org.apache.directory.server.kerberos.shared.crypto.encryption

Class NFold

java.lang.Object

org.apache.directory.server.kerberos.shared.crypto.encryption.NFold

public class NFold
extends java.lang.Object

An implementation of the n-fold algorithm, as required by RFC 3961, "Encryption and Checksum Specifications for Kerberos 5." "To n-fold a number X, replicate the input value to a length that is the least common multiple of n and the length of X. Before each repetition, the input is rotated to the right by 13 bit positions. The successive n-bit chunks are added together using 1's-complement addition (that is, with end-around carry) to yield a n-bit result."

Constructor Summary

Constructors

Constructor and Description
NFold()

Method Summary

Modifier and Type	Method and Description
private static int	getBit(byte[] data, int pos) Get a bit from a byte array at a given position.
protected static int	getLcm(int n1, int n2) For 2 numbers, return the least-common multiple.
static byte[]	nFold(int n, byte[] data) N-fold the data n times.
private static byte[]	rotateRight(byte[] in, int len, int step) Right-rotate the given byte array.
private static void	setBit(byte[] data, int pos, int val) Set a bit in a byte array at a given position.
protected static byte[]	sum(byte[] n1, byte[] n2, int len) Perform one's complement addition (addition with end-around carry).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

NFold

public NFold()

Method Detail

nFold

public static byte[] nFold(int n,
                           byte[] data)

N-fold the data n times.

Parameters:

n - The number of times to n-fold the data.

data - The data to n-fold.

Returns:

The n-folded data.

getLcm

protected static int getLcm(int n1,
                            int n2)

For 2 numbers, return the least-common multiple.

Parameters:

n1 - The first number.

n2 - The second number.

Returns:

The least-common multiple.

rotateRight

private static byte[] rotateRight(byte[] in,
                                  int len,
                                  int step)

Right-rotate the given byte array.

Parameters:

in - The byte array to right-rotate.

len - The length of the byte array to rotate.

step - The number of positions to rotate the byte array.

Returns:

The right-rotated byte array.

sum

protected static byte[] sum(byte[] n1,
                            byte[] n2,
                            int len)

Perform one's complement addition (addition with end-around carry). Note that for purposes of n-folding, we do not actually complement the result of the addition.

Parameters:

n1 - The first number.

n2 - The second number.

len - The length of the byte arrays to sum.

Returns:

The sum with end-around carry.

getBit

private static int getBit(byte[] data,
                          int pos)

Get a bit from a byte array at a given position.

Parameters:

data - The data to get the bit from.

pos - The position to get the bit at.

Returns:

The value of the bit.

setBit

private static void setBit(byte[] data,
                           int pos,
                           int val)

Set a bit in a byte array at a given position.

Parameters:

data - The data to set the bit in.

pos - The position of the bit to set.

The - value to set the bit to.