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For this RFC, original HTML is available from the RFC-Editor: RFC8886

INFORMATIONAL
Errata Exist
Internet Engineering Task Force (IETF)                         W. Kumari
Request for Comments: 8886                                        Google
Category: Informational                                         C. Doyle
ISSN: 2070-1721                                         Juniper Networks
                                                          September 2020


                         Secure Device Install

Abstract

   Deploying a new network device in a location where the operator has
   no staff of its own often requires that an employee physically travel
   to the location to perform the initial install and configuration,
   even in shared facilities with "remote-hands" (or similar) support.
   In many cases, this could be avoided if there were an easy way to
   transfer the initial configuration to a new device while still
   maintaining confidentiality of the configuration.

   This document extends existing vendor proprietary auto-install to
   provide limited confidentiality to initial configuration during
   bootstrapping of the device.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8886.

Copyright Notice

   Copyright (c) 2020 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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Overview
     2.1.  Example Scenario
   3.  Vendor Role
     3.1.  Device Key Generation
     3.2.  Directory Server
   4.  Operator Role
     4.1.  Administrative
     4.2.  Technical
     4.3.  Example Initial Customer Boot
   5.  Additional Considerations
     5.1.  Key Storage
     5.2.  Key Replacement
     5.3.  Device Reinstall
   6.  IANA Considerations
   7.  Security Considerations
   8.  Informative References
   Appendix A.  Proof of Concept
     A.1.  Step 1: Generating the Certificate
       A.1.1.  Step 1.1: Generate the Private Key
       A.1.2.  Step 1.2: Generate the Certificate Signing Request
       A.1.3.  Step 1.3: Generate the (Self-Signed) Certificate Itself
     A.2.  Step 2: Generating the Encrypted Configuration
       A.2.1.  Step 2.1: Fetch the Certificate
       A.2.2.  Step 2.2: Encrypt the Configuration File
       A.2.3.  Step 2.3: Copy Configuration to the Configuration
               Server
     A.3.  Step 3: Decrypting and Using the Configuration
       A.3.1.  Step 3.1: Fetch Encrypted Configuration File from
               Configuration Server
       A.3.2.  Step 3.2: Decrypt and Use the Configuration
   Acknowledgments
   Authors' Addresses

1.  Introduction

   In a growing, global network, significant amounts of time and money
   are spent deploying new devices and "forklift" upgrading existing
   devices.  In many cases, these devices are in shared facilities (for
   example, Internet Exchange Points (IXP) or "carrier-neutral data
   centers"), which have staff on hand that can be contracted to perform
   tasks including physical installs, device reboots, loading initial
   configurations, etc.  There are also a number of (often proprietary)
   protocols to perform initial device installs and configurations.  For
   example, many network devices will attempt to use DHCP [RFC2131] or
   DHCPv6 [RFC8415] to get an IP address and configuration server and
   then fetch and install a configuration when they are first powered
   on.

   The configurations of network devices contain a significant amount of
   security-related and proprietary information (for example, RADIUS
   [RFC2865] or TACACS+ [TACACS] secrets).  Exposing these to a third
   party to load onto a new device (or using an auto-install technique
   that fetches an unencrypted configuration file via TFTP [RFC1350]) or
   something similar is an unacceptable security risk for many
   operators, and so they send employees to remote locations to perform
   the initial configuration work; this costs time and money.

   There are some workarounds to this, such as asking the vendor to
   preconfigure the device before shipping it; asking the remote support
   to install a terminal server; providing a minimal, unsecured
   configuration and using that to bootstrap to a complete
   configuration; etc.  However, these are often clumsy and have
   security issues.  As an example, in the terminal server case, the
   console port connection could be easily snooped.

