allowing randomized derivation paths for user-provided keys

Reviewers: andrew, robert

Reviewed By: robert

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D6073

Author: Arik Sosman

package.json

@@ -1,6 +1,6 @@
 {
   "name": "bitgo",
-  "version": "3.4.9",
+  "version": "3.4.10",
   "description": "BitGo Javascript SDK",
   "main": "./src/index.js",
   "keywords": [

src/v2/baseCoin.js

@@ -105,6 +105,21 @@ BaseCoin.prototype.toJSON = function() {
   return undefined;
 };
 
+BaseCoin.prototype.deriveKeyWithSeed = function({ key, seed }) {
+  const derivationPathInput = bitcoin.crypto.hash256(`${seed}`).toString('hex');
+  const derivationPathParts = [
+    parseInt(derivationPathInput.slice(0, 7), 16),
+    parseInt(derivationPathInput.slice(7, 14), 16)
+  ];
+  const derivationPath = 'm/999999/' + derivationPathParts.join('/');
+  const keyNode = bitcoin.HDNode.fromBase58(key);
+  const derivedKeyNode = bitcoin.hdPath(keyNode).derive(derivationPath);
+  return {
+    key: derivedKeyNode.toBase58(),
+    derivationPath: derivationPath
+  };
+};
+
 BaseCoin.prototype.initiateRecovery = function(params) {
   const keys = [];
   const userKey = params.userKey; // Box A

src/v2/wallet.js

@@ -522,9 +522,14 @@ Wallet.prototype.signTransaction = function(params, callback) {
   if (!txPrebuild || typeof txPrebuild !== 'object') {
     throw new Error('txPrebuild must be an object');
   }
-  var userPrv = params.prv;
+  let userPrv = params.prv;
   if (userPrv && typeof userPrv !== 'string') {
     throw new Error('prv must be a string');
+  }
+  if (userPrv && params.coldDerivationSeed) {
+    // the derivation only makes sense when a key already exists
+    const derivation = this.baseCoin.deriveKeyWithSeed({ key: userPrv, seed: params.coldDerivationSeed });
+    userPrv = derivation.key;
   } else if (!userPrv) {
     if (!userKeychain || typeof userKeychain !== 'object') {
       throw new Error('keychain must be an object');

src/v2/wallets.js

@@ -183,6 +183,7 @@ Wallets.prototype.generateWallet = function(params, callback) {
   let backupKeychain;
   let bitgoKeychain;
   let userKeychainParams;
+  let derivationPath;
 
   const passphrase = params.passphrase;
   const canEncrypt = (!!passphrase && typeof passphrase === 'string');
@@ -195,6 +196,12 @@ Wallets.prototype.generateWallet = function(params, callback) {
     if (params.userKey) {
       userKeychain = { 'pub': params.userKey };
       userKeychainParams = userKeychain;
+      if (params.coldDerivationSeed) {
+        // the derivation only makes sense when a key already exists
+        const derivation = self.baseCoin.deriveKeyWithSeed({ key: params.userKey, seed: params.coldDerivationSeed });
+        derivationPath = derivation.derivationPath;
+        userKeychain.pub = derivation.key;
+      }
     } else {
       if (!canEncrypt) {
         throw new Error('cannot generate user keypair without passphrase');
@@ -296,6 +303,10 @@ Wallets.prototype.generateWallet = function(params, callback) {
       result.warning = 'Be sure to backup the backup keychain -- it is not stored anywhere else!';
     }
 
+    if (derivationPath) {
+      userKeychain.derivationPath = derivationPath;
+    }
+
     return result;
   })
   .nodeify(callback);

test/v2/wallets.js

@@ -171,6 +171,30 @@ describe('V2 Wallets:', function() {
       });
     });
 
+    it('should make wallet with provided user key and custom derivation path', function() {
+      var userXpub = keychains.create().pub; // random xpub
+      var params = {
+        label: label,
+        userKey: userXpub,
+        coldDerivationSeed: 'custom-derivation-seed',
+        passphrase: passphrase
+      };
+
+      return wallets.generateWallet(params)
+      .then(function(res) {
+        res.should.have.property('wallet');
+        res.should.have.property('userKeychain');
+        res.should.have.property('backupKeychain');
+        res.should.have.property('bitgoKeychain');
+
+        res.userKeychain.should.have.property('pub');
+        res.userKeychain.should.have.property('derivationPath');
+        res.userKeychain.derivationPath.should.equal('m/999999/112305623/88990619');
+        res.userKeychain.should.not.have.property('prv');
+        res.userKeychain.should.not.have.property('encryptedPrv');
+      });
+    });
+
     it('should generate wallet and freeze it', function() {
       var backupXpub = keychains.create().pub; // random xpub
       var userXpub = keychains.create().pub; // random xpub