From 3d3d3c0c8d62aa3148e14d3003ebcd1c8f954394 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B8r=E2=88=82=C2=A1?= <itsbrickpop@gmail.com>
Date: Thu, 4 Feb 2021 18:32:19 +0100
Subject: [PATCH] Allowing to decode points from the curve

---
 src/index.ts       | 13 +++++++++++--
 test/index.test.ts | 27 +++++++++++++++++----------
 2 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 235a2f4..7439abc 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -15,6 +15,11 @@ export const ecParams = { G, n }
 export type UserSecretData = { a: BigNumber, b: BigNumber, f: Point }
 export type UnblindedSignature = { s: BigNumber, f: Point }
 
+export function messageToBigNumber(message: string) {
+    const msg = Buffer.from(message, 'utf8')
+    return new BigNumber(msg)
+}
+
 export function hashBigNumber(m: BigNumber) {
     const mHex = m.toString(16)
 
@@ -24,10 +29,14 @@ export function hashBigNumber(m: BigNumber) {
         return keccak256('0x0' + mHex).slice(2) // Trim 0x
 }
 
-export function bigNumberFromString(s: string) {
+export function stringToBigNumber(s: string) {
     return new BigNumber(s)
 }
 
+export function decodePoint(hexPoint: string): Point {
+    return secp256k1.keyFromPublic(Buffer.from(hexPoint, "hex")).getPublic()
+}
+
 function random(bytes: number) {
     let k: BigNumber
     do {
@@ -96,7 +105,7 @@ export function verify(m: BigNumber, s: UnblindedSignature, q: Point) {
     const sG = G.mul(s.s)
 
     const hHex = hashBigNumber(m)
-    
+
     const h = new BigNumber(Buffer.from(hHex, "hex"))
 
     const rx = s.f.getX().mod(n)
diff --git a/test/index.test.ts b/test/index.test.ts
index fd7c29b..df67dd5 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -1,7 +1,9 @@
 import * as assert from 'assert'
 
 import {
-	bigNumberFromString,
+	stringToBigNumber,
+	messageToBigNumber,
+	decodePoint,
 	ecParams,
 	newKeyPair,
 	newRequestParameters,
@@ -15,26 +17,31 @@ import {
 } from "../src/index"
 
 describe("keccak256", function () {
-	it("keccak256", async () => {
-		const msg = Buffer.from("test", 'utf8')
-		const m = new BigNumber(msg)
+	it("should hash strings and big numbers", async () => {
+		const m = messageToBigNumber("test")
+		assert.strictEqual('1952805748', m.toString())
+
 		const hHex = hashBigNumber(m)
 		assert.strictEqual(hHex, '9c22ff5f21f0b81b113e63f7db6da94fedef11b2119b4088b89664fb9a3cb658')
 		const h = new BigNumber(Buffer.from(hHex, "hex"))
 		assert.strictEqual(h.toString(), '70622639689279718371527342103894932928233838121221666359043189029713682937432')
 	})
+
+	it("should decode points in the secp256k1 curve", () => {
+		const tokenR = "7cfe4af054e13b4e7231d876d23205fb5f939ac8185271ca6b64c635a365faae259fb8cabdb06dde39d1ebeada3cb75cb9739621a79c61a8cf1e9a38abaf782a"
+		const point = decodePoint("04" + tokenR)
+		assert.strictEqual(point.getX().toString(16), tokenR.substr(0, 64))
+		assert.strictEqual(point.getY().toString(16), tokenR.substr(64))
+	})
 })
 
-describe("test blind", function () {
-	it("should blind", async () => {
+describe("blind signatures", function () {
+	it("should blind, unblind and verify", async () => {
 		const { sk, pk } = newKeyPair()
 
 		const { k, signerR } = newRequestParameters()
 
-		const msg = new BigNumber(
-			Buffer.from("test", 'utf8')
-		)
-		assert.strictEqual('1952805748', msg.toString())
+		const msg = messageToBigNumber("test")
 
 		const { mBlinded, userSecretData } = blind(msg, signerR)