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Rfc2898DeriveBytes Class

Implements password-based key derivation functionality, PBKDF2, by using a pseudo-random number generator based on HMACSHA1.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Class Rfc2898DeriveBytes
	Inherits DeriveBytes
'Usage
Dim instance As Rfc2898DeriveBytes

/** @attribute ComVisibleAttribute(true) */ 
public class Rfc2898DeriveBytes extends DeriveBytes
ComVisibleAttribute(true) 
public class Rfc2898DeriveBytes extends DeriveBytes
Not applicable.

Rfc2898DeriveBytes takes a password, a salt, and an iteration count, and then generates keys through calls to the GetBytes method.

RFC 2898 includes methods for creating a key and initialization vector (IV) from a password and salt. You can use PBKDF2, a password-based key derivation function, to derive keys using a pseudo-random function that allows keys of virtually unlimited length to be generated. The Rfc2898DeriveBytes class can be used to produce a derived key from a base key and other parameters. In a password-based key derivation function, the base key is a password and the other parameters are a salt value and an iteration count.

For more information about PBKDF2, see RFC 2898, "PKCS #5: Password-Based Cryptography Specification Version 2.0," available on the Request for Comments Web site at http://www.rfc-editor.org. See section 5.2, "PBKDF2", for complete details.

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), a hex editor, or by simply opening up the assembly in a text editor such as Notepad.exe.

The following code example uses the Rfc2898DeriveBytes class to create two identical keys for the TripleDES class. It then encrypts and decrypts some data using the keys.

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



Public Class rfc2898test
    ' Generate a key k1 with password pwd1 and salt salt1.
    ' Generate a key k2 with password pwd1 and salt salt1.
    ' Encrypt data1 with key k1 using symmetric encryption, creating edata1.
    ' Decrypt edata1 with key k2 using symmetric decryption, creating data2.
    ' data2 should equal data1.
    Private Const usageText As String = "Usage: RFC2898 <password>" + vbLf + "You must specify the password for encryption." + vbLf

    Public Shared Sub Main(ByVal passwordargs() As String)
        'If no file name is specified, write usage text.
        If passwordargs.Length = 0 Then
            Console.WriteLine(usageText)
        Else
            Dim pwd1 As String = passwordargs(0)

            Dim salt1() As Byte = {&H0, &H1, &H2, &H3, &H4, &H5, &H6, &HF1, &HF0, &HEE, &H21, &H22, &H45}
            'data1 can be a string or contents of a file.
            Dim data1 As String = "Some test data"
            'The default iteration count is 1000 so the two methods use the same iteration count.
            Dim myIterations As Integer = 1000
            Try
                Dim k1 As New Rfc2898DeriveBytes(pwd1, salt1, myIterations)
                Dim k2 As New Rfc2898DeriveBytes(pwd1, salt1)
                ' Encrypt the data.
                Dim encAlg As TripleDES = TripleDES.Create()
                encAlg.Key = k1.GetBytes(16)
                Dim encryptionStream As New MemoryStream()
                Dim encrypt As New CryptoStream(encryptionStream, encAlg.CreateEncryptor(), CryptoStreamMode.Write)
                Dim utfD1 As Byte() = New System.Text.UTF8Encoding(False).GetBytes(data1)
                encrypt.Write(utfD1, 0, utfD1.Length)
                encrypt.FlushFinalBlock()
                encrypt.Close()
                Dim edata1 As Byte() = encryptionStream.ToArray()
                k1.Reset()

                ' Try to decrypt, thus showing it can be round-tripped.
                Dim decAlg As TripleDES = TripleDES.Create()
                decAlg.Key = k2.GetBytes(16)
                decAlg.IV = encAlg.IV
                Dim decryptionStreamBacking As New MemoryStream()
                Dim decrypt As New CryptoStream(decryptionStreamBacking, decAlg.CreateDecryptor(), CryptoStreamMode.Write)
                decrypt.Write(edata1, 0, edata1.Length)
                decrypt.Flush()
                decrypt.Close()
                k2.Reset()
                Dim data2 As String = New UTF8Encoding(False).GetString(decryptionStreamBacking.ToArray())

