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RSAOAEPKeyExchangeDeformatter Class

Updated: March 2011

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

System.Object
  System.Security.Cryptography.AsymmetricKeyExchangeDeformatter
    System.Security.Cryptography.RSAOAEPKeyExchangeDeformatter

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

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

The RSAOAEPKeyExchangeDeformatter type exposes the following members.

  NameDescription
Public methodRSAOAEPKeyExchangeDeformatterInitializes a new instance of the RSAOAEPKeyExchangeDeformatter class.
Public methodRSAOAEPKeyExchangeDeformatter(AsymmetricAlgorithm)Initializes a new instance of the RSAOAEPKeyExchangeDeformatter class with the specified key.
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  NameDescription
Public propertyParametersGets the parameters for the Optimal Asymmetric Encryption Padding (OAEP) key exchange. (Overrides AsymmetricKeyExchangeDeformatter.Parameters.)
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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 a hash function for a particular type. (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, 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.

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 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
                    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)
            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)
                    cs.Close()

                    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 'New

    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)
                        cs.Close()

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

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


.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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.

Date

History

Reason

March 2011

Replaced the example.

Customer feedback.

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