Common: derive Hash.otp secrets from the app key

packages/common/src/utils/hash.ts

@@ -1,7 +1,8 @@
 import { Secret, TOTP } from 'otpauth'
+import { appKey, env } from '../system'
 import { compare, genSalt, hash } from 'bcryptjs'
 
-import { env } from '../system'
+import { createHmac } from 'node:crypto'
 
 export class Hash {
   /**
@@ -42,10 +43,26 @@ export class Hash {
       issuer: env('APP_NAME', 'Roseed'),
       algorithm: 'SHA1',
       period, // in seconds.
-      secret: 'US3WHSG7X5KAPV27VANWKQHF3SH3HULL',
+      secret: Hash.otpSecret(label),
     })
   }
 
+  /**
+   * The OTP secret for a label, derived from the application key so codes
+   * differ per label and cannot be computed without the key.
+   *
+   * @param label
+   * @returns
+   */
+  private static otpSecret(label: string): Secret {
+    const key = appKey()
+    if (!key) throw new Error('APP_KEY is required to generate one-time passwords. Run `ark key:generate`.')
+
+    const digest = createHmac('sha256', key).update(`otp:${label}`).digest()
+
+    return new Secret({ buffer: new Uint8Array(digest).buffer })
+  }
+
   static totp(secret: string, label: string, issuer: string = env('APP_NAME', 'Roseed'), period: number = 30) {
     return new TOTP({
       issuer,

packages/common/tests/hash.test.ts

@@ -0,0 +1,47 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
+
+import { Hash } from '../src'
+import { randomBytes } from 'node:crypto'
+
+describe('Hash.otp', () => {
+  let previous: string | undefined
+
+  beforeEach(() => {
+    previous = process.env.APP_KEY
+    process.env.APP_KEY = randomBytes(32).toString('base64url')
+  })
+
+  afterEach(() => {
+    if (previous === undefined) {
+      delete process.env.APP_KEY
+    } else {
+      process.env.APP_KEY = previous
+    }
+  })
+
+  it('validates a code for the label it was generated for', () => {
+    const token = Hash.otp(6, 'alice@example.com:reset', 900).generate()
+
+    expect(Hash.otp(6, 'alice@example.com:reset', 900).validate({ token })).not.toBeNull()
+  })
+
+  it('gives each label its own secret', () => {
+    const alice = Hash.otp(6, 'alice@example.com:reset', 900)
+    const bob = Hash.otp(6, 'bob@example.com:reset', 900)
+
+    expect(alice.secret.base32).not.toBe(bob.secret.base32)
+    expect(bob.validate({ token: alice.generate() })).toBeNull()
+  })
+
+  it('derives the secret from the application key', () => {
+    const before = Hash.otp(6, 'alice@example.com:reset', 900).secret.base32
+
+    process.env.APP_KEY = randomBytes(32).toString('base64url')
+
+    expect(Hash.otp(6, 'alice@example.com:reset', 900).secret.base32).not.toBe(before)
+  })
+
+  it('no longer uses the fixed secret', () => {
+    expect(Hash.otp().secret.base32).not.toBe('US3WHSG7X5KAPV27VANWKQHF3SH3HULL')
+  })
+})