   An ideal solution in this space would protect both the
   confidentiality of device configuration in transit and the
   authenticity (and authorization status) of configuration to be used
   by the device.  The mechanism described in this document only
   addresses the former and makes no effort to do the latter, with the
   device accepting any configuration file that comes its way and is
   encrypted to the device's key (or not encrypted, as the case may be).
   Other solutions (such as Secure Zero Touch Provisioning (SZTP)
   [RFC8572], Bootstrapping Remote Secure Key Infrastructures (BRSKI)
   [BRSKI], and other voucher-based methods) are more fully featured but
   also require more complicated machinery.  This document describes
   something much simpler, at the cost of only providing limited
   protection.

   This document layers security onto existing auto-install solutions
   (one example of which is [Cisco_AutoInstall]) to provide a method to
   initially configure new devices while maintaining (limited)
   confidentiality of the initial configuration.  It is optimized for
   simplicity, for both the implementor and the operator.  It is
   explicitly not intended to be a fully featured system for managing
   installed devices nor is it intended to solve all use cases; rather,
   it is a simple targeted solution to solve a common operational issue
   where the network device has been delivered, fiber has been laid (as
   appropriate), and there is no trusted member of the operator's staff
   to perform the initial configuration.  This solution is only intended
   to increase confidentiality of the information in the configuration
   file and does not protect the device itself from loading a malicious
   configuration.

   This document describes a concept and some example ways of
   implementing this concept.  As devices have different capabilities
   and use different configuration paradigms, one method will not suit
   all, and so it is expected that vendors will differ in exactly how
   they implement this.

   This solution is specifically designed to be a simple method on top
   of exiting device functionality.  If devices do not support this new
   method, they can continue to use the existing functionality.  In
   addition, operators can choose to use this to protect their
   configuration information or can continue to use the existing
   functionality.

   The issue of securely installing devices is in no way a new issue nor
   is it limited to network devices; it occurs when deploying servers,
   PCs, Internet of Things (IoT) devices, and in many other situations.
   While the solution described in this document is obvious (encrypt the
   config, then decrypt it with a device key), this document only
   discusses the use for network devices, such as routers and switches.

2.  Overview

   Most network devices already include some sort of initial
   bootstrapping logic (sometimes called 'autoboot' or 'autoinstall').
   This generally works by having a newly installed, unconfigured device
   obtain an IP address for itself and discover the address of a
   configuration server (often called 'next-server', 'siaddr', or 'tftp-
   server-name') using DHCP or DHCPv6 (see [RFC2131] and [RFC8415]).
   The device then contacts this configuration server to download its
   initial configuration, which is often identified using the device's
   serial number, Media Access Control (MAC) address, or similar.  This
   document extends this (vendor-specific) paradigm by allowing the
   configuration file to be encrypted.

   This document uses the serial number of the device as a unique device
   identifier for simplicity; some vendors may not want to implement the
   system using the serial number as the identifier for business reasons
   (a competitor or similar could enumerate the serial numbers and
   determine how many devices have been manufactured).  Implementors are
   free to choose some other way of generating identifiers (e.g., a
   Universally Unique Identifier (UUID) [RFC4122]), but this will likely
   make it somewhat harder for operators to use (the serial number is
   usually easy to find on a device).

2.1.  Example Scenario

   Operator_A needs another peering router, and so they order another
   router from Vendor_B to be drop-shipped to the facility.  Vendor_B
   begins assembling the new device and tells Operator_A what the new
   device's serial number will be (SN:17894321).  When Vendor_B first
   installs the firmware on the device and boots it, the device
   generates a public-private key pair, and Vendor_B publishes the
   public key on its key server (in a public key certificate, for ease
   of use).

   While the device is being shipped, Operator_A generates the initial
   device configuration and fetches the certificate from Vendor_B key
   servers by providing the serial number of the new device.  Operator_A
   then encrypts the device configuration and puts this encrypted
   configuration on a (local) TFTP server.

