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

using System;

namespace Org.BouncyCastle.Crypto.Modes.Gcm{
  public class BasicGcmMultiplier
    : IGcmMultiplier
  {
    private byte[] H;

    public void Init(byte[] H)
    {
      this.H = (byte[])H.Clone();
    }

    public void MultiplyH(byte[] x)
    {
      byte[] z = new byte[16];

      for (int i = 0; i < 16; ++i)
      {
        byte h = H[i];
        for (int j = 7; j >= 0; --j)
        {
          if ((h & (1 << j)) != 0)
          {
            GcmUtilities.Xor(z, x);
          }

          bool lsb = (x[15] & 1) != 0;
          GcmUtilities.ShiftRight(x);
          if (lsb)
          {
            // R = new byte[]{ 0xe1, ... };
            //GcmUtilities.Xor(v, R);
            x[0] ^= (byte)0xe1;
          }
        }
      }

      Array.Copy(z, 0, x, 0, 16);        
    }
  }
}