feat: timingSafeStringEqual

Author: kirillgroshkov

src/security/crypto.util.test.ts

@@ -6,6 +6,7 @@ import {
   encryptObject,
   encryptRandomIVBuffer,
   encryptString,
+  timingSafeStringEqual,
 } from './crypto.util'
 
 const encKeyBuffer = Buffer.from(TEST_ENC_KEY, 'base64')
@@ -68,3 +69,15 @@ test('encryptObject, decryptObject', () => {
   // Should be deterministic:
   expect(encryptObject(obj1, encKeyBuffer)).toEqual(enc)
 })
+
+test('timingSafeStringEquals', () => {
+  const pw = 'hello!@#123'
+
+  expect(timingSafeStringEqual(undefined, pw)).toBe(false)
+  expect(timingSafeStringEqual('', pw)).toBe(false)
+  expect(timingSafeStringEqual('', '')).toBe(true)
+  expect(timingSafeStringEqual('abc', 'abc')).toBe(true)
+  expect(timingSafeStringEqual('abc', 'abd')).toBe(false)
+  expect(timingSafeStringEqual(pw, pw)).toBe(true)
+  expect(timingSafeStringEqual(pw, undefined)).toBe(false)
+})

src/security/crypto.util.ts

@@ -93,3 +93,20 @@ function getCryptoParams(secretKeyBuffer: Buffer): { key: Buffer; iv: Buffer } {
   const iv = md5AsBuffer(Buffer.concat([secretKeyBuffer, key]))
   return { key, iv }
 }
+
+/**
+ * Wraps `crypto.timingSafeEqual` and allows it to be used with String inputs:
+ *
+ * 1. Does length check first and short-circuits on length mismatch. Because `crypto.timingSafeEqual` only works with same-length inputs.
+ *
+ * Relevant read:
+ * https://medium.com/nerd-for-tech/checking-api-key-without-shooting-yourself-in-the-foot-javascript-nodejs-f271e47bb428
+ * https://codahale.com/a-lesson-in-timing-attacks/
+ * https://github.com/suryagh/tsscmp/blob/master/lib/index.js
+ *
+ * Returns true if inputs are equal, false otherwise.
+ */
+export function timingSafeStringEqual(s1: string | undefined, s2: string | undefined): boolean {
+  if (s1 === undefined || s2 === undefined || s1.length !== s2.length) return false
+  return crypto.timingSafeEqual(Buffer.from(s1), Buffer.from(s2))
+}