This documentation is archived and is not being maintained.

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)

public class Rfc2898DeriveBytes : DeriveBytes

The Rfc2898DeriveBytes type exposes the following members.

Public methodRfc2898DeriveBytes(String, Byte[])Initializes a new instance of the Rfc2898DeriveBytes class using a password and salt to derive the key.
Public methodRfc2898DeriveBytes(String, Int32)Initializes a new instance of the Rfc2898DeriveBytes class using the password and salt size to derive the key.
Public methodRfc2898DeriveBytes(Byte[], Byte[], Int32)Initializes a new instance of the Rfc2898DeriveBytes class using a password, a salt, and number of iterations to derive the key.
Public methodRfc2898DeriveBytes(String, Byte[], Int32)Initializes a new instance of the Rfc2898DeriveBytes class using a password, a salt, and number of iterations to derive the key.
Public methodRfc2898DeriveBytes(String, Int32, Int32)Initializes a new instance of the Rfc2898DeriveBytes class using a password, a salt size, and number of iterations to derive the key.

Public propertyIterationCountGets or sets the number of iterations for the operation.
Public propertySaltGets or sets the key salt value for the operation.

Public methodDispose()When overridden in a derived class, releases all resources used by the current instance of the DeriveBytes class. (Inherited from DeriveBytes.)
Protected methodDispose(Boolean)Releases the unmanaged resources used by the Rfc2898DeriveBytes class and optionally releases the managed resources. (Overrides DeriveBytes.Dispose(Boolean).)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetBytesReturns the pseudo-random key for this object. (Overrides DeriveBytes.GetBytes(Int32).)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodResetResets the state of the operation. (Overrides DeriveBytes.Reset().)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)

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 Ildasm.exe (MSIL Disassembler), 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 System;
using System.IO;
using System.Text;
using 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 string usageText = "Usage: RFC2898 <password>\nYou must specify the password for encryption.\n";
    public static void Main(string[] passwordargs)
        //If no file name is specified, write usage text.
        if (passwordargs.Length == 0)
            string pwd1 = passwordargs[0];
            // Create a byte array to hold the random value. 
            byte[] salt1 = new byte[8];
            using (RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider())
                // Fill the array with a random value.

            //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;
                Rfc2898DeriveBytes k1 = new Rfc2898DeriveBytes(pwd1, salt1, myIterations);
                Rfc2898DeriveBytes k2 = new Rfc2898DeriveBytes(pwd1, salt1);
                // Encrypt the data.
                TripleDES encAlg = TripleDES.Create();
                encAlg.Key = k1.GetBytes(16);
                MemoryStream encryptionStream = new MemoryStream();
                CryptoStream encrypt = new CryptoStream(encryptionStream, encAlg.CreateEncryptor(), CryptoStreamMode.Write);
                byte[] utfD1 = new System.Text.UTF8Encoding(false).GetBytes(data1);

                encrypt.Write(utfD1, 0, utfD1.Length);
                byte[] edata1 = encryptionStream.ToArray();

                // 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 = new MemoryStream();
                CryptoStream decrypt = new CryptoStream(decryptionStreamBacking, decAlg.CreateDecryptor(), CryptoStreamMode.Write);
                decrypt.Write(edata1, 0, edata1.Length);
                string data2 = new UTF8Encoding(false).GetString(decryptionStreamBacking.ToArray());

                if (!data1.Equals(data2))
                    Console.WriteLine("Error: The two values are not equal.");
                    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);


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.