   When the device arrives at the Point of Presence (POP), it gets
   installed in Operator_A's rack and cabled as instructed.  The new
   device powers up and discovers that it has not yet been configured.
   It enters its autoboot state and begins the DHCP process.
   Operator_A's DHCP server provides it with an IP address and the
   address of the configuration server.  The router uses TFTP to fetch
   its configuration file.  Note that all of this is existing
   functionality.  The device attempts to load the configuration file.
   As an added step, if the configuration file cannot be parsed, the
   device tries to use its private key to decrypt the file and, assuming
   it validates, proceeds to install the new, decrypted configuration.

   Only the "correct" device will have the required private key and be
   able to decrypt and use the configuration file (see Security
   Considerations (Section 7)).  An attacker would be able to connect to
   the network and get an IP address.  They would also be able to
   retrieve (encrypted) configuration files by guessing serial numbers
   (or perhaps the server would allow directory listing), but without
   the private keys, an attacker will not be able to decrypt the files.

3.  Vendor Role

   This section describes the vendor's roles and provides an overview of
   what the device needs to do.

3.1.  Device Key Generation

   Each device requires a public-private key pair and for the public
   part to be published and retrievable by the operator.  The
   cryptographic algorithm and key lengths to be used are out of the
   scope of this document.  This section illustrates one method, but, as
   with much of this document, the exact mechanism may vary by vendor.
   Enrollment over Secure Transport [RFC7030] and possibly the Simple
   Certificate Enrollment Protocol [RFC8894] are methods that vendors
   may want to consider.

   During the manufacturing stage, when the device is initially powered
   on, it will generate a public-private key pair.  It will send its
   unique device identifier and the public key to the vendor's directory
   server [RFC5280] to be published.  The vendor's directory server
   should only accept certificates that are from the manufacturing
   facility and that match vendor-defined policies (for example,
   extended key usage and extensions).  Note that some devices may be
   constrained and so may send the raw public key and unique device
   identifier to the certificate publication server, while more capable
   devices may generate and send self-signed certificates.  This
   communication with the directory server should be integrity protected
   and should occur in a controlled environment.

   This reference architecture needs a serialization format for the key
   material.  Due to the prevalence of tooling support for it on network
   devices, X.509 certificates are a convenient format to exchange
   public keys.  However, most of the metadata that would be used for
   revocation and aging will not be used and should be ignored by both
   the client and server.  In such cases, the signature on the
   certificate conveys no value, and the consumer of the certificate is
   expected to pin the end-entity key fingerprint (versus using a PKI
   and signature chain).

3.2.  Directory Server

   The directory server contains a database of certificates.  If newly
   manufactured devices upload certificates, the directory server can
   simply publish these; if the devices provide the raw public keys and
   unique device identifier, the directory server will need to wrap
   these in a certificate.

   The customers (e.g., Operator_A) query this server with the serial
   number (or other provided unique identifier) of a device and retrieve
   the associated certificate.  It is expected that operators will
   receive the unique device identifier (serial number) of devices when
   they purchase them and will download and store the certificate.  This
   means that there is not a hard requirement on the reachability of the
   directory server.

                         +------------+
        +------+         |            |
        |Device|         | Directory  |
        +------+         |   Server   |
                         +------------+
   +----------------+   +--------------+
   |   +---------+  |   |              |
   |   | Initial |  |   |              |
   |   |  boot?  |  |   |              |
   |   +----+----+  |   |              |
   |        |       |   |              |
   | +------v-----+ |   |              |
   | |  Generate  | |   |              |
   | |Self-signed | |   |              |
   | |Certificate | |   |              |
   | +------------+ |   |              |
   |        |       |   |   +-------+  |
   |        +-------|---|-->|Receive|  |
   |                |   |   +---+---+  |
   |                |   |       |      |
   |                |   |   +---v---+  |
   |                |   |   |Publish|  |
   |                |   |   +-------+  |
   |                |   |              |
   +----------------+   +--------------+

          Figure 1: Initial Certificate Generation and Publication

4.  Operator Role

4.1.  Administrative

   When purchasing a new device, the accounting department will need to
   get the unique device identifier (e.g., serial number) of the new
   device and communicate it to the operations group.

