Internet DRAFT - draft-wkumari-opsawg-sdi
draft-wkumari-opsawg-sdi
Network Working Group W. Kumari
Internet-Draft Google
Intended status: Informational C. Doyle
Expires: December 14, 2019 Juniper Networks
June 12, 2019
Secure Device Install
draft-wkumari-opsawg-sdi-04
Abstract
Deploying a new network device often requires that an employee
physically travel to a datacenter to perform the initial install and
configuration, even in shared datacenters with "smart-hands" type
support. In many cases, this could be avoided if there were a
standard, secure way to initially provision the devices.
This document extends existing auto-install / Zero-Touch Provisioning
mechanisms to make the process more secure.
[ Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. They will be removed before publication. This document is
being collaborated on in Github at: https://github.com/wkumari/draft-
wkumari-opsawg-sdi. The most recent version of the document, open
issues, etc should all be available here. The authors (gratefully)
accept pull requests. ]
[ Ed note: This document introduces concepts and serves as the basic
for discussion - because of this, it is conversational, and would
need to be firmed up before being published ]
Status of This Memo
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This Internet-Draft will expire on December 14, 2019.
Copyright Notice
Copyright (c) 2019 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4
2. Overview / Example Scenario . . . . . . . . . . . . . . . . . 4
3. Vendor Role / Requirements . . . . . . . . . . . . . . . . . 5
3.1. Device key generation . . . . . . . . . . . . . . . . . . 5
3.2. Certificate Publication Server . . . . . . . . . . . . . 5
4. Operator Role / Responsibilities . . . . . . . . . . . . . . 6
4.1. Administrative . . . . . . . . . . . . . . . . . . . . . 6
4.2. Technical . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Initial Customer Boot . . . . . . . . . . . . . . . . . . 7
5. Additional Considerations . . . . . . . . . . . . . . . . . . 9
5.1. Key storage . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Key replacement . . . . . . . . . . . . . . . . . . . . . 10
5.3. Device reinstall . . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 12
Appendix B. Demo / proof of concept . . . . . . . . . . . . . . 12
B.1. Step 1: Generating the certificate. . . . . . . . . . . . 13
B.1.1. Step 1.1: Generate the private key. . . . . . . . . . 13
B.1.2. Step 1.2: Generate the certificate signing request. . 13
B.1.3. Step 1.3: Generate the (self signed) certificate
itself. . . . . . . . . . . . . . . . . . . . . . . . 13
B.2. Step 2: Generating the encrypted config. . . . . . . . . 14
B.2.1. Step 2.1: Fetch the certificate. . . . . . . . . . . 14
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B.2.2. Step 2.2: Encrypt the config file. . . . . . . . . . 14
B.2.3. Step 2.3: Copy config to the config server. . . . . . 14
B.3. Step 3: Decrypting and using the config. . . . . . . . . 14
B.3.1. Step 3.1: Fetch encrypted config file from config
server. . . . . . . . . . . . . . . . . . . . . . . . 14
B.3.2. Step 3.2: Decrypt and use the config. . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
In a growing, global network, significant amounts of time and money
are spent simply deploying new devices and "forklift" upgrading
existing devices. In many cases, these devices are in shared
datacenters (for example, Internet Exchange Points (IXP) or "carrier
neutral datacenters"), 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 vendor proprietary) protocols to perform initial
device installs and configurations - for example, many network
devices will attempt to use DHCP to get an IP address and
configuration server, and then fetch and install a configuration when
they are first powered on.
Network device configurations contain a significant amount of
security related and / or proprietary information (for example,
RADIUS or TACACS+ secrets). Exposing these to a third party to load
onto a new device (or using an auto-install techniques which fetch an
(unencrypted) config file via something like TFTP) is simply not
acceptable to many operators, and so they have to send employees to
remote locations to perform the initial configuration work. As well
as having a significant monetary cost, it also takes significantly
longer to install devices and is generally inefficient.
There are some workarounds to this, such as asking the vendor to pre-
configure the devices before shipping it; asking the smart-hands to
install a terminal server; providing a minimal, unsecured
configuration and using that to bootstrap to a complete
configuration, etc; but these are often clumsy and have security
issues - for example, in the terminal server case, the console port
connection could be easily snooped.
