org.bouncycastle.math.raw

Class GF16

java.lang.Object

org.bouncycastle.math.raw.GF16

public class GF16
extends java.lang.Object

Constructor Summary

Constructors

Constructor and Description
GF16()

Method Summary

Modifier and Type	Method and Description
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) Multiplicative inverse in GF(16), table-free: a^14 = a^-1 (since a^15 = 1 for a !
static int	inv(int a) Multiplicative inverse in GF(16); table-free, branch-free (see inv(byte)).
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; table-free, branch-free (see mul(byte, byte)).
static long	mulAddStep16(long v, long m0, long m1, long m2, long m3) One step of the bitsliced, word-parallel GF(16) scalar-times-vector multiply-accumulate.
static long	mulFx8(int a, long b) Byte-lane parallel GF(16) multiply: multiplies the single GF(16) scalar a into up to eight GF(16) elements packed one-per-byte in b (each in the low nibble of its byte), all at once and table-free.
static int	sqr(int a) Constant-time GF(16) squaring over 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

mulAddStep16

public static long mulAddStep16(long v,
                                long m0,
                                long m1,
                                long m2,
                                long m3)

One step of the bitsliced, word-parallel GF(16) scalar-times-vector multiply-accumulate. Returns the contribution to XOR into the accumulator for a single 16-nibble packed input limb v, given the four broadcast scalar-bit masks m0..m3 (each 0 or -1, one per bit of the GF(16) scalar). The caller hoists the mask computation outside its limb loop.

This is the constant-time, table-free GF(16) kernel shared by UOV's GF.vecMadd16 and MAYO's GF16Utils.mVecMulAdd: a mask-select on the scalar bits plus a SWAR multiply-by-x that folds x+1 (0x3) per nibble for the field polynomial x^4 + x + 1. No data-dependent branch and no secret-indexed table.

Parameters:

v - 16 GF(16) nibbles packed into a long.

m0 - broadcast mask (0 or -1) for scalar bit 0.

m1 - broadcast mask (0 or -1) for scalar bit 1.

m2 - broadcast mask (0 or -1) for scalar bit 2.

m3 - broadcast mask (0 or -1) for scalar bit 3.

Returns:

the multiply-accumulate contribution for this limb.

mul

public static byte mul(byte a,
                       byte b)

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

Table-free, branch-free carryless multiply followed by reduction modulo x^4 + x + 1, so the multiply carries no secret-indexed memory access (no L3 cache-timing side channel) — the form used by the SNOVA and MAYO reference implementations' production (Opt / AVX2) builds. 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; table-free, branch-free (see mul(byte, byte)). 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)

mulFx8

public static long mulFx8(int a,
                          long b)

Byte-lane parallel GF(16) multiply: multiplies the single GF(16) scalar a into up to eight GF(16) elements packed one-per-byte in b (each in the low nibble of its byte), all at once and table-free. The batched, constant-time form of mul(int, int) used to multiply a scalar by a whole packed matrix row (the SNOVA / MAYO mul_fx8).

Parameters:

a - a GF(16) scalar (only the lower 4 bits are used)

b - up to eight GF(16) elements, one per byte lane

Returns:

the eight products, one per byte lane

sqr

public static int sqr(int a)

Constant-time GF(16) squaring over x^4 + x + 1. Squaring is GF(2)-linear, so a^2 is just the bit-spread of a (interleave a zero between each bit, via Interleave.expand4to8(int)) reduced mod 0x13. x^4 = x + 1 means the folded-down high nibble multiplies by 0x3, computed branchlessly as d ^ (d<<1) = d * (1 + x); one fold suffices here (unlike GF(256)) because 0x3 is degree 1. Returns the same value as mul(a, a) but with no per-term work — table-free, branchless, and faster (~1.35x on HotSpot C2), so it replaces the squarings in inv(int).

inv

public static byte inv(byte a)

Multiplicative inverse in GF(16), table-free: a^14 = a^-1 (since a^15 = 1 for a != 0; 0 maps to 0), so the inverse carries no secret-indexed memory access. Matches the SNOVA / MAYO reference gf16_inv / inverse_f.

inv

public static int inv(int a)

Multiplicative inverse in GF(16); table-free, branch-free (see inv(byte)). The three squarings go through sqr(int); the two genuine products through mul(int, int).

Parameters:

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

Returns:

the inverse a^-1 in GF(16), or 0 when a == 0

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)