PasswordDeriveBytes Class

Definition

Namespace:

System.Security.Cryptography

Assemblies:

netstandard.dll, System.Security.Cryptography.dll

Source:

PasswordDeriveBytes.cs

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

C#

public class PasswordDeriveBytes : System.Security.Cryptography.DeriveBytes

Inheritance

Object

DeriveBytes

PasswordDeriveBytes

Examples

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

C#

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;
        }
    }
}

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.

Important

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

Constructors

PasswordDeriveBytes(Byte[], Byte[], CspParameters)	Initializes a new instance of the PasswordDeriveBytes class specifying the password, key salt, and cryptographic service provider (CSP) to use to derive the key.
PasswordDeriveBytes(Byte[], Byte[], String, Int32, CspParameters)	Initializes a new instance of the PasswordDeriveBytes class specifying the password, key salt, hash name, iterations, and cryptographic service provider (CSP) to use to derive the key.
PasswordDeriveBytes(Byte[], Byte[], String, Int32)	Initializes a new instance of the PasswordDeriveBytes class specifying the password, key salt, hash name, and iterations to use to derive the key.
PasswordDeriveBytes(Byte[], Byte[])	Initializes a new instance of the PasswordDeriveBytes class specifying the password and key salt to use to derive the key.
PasswordDeriveBytes(String, Byte[], CspParameters)	Initializes a new instance of the PasswordDeriveBytes class with the password, key salt, and cryptographic service provider (CSP) parameters to use to derive the key.
PasswordDeriveBytes(String, Byte[], String, Int32, CspParameters)	Initializes a new instance of the PasswordDeriveBytes class with the password, key salt, hash name, number of iterations, and cryptographic service provider (CSP) parameters to use to derive the key.
PasswordDeriveBytes(String, Byte[], String, Int32)	Initializes a new instance of the PasswordDeriveBytes class with the password, key salt, hash name, and number of iterations to use to derive the key.
PasswordDeriveBytes(String, Byte[])	Initializes a new instance of the PasswordDeriveBytes class with the password and key salt to use to derive the key.

Properties

HashName	Gets or sets the name of the hash algorithm for the operation.
IterationCount	Gets or sets the number of iterations for the operation.
Salt	Gets or sets the key salt value for the operation.

Methods

CryptDeriveKey(String, String, Int32, Byte[])	Derives a cryptographic key from the PasswordDeriveBytes object.
Dispose()	When overridden in a derived class, releases all resources used by the current instance of the DeriveBytes class. (Inherited from DeriveBytes)
Dispose(Boolean)	Releases the unmanaged resources used by the PasswordDeriveBytes class and optionally releases the managed resources.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetBytes(Int32)	Obsolete. Returns pseudo-random key bytes.
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
Reset()	Resets the state of the operation.
ToString()	Returns a string that represents the current object. (Inherited from Object)

Applies to

See also

• Cryptographic Services