This document layers security onto existing auto-install solutions to
provide a secure method to initially configure new devices. It is
optimized for simplicity, both for the implementor and the operator;
it is explicitly not intended to be an "all singing, all dancing"
fully featured system for managing installed / deployed devices, nor
is it intended to solve all use-cases - rather it is a simple
targeted solution to solve a common operational issue. Solutions
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such as Secure Zero Touch Provisioning (SZTP)" [RFC8572] are much
more fully featured, but also more complex to implement and / or are
not widely deployed yet.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Overview / Example Scenario
Sirius Cybernetics Corp needs another peering router, and so they
order another router from Acme Network Widgets, to be drop-shipped to
the Point of Presence (POP) / datacenter. Acme begins assembling the
new device, and tells Sirius what the new device's serial number will
be (SN:17894321). When Acme first installs the firmware on the
device and boots it, the device generates a public-private keypair,
and Acme publishes it on their keyserver (in a certificate, for ease
of use).
While the device is being shipped, Sirius generates the initial
device configuration, fetches the certificate from Acme keyservers by
providing the serial number of the new device. Sirius then encrypts
the device configuration and puts this encrypted config on a (local)
TFTP server.
When the device arrives at the POP, it gets installed in Sirius'
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. Sirius' DHCP server
provides it with an IP address and the address of the configuration
server. The router uses TFTP to fetch its config file (note that all
this is existing functionality). The device attempts to load the
config file - if the config file is unparsable, (new functionality)
the devies tries to uses its private key to decrypt the file, and,
assuming it validates, installs the new configuration.
Only the "correct" device will have the required private key and be
able to decrypt and use the config file (See Security
Considerations). An attacker would be able to connect to the network
and get an IP address. They would also be able to retrieve
(encrypted) config 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.
This document uses the serial number of the device as a unique
identifier for simplicity; some vendors may not want to implement the
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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 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, a more complex system is likely harder to track).
[ Ed note: This example uses TFTP because that is what many vendors
use in their auto-install / ZTP feature. It could easily instead be
HTTP, FTP, etc. ]
3. Vendor Role / Requirements
This section describes the vendors roles and responsibilities and
provides an overview of what the device needs to do.
3.1. Device key generation
During the manufacturing stage, when the device is intially powered
on, it will generate a public-private keypair. It will send its
unique identifier and the public key to the vendor's Certificate
Publication Server to be published. The mechanism used to do this is
left undefined. Note that some devices may be contrained, and so may
send the raw public key and unique identifier to the certificate
publication server, while mode capable devices may generate and send
self-signed certifcates.
3.2. Certificate Publication Server
The certificate publication server contains a database of
certificates. If newly manufactured devices upload certificates the
certificate publication server can simply publish these, if the
devices provide raw public keys and unique identfiers the certificate
publication server will need to wrap these in a certificate. Note
that the certificat publication server MUST only accept certifcates
or keys from the vendor's manufacturing facilities.
The customers (e.g Sirius Cybernetics Corp) 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 identifier (serial number) of
devices when they purchase them, and will download and store / cache
the certificate. This means that there is not a hard requirement on
the uptime / reachability of the certificate publication server.
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+------------+
+------+ |Certificate |
|Device| |Publication |
+------+ | Server |
+------------+
+----------------+ +--------------+
| +---------+ | | |
| | Initial | | | |
| | boot? | | | |
| +----+----+ | | |
| | | | |
| +------v-----+ | | |
| | Generate | | | |
| |Self-signed | | | |
| |Certificate | | | |
| +------------+ | | |
| | | | +-------+ |
| +-------|---|-->|Receive| |
| | | +---+---+ |
| | | | |
| | | +---v---+ |
| | | |Publish| |
| | | +-------+ |
| | | |
+----------------+ +--------------+
Initial certificate generation and publication.
