RSAOAEPKeyExchangeDeformatter Class


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Decrypts Optimal Asymmetric Encryption Padding (OAEP) key exchange data.

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


Public Class RSAOAEPKeyExchangeDeformatter
	Inherits AsymmetricKeyExchangeDeformatter


Initializes a new instance of the RSAOAEPKeyExchangeDeformatter class.


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


Gets the parameters for the Optimal Asymmetric Encryption Padding (OAEP) key exchange.(Overrides AsymmetricKeyExchangeDeformatter.Parameters.)


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, for example, 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 RSAOAEPKeyExchangeFormatter to create the key exchange message with 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 RSAOAEPKeyExchangeDeformatter 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)
        Using bob As New Bob()
            Using rsaKey As New RSACryptoServiceProvider()
                    ' Get Bob's public 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)
            End Using
        End Using

    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)
        Using aes = New AesCryptoServiceProvider()

            iv = aes.IV

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

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

                    encryptedMessage = ciphertext.ToArray()
                End Using
            End Using
        End Using

    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 'NewNew

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

        Using aes = New AesCryptoServiceProvider()

            aes.IV = iv

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

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

                        Dim message As String = Encoding.UTF8.GetString(plaintext.ToArray())
                End Using
            End Using
        End Using

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

.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.

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