4.2.  Technical

   The operator will contact the vendor's publication server and
   download the certificate (by providing the unique device identifier
   of the device).  The operator fetches the certificate using a secure
   transport that authenticates the source of the certificate, such as
   HTTPS (confidentiality protection can provide some privacy and
   metadata-leakage benefit but is not key to the primary mechanism of
   this document).  The operator will then encrypt the initial
   configuration (for example, using S/MIME [RFC8551]) using the key in
   the certificate and place it on their configuration server.

   See Appendix A for examples.

                         +------------+
      +--------+         |            |
      |Operator|         | Directory  |
      +--------+         |   Server   |
                         +------------+
   +----------------+  +----------------+
   | +-----------+  |  |  +-----------+ |
   | |   Fetch   |  |  |  |           | |
   | |  Device   |<------>|Certificate| |
   | |Certificate|  |  |  |           | |
   | +-----+-----+  |  |  +-----------+ |
   |       |        |  |                |
   | +-----v------+ |  |                |
   | |  Encrypt   | |  |                |
   | |   Device   | |  |                |
   | |   Config   | |  |                |
   | +-----+------+ |  |                |
   |       |        |  |                |
   | +-----v------+ |  |                |
   | |  Publish   | |  |                |
   | |    TFTP    | |  |                |
   | |   Server   | |  |                |
   | +------------+ |  |                |
   |                |  |                |
   +----------------+  +----------------+

   Figure 2: Fetching the Certificate, Encrypting the Configuration, and
                   Publishing the Encrypted Configuration

4.3.  Example Initial Customer Boot

   When the device is first booted by the customer (and on subsequent
   boots), if the device does not have a valid configuration, it will
   use existing auto-install functionality.  As an example, it performs
   DHCP Discovery until it gets a DHCP offer including DHCP option 66
   (Server-Name) or 150 (TFTP server address), contacts the server
   listed in these DHCP options, and downloads its configuration file.
   Note that this is existing functionality (for example, Cisco devices
   fetch the config file named by the Bootfile-Name DHCP option (67)).

   After retrieving the configuration file, the device needs to
   determine if it is encrypted or not.  If it is not encrypted, the
   existing behavior is used.  If the configuration is encrypted, the
   process continues as described in this document.  If the device has
   been configured to only support encrypted configuration and
   determines that the configuration file is not encrypted, it should
   abort.  The method used to determine if the configuration is
   encrypted or not is implementation dependent; there are a number of
   (obvious) options, including having a magic string in the file
   header, using a file name extension (e.g., config.enc), or using
   specific DHCP options.

   If the file is encrypted, the device will attempt to decrypt and
   parse the file.  If able, it will install the configuration and start
   using it.  If it cannot decrypt the file or if parsing the
   configuration fails, the device will either abort the auto-install
   process or repeat this process until it succeeds.  When retrying,
   care should be taken to not overwhelm the server hosting the
   encrypted configuration files.  It is suggested that the device retry
   every 5 minutes for the first hour and then every hour after that.
   As it is expected that devices may be installed well before the
   configuration file is ready, a maximum number of retries is not
   specified.

   Note that the device only needs to be able to download the
   configuration file; after the initial power on in the factory, it
   never needs to access the Internet, vendor, or directory server.  The
   device (and only the device) has the private key and so has the
   ability to decrypt the configuration file.

