ISO7816d4Padding.cs :  » PDF » iTextSharp » Org » BouncyCastle » Crypto » Paddings » C# / CSharp Open Source

using System;

using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Security;

namespace Org.BouncyCastle.Crypto.Paddings{
  /**
   * A padder that adds the padding according to the scheme referenced in
   * ISO 7814-4 - scheme 2 from ISO 9797-1. The first byte is 0x80, rest is 0x00
   */
  public class ISO7816d4Padding
    : IBlockCipherPadding
  {
    /**
     * Initialise the padder.
     *
     * @param random - a SecureRandom if available.
     */
    public void Init(
      SecureRandom random)
    {
      // nothing to do.
    }

    /**
     * Return the name of the algorithm the padder implements.
     *
     * @return the name of the algorithm the padder implements.
     */
    public string PaddingName
    {
      get { return "ISO7816-4"; }
    }

    /**
     * add the pad bytes to the passed in block, returning the
     * number of bytes added.
     */
    public int AddPadding(
      byte[]  input,
      int    inOff)
    {
      int added = (input.Length - inOff);

      input[inOff]= (byte) 0x80;
      inOff ++;

      while (inOff < input.Length)
      {
        input[inOff] = (byte) 0;
        inOff++;
      }

      return added;
    }

    /**
     * return the number of pad bytes present in the block.
     */
    public int PadCount(
      byte[] input)
    {
      int count = input.Length - 1;

      while (count > 0 && input[count] == 0)
      {
        count--;
      }

      if (input[count] != (byte)0x80)
      {
        throw new InvalidCipherTextException("pad block corrupted");
      }

      return input.Length - count;
    }
  }
}