GcmUtilities.cs :  » PDF » iTextSharp » Org » BouncyCastle » Crypto » Modes » Gcm » C# / CSharp Open Source

using System;

using Org.BouncyCastle.Crypto.Utilities;

namespace Org.BouncyCastle.Crypto.Modes.Gcm{
  internal abstract class GcmUtilities
  {
    internal static uint[] AsUints(byte[] bs)
    {
      uint[] us = new uint[4];
      us[0] = Pack.BE_To_UInt32(bs, 0);
      us[1] = Pack.BE_To_UInt32(bs, 4);
      us[2] = Pack.BE_To_UInt32(bs, 8);
      us[3] = Pack.BE_To_UInt32(bs, 12);
      return us;
    }

    // P is the value with only bit i=1 set
    internal static void MultiplyP(uint[] x)
    {
      bool lsb = (x[3] & 1) != 0;
      ShiftRight(x);
      if (lsb)
      {
        // R = new uint[]{ 0xe1000000, 0, 0, 0 };
        //Xor(v, R);
        x[0] ^= 0xe1000000;
      }
    }

    internal static void MultiplyP8(uint[] x)
    {
      for (int i = 8; i != 0; --i)
      {
        MultiplyP(x);
      }
    }

    internal static void ShiftRight(byte[] block)
    {
      int i = 0;
      byte bit = 0;
      for (;;)
      {
        byte b = block[i];
        block[i] = (byte)((b >> 1) | bit);
        if (++i == 16) break;
        bit = (byte)(b << 7);
      }
    }

    internal static void ShiftRight(uint[] block)
    {
      int i = 0;
      uint bit = 0;
      for (;;)
      {
        uint b = block[i];
        block[i] = (b >> 1) | bit;
        if (++i == 4) break;
        bit = b << 31;
      }
    }

    internal static void Xor(byte[] block, byte[] val)
    {
      for (int i = 15; i >= 0; --i)
      {
        block[i] ^= val[i];
      }
    }

    internal static void Xor(uint[] block, uint[] val)
    {
      for (int i = 3; i >= 0; --i)
      {
        block[i] ^= val[i];
      }
    }
  }
}