From f04a29dfef2dff3859c1f30197d57abaa899689a Mon Sep 17 00:00:00 2001
From: Michael Drury <me@michaeldrury.co.uk>
Date: Mon, 14 Feb 2022 21:37:40 +0000
Subject: [PATCH] Using 10K iteration string stretching for encryption.

---
 .../src/middleware/authenticated.js           |  5 ++--
 .../backend-core/src/security/encryption.js   | 26 ++++++++++++-------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/packages/backend-core/src/middleware/authenticated.js b/packages/backend-core/src/middleware/authenticated.js
index 0cb56b5b69..1e920739c4 100644
--- a/packages/backend-core/src/middleware/authenticated.js
+++ b/packages/backend-core/src/middleware/authenticated.js
@@ -23,9 +23,10 @@ async function checkApiKey(apiKey, populateUser) {
   if (apiKey === env.INTERNAL_API_KEY) {
     return { valid: true }
   }
-  apiKey = decrypt(apiKey)
-  const tenantId = apiKey.split(SEPARATOR)[0]
+  const decrypted = decrypt(apiKey)
+  const tenantId = decrypted.split(SEPARATOR)[0]
   const db = getGlobalDB(tenantId)
+  // api key is encrypted in the database
   const userId = await queryGlobalView(
     ViewNames.BY_API_KEY,
     {
diff --git a/packages/backend-core/src/security/encryption.js b/packages/backend-core/src/security/encryption.js
index 8bb7def541..c31f597652 100644
--- a/packages/backend-core/src/security/encryption.js
+++ b/packages/backend-core/src/security/encryption.js
@@ -3,24 +3,30 @@ const env = require("../environment")
 
 const ALGO = "aes-256-ctr"
 const SECRET = env.JWT_SECRET
-const SEPARATOR = "/"
+const SEPARATOR = "-"
+const ITERATIONS = 10000
+const RANDOM_BYTES = 16
+const STRETCH_LENGTH = 32
+
+function stretchString(string, salt) {
+  return crypto.pbkdf2Sync(string, salt, ITERATIONS, STRETCH_LENGTH, "sha512")
+}
 
 exports.encrypt = input => {
-  const random = crypto.randomBytes(16)
-  const cipher = crypto.createCipheriv(ALGO, SECRET, random)
+  const salt = crypto.randomBytes(RANDOM_BYTES)
+  const stretched = stretchString(SECRET, salt)
+  const cipher = crypto.createCipheriv(ALGO, stretched, salt)
   const base = cipher.update(input)
   const final = cipher.final()
   const encrypted = Buffer.concat([base, final]).toString("hex")
-  return `${random.toString("hex")}${SEPARATOR}${encrypted}`
+  return `${salt.toString("hex")}${SEPARATOR}${encrypted}`
 }
 
 exports.decrypt = input => {
-  const [random, encrypted] = input.split(SEPARATOR)
-  const decipher = crypto.createDecipheriv(
-    ALGO,
-    SECRET,
-    Buffer.from(random, "hex")
-  )
+  const [salt, encrypted] = input.split(SEPARATOR)
+  const saltBuffer = Buffer.from(salt, "hex")
+  const stretched = stretchString(SECRET, saltBuffer)
+  const decipher = crypto.createDecipheriv(ALGO, stretched, saltBuffer)
   const base = decipher.update(Buffer.from(encrypted, "hex"))
   const final = decipher.final()
   return Buffer.concat([base, final]).toString()