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<?php
/**
* Binary Finite Fields
*
* In a binary finite field numbers are actually polynomial equations. If you
* represent the number as a sequence of bits you get a sequence of 1's or 0's.
* These 1's or 0's represent the coefficients of the x**n, where n is the
* location of the given bit. When you add numbers over a binary finite field
* the result should have a coefficient of 1 or 0 as well. Hence addition
* and subtraction become the same operation as XOR.
* eg. 1 + 1 + 1 == 3 % 2 == 1 or 0 - 1 == -1 % 2 == 1
*
* PHP version 5 and 7
*
* @author Jim Wigginton <terrafrost@php.net>
* @copyright 2017 Jim Wigginton
* @license http://www.opensource.org/licenses/mit-license.html MIT License
*/
namespace phpseclib3\Math\BinaryField;
use phpseclib3\Common\Functions\Strings;
use phpseclib3\Math\BigInteger;
use phpseclib3\Math\BinaryField;
use phpseclib3\Math\Common\FiniteField\Integer as Base;
/**
* Binary Finite Fields
*
* @author Jim Wigginton <terrafrost@php.net>
*/
class Integer extends Base
{
/**
* Holds the BinaryField's value
*
* @var string
*/
protected $value;
/**
* Keeps track of current instance
*
* @var int
*/
protected $instanceID;
/**
* Holds the PrimeField's modulo
*
* @var array<int, string>
*/
protected static $modulo;
/**
* Holds a pre-generated function to perform modulo reductions
*
* @var callable[]
*/
protected static $reduce;
/**
* Default constructor
*/
public function __construct($instanceID, $num = '')
{
$this->instanceID = $instanceID;
if (!strlen($num)) {
$this->value = '';
} else {
$reduce = static::$reduce[$instanceID];
$this->value = $reduce($num);
}
}
/**
* Set the modulo for a given instance
* @param int $instanceID
* @param string $modulo
*/
public static function setModulo($instanceID, $modulo)
{
static::$modulo[$instanceID] = $modulo;
}
/**
* Set the modulo for a given instance
*/
public static function setRecurringModuloFunction($instanceID, callable $function)
{
static::$reduce[$instanceID] = $function;
}
/**
* Tests a parameter to see if it's of the right instance
*
* Throws an exception if the incorrect class is being utilized
*/
private static function checkInstance(self $x, self $y)
{
if ($x->instanceID != $y->instanceID) {
throw new \UnexpectedValueException('The instances of the two BinaryField\Integer objects do not match');
}
}
/**
* Tests the equality of two numbers.
*
* @return bool
*/
public function equals(self $x)
{
static::checkInstance($this, $x);
return $this->value == $x->value;
}
/**
* Compares two numbers.
*
* @return int
*/
public function compare(self $x)
{
static::checkInstance($this, $x);
$a = $this->value;
$b = $x->value;
$length = max(strlen($a), strlen($b));
$a = str_pad($a, $length, "\0", STR_PAD_LEFT);
$b = str_pad($b, $length, "\0", STR_PAD_LEFT);
return strcmp($a, $b);
}
/**
* Returns the degree of the polynomial
*
* @param string $x
* @return int
*/
private static function deg($x)
{
$x = ltrim($x, "\0");
$xbit = decbin(ord($x[0]));
$xlen = $xbit == '0' ? 0 : strlen($xbit);
$len = strlen($x);
if (!$len) {
return -1;
}
return 8 * strlen($x) - 9 + $xlen;
}
/**
* Perform polynomial division
*
* @return string[]
* @link https://en.wikipedia.org/wiki/Polynomial_greatest_common_divisor#Euclidean_division
*/
private static function polynomialDivide($x, $y)
{
// in wikipedia's description of the algorithm, lc() is the leading coefficient. over a binary field that's
// always going to be 1.
