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<?php
declare(strict_types=1);
/*
* The MIT License (MIT)
*
* Copyright (c) 2014-2020 Spomky-Labs
*
* This software may be modified and distributed under the terms
* of the MIT license. See the LICENSE file for details.
*/
namespace Jose\Component\Core\Util\Ecc;
use Brick\Math\BigInteger;
use function is_null;
use RuntimeException;
/**
* @internal
*/
class Curve
{
/**
* Elliptic curve over the field of integers modulo a prime.
*
* @var BigInteger
*/
private $a;
/**
* @var BigInteger
*/
private $b;
/**
* @var BigInteger
*/
private $prime;
/**
* Binary length of keys associated with these curve parameters.
*
* @var int
*/
private $size;
/**
* @var Point
*/
private $generator;
public function __construct(int $size, BigInteger $prime, BigInteger $a, BigInteger $b, Point $generator)
{
$this->size = $size;
$this->prime = $prime;
$this->a = $a;
$this->b = $b;
$this->generator = $generator;
}
public function __toString(): string
{
return 'curve('.Math::toString($this->getA()).', '.Math::toString($this->getB()).', '.Math::toString($this->getPrime()).')';
}
public function getA(): BigInteger
{
return $this->a;
}
public function getB(): BigInteger
{
return $this->b;
}
public function getPrime(): BigInteger
{
return $this->prime;
}
public function getSize(): int
{
return $this->size;
}
/**
* @throws RuntimeException if the curve does not contain the point
*/
public function getPoint(BigInteger $x, BigInteger $y, ?BigInteger $order = null): Point
{
if (!$this->contains($x, $y)) {
throw new RuntimeException('Curve '.$this->__toString().' does not contain point ('.Math::toString($x).', '.Math::toString($y).')');
}
$point = Point::create($x, $y, $order);
if (!is_null($order)) {
$mul = $this->mul($point, $order);
if (!$mul->isInfinity()) {
throw new RuntimeException('SELF * ORDER MUST EQUAL INFINITY.');
}
}
return $point;
}
/**
* @throws RuntimeException if the coordinates are out of range
*/
public function getPublicKeyFrom(BigInteger $x, BigInteger $y): PublicKey
{
$zero = BigInteger::zero();
if ($x->compareTo($zero) < 0 || $y->compareTo($zero) < 0 || $this->generator->getOrder()->compareTo($x) <= 0 || $this->generator->getOrder()->compareTo($y) <= 0) {
throw new RuntimeException('Generator point has x and y out of range.');
}
$point = $this->getPoint($x, $y);
return new PublicKey($point);
}
public function contains(BigInteger $x, BigInteger $y): bool
{
return Math::equals(
ModularArithmetic::sub(
$y->power(2),
Math::add(
Math::add(
$x->power(3),
$this->getA()->multipliedBy($x)
),
$this->getB()
),
$this->getPrime()
),
BigInteger::zero()
);
}
public function add(Point $one, Point $two): Point
{
if ($two->isInfinity()) {
return clone $one;
}
if ($one->isInfinity()) {
return clone $two;
}
if ($two->getX()->isEqualTo($one->getX())) {
if ($two->getY()->isEqualTo($one->getY())) {
return $this->getDouble($one);
}
return Point::infinity();
}
$slope = ModularArithmetic::div(
$two->getY()->minus($one->getY()),
$two->getX()->minus($one->getX()),
$this->getPrime()
);
$xR = ModularArithmetic::sub(
$slope->power(2)->minus($one->getX()),
$two->getX(),
$this->getPrime()
);
$yR = ModularArithmetic::sub(
$slope->multipliedBy($one->getX()->minus($xR)),
$one->getY(),
$this->getPrime()
);
return $this->getPoint($xR, $yR, $one->getOrder());
}
public function mul(Point $one, BigInteger $n): Point
{
if ($one->isInfinity()) {
return Point::infinity();
}
/** @var BigInteger $zero */
$zero = BigInteger::zero();
if ($one->getOrder()->compareTo($zero) > 0) {
$n = $n->mod($one->getOrder());
}
if ($n->isEqualTo($zero)) {
return Point::infinity();
}
/** @var Point[] $r */
$r = [
Point::infinity(),
clone $one,
];
$k = $this->getSize();
$n1 = str_pad(Math::baseConvert(Math::toString($n), 10, 2), $k, '0', STR_PAD_LEFT);
for ($i = 0; $i < $k; ++$i) {
$j = $n1[$i];
Point::cswap($r[0], $r[1], $j ^ 1);
$r[0] = $this->add($r[0], $r[1]);
$r[1] = $this->getDouble($r[1]);
Point::cswap($r[0], $r[1], $j ^ 1);
}
$this->validate($r[0]);
return $r[0];
}
/**
* @param Curve $other
*/
public function cmp(self $other): int
{
$equal = $this->getA()->isEqualTo($other->getA())
&& $this->getB()->isEqualTo($other->getB())
&& $this->getPrime()->isEqualTo($other->getPrime());
return $equal ? 0 : 1;
}
/**
* @param Curve $other
*/
public function equals(self $other): bool
{
return 0 === $this->cmp($other);
}
public function getDouble(Point $point): Point
{
if ($point->isInfinity()) {
return Point::infinity();
}
$a = $this->getA();
$threeX2 = BigInteger::of(3)->multipliedBy($point->getX()->power(2));
$tangent = ModularArithmetic::div(
$threeX2->plus($a),
BigInteger::of(2)->multipliedBy($point->getY()),
$this->getPrime()
);
$x3 = ModularArithmetic::sub(
$tangent->power(2),
BigInteger::of(2)->multipliedBy($point->getX()),
$this->getPrime()
);
$y3 = ModularArithmetic::sub(
$tangent->multipliedBy($point->getX()->minus($x3)),
$point->getY(),
$this->getPrime()
);
return $this->getPoint($x3, $y3, $point->getOrder());
}
public function createPrivateKey(): PrivateKey
{
return PrivateKey::create($this->generate());
}
public function createPublicKey(PrivateKey $privateKey): PublicKey
{
$point = $this->mul($this->generator, $privateKey->getSecret());
return new PublicKey($point);
}
public function getGenerator(): Point
{
return $this->generator;
}
/**
* @throws RuntimeException if the point is invalid
*/
private function validate(Point $point): void
{
if (!$point->isInfinity() && !$this->contains($point->getX(), $point->getY())) {
throw new RuntimeException('Invalid point');
}
}
private function generate(): BigInteger
{
$max = $this->generator->getOrder();
$numBits = $this->bnNumBits($max);
$numBytes = (int) ceil($numBits / 8);
// Generate an integer of size >= $numBits
$bytes = BigInteger::randomBits($numBytes);
$mask = BigInteger::of(2)->power($numBits)->minus(1);
return $bytes->and($mask);
}
/**
* Returns the number of bits used to store this number. Non-significant upper bits are not counted.
*
* @see https://www.openssl.org/docs/crypto/BN_num_bytes.html
*/
private function bnNumBits(BigInteger $x): int
{
$zero = BigInteger::of(0);
if ($x->isEqualTo($zero)) {
return 0;
}
$log2 = 0;
while (!$x->isEqualTo($zero)) {
$x = $x->shiftedRight(1);
++$log2;
}
return $log2;
}
}