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PasswordDeriveBytes Class

Derives a key from a password using an extension of the PBKDF1 algorithm.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Class PasswordDeriveBytes _
	Inherits DeriveBytes
'Usage
Dim instance As PasswordDeriveBytes

This class uses an extension of the PBKDF1 algorithm defined in the PKCS#5 v2.0 standard to derive bytes suitable for use as key material from a password. The standard is documented in IETF RRC 2898.

Security noteSecurity Note:

Never hard-code a password within your source code. Hard coded passwords can be retrieved from an assembly using the MSIL Disassembler (Ildasm.exe) tool, a hex editor, or by simply opening up the assembly in a text editor like notepad.exe.

The following code example creates a key from a password using the PasswordDeriveBytes class.

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



Module PasswordDerivedBytesExample


    Sub Main(ByVal args() As String)

        ' Get a password from the user.
        Console.WriteLine("Enter a password to produce a key:")

        Dim pwd As Byte() = Encoding.Unicode.GetBytes(Console.ReadLine())

        Dim salt As Byte() = CreateRandomSalt(7)

        ' Create a TripleDESCryptoServiceProvider object. 
        Dim tdes As New TripleDESCryptoServiceProvider()

        Try
            Console.WriteLine("Creating a key with PasswordDeriveBytes...")

            ' Create a PasswordDeriveBytes object and then create  
            ' a TripleDES key from the password and salt. 
            Dim pdb As New PasswordDeriveBytes(pwd, salt)


            ' Create the key and set it to the Key property 
            ' of the TripleDESCryptoServiceProvider object.
            tdes.Key = pdb.CryptDeriveKey("TripleDES", "SHA1", 192, tdes.IV)


            Console.WriteLine("Operation complete.")
        Catch e As Exception
            Console.WriteLine(e.Message)
        Finally 
            ' Clear the buffers
            ClearBytes(pwd)
            ClearBytes(salt)

            ' Clear the key.
            tdes.Clear()
        End Try

        Console.ReadLine()

    End Sub 


    '******************************************************** 
    '* Helper methods: 
    '* createRandomSalt: Generates a random salt value of the  
    '*                   specified length.   
    '* 
    '* clearBytes: Clear the bytes in a buffer so they can't  
    '*             later be read from memory. 
    '******************************************************** 
    Function CreateRandomSalt(ByVal length As Integer) As Byte()
        ' Create a buffer 
        Dim randBytes() As Byte

        If length >= 1 Then
            randBytes = New Byte(length) {}
        Else
            randBytes = New Byte(0) {}
        End If 

        ' Create a new RNGCryptoServiceProvider. 
        Dim rand As New RNGCryptoServiceProvider()

        ' Fill the buffer with random bytes.
        rand.GetBytes(randBytes)

        ' return the bytes. 
        Return randBytes

    End Function 


    Sub ClearBytes(ByVal buffer() As Byte)
        ' Check arguments. 
        If buffer Is Nothing Then 
            Throw New ArgumentException("buffer")
        End If 

        ' Set each byte in the buffer to 0. 
        Dim x As Integer 
        For x = 0 To buffer.Length - 1
            buffer(x) = 0
        Next x

    End Sub 
End Module

System.Object
  System.Security.Cryptography.DeriveBytes
    System.Security.Cryptography.PasswordDeriveBytes

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

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

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