ecdsa-methods

ellipticcurve/curve.js

@@ -7,6 +7,7 @@
 const BigInt = require("big-integer");
 const Point = require("./point").Point;
 const modulo = require("./utils/integer").modulo;
+const EcdsaMath = require("./math");
 
 
 class CurveFp {
@@ -41,6 +42,18 @@ class CurveFp {
     get oid() {
         return this._oid.slice();
     }
+
+    y(x, isEven) 
+    {
+        let ySquared = (((x.value ** BigInt(3).value) % this.P.value) + this.A.value * x.value + this.B.value) % this.P.value
+        let y = EcdsaMath.modularSquareRoot(ySquared, this.P.value)
+        if (isEven != ((y % BigInt(2).value).toString() == "0"))
+        {
+            y = this.P.value - y;
+        }
+        return BigInt(y)
+    }
+
 };
 
 

ellipticcurve/math.js

@@ -2,6 +2,20 @@ const Point = require("./point").Point;
 const modulo = require("./utils/integer").modulo;
 const BigInt = require("big-integer");
 
+var modularSquareRoot = function(value, prime){
+
+    let base = value
+    let exp = (prime + BigInt(1).value) / BigInt(4).value
+    let p = prime
+
+    var result = 1n;
+    while (exp !== 0n) {
+        if (exp % 2n === 1n) result = result * base % p;
+        base = base * base % p;
+        exp >>= 1n;
+    }
+    return result;
+}
 
 var multiply = function (p, n, N, A, P) {
     // Fast way to multily point and scalar in elliptic curves
@@ -184,7 +198,7 @@ var jacobianMultiply = function (p, n, N, A, P) {
     throw new Error("logical failure: p: " + p + ", n: " + n + ", N: " + N + ", A: " + A + ", P: " + P);
 };
 
-
+exports.modularSquareRoot = modularSquareRoot;
 exports.multiply = multiply;
 exports.add = add;
 exports.inv = inv;

ellipticcurve/publicKey.js

@@ -3,6 +3,7 @@ const EcdsaCurve = require("./curve");
 const Point = require("./point").Point;
 const der = require("./utils/der");
 const Math = require("./math");
+const { PrivateKey } = require("..");
 
 
 class PublicKey {
@@ -21,6 +22,19 @@ class PublicKey {
         return xString + yString;
     };
 
+    toCompressed(encoded=false) {
+        let baseLen = this.curve.length();
+
+        if ((this.point.y["value"] % BigInt("2")).toString() == "0")
+        {
+            var parityTag = "02";
+        } else {
+            var parityTag = "03";
+        }
+        let xString = BinaryAscii.hexFromBinary(BinaryAscii.stringFromNumber(this.point.x, baseLen))
+        return parityTag + xString
+    }
+
     toDer () {
         let encodeEcAndOid = der.encodeSequence(der.encodeOid([1, 2, 840, 10045, 2, 1]), der.encodeOid(this.curve.oid));
 
@@ -102,6 +116,21 @@ class PublicKey {
         }
         return publicKey
     };
+
+    static fromCompressed(string, curve=EcdsaCurve.secp256k1)
+    {
+        let parityTag = string.slice(0, 2);
+        let xString = string.slice(2, string.length);
+
+        if (!["02", "03"].includes(parityTag)) 
+        {
+            throw new Error("Compressed string should start with 02 or 03");
+        }
+        let isEven = parityTag == "02"
+        let x = BinaryAscii.numberFromHex(xString)
+        let y = curve.y(x, isEven=isEven)
+        return new PublicKey(new Point(x, y), curve)
+    };
 };
 
 

test/test.js

@@ -137,6 +137,58 @@ describe("PublicKey test", function() {
         });
     });
 });
+
+describe("ComPubKeyTest", function() {
+    describe("#testBatch()", function() {
+        it("should validate publicKey x and y points", function() {
+            this.timeout(10000);
+            for (let i = 0; i < 1000; i++) {
+                let privateKey = new PrivateKey()
+                let publicKey = privateKey.publicKey()
+                let publicKeyString = publicKey.toCompressed()
+                let recoveredPublicKey = PublicKey.fromCompressed(publicKeyString, publicKey.curve)
+
+                assert.equal(publicKey.point.x.value, recoveredPublicKey.point.x.value)
+                assert.equal(publicKey.point.y.value, recoveredPublicKey.point.y.value)
+            }
+        });
+    });
+    describe("#testFromCompressedEven()", function() {
+        it("should validate publicKey from Even compressed", function() {
+            let publicKeyCompressed = "0252972572d465d016d4c501887b8df303eee3ed602c056b1eb09260dfa0da0ab2"
+            let publicKey = PublicKey.fromCompressed(publicKeyCompressed)
+            let publicKey2 = PublicKey.fromPem("\n-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEUpclctRl0BbUxQGIe43zA+7j7WAsBWse\nsJJg36DaCrKIdC9NyX2e22/ZRrq8AC/fsG8myvEXuUBe15J1dj/bHA==\n-----END PUBLIC KEY-----\n")
+
+            assert.equal(publicKey.toPem(), publicKey2.toPem());
+        });
+    });
+    describe("#testFromCompressedOdd()", function() {
+        it("should validate publicKey from Odd compressed", function() {
+            let publicKeyCompressed = "0318ed2e1ec629e2d3dae7be1103d4f911c24e0c80e70038f5eb5548245c475f50"
+            let publicKey = PublicKey.fromCompressed(publicKeyCompressed)
+            let publicKey2 = PublicKey.fromPem("\n-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEGO0uHsYp4tPa574RA9T5EcJODIDnADj1\n61VIJFxHX1BMIg0B4cpBnLG6SzOTthXpndIKpr8HEHj3D9lJAI50EQ==\n-----END PUBLIC KEY-----\n")
+
+            assert.equal(publicKey.toPem(), publicKey2.toPem());
+        });
+    });
+    describe("#testToCompressedEven()", function() {
+        it("should validate publicKey to Even compressed", function() {
+            let publicKey = PublicKey.fromPem("\n-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEUpclctRl0BbUxQGIe43zA+7j7WAsBWse\nsJJg36DaCrKIdC9NyX2e22/ZRrq8AC/fsG8myvEXuUBe15J1dj/bHA==\n-----END PUBLIC KEY-----\n")
+            let publicKeyCompressed = publicKey.toCompressed()
+
+            assert.equal(publicKeyCompressed, "0252972572d465d016d4c501887b8df303eee3ed602c056b1eb09260dfa0da0ab2");
+        });
+    });
+    describe("#testToCompressedOdd()", function() {
+        it("should validate publicKey to Odd compressed", function() {
+            let publicKey = PublicKey.fromPem("-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEGO0uHsYp4tPa574RA9T5EcJODIDnADj1\n61VIJFxHX1BMIg0B4cpBnLG6SzOTthXpndIKpr8HEHj3D9lJAI50EQ==\n-----END PUBLIC KEY-----")
+            let publicKeyCompressed = publicKey.toCompressed()
+
+            assert.equal(publicKeyCompressed, "0318ed2e1ec629e2d3dae7be1103d4f911c24e0c80e70038f5eb5548245c475f50");
+        });
+    });
+});
+
 describe("Signature test", function() {
     describe("#testDerConversion()", function() {
         it("should validate DER signature generation and convertion", function() {