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Network Working Group                                      S. Nandakumar
Internet-Draft                                               C. Jennings
Intended status: Standards Track                               S. Cooley
Expires: May 3, 2018                                               Cisco
                                                        October 30, 2017


        Solution Architecture - Secure Firmware Upgrade (SecFU)
              draft-nandakumar-suit-secfu-solution-arch-00

Abstract

   This specification defines a solution architecture for performing
   secure firmware upgrade for Internet of Things (IoT).  The ulterior
   motive is to have a framework that is simple, secure, and that uses
   most common formats and standards in the industry and that works over
   Internet.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Device Considerations . . . . . . . . . . . . . . . . . . . .   3
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Solution Components . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Manifest  . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  Manifest Format . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Manifest Security . . . . . . . . . . . . . . . . . . . .   6
     5.4.  Manifest Optional Extensions  . . . . . . . . . . . . . .   6
     5.5.  Firmware Server Discovery . . . . . . . . . . . . . . . .   6
     5.6.  Firmware Download protocol  . . . . . . . . . . . . . . .   7
       5.6.1.  Validation Procedures . . . . . . . . . . . . . . . .   7
       5.6.2.  Manifest Download . . . . . . . . . . . . . . . . . .   8
       5.6.3.  Firmware Download . . . . . . . . . . . . . . . . . .   8
   6.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Internet of Things (IOT) represents a plethora of devices that come
   in varying flavors of constrained sizes, computing power, and
   operating considerations.  These devices usually need minimal or no
   management for their operation.

   Vulnerabilities within IOT devices have raised serious concerns.
   There needs to be a way to install or update the firmware on these
   devices in an automated and secure fashion.  A common challenge with
   the existing firmware update mechanism is they do not work in an
   automated manner in many environments where IoT devices are deployed.
   Hence, there is a need to define a firmware update solution that is
   light weight, secure, can operate in variety of deployment
   environments, and is built on well established standards.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "SHOULD", "SHOULD
   NOT", "MAY", and "OPTIONAL" are to be interpreted as described in RFC
   2119 [RFC2119] and indicate requirement levels for compliant
   implementations.




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3.  Device Considerations

   This draft targets devices that have a boot loader that run in less
   than 100K bytes of flash and less than 32K bytes of RAM.

   There are certain types of devices that delete the firmware image,
   except for the boot-loader, before proceeding with the upgrade.
   Alternatively, many devices have sufficient storage to completely
   download a new firmware image before updating.  This solution should
   be naturally applicable to both.

4.  Solution Overview

   draft-nandakumar-suit-secfu-requirements captures various
   requirements that drives the solution defined in this specification.

   Below is a high-level solution flow for a successful firmware update
   on a IoT device.

































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                        Successful Firmware Update Flow

                              on-ready to update
                                   firmware
                                      |
                                      |
                           Can access firmware sever
                             in the local domain ?
                                      |
                                      |
                              ------------------
                         Yes  |                | No
                              |                |
                     Download signed        Download signed
                     manifest from           manifest from
                     local server           manufacturer's
                     well-known URL         pre-configured URL
                              |                 |
                              |                 |
                             Validate manifest via
                             pre-installed public key
                                       |
                                       |
                           Download the firmware image
                           from the location in manifest
                                       |
                                       |
                              verify commit hashes
                              on the firmware image
                                       |
                                       |
                              complete installation

5.  Solution Components

   Following several sub-sections define various components that makes
   up the proposed solution architecture

5.1.  Manifest

   A firmware manifest serves as information representation for metadata
   about the firmware.  A manifest file identifies information about the
   actual firmware image, its location, applicable device(s), and so on.
   It is cryptographically signed by the provider (usually the
   manufacturer) of the firmware.






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                              Minimal Manifest in JSON format

              {
                "manifestVersion" : "1.0",
                "timestamp": "2017-12-10T15:12:15Z",
                "manufacturer": "manufacturer.com",
                "model": "c7960",
                "firmwareVersion": "10.4.12",
                "firmwareLocation": "well-known location",
                "firmwareCryptoInfo": {
                  {
                    "commitHash": [
                      {
                        "digestAlgo": "sha256",
                        "hash": "..................."
                      },
                      {
                        "digestAlgo": "sha512",
                        "hash": "..................."
                      }
                    ]
                  }
                }
                "key-info": <most recent public key info>
              }


   Above shows example of a minimally defined manifest that identifies
   the mandatory attributes as explained below

   o  manifestVersion: Version of the manifest

   o  timestamp: Time when the manifest was created.

   o  manufacturer: An identifier of the manufacturer providing the
      firmware image, represented as String

   o  model: Device Model, a String

   o  firmwareVersion: Firmware Version in the format
      "major.minor.revision"

   o  firmwareLocation: Location of the firmware images.  This can be an
      absolute URI or a relative URI that is relative to where the
      manifest was downloaded from.

   o  firmwareCryptoInfo: Commit Hash information




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5.2.  Manifest Format

   JSON representation is recommended as the default format for
   describing the manifest.  Optionally, formats such as CBOR (see
   example section) can be used for the same.  If more than one format
   is used, the IoT device can pick one based on its implementation.
   The firmware download protocol identifies the right format supported
   by the IoT device.