$q = chr(0);
$d = static::deg($y);
$r = $x;
while (($degr = static::deg($r)) >= $d) {
$s = '1' . str_repeat('0', $degr - $d);
$s = BinaryField::base2ToBase256($s);
$length = max(strlen($s), strlen($q));
$q = !isset($q) ? $s :
str_pad($q, $length, "\0", STR_PAD_LEFT) ^
str_pad($s, $length, "\0", STR_PAD_LEFT);
$s = static::polynomialMultiply($s, $y);
$length = max(strlen($r), strlen($s));
$r = str_pad($r, $length, "\0", STR_PAD_LEFT) ^
str_pad($s, $length, "\0", STR_PAD_LEFT);
}
return [ltrim($q, "\0"), ltrim($r, "\0")];
}
/**
* Perform polynomial multiplation in the traditional way
*
* @return string
* @link https://en.wikipedia.org/wiki/Finite_field_arithmetic#Multiplication
*/
private static function regularPolynomialMultiply($x, $y)
{
$precomputed = [ltrim($x, "\0")];
$x = strrev(BinaryField::base256ToBase2($x));
$y = strrev(BinaryField::base256ToBase2($y));
if (strlen($x) == strlen($y)) {
$length = strlen($x);
} else {
$length = max(strlen($x), strlen($y));
$x = str_pad($x, $length, '0');
$y = str_pad($y, $length, '0');
}
$result = str_repeat('0', 2 * $length - 1);
$result = BinaryField::base2ToBase256($result);
$size = strlen($result);
$x = strrev($x);
// precompute left shift 1 through 7
for ($i = 1; $i < 8; $i++) {
$precomputed[$i] = BinaryField::base2ToBase256($x . str_repeat('0', $i));
}
for ($i = 0; $i < strlen($y); $i++) {
if ($y[$i] == '1') {
$temp = $precomputed[$i & 7] . str_repeat("\0", $i >> 3);
$result ^= str_pad($temp, $size, "\0", STR_PAD_LEFT);
}
}
return $result;
}
/**
* Perform polynomial multiplation
*
* Uses karatsuba multiplication to reduce x-bit multiplications to a series of 32-bit multiplications
*
* @return string
* @link https://en.wikipedia.org/wiki/Karatsuba_algorithm
*/
private static function polynomialMultiply($x, $y)
{
if (strlen($x) == strlen($y)) {
$length = strlen($x);
} else {
$length = max(strlen($x), strlen($y));
$x = str_pad($x, $length, "\0", STR_PAD_LEFT);
$y = str_pad($y, $length, "\0", STR_PAD_LEFT);
}
switch (true) {
case PHP_INT_SIZE == 8 && $length <= 4:
return $length != 4 ?
self::subMultiply(str_pad($x, 4, "\0", STR_PAD_LEFT), str_pad($y, 4, "\0", STR_PAD_LEFT)) :
self::subMultiply($x, $y);
case PHP_INT_SIZE == 4 || $length > 32:
return self::regularPolynomialMultiply($x, $y);
}
$m = $length >> 1;
$x1 = substr($x, 0, -$m);
$x0 = substr($x, -$m);
$y1 = substr($y, 0, -$m);
$y0 = substr($y, -$m);
$z2 = self::polynomialMultiply($x1, $y1);
$z0 = self::polynomialMultiply($x0, $y0);
$z1 = self::polynomialMultiply(
self::subAdd2($x1, $x0),
self::subAdd2($y1, $y0)
);
$z1 = self::subAdd3($z1, $z2, $z0);
$xy = self::subAdd3(
$z2 . str_repeat("\0", 2 * $m),
$z1 . str_repeat("\0", $m),
$z0
);
return ltrim($xy, "\0");
}
/**
* Perform polynomial multiplication on 2x 32-bit numbers, returning
* a 64-bit number
*
* @param string $x
* @param string $y
* @return string
* @link https://www.bearssl.org/constanttime.html#ghash-for-gcm
*/
private static function subMultiply($x, $y)
{
$x = unpack('N', $x)[1];
$y = unpack('N', $y)[1];
$x0 = $x & 0x11111111;
$x1 = $x & 0x22222222;
$x2 = $x & 0x44444444;
$x3 = $x & 0x88888888;
$y0 = $y & 0x11111111;
$y1 = $y & 0x22222222;
$y2 = $y & 0x44444444;
$y3 = $y & 0x88888888;
$z0 = ($x0 * $y0) ^ ($x1 * $y3) ^ ($x2 * $y2) ^ ($x3 * $y1);
$z1 = ($x0 * $y1) ^ ($x1 * $y0) ^ ($x2 * $y3) ^ ($x3 * $y2);
$z2 = ($x0 * $y2) ^ ($x1 * $y1) ^ ($x2 * $y0) ^ ($x3 * $y3);
$z3 = ($x0 * $y3) ^ ($x1 * $y2) ^ ($x2 * $y1) ^ ($x3 * $y0);
$z0 &= 0x1111111111111111;
$z1 &= 0x2222222222222222;
$z2 &= 0x4444444444444444;
$z3 &= -8608480567731124088; // 0x8888888888888888 gets interpreted as a float
$z = $z0 | $z1 | $z2 | $z3;
return pack('J', $z);
}
/**
* Adds two numbers
*
* @param string $x
* @param string $y
* @return string
*/
private static function subAdd2($x, $y)
{
$length = max(strlen($x), strlen($y));
$x = str_pad($x, $length, "\0", STR_PAD_LEFT);
$y = str_pad($y, $length, "\0", STR_PAD_LEFT);
return $x ^ $y;
}
/**
* Adds three numbers
*
* @param string $x
* @param string $y
* @return string
*/
private static function subAdd3($x, $y, $z)
{
$length = max(strlen($x), strlen($y), strlen($z));
$x = str_pad($x, $length, "\0", STR_PAD_LEFT);
$y = str_pad($y, $length, "\0", STR_PAD_LEFT);
$z = str_pad($z, $length, "\0", STR_PAD_LEFT);
return $x ^ $y ^ $z;
}
/**
* Adds two BinaryFieldIntegers.
