feat: new APIs (getPrivateKeyFromEthSignature, privateToStarkKey) (#3)

CHANGELOG.md

@@ -4,7 +4,6 @@ All notable changes to this project will be documented in this file. See [standa
 
 ### 0.0.1 (2022-03-08)
 
-
 ### Features
 
-* init project ([9759ffa](https://github.com/starkware-libs/starkware-crypto-utils/commit/9759ffac52538345524c90a784e653c95d8899f5))
+- init project ([9759ffa](https://github.com/starkware-libs/starkware-crypto-utils/commit/9759ffac52538345524c90a784e653c95d8899f5))

README.md

@@ -59,6 +59,8 @@ const starkwareCrypto = require('@starkware-industries/starkware-crypto-utils');
 
     keyDerivation: {
       StarkExEc: ec.n, // Data.
+      getPrivateKeyFromEthSignature,
+      privateToStarkKey, 
       getKeyPairFromPath,
       getAccountPath,
       grindKey // Function.

package.json

@@ -57,10 +57,10 @@
   },
   "devDependencies": {
     "chai": "^4.3.6",
-    "eslint": "^8.8.0",
+    "eslint": "^8.11.0",
     "eslint-config-prettier": "^8.3.0",
     "eslint-plugin-prettier": "^4.0.0",
-    "mocha": "^8.4.0",
+    "mocha": "^9.2.2",
     "prettier": "^2.5.1",
     "standard-version": "^9.3.2"
   }

src/config/keys_precomputed.json

@@ -27,5 +27,6 @@
   "0x4615f94598cd756ad1a551d7e57fd725916adfd0054eb773ceb482eef87d0b2": "0x1ee5b8d612102a2408cde59ce52a6498d2e38fe8789bb26d400dea310684ec9",
   "0x6ade54b7debd7ca1d4e8e932f9545f8fa4024d73be1efcc86df86367fc333f8": "0x37de3bf52412b2fb9b0030d232ca9dd921cd8f71fd67975cdc62546826e121",
   "0x618e7467dd24c2a3449c4df640439c12cdd0f8ea779afcee6e252b2cf494354": "0x71c2b578c432f2d305d3808bb645ecc46dd670cb43d4f4a076f75ccbff74fbc",
-  "0x7eae185e1f41ec76d214d763f0592f194933622a9dd5f3d52d0209f71619c1a": "0x2b0160052e70176e5b0ff2a6eff90896ae07b732fc27219e36e077735abd57e"
+  "0x7eae185e1f41ec76d214d763f0592f194933622a9dd5f3d52d0209f71619c1a": "0x2b0160052e70176e5b0ff2a6eff90896ae07b732fc27219e36e077735abd57e",
+  "0x178047D3869489C055D7EA54C014FFB834A069C9595186ABE04EA4D1223A03F": "0x1895a6a77ae14e7987b9cb51329a5adfb17bd8e7c638f92d6892d76e51cebcf"
 }

src/js/key_derivation.js

@@ -20,6 +20,10 @@ const encUtils = require('enc-utils');
 const BN = require('bn.js');
 const hash = require('hash.js');
 const {ec} = require('./signature.js');
+const assert = require('assert');
+
+const ETH_SIGNATURE_LENGTH = 130;
+const STARK_PRIVATE_KEY_LENGTH = 63;
 
 /*
  Returns an integer from a given section of bits out of a hex string.
@@ -34,6 +38,38 @@ function getIntFromBits(hex, start, end = undefined) {
   return int;
 }
 
