Provides a basic API for using block cipher padding algorithms.

## Package overview

A padding scheme is merely a standard method of ensuring that the input to be encrypted is a multiple of the cipher's block size.

The following diagram shows the important classes participating in this package:

The following example pads an input buffer, transforms the padded buffer with already-initialized `IMode` instances, then unpads the output buffer.

    IPad padding = IPad.getInstance("PKCS7");
    padding.init(blockSize);

    byte[] pad = padding.pad(input, 0, input.length);
    byte[] pt = new byte[input.length + pad.length];
    byte[] ct = new byte[pt.length];
    byte[] cpt = new byte[pt.length];
    System.arraycopy(input, 0, pt, 0, input.length);
    System.arraycopy(pad, 0, pt, input.length, pad.length);

    for (int i = 0; i + blockSize < pt.length; i += blockSize)
      {
        enc.update(pt, i, ct, i);
      }

    for (int i = 0; i + blockSize < ct.length; i += blockSize)
      {
        dec.update(ct, i, cpt, i);
      }

    int unpad = padding.unpad(cpt, 0, cpt.length);
    byte[] output = new byte[cpt.length - unpad];
    System.arraycopy(cpt, 0, output, 0, output.length);