Derive deterministic app passwords (#110)

logic/apps.js

@@ -1,5 +1,6 @@
 const diskLogic = require('logic/disk.js');
 const NodeError = require('models/errors.js').NodeError;
+const deriveEntropy = require('modules/derive-entropy');
 
 async function get(query) {
   let apps = await diskLogic.readAppRegistry();
@@ -13,6 +14,15 @@ async function get(query) {
     }
   }));
 
+  // Derive all passwords concurrently
+  await Promise.all(apps.filter(app => app.deterministicPassword).map(async app => {
+    try {
+      app.defaultPassword = await deriveEntropy(`app-${app.id}-seed-APP_PASSWORD`);
+    } catch(e) {
+      app.defaultPassword = '';
+    }
+  }));
+
   if (query.installed === true) {
     const {installedApps} = await diskLogic.readUserFile();
     apps = apps.filter(app => installedApps.includes(app.id));

modules/derive-entropy.js

@@ -0,0 +1,16 @@
+const {promisify} = require('util');
+const readFile = promisify(require('fs').readFile);
+const crypto = require('crypto');
+
+const constants = require('utils/const.js');
+
+const deriveEntropy = async indentifier => {
+  const umbrel_seed = await readFile(constants.UMBREL_SEED_FILE);
+
+  return crypto
+    .createHmac('sha256', umbrel_seed)
+    .update(indentifier)
+    .digest('hex');
+};
+
+module.exports = deriveEntropy;