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CryptoStream Class

Defines a stream that links data streams to cryptographic transformations.

Namespace:  System.Security.Cryptography
Assembly:  mscorlib (in mscorlib.dll)
'Declaration
<ComVisibleAttribute(True)> _
Public Class CryptoStream _
	Inherits Stream _
	Implements IDisposable
'Usage
Dim instance As CryptoStream

The common language runtime uses a stream-oriented design for cryptography. The core of this design is CryptoStream. Any cryptographic objects that implement CryptoStream can be chained together with any objects that implement Stream, so the streamed output from one object can be fed into the input of another object. The intermediate result (the output from the first object) does not need to be stored separately.

You should always explicitly close your CryptoStream object after you are done using it by calling the Close method. Doing so flushes the stream and causes all remain blocks of data to be processed by the CryptoStream object. However, if an exception occurs before you call the Close method, the CryptoStream object might not be closed. To ensure that the Close method always gets called, place your call to the Close method within the finally block of a try/catch statement.

The following example demonstrates how to use a CryptoStream to encrypt a string. This method uses RijndaelManaged class with the specified Key and initialization vector (IV).

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



Class RijndaelExample

    Public Shared Sub Main()
        Try 

            Dim original As String = "Here is some data to encrypt!" 

            ' Create a new instance of the Rijndael 
            ' class.  This generates a new key and initialization  
            ' vector (IV). 
            Using myRijndael = Rijndael.Create()

                ' Encrypt the string to an array of bytes. 
                Dim encrypted As Byte() = EncryptStringToBytes(original, myRijndael.Key, myRijndael.IV)

                ' Decrypt the bytes to a string. 
                Dim roundtrip As String = DecryptStringFromBytes(encrypted, myRijndael.Key, myRijndael.IV)

                'Display the original data and the decrypted data.
                Console.WriteLine("Original:   {0}", original)
                Console.WriteLine("Round Trip: {0}", roundtrip)
            End Using 
        Catch e As Exception
            Console.WriteLine("Error: {0}", e.Message)
        End Try 

    End Sub 'Main

    Shared Function EncryptStringToBytes(ByVal plainText As String, ByVal Key() As Byte, ByVal IV() As Byte) As Byte()
        ' Check arguments. 
        If plainText Is Nothing OrElse plainText.Length <= 0 Then 
            Throw New ArgumentNullException("plainText")
        End If 
        If Key Is Nothing OrElse Key.Length <= 0 Then 
            Throw New ArgumentNullException("Key")
        End If 
        If IV Is Nothing OrElse IV.Length <= 0 Then 
            Throw New ArgumentNullException("Key")
        End If 
        Dim encrypted() As Byte
        ' Create an Rijndael object 
        ' with the specified key and IV. 
        Using rijAlg = Rijndael.Create()

            rijAlg.Key = Key
            rijAlg.IV = IV

            ' Create a decrytor to perform the stream transform. 
            Dim encryptor As ICryptoTransform = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV)
            ' Create the streams used for encryption. 
            Using msEncrypt As New MemoryStream()
                Using csEncrypt As New CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)
                    Using swEncrypt As New StreamWriter(csEncrypt)

                        'Write all data to the stream.
                        swEncrypt.Write(plainText)
                    End Using
                    encrypted = msEncrypt.ToArray()
                End Using 
            End Using 
        End Using 

        ' Return the encrypted bytes from the memory stream. 
        Return encrypted

    End Function 'EncryptStringToBytes

    Shared Function DecryptStringFromBytes(ByVal cipherText() As Byte, ByVal Key() As Byte, ByVal IV() As Byte) As String 
        ' Check arguments. 
        If cipherText Is Nothing OrElse cipherText.Length <= 0 Then 
            Throw New ArgumentNullException("cipherText")
        End If 
        If Key Is Nothing OrElse Key.Length <= 0 Then 
            Throw New ArgumentNullException("Key")
        End If 
        If IV Is Nothing OrElse IV.Length <= 0 Then 
            Throw New ArgumentNullException("Key")
        End If 
        ' Declare the string used to hold 
        ' the decrypted text. 
        Dim plaintext As String = Nothing 

        ' Create an Rijndael object 
        ' with the specified key and IV. 
        Using rijAlg = Rijndael.Create()
            rijAlg.Key = Key
            rijAlg.IV = IV

            ' Create a decrytor to perform the stream transform. 
            Dim decryptor As ICryptoTransform = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV)

            ' Create the streams used for decryption. 
            Using msDecrypt As New MemoryStream(cipherText)

                Using csDecrypt As New CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)

                    Using srDecrypt As New StreamReader(csDecrypt)


                        ' Read the decrypted bytes from the decrypting stream 
                        ' and place them in a string.
                        plaintext = srDecrypt.ReadToEnd()
                    End Using 
                End Using 
            End Using 
        End Using 

        Return plaintext

    End Function 'DecryptStringFromBytes 
End Class
System.Object
  System.MarshalByRefObject
    System.IO.Stream
      System.Security.Cryptography.CryptoStream
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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

.NET Framework

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

.NET Compact Framework

Supported in: 3.5, 2.0
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