CipherKeyGenerator.cs :  » PDF » iTextSharp » Org » BouncyCastle » Crypto » C# / CSharp Open Source

using System;

using Org.BouncyCastle.Security;

namespace Org.BouncyCastle.Crypto{
  /**
   * The base class for symmetric, or secret, cipher key generators.
   */
  public class CipherKeyGenerator
  {
    protected internal SecureRandom  random;
    protected internal int      strength;
    private bool uninitialised = true;
    private int defaultStrength;

    public CipherKeyGenerator()
    {
    }

    internal CipherKeyGenerator(
      int defaultStrength)
    {
      if (defaultStrength < 1)
        throw new ArgumentException("strength must be a positive value", "defaultStrength");

      this.defaultStrength = defaultStrength;
    }

    public int DefaultStrength
    {
      get { return defaultStrength; }
    }

    /**
     * initialise the key generator.
     *
     * @param param the parameters to be used for key generation
     */
    public void Init(
      KeyGenerationParameters parameters)
    {
      if (parameters == null)
        throw new ArgumentNullException("parameters");

      this.uninitialised = false;

      engineInit(parameters);
    }

    protected virtual void engineInit(
      KeyGenerationParameters parameters)
    {
      this.random = parameters.Random;
      this.strength = (parameters.Strength + 7) / 8;
    }

    /**
     * Generate a secret key.
     *
     * @return a byte array containing the key value.
     */
    public byte[] GenerateKey()
    {
      if (uninitialised)
      {
        if (defaultStrength < 1)
          throw new InvalidOperationException("Generator has not been initialised");

        uninitialised = false;

        engineInit(new KeyGenerationParameters(new SecureRandom(), defaultStrength));
      }

      return engineGenerateKey();
    }

    protected virtual byte[] engineGenerateKey()
    {
      return random.GenerateSeed(strength);
    }
  }
}