+/*
+ Returns true if the given string is a hex string of length hexLength, and false otherwise.
+*/
+function isHexOfLength(hex, hexLength) {
+  const regex = new RegExp('^[0-9a-fA-F]{' + hexLength + '}$');
+  return regex.test(hex);
+}
+
+/*
+ Returns a private stark key based on a given Eth signature.
+ The given signature should be a 130 character hex string produced by the user signing a
+ predetermined message in order to guarantee getting the same private key each time it is invoked.
+*/
+function getPrivateKeyFromEthSignature(ethSignature) {
+  const ethSignatureFixed = ethSignature.replace(/^0x/, '');
+  assert(isHexOfLength(ethSignatureFixed, ETH_SIGNATURE_LENGTH));
+  const r = ethSignatureFixed.substring(0, 64);
+  return grindKey(r, ec.n);
+}
+
+/*
+ Returns a public stark key given the private key.
+ The private key should be a random hex string of length up to 63 characters.
+*/
+function privateToStarkKey(privateKey) {
+  const privateKeyFixed = privateKey.replace(/^0x/, '');
+  assert(privateKeyFixed.length <= STARK_PRIVATE_KEY_LENGTH);
+  assert(isHexOfLength(privateKeyFixed, privateKeyFixed.length));
+  const keyPair = ec.keyFromPrivate(privateKeyFixed, 'hex');
+  return keyPair.getPublic().getX().toJSON();
+}
+
 /*
  Derives key-pair from given mnemonic string and path.
  mnemonic should be a sentence comprised of 12 words with single spaces between them.
@@ -117,7 +153,10 @@ function hashKeyWithIndex(key, index) {
 
 module.exports = {
   StarkExEc: ec.n, // Data.
+  getPrivateKeyFromEthSignature,
+  privateToStarkKey,
   getKeyPairFromPath,
   getAccountPath,
-  grindKey // Function.
+  grindKey
+  // Function.
 };

test/js/key_derivation.spec.js

@@ -3,8 +3,11 @@ const {
   StarkExEc,
   getKeyPairFromPath,
   getAccountPath,
+  privateToStarkKey,
+  getPrivateKeyFromEthSignature,
   grindKey
 } = require(`${SRC_DIR_PATH}/key_derivation`);
+const precomputedKeys = require(`${CONFIG_DIR_PATH}/keys_precomputed.json`);
 
 const layer = 'starkex';
 const application = 'starkdeployement';
@@ -48,3 +51,23 @@ describe('Key grinding', () => {
     );
   });
 });
+
+describe('Private to stark key', () => {
+  it('should derive public stark key from private correctly', () => {
+    Object.entries(precomputedKeys).forEach(([privKey, expectedPubKey]) => {
+      const pubKey = '0x' + privateToStarkKey(privKey);
+      expect(pubKey).to.equal(expectedPubKey);
+    });
+  });
+});
+
+describe('Private stark key from eth signature', () => {
+  it('should derive private stark key from eth signature correctly', () => {
+    const ethSignature =
+      '0x21fbf0696d5e0aa2ef41a2b4ffb623bcaf070461d61cf7251c74161f82fec3a43' +
+      '70854bc0a34b3ab487c1bc021cd318c734c51ae29374f2beb0e6f2dd49b4bf41c';
+    expect(getPrivateKeyFromEthSignature(ethSignature)).to.equal(
+      '766f11e90cd7c7b43085b56da35c781f8c067ac0d578eabdceebc4886435bda'
+    );
+  });
+});

test/js/signature.spec.js

@@ -1,6 +1,5 @@
 /* eslint-disable no-unused-expressions */
 const starkwareCrypto = require(`${SRC_DIR_PATH}/signature.js`);
-const precomputedKeys = require(`${CONFIG_DIR_PATH}/keys_precomputed.json`);
 const rfc6979TestData = require('../config/rfc6979_signature_test_vector.json');
 const testData = require('../config/signature_test_data.json');
 const BN = require('bn.js');
@@ -23,21 +22,6 @@ function randomString(characters, length) {
   return result;
 }
 
-describe('Key computation', () => {
-  it('should derive public key correctly', () => {
-    for (const privKey in precomputedKeys) {
-      if ({}.hasOwnProperty.call(precomputedKeys, privKey)) {
-        // Drop the '0x' prefix.
-        const fixedPrivKey = privKey.substring(2);
-        const keyPair = starkwareCrypto.ec.keyFromPrivate(fixedPrivKey, 'hex');
-        const pubKey = '0x' + keyPair.getPublic().getX().toString('hex');
-        const expectedPubKey = precomputedKeys[privKey];
-        expect(expectedPubKey).to.equal(pubKey);
-      }
-    }
-  });
-});
-
 describe('Verify', () => {
   // Generate BN of 1.
   const oneBn = new BN('1', 16);