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RSAPKCS1KeyExchangeDeformatter Class

Decrypts the PKCS #1 key exchange data.

System.Object
  System.Security.Cryptography.AsymmetricKeyExchangeDeformatter
    System.Security.Cryptography.RSAPKCS1KeyExchangeDeformatter

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

'Declaration
<ComVisibleAttribute(True)> _
Public Class RSAPKCS1KeyExchangeDeformatter _
	Inherits AsymmetricKeyExchangeDeformatter

The RSAPKCS1KeyExchangeDeformatter type exposes the following members.

  NameDescription
Public methodRSAPKCS1KeyExchangeDeformatterInitializes a new instance of the RSAPKCS1KeyExchangeDeformatter class.
Public methodRSAPKCS1KeyExchangeDeformatter(AsymmetricAlgorithm)Initializes a new instance of the RSAPKCS1KeyExchangeDeformatter class with the specified key.
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  NameDescription
Public propertyParametersGets the parameters for the PKCS #1 key exchange. (Overrides AsymmetricKeyExchangeDeformatter.Parameters.)
Public propertyRNGGets or sets the random number generator algorithm to use in the creation of the key exchange.
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  NameDescription
Public methodDecryptKeyExchangeExtracts secret information from the encrypted key exchange data. (Overrides AsymmetricKeyExchangeDeformatter.DecryptKeyExchange(Byte()).)
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSetKeySets the private key to use for decrypting the secret information. (Overrides AsymmetricKeyExchangeDeformatter.SetKey(AsymmetricAlgorithm).)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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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.

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

Imports System
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 'Main


    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 'Send 
End Class 'Alice

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

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

    End Sub 'New 

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

.NET Framework

Supported in: 4.6, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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