5.3.  Manifest Security

   The Manifest file MUST be cryptographically signed by the private key
   of the manufacturer or the provider of the firmware.  This is to
   ensure source authenticity and to protect integrity of the manifest
   and the firmware itself.

   JWS is the format recommended to store the signed manifest.

                   signed_manifest := JWS(manifest.json)

   If CBOR is used for describing the manifest, COSE is recommended for
   signing.

   Optionally, the proposed solution also recommends hash based
   signatures (hash-sigs) to sign the manifest.

         signed_manifest := hash-sigs(manifest.json, private-key)

5.4.  Manifest Optional Extensions

   There may be scenarios where the minimalistic manifest defined above
   may not capture all the requirements for a given deployment setting.
   In those circumstances, the manifest can be optionally extended to
   meet the requirements in a extensional specifications.

5.5.  Firmware Server Discovery

   When it is time for an IoT device to perform a firmware upgrade, the
   device performs couple of steps to decide the location to download
   the needed firmware.  A device might need to download the new
   firmware when it is either booting for the first time after
   deployment or there is a need to upgrade to a newer firmware.

   The server discovery procedure starts with the boot-loader attempting
   to access a server that is local to the domain in which the device
   operates.  The URL to look for a local server is automatically
   generated using the DHCP domain name.




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   For example, if the domain name was example.com, and the device was a
   Cisco 7960, the HTTP URL might be

http://_firmware.example.com/.wellknown/firmware/cisco.com/c7960/manifest.json

   In situations where the IoT device cannot access the Internet
   (factory/enterprise settings, for example), the aforementioned
   approach might be the only way for the device to perform any kind of
   firmware or security updates.

   However, if the local server cannot be reached or not deployed (say
   home environments), the device proceeds to download the manifest and
   firmware from the firmware server URL pre-configured in the boot-
   loader by the manufacturer of the device.  For example

http://_firmware.cisco.com/.wellknown/firmware/cisco.com/c7960/manifest.json

   If either of the procedures doesn't work, the IoT device is either
   unusable or might end up running an old version of the firmware.

5.6.  Firmware Download protocol

   One can envision two possibilities while downloading the firmware:

   o  Scenarios where the IoT device downloads firmware directly.  This
      is done in order to minimize number of connections.  In this
      scenario, the firmware image must have a digital signature
      included within the downloaded firmware.  The exact placement of
      this digital signature (prepended, appended, etc) is up to the
      device manufacturer, but it MUST provided source and integrity
      guarantees on the entirety of the firmware image and must be
      verified by the device prior to upgrade.

   o  Scenarios where a manifest is retrieved and followed by
      downloading the actual firmware image.

5.6.1.  Validation Procedures

   The downloaded manifest and firmware is validated before being used:

   o  Manifest file signature is validated for source and integrity
      verification.  If encrypted, the manifest is decrypted before
      proceeding with the firmware download.

   o  On successful validation of the manifest, the device verifies the
      commit hashes for component(s) of the firmware downloaded against
      the ones provided in the "firmwareCryptoInfo" section of the
      manifest.



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5.6.2.  Manifest Download

   Firmware download protocol enables choosing the approach appropriate
   to the IoT device for downloading the manifest file.

   For example, on performing the "Firmware Server Discovery", if a
   local server is chosen, the device forms a query URL by constructing
   an endpoint at ".well-known/manifest/<manufacturer>/<model-
   no>/manifest.json"

   Then a HTTP GET request is sent to that URL.  For example

http://_firmware.example.com/.wellknown/manifest/cisco.com/c7960/manifest.json

   The response would be a JSON result of the manifest file.  Similarly,
   the end-point supporting CBOR parsing can request for the CBOR
   version of the mannifest.

5.6.3.  Firmware Download

   Once the manifest is downloaded and validated, the device proceeds to
   download the firmware image from the location identified in the
   firmware manifest.  There might be situations where a firmware image
   is split into multiple files to imply a functional division of the
   components.  This type of firmware can be used by devices that are
   memory constrained and thus loading the complete image might not be
   possible.  The manifest file may contain the information to indicate
   the same.

   Above example shows use of HTTP as the communication protocol to talk
   to the firmware server.  If the end-point is capable of doing COAP or
   other protocols, a similar process as above can be applied to
   retrieve the manifest and the firmware from a well-known place on the
   local server.

6.  IANA Consideration

   TODO

7.  Security Considerations

   TODO - Talk about roaming IoT Device

8.  Acknowledgements







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9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
              editor.org/info/rfc2119>.

Authors' Addresses

   Suhas Nandakumar
   Cisco

   Email: snandaku@cisco.com


   Cullen Jennings
   Cisco

   Email: fluffy@iii.ca


   Shaun Cooley
   Cisco

   Email: scooley@cisco.com


























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