             +--------+                +--------------+
             | Device |                |Config server |
             +--------+                |(e.g., TFTP)  |
                                       +--------------+
   +---------------------------+    +------------------+
   | +-----------+             |    |                  |
   | |           |             |    |                  |
   | |   DHCP    |             |    |                  |
   | |           |             |    |                  |
   | +-----+-----+             |    |                  |
   |       |                   |    |                  |
   | +-----v------+            |    |  +-----------+   |
   | |            |            |    |  | Encrypted |   |
   | |Fetch config|<------------------>|  config   |   |
   | |            |            |    |  |   file    |   |
   | +-----+------+            |    |  +-----------+   |
   |       |                   |    |                  |
   |       X                   |    |                  |
   |      / \                  |    |                  |
   |     /   \ N    +--------+ |    |                  |
   |    | Enc?|---->|Install,| |    |                  |
   |     \   /      |  Boot  | |    |                  |
   |      \ /       +--------+ |    |                  |
   |       V                   |    |                  |
   |       |Y                  |    |                  |
   |       |                   |    |                  |
   | +-----v------+            |    |                  |
   | |Decrypt with|            |    |                  |
   | |private key |            |    |                  |
   | +-----+------+            |    |                  |
   |       |                   |    |                  |
   |       v                   |    |                  |
   |      / \                  |    |                  |
   |     /   \ Y    +--------+ |    |                  |
   |    |Sane?|---->|Install,| |    |                  |
   |     \   /      |  Boot  | |    |                  |
   |      \ /       +--------+ |    |                  |
   |       V                   |    |                  |
   |       |N                  |    |                  |
   |       |                   |    |                  |
   |  +----v---+               |    |                  |
   |  |Retry or|               |    |                  |
   |  | abort  |               |    |                  |
   |  +--------+               |    |                  |
   |                           |    |                  |
   +---------------------------+    +------------------+

        Figure 3: Device Boot, Fetch, and Install Configuration File

5.  Additional Considerations

5.1.  Key Storage

   Ideally, the key pair would be stored in a Trusted Platform Module
   (TPM) on something that is identified as the "router" -- for example,
   the chassis/backplane.  This is so that a key pair is bound to what
   humans think of as the "device" and not, for example, (redundant)
   routing engines.  Devices that implement IEEE 802.1AR [IEEE802-1AR]
   could choose to use the Initial Device Identifier (IDevID) for this
   purpose.

5.2.  Key Replacement

   It is anticipated that some operator may want to replace the (vendor-
   provided) keys after installing the device.  There are two options
   when implementing this: a vendor could allow the operator's key to
   completely replace the initial device-generated key (which means
   that, if the device is ever sold, the new owner couldn't use this
   technique to install the device), or the device could prefer the
   operator's installed key.  This is an implementation decision left to
   the vendor.

5.3.  Device Reinstall

   Increasingly, operations are moving towards an automated model of
   device management, whereby portions of the configuration (or the
   entire configuration) are programmatically generated.  This means
   that operators may want to generate an entire configuration after the
   device has been initially installed and ask the device to load and
   use this new configuration.  It is expected (but not defined in this
   document, as it is vendor specific) that vendors will allow the
   operator to copy a new, encrypted configuration (or part of a
   configuration) onto a device and then request that the device decrypt
   and install it (e.g., 'load replace <filename> encrypted').  The
   operator could also choose to reset the device to factory defaults
   and allow the device to act as though it were the initial boot (see
   Section 4.3).

6.  IANA Considerations

   This document has no IANA actions.

7.  Security Considerations

   This reference architecture is intended to incrementally improve upon
   commonly accepted "auto-install" practices used today that may
   transmit configurations unencrypted (e.g., unencrypted configuration
   files that can be downloaded connecting to unprotected ports in data
   centers, mailing initial configuration files on flash drives, or
   emailing configuration files and asking a third party to copy and
   paste them over a serial terminal) or allow unrestricted access to
   these configurations.

   This document describes an object-level security design to provide
   confidentiality assurances for the configuration stored at rest on
   the configuration server and for configuration while it is in transit
   between the configuration server and the unprovisioned device, even
   if the underlying transport does not provide this security service.

   The architecture provides no assurances about the source of the
   encrypted configuration or protect against theft and reuse of
   devices.

