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TripleDESCryptoServiceProvider.CreateDecryptor Method (Byte(), Byte())

Creates a symmetric TripleDES decryptor object with the specified key (Key) and initialization vector (IV).

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

'Declaration
Public Overrides Function CreateDecryptor ( _
	rgbKey As Byte(), _
	rgbIV As Byte() _
) As ICryptoTransform

Parameters

rgbKey
Type: System.Byte()

The secret key to use for the symmetric algorithm.

rgbIV
Type: System.Byte()

The initialization vector to use for the symmetric algorithm.

Return Value

Type: System.Security.Cryptography.ICryptoTransform
A symmetric TripleDES decryptor object.

ExceptionCondition
CryptographicException

The value of the Mode property is OFB.

-or-

The value of the Mode property is CFB and the value of the FeedbackSize property is not 8.

-or-

An invalid key size was used.

-or-

The algorithm key size was not available.

This method decrypts an encrypted message created using the CreateEncryptor overload with the same parameters.

The following code example creates a TripleDESCryptoServiceProvider object and uses it to encrypt and decrypt data in a file.

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

Module TrippleDESCSPSample

    Sub Main()
        Try 
            ' Create a new TripleDESCryptoServiceProvider object 
            ' to generate a key and initialization vector (IV). 
            Dim tDESalg As New TripleDESCryptoServiceProvider

            ' Create a string to encrypt. 
            Dim sData As String = "Here is some data to encrypt." 
            Dim FileName As String = "CText.txt" 

            ' Encrypt text to a file using the file name, key, and IV.
            EncryptTextToFile(sData, FileName, tDESalg.Key, tDESalg.IV)

            ' Decrypt the text from a file using the file name, key, and IV. 
            Dim Final As String = DecryptTextFromFile(FileName, tDESalg.Key, tDESalg.IV)

            ' Display the decrypted string to the console.
            Console.WriteLine(Final)
        Catch e As Exception
            Console.WriteLine(e.Message)
        End Try 
    End Sub 


    Sub EncryptTextToFile(ByVal Data As String, ByVal FileName As String, ByVal Key() As Byte, ByVal IV() As Byte)
        Try 
            ' Create or open the specified file. 
            Dim fStream As FileStream = File.Open(FileName, FileMode.OpenOrCreate)

            ' Create a CryptoStream using the FileStream  
            ' and the passed key and initialization vector (IV). 
            Dim cStream As New CryptoStream(fStream, _
                                            New TripleDESCryptoServiceProvider().CreateEncryptor(Key, IV), _
                                            CryptoStreamMode.Write)

            ' Create a StreamWriter using the CryptoStream. 
            Dim sWriter As New StreamWriter(cStream)

            ' Write the data to the stream  
            ' to encrypt it.
            sWriter.WriteLine(Data)

            ' Close the streams and 
            ' close the file.
            sWriter.Close()
            cStream.Close()
            fStream.Close()
        Catch e As CryptographicException
            Console.WriteLine("A Cryptographic error occurred: {0}", e.Message)
        Catch e As UnauthorizedAccessException
            Console.WriteLine("A file error occurred: {0}", e.Message)
        End Try 
    End Sub 


    Function DecryptTextFromFile(ByVal FileName As String, ByVal Key() As Byte, ByVal IV() As Byte) As String 
        Try 
            ' Create or open the specified file.  
            Dim fStream As FileStream = File.Open(FileName, FileMode.OpenOrCreate)

            ' Create a CryptoStream using the FileStream  
            ' and the passed key and initialization vector (IV). 
            Dim cStream As New CryptoStream(fStream, _
                                            New TripleDESCryptoServiceProvider().CreateDecryptor(Key, IV), _
                                            CryptoStreamMode.Read)

            ' Create a StreamReader using the CryptoStream. 
            Dim sReader As New StreamReader(cStream)

            ' Read the data from the stream  
            ' to decrypt it. 
            Dim val As String = sReader.ReadLine()