                If Not data1.Equals(data2) Then
                    Console.WriteLine("Error: The two values are not equal.")
                Else
                    Console.WriteLine("The two values are equal.")
                    Console.WriteLine("k1 iterations: {0}", k1.IterationCount)
                    Console.WriteLine("k2 iterations: {0}", k2.IterationCount)
                End If
            Catch e As Exception
                Console.WriteLine("Error: ", e)
            End Try
        End If

    End Sub
End Class

import System.*;
import System.IO.*;
import System.Text.*;
import System.Security.Cryptography.*;

public class rfc2898test
{
    // Generate a key k1 with password pwd1 and salt salt1.
    // Generate a key k2 with password pwd1 and salt salt1.
    // Encrypt data1 with key k1 using symmetric encryption, creating eData1.
    // Decrypt eData1 with key k2 using symmetric decryption, creating data2.
    // data2 should equal data1.
    private static String usageText = "Usage: RFC2898 <password>\n"
        + "You must specify the password for encryption.\n";

    public static void main(String[] passwordArgs)
    {
        //If no file name is specified, write usage text.
        if (passwordArgs.get_Length() == 0) {
            Console.WriteLine(usageText);
        }
        else {
            String pwd1 = (String)passwordArgs.get_Item(0);

            ubyte salt1[] = new ubyte[] { 0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6,
                0xF1, 0xF0, 0xEE, 0x21, 0x22, 0x45 };
            //data1 can be a string or contents of a file.
            String data1 = "Some test data";
            //The default iteration count is 1000 so the two methods use the
            //same iteration count.
            int myIterations = 1000;
            try {
                Rfc2898DeriveBytes k1 = new Rfc2898DeriveBytes(pwd1, salt1,
                    myIterations);
                Rfc2898DeriveBytes k2 = new Rfc2898DeriveBytes(pwd1, salt1);
                // Encrypt the data.
                TripleDES encAlg = TripleDES.Create();
                encAlg.set_Key(k1.GetBytes(16));
                MemoryStream encryptionStream = new MemoryStream();
                CryptoStream encrypt = new CryptoStream(encryptionStream, 
                    encAlg.CreateEncryptor(), CryptoStreamMode.Write);
                ubyte utfD1[] = (new System.Text.UTF8Encoding(false)).
                    GetBytes(data1);
                encrypt.Write(utfD1, 0, utfD1.get_Length());
                encrypt.FlushFinalBlock();
                encrypt.Close();
                ubyte eData1[] = encryptionStream.ToArray();
                k1.Reset();
                // Try to decrypt, thus showing it can be round-tripped.
                TripleDES decAlg = TripleDES.Create();
                decAlg.set_Key(k2.GetBytes(16));
                decAlg.set_IV(encAlg.get_IV());
                MemoryStream decryptionStreamBacking = new MemoryStream();
                CryptoStream decrypt = new CryptoStream(decryptionStreamBacking, 
                    decAlg.CreateDecryptor(), CryptoStreamMode.Write);
                decrypt.Write(eData1, 0, eData1.get_Length());
                decrypt.Flush();
                decrypt.Close();
                k2.Reset();
                String data2 = (new UTF8Encoding(false)).
                    GetString(decryptionStreamBacking.ToArray());
                if (!(data1.Equals(data2))) {
                    Console.WriteLine("Error: The two values are not equal.");
                }
                else {
                    Console.WriteLine("The two values are equal.");
                    Console.WriteLine("k1 iterations: {0}", (System.Int32)k1.
                        get_IterationCount());
                    Console.WriteLine("k2 iterations: {0}", (System.Int32)k2.
                        get_IterationCount());
                }
            }           
            catch (System.Exception e) {
                Console.WriteLine("Error: ", e);
            }
        }
    } //main
} //rfc2898test

System.Object
   System.Security.Cryptography.DeriveBytes
    System.Security.Cryptography.Rfc2898DeriveBytes

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 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

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