4. Operator Role / Responsibilities
4.1. Administrative
When purchasing a new device, the accounting department will need to
get the unique device identifier (likely 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 SHOULD fetch the certificate using a
secure transport (e.g HTTPS). The operator will then encrypt the
initial configuration to the key in the certifcate, and place it on
their TFTP server. See Appendix B for examples.
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+------------+
+--------+ |Certificate |
|Operator| |Publication |
+--------+ | Server |
+------------+
+----------------+ +----------------+
| +-----------+ | | +-----------+ |
| | Fetch | | | | | |
| | Device |<------>|Certificate| |
| |Certificate| | | | | |
| +-----+-----+ | | +-----------+ |
| | | | |
| +-----v------+ | | |
| | Encrypt | | | |
| | Device | | | |
| | Config | | | |
| +-----+------+ | | |
| | | | |
| +-----v------+ | | |
| | Publish | | | |
| | TFTP | | | |
| | Server | | | |
| +------------+ | | |
| | | |
+----------------+ +----------------+
Fetching the certificate, encrypting the configuration, publishing
the encrypted configuration.
4.3. Initial Customer Boot
When the device is first booted by the customer (and on subsequent
boots), if the device has no valid configuration, it will use
existing auto-install type functionality - it performs DHCP Discovery
until it gets a DHCP offer including DHCP option 66 or 150, contact
the server listed in these DHCP options and download its config file.
After retrieving the config file, the device will examine the file
and determine if it seems to be a valid config, and if so, proceeds
as it normally would. Note that this is existing functionality (for
example, Cisco devices fetch the config file named by the Bootfile-
Name DHCP option (67)).
If the file appears be "garbage", the device will attempt to decrypt
the configuration file using its private key. If it is able to
decrypt and validate the file it will install the configuration, and
start using it. The exact method that the device uses to determine
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if a config file is "valid" is implementation specific, but a normal
config file looks significantly different to an encrypted blob.
Note that the device only needs DHCP and to be able to download the
config file; after the initial power-on in the factory it never need
to access the Internet or vendor or certifcate publication server -
it (and only it) has the private key and so has the ability to
decrypt the config file.
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+--------+ +--------------+
| Device | |Config server |
+--------+ | (e.g TFTP) |
+--------------+
+---------------------------+ +------------------+
| +-----------+ | | |
| | | | | |
| | DHCP | | | |
| | | | | |
| +-----+-----+ | | |
| | | | |
| +-----v------+ | | +-----------+ |
| | | | | | Encrypted | |
| |Fetch config|<------------------>| config | |
| | | | | | file | |
| +-----+------+ | | +-----------+ |
| | | | |
| X | | |
| / \ | | |
| / \ Y +--------+ | | |
| |Sane?|---->|Install,| | | |
| \ / | Boot | | | |
| \ / +--------+ | | |
| V | | |
| |N | | |
| | | | |
| +-----v------+ | | |
| |Decrypt with| | | |
| |private key | | | |
| +-----+------+ | | |
| | | | |
| | +--------+ | | |
| | |Install,| | | |
| +------->| Boot | | | |
| +--------+ | | |
| | | |
| | | |
+---------------------------+ +------------------+
Device boot, fetch and install config file
5. Additional Considerations
5.1. Key storage
Ideally, the keypair would be stored in a TPM on something which is
identified as the "router" - for example, the chassis / backplane.
This is so that a keypair is bound to what humans think of as the
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"device", and not, for example (redundant) routing engines. Devices
which implement IEEE 802.1AR could choose to use the 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
operators installed key. This is an implementation decision left to
the vendor.
5.3. Device reinstall
Increasingly, operations is moving towards an automated model of
device management, whereby portions (or the entire) configuration is
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 config (or part of a config) 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 makes no requests of the IANA.
7. Security Considerations
This mechanism is intended to replace either expensive (traveling
employees) or insecure mechanisms of installing newly deployed
devices such as: unencrypted config files which can be downloaded by
connecting to unprotected ports in datacenters, mailing initial
config files on flash drives, or emailing config files and asking a
third-party to copy and paste it over a serial terminal. It does not
protect against devices with malicious firmware, nor theft and reuse
of devices.
