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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)

[ComVisibleAttribute(true)]
public ref class Rfc2898DeriveBytes : public DeriveBytes

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. 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 by using the MSIL Disassembler (Ildasm.exe), by using a hexadecimal 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.

using namespace System;
using namespace System::IO;
using namespace System::Text;
using namespace System::Security::Cryptography;

// 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. 

int main()
{
   array<String^>^passwordargs = Environment::GetCommandLineArgs();
   String^ usageText = "Usage: RFC2898 <password>\nYou must specify the password for encryption.\n";

   //If no file name is specified, write usage text. 
   if ( passwordargs->Length == 1 )
   {
	  Console::WriteLine( usageText );
   }
   else
   {
	  String^ pwd1 = passwordargs[ 1 ];
	  
	  array<Byte>^salt1 = gcnew array<Byte>(8);
	  RNGCryptoServiceProvider ^ rngCsp = gcnew RNGCryptoServiceProvider();
		 rngCsp->GetBytes(salt1);
	  //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 = gcnew Rfc2898DeriveBytes( pwd1,salt1,myIterations );
		 Rfc2898DeriveBytes ^ k2 = gcnew Rfc2898DeriveBytes( pwd1,salt1 );

		 // Encrypt the data.
		 TripleDES^ encAlg = TripleDES::Create();
		 encAlg->Key = k1->GetBytes( 16 );
		 MemoryStream^ encryptionStream = gcnew MemoryStream;
		 CryptoStream^ encrypt = gcnew CryptoStream( encryptionStream,encAlg->CreateEncryptor(),CryptoStreamMode::Write );
		 array<Byte>^utfD1 = (gcnew System::Text::UTF8Encoding( false ))->GetBytes( data1 );

		 encrypt->Write( utfD1, 0, utfD1->Length );
		 encrypt->FlushFinalBlock();
		 encrypt->Close();
		 array<Byte>^edata1 = encryptionStream->ToArray();
		 k1->Reset();

		 // Try to decrypt, thus showing it can be round-tripped.
		 TripleDES^ decAlg = TripleDES::Create();
		 decAlg->Key = k2->GetBytes( 16 );
		 decAlg->IV = encAlg->IV;
		 MemoryStream^ decryptionStreamBacking = gcnew MemoryStream;
		 CryptoStream^ decrypt = gcnew CryptoStream( decryptionStreamBacking,decAlg->CreateDecryptor(),CryptoStreamMode::Write );

		 decrypt->Write( edata1, 0, edata1->Length );
		 decrypt->Flush();
		 decrypt->Close();
		 k2->Reset();

		 String^ data2 = (gcnew 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}", k1->IterationCount );
			Console::WriteLine( "k2 iterations: {0}", k2->IterationCount );
		 }
	  }

	  catch ( Exception^ e ) 
	  {
		 Console::WriteLine( "Error: ", e );
	  }
   }
}

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 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

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