Network Working Group W. Kumari
Internet-Draft Google
Intended status: Informational July 8, 2016
Expires: January 9, 2017
Secure Device Install
draft-wkumari-opsawg-sdi-00
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 was a
standard, secure way to initially provision the devices.
This document extended existing auto-install / Zero-Touch
Provisioning 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 January 9, 2017.
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Copyright Notice
Copyright (c) 2016 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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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Overview / Example Scenario . . . . . . . . . . . . . . . . . 4
3. Vendor Role / Requirements . . . . . . . . . . . . . . . . . 4
3.1. CA Infrastructure . . . . . . . . . . . . . . . . . . . . 4
3.2. Certificate Publication Server . . . . . . . . . . . . . 5
3.3. Initial Device Boot . . . . . . . . . . . . . . . . . . . 5
3.4. Subsequent Boots . . . . . . . . . . . . . . . . . . . . 5
4. Operator Role / Responsibilities . . . . . . . . . . . . . . 6
4.1. Administrative . . . . . . . . . . . . . . . . . . . . . 6
4.2. Technical . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Future enhancements / Discussion . . . . . . . . . . . . . . 6
5.1. Key storage . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Key replacement . . . . . . . . . . . . . . . . . . . . . 6
5.3. Device reinstall . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8
Appendix B. Demo / proof of concept . . . . . . . . . . . . . . 8
B.1. Step 1: Generating the certificate. . . . . . . . . . . . 8
B.1.1. Step 1.1: Generate the private key. . . . . . . . . . 8
B.1.2. Step 1.2: Generate the certificate signing request. . 8
B.1.3. Step 1.3: Generate the (self signed) certificate
itself. . . . . . . . . . . . . . . . . . . . . . . . 9
B.2. Step 2: Generating the encrypted config. . . . . . . . . 9
B.2.1. Step 2.1: Fetch the certificate. . . . . . . . . . . 9
B.2.2. Step 2.2: Encrypt the config file. . . . . . . . . . 9
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B.2.3. Step 2.3: Copy config to the config server. . . . . . 10
B.3. Step 3: Decrypting and using the config. . . . . . . . . 10
B.3.1. Step 3.1: Fetch encrypted config file from config
server. . . . . . . . . . . . . . . . . . . . . . . . 10
B.3.2. Step 3.2: Decrypt and use the config. . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
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 which can be
contracted to perform things like physical installs, reboot devices,
load 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 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.
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].
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2. Overview / Example Scenario
Sirius Cybernetics Corp needs another peering router, and so they
order another router from Acme Network Widgets, to be dropped-shipped
to a POP. Acme begins assembling the new device, and tells Sirius
what the new device's serial number will be (SN:17894321). During
the initial boot / testing, the router generates a public-private
keypair, and publishes the public part to Acme's keyserver (in a
certificate, for ease of use).
While Acme is shipping the new device, Sirius begins generating the
initial device configuration. Once the config is ready, Sirius
contacts the Acme keyserver, provides the serial number of the new
device and fetches the device's public key. Sirius then encrypts the
device configuration and puts this encrypted config on a (local) TFTP
server.
When the POP recieves the new device, they install it in Sirius'
rack, and connect the cables as instructed. The new device powers up
and discovers that it has not yet been configured. It enters its
autoboot state, and begins DHCPing. Sirius' DHCP server provides it
with an IP address and the address of the configuration server. The
router uses TFTP to fetch a file named according to its serial number
(acme_17894321.cfg). It then uses its private key to decrypt this
file, and, assuming it validates, install 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
they will not be able to decrypt the files.
[ 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. CA Infrastructure
The vendor needs to run some (simple) CA infrastructure to sign and
publish certificates. When a device is initially powered on (in the
factory) it will generate a public / private keypair and a
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Certificate Signing Request (CSR), with the commonName being the
Serial Number of the device [TODO(WK): Define Serial Number (RE,
chassis, ?)]. The device sends this CSR to the CA, which signs the
CSR, returns the certificate to the device and also sends it to a
certificate publication server.
3.2. Certificate Publication Server
The certificate publication server contains a database of all signed
certificates. Customers (e.g Sirius Cybernetics Corp) query this
server with a serial number, and retrieve the associated certificate.
It is expected that operators will receive the serial numbers of
newly purchased devices when they purchase them, and that some
automated system 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.
[ Ed: The vendor may not want to expose (for commercial reasons) how
many devices it has made. This can be mitigated by using non-
contiguous serial numbers, and simply creating "fake devices", etc. ]
3.3. Initial Device Boot
When the device is very first powered on, it will generate its
keypair. It then generates a CSR (including the device serial
number) and sends it to the vendor's CA, which signs the certificate.
The device receives the signed certificate and stores it.
3.4. Subsequent Boots
After the initial boot, it the device has no (valid) configuration
file, it will perform standard an auto-install type functionality.
For example, it will perform DHCP Discovery until it gets a DHCP
offer including DHCP option 66 or 150. It will contact the server
listed in these DHCP options and download a configuration file named
config_<serial_number>.cfg. This is all existing (often vendor
proprietary) functionality.
After retrieving the config file, Secure Device Install devices 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.
[ Ed note: SDI will also allows additional functionality, like always
storing the configs encrypted, having the device store its config
encrypted in flash (so that e.g RMAing a routing engine will not leak
config, etc. I'm not describing this in detail because:
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1. I want to keep this document simple and focused and, more
importantly
2. I left converting this into ID format until the draft cuff-off
and have run out of time :-) ]
4. Operator Role / Responsibilities
4.1. Administrative
When purchasing a new device, the accounting department will need to
get the 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 serial number of the
device). They will then encrypt the initial configuration to that
key, and place it on the TFTP server, named config_<SN>.enc. See
Appendix B for examples.
5. Future enhancements / Discussion
[ Ed note: Ed / RFC Editor to remove this section before publication.
]
5.1. Key storage
Currently most network devices will store the private key in NV
storage (NVRAM / Flash / Disk), but some vendors are already planning
on including a TPM module in their devices. 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 "device", and not,
for example, (redundant) routing engines.
5.2. Key replacement
It is anticipated that some operator may want to replace the (vendor
provided) keys after installing the device. This would remove (some)
concerns that the vendor may have kept a copy of the private key, or
that the device may have been intercepted during shipping and the
private key duplicated. This would also allow for the use of
certificates signed by the operator's CA (e.g using RFC7030 -
Enrollment over Secure Transport) this is a trivial operation, but is
not described here (to avoid cluttering up the doc).
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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 too vendor
specific) that vendors will allow the operator to e.g scp 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)).
6. IANA Considerations
This document contains no IANA considerations.Template: Fill this in!
7. Security Considerations
This needs to be completed, including:
1. We are trusting the vendor to have not kept a copy of the private
key when the device initially generated its keypair.
Unfortunately you are already trusting the vendor in many ways -
it could have included a backdoor in it's code, etc.
2. Devices should be storing their keying information in something
like a TPM, to help mitigate the private key being extracted (e.g
read off disk) in shipping, when the device is first unpacked by
smart-hands, etc). A number of vendors are already discussing
including TPM for other security functions.
8. Acknowledgements
The authors wish to thank some folk.
9. References
9.1. Normative References
[IANA.AS_Numbers]
IANA, "Autonomous System (AS) Numbers",
<http://www.iana.org/assignments/as-numbers>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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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.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01
o Nothing changed in the template!
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.
It uses OpenSSL from the command line, in production something more
automated would be used. In this example, the serial number of the
router is 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.
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$ 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).
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
definetly not the best way to do this.
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$ 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
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
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Author's Address
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
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