*
* @return static
*/
public function add(self $y)
{
static::checkInstance($this, $y);
$length = strlen(static::$modulo[$this->instanceID]);
$x = str_pad($this->value, $length, "\0", STR_PAD_LEFT);
$y = str_pad($y->value, $length, "\0", STR_PAD_LEFT);
return new static($this->instanceID, $x ^ $y);
}
/**
* Subtracts two BinaryFieldIntegers.
*
* @return static
*/
public function subtract(self $x)
{
return $this->add($x);
}
/**
* Multiplies two BinaryFieldIntegers.
*
* @return static
*/
public function multiply(self $y)
{
static::checkInstance($this, $y);
return new static($this->instanceID, static::polynomialMultiply($this->value, $y->value));
}
/**
* Returns the modular inverse of a BinaryFieldInteger
*
* @return static
*/
public function modInverse()
{
$remainder0 = static::$modulo[$this->instanceID];
$remainder1 = $this->value;
if ($remainder1 == '') {
return new static($this->instanceID);
}
$aux0 = "\0";
$aux1 = "\1";
while ($remainder1 != "\1") {
list($q, $r) = static::polynomialDivide($remainder0, $remainder1);
$remainder0 = $remainder1;
$remainder1 = $r;
// the auxiliary in row n is given by the sum of the auxiliary in
// row n-2 and the product of the quotient and the auxiliary in row
// n-1
$temp = static::polynomialMultiply($aux1, $q);
$aux = str_pad($aux0, strlen($temp), "\0", STR_PAD_LEFT) ^
str_pad($temp, strlen($aux0), "\0", STR_PAD_LEFT);
$aux0 = $aux1;
$aux1 = $aux;
}
$temp = new static($this->instanceID);
$temp->value = ltrim($aux1, "\0");
return $temp;
}
/**
* Divides two PrimeFieldIntegers.
*
* @return static
*/
public function divide(self $x)
{
static::checkInstance($this, $x);
$x = $x->modInverse();
return $this->multiply($x);
}
/**
* Negate
*
* A negative number can be written as 0-12. With modulos, 0 is the same thing as the modulo
* so 0-12 is the same thing as modulo-12
*
* @return object
*/
public function negate()
{
$x = str_pad($this->value, strlen(static::$modulo[$this->instanceID]), "\0", STR_PAD_LEFT);
return new static($this->instanceID, $x ^ static::$modulo[$this->instanceID]);
}
/**
* Returns the modulo
*
* @return string
*/
public static function getModulo($instanceID)
{
return static::$modulo[$instanceID];
}
/**
* Converts an Integer to a byte string (eg. base-256).
*
* @return string
*/
public function toBytes()
{
return str_pad($this->value, strlen(static::$modulo[$this->instanceID]), "\0", STR_PAD_LEFT);
}
/**
* Converts an Integer to a hex string (eg. base-16).
*
* @return string
*/
public function toHex()
{
return Strings::bin2hex($this->toBytes());
}
/**
* Converts an Integer to a bit string (eg. base-2).
*
* @return string
*/
public function toBits()
{
//return str_pad(BinaryField::base256ToBase2($this->value), strlen(static::$modulo[$this->instanceID]), '0', STR_PAD_LEFT);
return BinaryField::base256ToBase2($this->value);
}
/**
* Converts an Integer to a BigInteger
*
* @return string
*/
public function toBigInteger()
{
return new BigInteger($this->value, 256);
}
/**
* __toString() magic method
*
*/
public function __toString()
{
return (string) $this->toBigInteger();
}
/**
* __debugInfo() magic method
*
*/
public function __debugInfo()
{
return ['value' => $this->toHex()];
}
}
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