Add support for encrypted second password hashes

src/function/dh/decrypt.ts

@@ -0,0 +1,125 @@
+/*
+ * server component for the TimeLimit App
+ * Copyright (C) 2019 - 2022 Jonas Lochmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import * as Sequelize from 'sequelize'
+import { createDecipheriv, createPrivateKey, createPublicKey, diffieHellman } from 'crypto'
+import { Database } from '../../database'
+import { calculateExpireTime } from '../../database/devicedhkey'
+import { isVersionId } from '../../util/token'
+
+export async function decrypt({
+  database, transaction, familyId, deviceId, encryptedData, authData
+}: {
+  database: Database
+  transaction: Sequelize.Transaction
+  familyId: string
+  deviceId: string
+  encryptedData: string
+  authData: Buffer
+}) {
+  const parts = encryptedData.split('.')
+
+  if (parts.length !== 3) throw new MalformedDataDecryptException('expected three parts')
+
+  const ivAndEncrypted = Buffer.from(parts[0], 'base64')
+  const otherPublicKey = Buffer.from(parts[1], 'base64')
+  const keyId = parts[2]
+
+  if (ivAndEncrypted.length < 12 + 16) throw new MalformedDataDecryptException('too short for iv and auth tag')
+
+  if (!isVersionId(keyId)) throw new KeyNotFoundDecryptException('invalid key id')
+
+  const databaseKeyEntry = await database.deviceDhKey.findOne({
+    where: {
+      familyId,
+      deviceId,
+      version: keyId
+    },
+    transaction
+  })
+
+  if (!databaseKeyEntry) throw new KeyNotFoundDecryptException('private key not found')
+
+  if (databaseKeyEntry.expireAt === null) {
+    databaseKeyEntry.expireAt = calculateExpireTime(BigInt(Date.now())).toString(10)
+    await databaseKeyEntry.save({ transaction })
+  } else {
+    if (BigInt(databaseKeyEntry.expireAt) < BigInt(Date.now())) throw new KeyExpiredDecryptException()
+  }
+
+  const privateKey = (() => {
+    try {
+      return createPrivateKey({
+        key: databaseKeyEntry.privateKey,
+        format: 'der',
+        type: 'pkcs8'
+      })
+    } catch (ex) {
+      throw new MalformedPrivateKeyException()
+    }
+  })()
+
+  const decodedOtherPublicKey = (() => {
+    try {
+      return createPublicKey({
+        key: otherPublicKey,
+        format: 'der',
+        type: 'spki'
+      })
+    } catch (ex) {
+      throw new MalformedPublicKeyException()
+    }
+  })()
+
+  const sharedSecret = (() => {
+    try {
+      return diffieHellman({
+        privateKey,
+        publicKey: decodedOtherPublicKey
+      })
+    } catch (ex) {
+      throw new MalformedNoMatchingKeysException()
+    }
+  })()
+
+  try {
+    const decipher = createDecipheriv('aes-128-gcm', sharedSecret.slice(0, 16), ivAndEncrypted.slice(0, 12), {
+      authTagLength: 16
+    })
+
+    decipher.setAuthTag(ivAndEncrypted.slice(ivAndEncrypted.length - 16, ivAndEncrypted.length))
+    decipher.setAAD(authData)
+
+    const decryptedData = Buffer.concat([
+      decipher.update(ivAndEncrypted.slice(12, ivAndEncrypted.length - 16)),
+      decipher.final()
+    ])
+
+    return decryptedData
+  } catch (ex) {
+    throw new MalformedAuthenticationException()
+  }
+}
+
+export class DecryptException extends Error {}
+class MalformedDataDecryptException extends DecryptException { constructor(message: string) { super('malformed data: ' + message) } }
+class MalformedPrivateKeyException extends DecryptException { constructor() { super('private key') } }
+class MalformedPublicKeyException extends DecryptException { constructor() { super('public key') } }
+class MalformedNoMatchingKeysException extends DecryptException { constructor() { super('no matching keys') } }
+class MalformedAuthenticationException extends DecryptException { constructor() { super('authentication data') } }
+class KeyExpiredDecryptException extends DecryptException { constructor() { super('key expired') } }
+class KeyNotFoundDecryptException extends DecryptException { constructor(message: string) { super('key not found: ' + message) } }