PasswordDeriveBytes Class

Definition

public ref class PasswordDeriveBytes : System::Security::Cryptography::DeriveBytes

public class PasswordDeriveBytes : System.Security.Cryptography.DeriveBytes

[System.Runtime.InteropServices.ComVisible(true)]
public class PasswordDeriveBytes : System.Security.Cryptography.DeriveBytes

type PasswordDeriveBytes = class
 inherit DeriveBytes

[<System.Runtime.InteropServices.ComVisible(true)>]
type PasswordDeriveBytes = class
 inherit DeriveBytes

Public Class PasswordDeriveBytes
Inherits DeriveBytes

Inheritance

Object

DeriveBytes

PasswordDeriveBytes

Attributes

ComVisibleAttribute

Examples

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

using System;
using System.Security.Cryptography;
using System.Text;

public class PasswordDerivedBytesExample
{

 public static void Main(String[] args)
 {

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

 byte[] pwd = Encoding.Unicode.GetBytes(Console.ReadLine());

 byte[] salt = CreateRandomSalt(7);

 // Create a TripleDESCryptoServiceProvider object.
 TripleDESCryptoServiceProvider tdes = 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.
 PasswordDeriveBytes pdb = new PasswordDeriveBytes(pwd, salt);


 // Create the key and set it to the Key property
 // of the TripleDESCryptoServiceProvider object.
 // This example uses the SHA1 algorithm.
 // Due to collision problems with SHA1, Microsoft recommends SHA256 or better.
 tdes.Key = pdb.CryptDeriveKey("TripleDES", "SHA1", 192, tdes.IV);


 Console.WriteLine("Operation complete.");
 }
 catch (Exception e)
 {
 Console.WriteLine(e.Message);
 }
 finally
 {
 // Clear the buffers
 ClearBytes(pwd);
 ClearBytes(salt);

 // Clear the key.
 tdes.Clear();
 }

 Console.ReadLine();
 }

 //////////////////////////////////////////////////////////
 // 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.
 //////////////////////////////////////////////////////////

 public static byte[] CreateRandomSalt(int length)
 {
 // Create a buffer
 byte[] randBytes;

 if (length >= 1)
 {
 randBytes = new byte[length];
 }
 else
 {
 randBytes = new byte[1];
 }

 using (RandomNumberGenerator rng = RandomNumberGenerator.Create())
 {
 // Fill the buffer with random bytes.
 rng.GetBytes(randBytes);
 }

 // return the bytes.
 return randBytes;
 }

 public static void ClearBytes(byte[] buffer)
 {
 // Check arguments.
 if (buffer == null)
 {
 throw new ArgumentException("buffer");
 }

 // Set each byte in the buffer to 0.
 for (int x = 0; x < buffer.Length; x++)
 {
 buffer[x] = 0;
 }
 }
}

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.
 ' This example uses the SHA1 algorithm.
 ' Due to collision problems with SHA1, Microsoft recommends SHA256 or better.
 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 RandomNumberGenerator.
 Using rand As RandomNumberGenerator = RandomNumberGenerator.Create()
 ' Fill the buffer with random bytes.
 rand.GetBytes(randBytes)
 End Using

 ' 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

Remarks

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.

See also

• Cryptographic Services