   An attacker (e.g., a malicious data center employee, person in the
   supply chain, etc.) who has physical access to the device before it
   is connected to the network or who manages to exploit it once
   installed may be able to extract the device private key (especially
   if it is not stored in a TPM), pretend to be the device when
   connecting to the network, and download and extract the (encrypted)
   configuration file.

   An attacker with access to the configuration server (or the ability
   to route traffic to configuration server under their control) and the
   device's public key could return a configuration of the attacker's
   choosing to the unprovisioned device.

   This mechanism does not protect against a malicious vendor.  While
   the key pair should be generated on the device and the private key
   should be securely stored, the mechanism cannot detect or protect
   against a vendor who claims to do this but instead generates the key
   pair off device and keeps a copy of the private key.  It is largely
   understood in the operator community that a malicious vendor or
   attacker with physical access to the device is largely a "Game Over"
   situation.

   Even when using a secure bootstrap mechanism, security-conscious
   operators may wish to bootstrap devices with a minimal or less-
   sensitive configuration and then replace this with a more complete
   one after install.

8.  Informative References

   [BRSKI]    Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", Work in Progress, Internet-
              Draft, draft-ietf-anima-bootstrapping-keyinfra-44, 21
              September 2020, <https://tools.ietf.org/html/draft-ietf-
              anima-bootstrapping-keyinfra-44>.

   [Cisco_AutoInstall]
              Cisco Systems, Inc., "Using AutoInstall to Remotely
              Configure Cisco Networking Devices", Configuration
              Fundamentals Configuration Guide, Cisco IOS Release 15M&T,
              January 2018, <https://www.cisco.com/c/en/us/td/docs/ios-
              xml/ios/fundamentals/configuration/15mt/fundamentals-15-
              mt-book/cf-autoinstall.html>.

   [IEEE802-1AR]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks - Secure Device Identity", IEEE Std 802-1AR, June
              2018,
              <https://standards.ieee.org/standard/802_1AR-2018.html>.

   [RFC1350]  Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,
              RFC 1350, DOI 10.17487/RFC1350, July 1992,
              <https://www.rfc-editor.org/info/rfc1350>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,
              <https://www.rfc-editor.org/info/rfc2865>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/info/rfc4122>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <https://www.rfc-editor.org/info/rfc7030>.

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,
              <https://www.rfc-editor.org/info/rfc8415>.

   [RFC8551]  Schaad, J., Ramsdell, B., and S. Turner, "Secure/
              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
              Message Specification", RFC 8551, DOI 10.17487/RFC8551,
              April 2019, <https://www.rfc-editor.org/info/rfc8551>.

   [RFC8572]  Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
              Touch Provisioning (SZTP)", RFC 8572,
              DOI 10.17487/RFC8572, April 2019,
              <https://www.rfc-editor.org/info/rfc8572>.

   [RFC8894]  Gutmann, P., "Simple Certificate Enrolment Protocol",
              RFC 8894, DOI 10.17487/RFC8894, September 2020,
              <https://www.rfc-editor.org/info/rfc8894>.

   [TACACS]   Dahm, T., Ota, A., Medway Gash, D., Carrel, D., and L.
              Grant, "The TACACS+ Protocol", Work in Progress, Internet-
              Draft, draft-ietf-opsawg-tacacs-18, 20 March 2020,
              <https://tools.ietf.org/html/draft-ietf-opsawg-tacacs-18>.

Appendix A.  Proof of Concept

   This section contains a proof of concept of the system.  It is only
   intended for illustration and is not intended to be used in
   production.

   It uses OpenSSL from the command line.  In production, something more
   automated would be used.  In this example, the unique device
   identifier is the serial number of the router, SN19842256.

A.1.  Step 1: Generating the Certificate

   This step is performed by the router.  It generates a key, then a
   Certificate Signing Request (CSR), and then a self-signed
   certificate.

