org.bouncycastle.util
Class GF16

java.lang.Object
  org.bouncycastle.util.GF16

public class GF16

extends java.lang.Object

Constructor Summary

GF16()

Method Summary

static void	decode(byte[] input, byte[] output, int outputLen) Decodes an encoded byte array.
static void	decode(byte[] input, int inOff, byte[] output, int outOff, int outputLen)
static void	encode(byte[] input, byte[] output, int inputLen) Encodes an array of 4-bit values into a byte array.
static void	encode(byte[] input, byte[] output, int outOff, int inputLen)
static byte	innerProduct(byte[] a, int aOff, byte[] b, int bOff, int rank)
static byte	inv(byte a) Computes the multiplicative inverse in GF(16) for a GF(16) element.
static byte	mul(byte a, byte b) GF(16) multiplication mod x^4 + x + 1.
static int	mul(int a, int b) GF(16) multiplication mod x^4 + x + 1.

Methods inherited from class java.lang.Object

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

Constructor Detail

GF16

public GF16()

Method Detail

mul

public static byte mul(byte a,
                       byte b)

GF(16) multiplication mod x^4 + x + 1.

This method multiplies two elements in GF(16) (represented as integers 0–15) using carryless multiplication followed by reduction modulo x^4 + x + 1. Please ensure a <= 0x0F and b <= 0x0F

Parameters:

a - an element in GF(16) (only the lower 4 bits are used)

b - an element in GF(16) (only the lower 4 bits are used)

Returns:

the product a * b in GF(16)

mul

public static int mul(int a,
                      int b)

GF(16) multiplication mod x^4 + x + 1.

This method multiplies two elements in GF(16) (represented as integers 0–15) using carryless multiplication followed by reduction modulo x^4 + x + 1. Please ensure a <= 0x0F and b <= 0x0F

Parameters:

a - an element in GF(16) (only the lower 4 bits are used)

b - an element in GF(16) (only the lower 4 bits are used)

Returns:

the product a * b in GF(16)

inv

public static byte inv(byte a)

Computes the multiplicative inverse in GF(16) for a GF(16) element.

decode

public static void decode(byte[] input,
                          byte[] output,
                          int outputLen)

Decodes an encoded byte array. Each byte in the input contains two nibbles (4-bit values); the lower nibble is stored first, followed by the upper nibble.

Parameters:

input - the input byte array (each byte holds two 4-bit values)

output - the output array that will hold the decoded nibbles (one per byte)

outputLen - the total number of nibbles to decode

decode

public static void decode(byte[] input,
                          int inOff,
                          byte[] output,
                          int outOff,
                          int outputLen)

encode

public static void encode(byte[] input,
                          byte[] output,
                          int inputLen)

Encodes an array of 4-bit values into a byte array. Two 4-bit values are packed into one byte, with the first nibble stored in the lower 4 bits and the second nibble stored in the upper 4 bits.

Parameters:

input - the input array of 4-bit values (stored as bytes, only lower 4 bits used)

output - the output byte array that will hold the encoded bytes

inputLen - the number of nibbles in the input array

encode

public static void encode(byte[] input,
                          byte[] output,
                          int outOff,
                          int inputLen)

innerProduct

public static byte innerProduct(byte[] a,
                                int aOff,
                                byte[] b,
                                int bOff,
                                int rank)