An attacker (e.g a malicious datacenter employee) who has physical
access to the device before it is connected to the network the
attacker may be able to extract the device private key (especially if
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it isn't stored in a TPM), pretend to be the device when connecting
to the network, and download and extract the (encrypted) config file.
This mechanism does not protect against a malicious vendor - while
the keypair 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
keypair 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 bootstrapping mechanism, security conscious
operators may wish to bootstrapping devices with a minimal / less
sensitive config, and then replace this with a more complete one
after install.
8. Acknowledgements
The authors wish to thank everyone who contributed, including Benoit
Claise, Sam Ribeiro, Michael Richardson, Sean Turner and Kent Watsen.
Joe Clarke provided significant comments and review.
9. References
9.1. 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>.
9.2. Informative References
[I-D.ietf-sidr-iana-objects]
Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
progress), May 2011.
[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>.
[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>.
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Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01
o Nothing changed in the template!
From -01 to -03:
o See github commit log (AKA, we forgot to update this!)
o Added Colin Doyle.
From -03 to -04:
Addressed a number of comments received before / at IETF104 (Prague).
These include:
o Pointer to https://datatracker.ietf.org/doc/draft-ietf-netconf-
zerotouch -- included reference to (now) RFC8572 (KW)
o Suggested that 802.1AR IDevID (or similar) could be used. Stress
that this is designed for simplicity (MR)
o Added text to explain that any unique device identifier can be
used, not just serial number - serial number is simple and easy,
but anything which is unique (and can be communicated to the
customer) will work (BF).
o Lots of clarifications from Joe Clarke.
o Make it clear it should first try use the config, and if it
doesn't work, then try decrypt and use it.
o The CA part was confusing people - the certificate is simply a
wrapper for the key, and the Subject just an index, and so removed
that.
o Added a bunch of ASCII diagrams
Appendix B. Demo / proof of concept
This section contains a rough demo / proof of concept of the system.
It is only intended for illustration; presumably things like
algorithms, key lengths, format / containers will provide much fodder
for discussion.
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It uses OpenSSL from the command line, in production something more
automated would be used. In this example, the unique identifier is
the serial number of the router, SN19842256.
B.1. Step 1: Generating the certificate.
This step is performed by the router. It generates a key, then a
csr, and then a self signed certificate.
B.1.1. Step 1.1: Generate the private key.
$ openssl genrsa -out key.pem 2048
Generating RSA private key, 2048 bit long modulus
.................................................
.................................................
..........................+++
...................+++
e is 65537 (0x10001)
B.1.2. Step 1.2: Generate the certificate signing request.
$ openssl req -new -key key.pem -out SN19842256.csr
Country Name (2 letter code) [AU]:.
State or Province Name (full name) [Some-State]:.
Locality Name (eg, city) []:.
Organization Name (eg, company) [Internet Widgits Pty Ltd]:.
Organizational Unit Name (eg, section) []:.
Common Name (e.g. server FQDN or YOUR name) []:SN19842256
Email Address []:.
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:.
B.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 keyserver for
publication (not shown).
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B.2. Step 2: Generating the encrypted config.
The operator now wants to deploy the new router.
They generate the initial config (using whatever magic tool generates
router configs!), fetch the router's certificate and encrypt the
config file to that key. This is done by the operator.
B.2.1. Step 2.1: Fetch the certificate.
$ wget http://keyserv.example.net/certificates/SN19842256.crt
B.2.2. Step 2.2: Encrypt the config file.
I'm using S/MIME 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-----
B.2.3. Step 2.3: Copy config to the config server.
$ scp SN19842256.enc config.example.com:/tftpboot
B.3. Step 3: Decrypting and using the config.
When the router connects to the operator's network it will detect
that 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
config 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 config file (ending in .enc)). It
will then then decrypt the config file, and install it.
B.3.1. Step 3.1: Fetch encrypted config file from config server.
$ tftp 192.0.2.1 -c get SN19842256.enc
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B.3.2. Step 3.2: Decrypt and use the config.
$ 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 config:
$ 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
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Colin Doyle
Juniper Networks
1133 Innovation Way
Sunnyvale, CA 94089
US
Email: cdoyle@juniper.net
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