            ' Close the streams and 
            ' close the file.
            sReader.Close()
            cStream.Close()
            fStream.Close()

            ' Return the string.  
            Return val
        Catch e As CryptographicException
            Console.WriteLine("A Cryptographic error occurred: {0}", e.Message)
            Return Nothing 
        Catch e As UnauthorizedAccessException
            Console.WriteLine("A file error occurred: {0}", e.Message)
            Return Nothing 
        End Try 
    End Function 
End Module

The following code example creates a TripleDESCryptoServiceProvider object and uses it to encrypt and decrypt data in memory.

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

Module TrippleDESCSPSample

    Sub Main()
        Try 
            ' Create a new TripleDESCryptoServiceProvider object 
            ' to generate a key and initialization vector (IV). 
            Dim tDESalg As New TripleDESCryptoServiceProvider

            ' Create a string to encrypt. 
            Dim sData As String = "Here is some data to encrypt." 

            ' Encrypt the string to an in-memory buffer. 
            Dim Data As Byte() = EncryptTextToMemory(sData, tDESalg.Key, tDESalg.IV)

            ' Decrypt the buffer back to a string. 
            Dim Final As String = DecryptTextFromMemory(Data, tDESalg.Key, tDESalg.IV)

            ' Display the decrypted string to the console.
            Console.WriteLine(Final)
        Catch e As Exception
            Console.WriteLine(e.Message)
        End Try 
    End Sub 


    Function EncryptTextToMemory(ByVal Data As String, ByVal Key() As Byte, ByVal IV() As Byte) As Byte()
        Try 
            ' Create a MemoryStream. 
            Dim mStream As New MemoryStream

            ' Create a CryptoStream using the MemoryStream  
            ' and the passed key and initialization vector (IV). 
            Dim cStream As New CryptoStream(mStream, _
                                            New TripleDESCryptoServiceProvider().CreateEncryptor(Key, IV), _
                                            CryptoStreamMode.Write)

            ' Convert the passed string to a byte array. 
            Dim toEncrypt As Byte() = New ASCIIEncoding().GetBytes(Data)

            ' Write the byte array to the crypto stream and flush it.
            cStream.Write(toEncrypt, 0, toEncrypt.Length)
            cStream.FlushFinalBlock()

            ' Get an array of bytes from the  
            ' MemoryStream that holds the  
            ' encrypted data. 
            Dim ret As Byte() = mStream.ToArray()

            ' Close the streams.
            cStream.Close()
            mStream.Close()

            ' Return the encrypted buffer. 
            Return ret
        Catch e As CryptographicException
            Console.WriteLine("A Cryptographic error occurred: {0}", e.Message)
            Return Nothing 
        End Try 
    End Function 


    Function DecryptTextFromMemory(ByVal Data() As Byte, ByVal Key() As Byte, ByVal IV() As Byte) As String 
        Try 
            ' Create a new MemoryStream using the passed  
            ' array of encrypted data. 
            Dim msDecrypt As New MemoryStream(Data)

            ' Create a CryptoStream using the MemoryStream  
            ' and the passed key and initialization vector (IV). 
            Dim csDecrypt As New CryptoStream(msDecrypt, _
                                              New TripleDESCryptoServiceProvider().CreateDecryptor(Key, IV), _
                                              CryptoStreamMode.Read)

            ' Create buffer to hold the decrypted data. 
            Dim fromEncrypt(Data.Length - 1) As Byte 

            ' Read the decrypted data out of the crypto stream 
            ' and place it into the temporary buffer.
            csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length)

            'Convert the buffer into a string and return it. 
            Return New ASCIIEncoding().GetString(fromEncrypt)
        Catch e As CryptographicException
            Console.WriteLine("A Cryptographic error occurred: {0}", e.Message)
            Return Nothing 
        End Try 
    End Function 
End Module

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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.

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