateEncryptor(), CryptoStreamMode.Write)
                Try
                    Dim plaintextMessage As Byte() = Encoding.UTF8.GetBytes(secretMessage)
                    cs.Write(plaintextMessage, 0, plaintextMessage.Length)
                    cs.Close()

                    encryptedMessage = ciphertext.ToArray()
                Finally
                    cs.Dispose()
                End Try
            Finally
                ciphertext.Dispose()
            End Try
        Finally
            aes.Dispose()
        End Try

    End Sub
End Class

Public Class Bob
    Implements IDisposable
    Public key() As Byte
    Private rsaKey As New RSACryptoServiceProvider()

    Public Sub New()
        key = rsaKey.ExportCspBlob(False)

    End Sub

    Public Sub Receive(ByVal iv() As Byte, ByVal encryptedSessionKey() As Byte, ByVal encryptedMessage() As Byte)

        Dim aes = New AesCryptoServiceProvider()
        Try
            aes.IV = iv

            ' Decrypt the session key
            Dim keyDeformatter As New RSAPKCS1KeyExchangeDeformatter(rsaKey)
            aes.Key = keyDeformatter.DecryptKeyExchange(encryptedSessionKey)

            ' Decrypt the message
            Dim plaintext As New MemoryStream()
            Try
                Dim cs As New CryptoStream(plaintext, aes.CreateDecryptor(), CryptoStreamMode.Write)
                Try
                    cs.Write(encryptedMessage, 0, encryptedMessage.Length)
                    cs.Close()

                    Dim message As String = Encoding.UTF8.GetString(plaintext.ToArray())
                    Console.WriteLine(message)
                Finally
                    cs.Dispose()
                End Try
            Finally
                plaintext.Dispose()
            End Try
        Finally
            aes.Dispose()
        End Try

    End Sub
    Public Overloads Sub Dispose() Implements IDisposable.Dispose
        rsaKey.Dispose()
    End Sub
End Class

Remarks

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 RSAPKCS1KeyExchangeDeformatter to receive the key exchange and extract the secret information from it.

Caution

We recommend that you do 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.

Constructors

RSAPKCS1KeyExchangeFormatter()	Initializes a new instance of the RSAPKCS1KeyExchangeFormatter class.
RSAPKCS1KeyExchangeFormatter(AsymmetricAlgorithm)	Initializes a new instance of the RSAPKCS1KeyExchangeFormatter class with the specified key.

Properties

Parameters	Gets the parameters for the PKCS #1 key exchange.
Rng	Gets or sets the random number generator algorithm to use in the creation of the key exchange.

Methods

CreateKeyExchange(Byte[], Type)	Creates the encrypted key exchange data from the specified input data.
CreateKeyExchange(Byte[])	Creates the encrypted key exchange data from the specified input data.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
SetKey(AsymmetricAlgorithm)	Sets the public key to use for encrypting the key exchange data.
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• Cryptographic Services