Merge pull request #21 from starkbank/feature/ecdsa-methods

Add toCompressed and fromCompressed method

Author: luistarkbank

CHANGELOG.md

@@ -13,6 +13,10 @@ Given a version number MAJOR.MINOR.PATCH, increment:
 
 
 ## [Unreleased]
+### Added
+- toCompressed and fromCompressed to PublicKey resource
+- modularSquareRoot to Math resource
+- Y to curve method
 
 ## [2.0.2] - 2022-10-27
 ### Fixed

src/curve.php

@@ -59,6 +59,18 @@ function oidString()
         return join(".", $this->oid);
     }
 
+    function y($x, $isEven)
+    {
+        $ySquared = gmp_mod(gmp_add(gmp_add(gmp_powm($x, 3, $this->P), gmp_mul($this->A, $x)), $this->B), $this->P);
+        $y = Math::modularSquareRoot($ySquared, $this->P);
+
+        if ($isEven != (gmp_intval(gmp_mod($y, 2)) == 0))
+        {
+            $y = gmp_sub($this->P, $y);
+        }
+        return $y;
+    }
+
     public static $supportedCurves = [];
     public static $_curvesByOid = [];
 

src/math.php

@@ -7,6 +7,11 @@
 
 class Math
 {
+    public static function modularSquareRoot($value, $prime)
+    {
+        return gmp_powm($value, gmp_div_q(gmp_add($prime, 1), 4), $prime);
+    }
+
     /**
     Fast way to multiply point and scalar in elliptic curves
 

src/publickey.php

@@ -14,6 +14,8 @@ class PublicKey
 {
     private static $pemTemplate = "-----BEGIN PUBLIC KEY-----\n{content}\n-----END PUBLIC KEY-----\n";
     private static $ecdsaPublicKeyOid = array(1, 2, 840, 10045, 2, 1);
+    private static $evenTag = "02";
+    private static $oddTag = "03";
     public $point;
     public $curve;
 
@@ -35,6 +37,21 @@ function toString($encoded=false)
         return $string;
     }
 
+    function toCompressed() 
+    {
+        $baseLength = gmp_intval(2 * $this->curve->length());
+        
+        if (gmp_intval($this->point->y % 2) == 0)
+        {
+            $parityTag = self::$evenTag;
+        } else {
+            $parityTag = self::$oddTag;
+        }
+
+        $xHex = str_pad(Binary::hexFromInt($this->point->x), $baseLength, "0", STR_PAD_LEFT);
+        return $parityTag . $xHex;
+    }
+
     function toDer()
     {
         $hexadecimal = Der::encodeConstructed(
@@ -99,4 +116,22 @@ static function fromString($string, $curve=null, $validatePoint=true)
             throw new Exception(sprintf("Point (%d,%d) * %s.N is not at infinity", $p->x, $p->y, $curve->name));
         return $publicKey;
     }
+
+    static function fromCompressed($string, $curve=null)
+    {
+        $curve = is_null($curve) ? Curve::$supportedCurves["secp256k1"] : $curve;
+        $parityTag = substr($string, 0, 2);
+        $xHex = substr($string, 2, strlen($string));
+
+        if (!in_array($parityTag, array(self::$evenTag, self::$oddTag)))
+        {
+            throw new Exception(sprintf("Compressed string should start with 02 or 03"));
+        }
+
+        $x = Binary::intFromHex($xHex);
+        $isEven = $parityTag === self::$evenTag;
+        $y = $curve->y($x, $isEven);
+        
+        return new PublicKey($point=new Point(Binary::intFromHex($x), Binary::intFromHex($y)), $curve=$curve);
+    }
 }

tests/test.php

@@ -24,6 +24,7 @@ public function run() {
 }
 
 include_once("testPublicKey.php");
+include_once("testCompPubKey.php");
 include_once("testEcdsa.php");
 include_once("testPrivateKey.php");
 include_once("testSignature.php");

tests/testCompPubKey.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace EllipticCurve\Test;
+
+use EllipticCurve\PublicKey;
+use EllipticCurve\Test\TestCase;
+
+
+echo "\n\nRunning Compressed Public Key Test tests:";
+\Test\printHeader("Compressed Public Key Test");
+
+
+class TestCompPubKey extends TestCase
+{
+    public function testBatch()
+    {
+        for ($i = 1; $i <= 1000; $i++) {
+            $privateKey = new \EllipticCurve\PrivateKey();
+            $publicKey = $privateKey->publicKey();
+            $publicKeyString = $publicKey->toCompressed();
+            $recoveredPublicKey = \EllipticCurve\PublicKey::fromCompressed($publicKeyString, $publicKey->curve);
+            \Test\assertEqual($publicKey->point->x, $recoveredPublicKey->point->x);
+            \Test\assertEqual($publicKey->point->y, $recoveredPublicKey->point->y);
+        }
+        
+    }
+
+    public function testFromCompressedEven()
+    {
+        $publicKeyCompressed = "0252972572d465d016d4c501887b8df303eee3ed602c056b1eb09260dfa0da0ab2";
+        $publicKey1 = \EllipticCurve\PublicKey::fromCompressed($publicKeyCompressed);
+        $publicKey2 = \EllipticCurve\PublicKey::fromPem("\n-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEUpclctRl0BbUxQGIe43zA+7j7WAsBWse\nsJJg36DaCrKIdC9NyX2e22/ZRrq8AC/fsG8myvEXuUBe15J1dj/bHA==\n-----END PUBLIC KEY-----\n");
+        \Test\assertEqual($publicKey1->toPem(), $publicKey2->toPem());
+    }
+
+    public function testFromCompressedOdd()
+    {
+        $publicKeyCompressed = "0318ed2e1ec629e2d3dae7be1103d4f911c24e0c80e70038f5eb5548245c475f50";
+        $publicKey1 = \EllipticCurve\PublicKey::fromCompressed($publicKeyCompressed);
+        $publicKey2 = \EllipticCurve\PublicKey::fromPem("\n-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEGO0uHsYp4tPa574RA9T5EcJODIDnADj1\n61VIJFxHX1BMIg0B4cpBnLG6SzOTthXpndIKpr8HEHj3D9lJAI50EQ==\n-----END PUBLIC KEY-----\n");
+        \Test\assertEqual($publicKey1->toPem(), $publicKey2->toPem());      
+    }
+
+    public function testToCompressedEven()
+    {
+        $publicKey = \EllipticCurve\PublicKey::fromPem("-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEUpclctRl0BbUxQGIe43zA+7j7WAsBWse\nsJJg36DaCrKIdC9NyX2e22/ZRrq8AC/fsG8myvEXuUBe15J1dj/bHA==\n-----END PUBLIC KEY-----");
+        $publicKeyCompressed = $publicKey->toCompressed();
+        \Test\assertEqual($publicKeyCompressed, "0252972572d465d016d4c501887b8df303eee3ed602c056b1eb09260dfa0da0ab2");
+        
+    }
+
+    public function testToCompressedOdd()
+    {
+        $publicKey = \EllipticCurve\PublicKey::fromPem("-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEGO0uHsYp4tPa574RA9T5EcJODIDnADj1\n61VIJFxHX1BMIg0B4cpBnLG6SzOTthXpndIKpr8HEHj3D9lJAI50EQ==\n-----END PUBLIC KEY-----");
+        $publicKeyCompressed = $publicKey->toCompressed();
+        \Test\assertEqual($publicKeyCompressed, "0318ed2e1ec629e2d3dae7be1103d4f911c24e0c80e70038f5eb5548245c475f50");     
+    }
+}
+
+
+$tests = new TestCompPubKey();
+$tests->run();