Package gnu.crypto.pad

Provides a basic API for using block cipher padding algorithms.

See:
Description

Interface Summary

IPad	The basic visible methods of any padding algorithm.

Class Summary

BasePad	An abstract class to facilitate implementing padding algorithms.
PadFactory	A Factory to instantiate padding schemes.
PKCS1_V1_5	A padding algorithm implementation of the EME-PKCS1-V1.5 encoding/decoding algorithm as described in section 7.2 of RFC-3447.
PKCS7	The implementation of the PKCS7 padding algorithm.
TBC	The implementation of the Trailing Bit Complement (TBC) padding algorithm.

Exception Summary

WrongPaddingException

A checked exception that indicates that a padding algorithm did not find the expected padding bytes when unpadding some data.

Package gnu.crypto.pad Description

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);