A.1.1.  Step 1.1: Generate the Private Key

   $ openssl ecparam -out privatekey.key -name prime256v1 -genkey
   $

A.1.2.  Step 1.2: Generate the Certificate Signing Request

   $ openssl req -new -key key.pem -out SN19842256.csr
   Common Name (e.g., server FQDN or YOUR name) []:SN19842256

A.1.3.  Step 1.3: Generate the (Self-Signed) Certificate Itself

   $ openssl req -x509 -days 36500 -key key.pem -in SN19842256.csr
   -out SN19842256.crt

   The router then sends the key to the vendor's key server for
   publication (not shown).

A.2.  Step 2: Generating the Encrypted Configuration

   The operator now wants to deploy the new router.

   They generate the initial configuration (using whatever magic tool
   generates router configs!), fetch the router's certificate, and
   encrypt the configuration file to that key.  This is done by the
   operator.

A.2.1.  Step 2.1: Fetch the Certificate

   $ wget http://keyserv.example.net/certificates/SN19842256.crt

A.2.2.  Step 2.2: Encrypt the Configuration File

   S/MIME is used here because it is simple to demonstrate.  This is
   almost definitely not the best way to do this.

   $ openssl smime -encrypt -aes-256-cbc -in SN19842256.cfg\
      -out SN19842256.enc -outform PEM SN19842256.crt
   $ more SN19842256.enc
   -----BEGIN PKCS7-----
   MIICigYJKoZIhvcNAQcDoIICezCCAncCAQAxggE+MIIBOgIBADAiMBUxEzARBgNV
   BAMMClNOMTk4NDIyNTYCCQDJVuBlaTOb1DANBgkqhkiG9w0BAQEFAASCAQBABvM3
   ...
   LZoq08jqlWhZZWhTKs4XPGHUdmnZRYIP8KXyEtHt
   -----END PKCS7-----

A.2.3.  Step 2.3: Copy Configuration to the Configuration Server

   $ scp SN19842256.enc config.example.com:/tftpboot

A.3.  Step 3: Decrypting and Using the Configuration

   When the router connects to the operator's network, it will detect
   that it does not have a valid configuration file and will start the
   "autoboot" process.  This is a well-documented process, but the high-
   level overview is that it will use DHCP to obtain an IP address and
   configuration server.  It will then use TFTP to download a
   configuration file, based upon its serial number (this document
   modifies the solution to fetch an encrypted configuration file
   (ending in .enc)).  It will then decrypt the configuration file and
   install it.

A.3.1.  Step 3.1: Fetch Encrypted Configuration File from Configuration
        Server

   $ tftp 2001:0db8::23 -c get SN19842256.enc

A.3.2.  Step 3.2: Decrypt and Use the Configuration

   $ openssl smime -decrypt -in SN19842256.enc -inform pkcs7\
      -out config.cfg -inkey key.pem

   If an attacker does not have the correct key, they will not be able
   to decrypt the configuration file:

   $ openssl smime -decrypt -in SN19842256.enc -inform pkcs7\
      -out config.cfg -inkey wrongkey.pem
   Error decrypting PKCS#7 structure
   140352450692760:error:06065064:digital envelope
    routines:EVP_DecryptFinal_ex:bad decrypt:evp_enc.c:592:
   $ echo $?
   4

Acknowledgments

   The authors wish to thank everyone who contributed, including Benoit
   Claise, Francis Dupont, Mirja Kuehlewind, Sam Ribeiro, Michael
   Richardson, Sean Turner, and Kent Watsen.  Joe Clarke also provided
   significant comments and review, and Tom Petch provided significant
   editorial contributions to better describe the use cases and clarify
   the scope.

   Roman Danyliw and Benjamin Kaduk also provided helpful text,
   especially around the certificate usage and security considerations.

Authors' Addresses

   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA 94043
   United States of America

   Email: warren@kumari.net


   Colin Doyle
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA 94089
   United States of America

   Email: cdoyle@juniper.net


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