Network Working Group R. Bush
Internet-Draft IIJ Lab / Dragon Research Lab
Intended status: Standards Track S. Turner
Expires: December 17, 2016 IECA, Inc.
K. Patel
Cisco Systems
June 15, 2016
Router Keying for BGPsec
draft-ietf-sidr-rtr-keying-12
Abstract
BGPsec-speaking routers are provisioned with private keys in order to
sign BGPsec announcements. The corresponding public keys are
published in the global Resource Public Key Infrastructure, enabling
verification of BGPsec messages. This document describes two methods
of generating the public-private key-pairs: router-driven and
operator-driven.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
be interpreted as described in RFC 2119 [RFC2119] only when they
appear in all upper case. They may also appear in lower or mixed
case as English words, without normative meaning.
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
and may be updated, replaced, or obsoleted by other documents at any
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 5, 2016.
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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
(http://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
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Management / Router Communication . . . . . . . . . . . . . . 4
3. Exchanging Certificates . . . . . . . . . . . . . . . . . . . 4
4. Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. PKCS#10 Generation . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Router-Generated Keys . . . . . . . . . . . . . . . . . . 5
5.2. Operator-Generated Keys . . . . . . . . . . . . . . . . . 5
6. Installing Signed Keys . . . . . . . . . . . . . . . . . . . . 5
7. Key Management . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Key Validity . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Key Roll-Over . . . . . . . . . . . . . . . . . . . . . . 7
7.3. Key Revocation . . . . . . . . . . . . . . . . . . . . . . 8
7.4. Router Replacement . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Management/Router Channel Security . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
BGPsec-speaking routers are provisioned with private keys, which
allow them to digitally sign BGPsec announcements. To verify the
signature, the public key, in the form of a certificate [I-D.ietf-
sidr-bgpsec-pki-profiles], is published in the Resource Public Key
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Infrastructure (RPKI). This document describes provisioning of
BGPsec-speaking routers with the appropriate public- private key-
pairs. There are two sub-methods, router-driven and operator-driven.
These two sub-methods differ in where the keys are generated: on the
router in the router-driven method, and elsewhere in the operator-
driven method. Routers are required to support at least one of the
methods in order to work in various deployment environments. Some
routers may not allow the private key to be off-loaded while others
may. While off-loading private keys would ease swapping of routing
engines, exposure of private keys is a well known security risk.
In the operator-driven method, the operator generates the private/
public key-pair and sends it to the router, perhaps in a PKCS#8
package [RFC5958].
In the router-driven method, the router generates its own public/
private key-pair, uses the private key to sign a PKCS#10
certification request [I-D.ietf-sidr-bgpsec-pki-profiles], which
includes the public key), and returns the certification request to
the operator to be forwarded to the RPKI Certification Authority
(CA). The CA returns a PKCS#7, which includes the certified public
key in the form of a certificate, to the operator for loading into
the router; and the CA also publishes the certificate in the RPKI.
The router-driven model mirrors the model used by traditional PKI
subscribers; the private key never leaves trusted storage (e.g.,
Hardware Security Module). This is by design and supports classic
PKI Certification Policies for (often human) subscribers which
require the private key only ever be controlled by the subscriber to
ensure that no one can impersonate the subscriber. For non-humans,
this model does not always work. For example, when an operator wants
to support hot-swappable routers the same private key needs to be
installed in the soon-to-be online router that was used by the the
soon-to-be offline router. This motivated the operator-driven model.
The remainder of this document describes how operators can use the
two methods to provision new and existing routers.
Useful References: [I-D.ietf-sidr-bgpsec-overview] gives an overview
of the BGPsec protocol, [I-D.ietf-sidr-bgpsec-protocol] gives the
gritty details, [I-D.ietf-sidr-bgpsec-pki-profiles] specifies the
format for the PKCS #10 request, and [I-D.ietf-sidr-bgpsec-algs]
specifies the algorithms used to generate the signature.
Useful Formats: Formats for the objects used by routers are:
Private keys see [I-D.ietf-sidr-bgpsec-algs] concerning local storage
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and Section 6 concerning PKCS#8 for operator-generated keys.
Public key certificates see [I-D.ietf-sidr-bgpsec-pki-profiles]
Certificate Status Request (CSR) see [I-D.ietf-sidr-bgpsec-pki-
profiles] concerning the PKCS#10 requests and PKCS#7 responses.
2. Management / Router Communication
Operators are free to use either the router-driven or operator-driven
method as supported by the platform. Regardless of the method
chosen, operators first establish a secure communication channel
between the management system and the router. How this channel is
established is router-specific and is beyond scope of this document.
Though other configuration mechanisms might be used, e.g. NetConf
(see [RFC6470]); for simplicity, in this document, the communication
channel between the management platform and the router is assumed to
be an SSH-protected CLI. See Appendix A for security considerations
for this channel.
3. Exchanging Certificates
The operator management station can exchange certificate requests and
certificates with routers and with the RPKI CA infrastructure using
the application/pkcs10 media type [RFC5967] and application/
pkcs7-mime [RFC5751], respectively, and may use FTP or HTTP per
[RFC2585], or the Enrollment over Secure Transport [RFC7030].
4. Set-Up
To start, the operator uses the communication channel to install the
appropriate RPKI Trust Anchor' Certificate (TA Cert) in the router.
This will later enable the router to validate the router certificate
returned in the PKCS#7.
The operator also configures the Autonomous System (AS) number to be
used in the generated router certificate. This may be the sole AS
configured on the router, or an operator choice if the router is
configured with multiple ASs.
The operator configures or extracts from the router the BGP RouterID
to be used in the generated certificate. In the case where the
operator has chosen not to use unique per-router certificates, a
RouterID of 0 may be used.
5. PKCS#10 Generation
The private key, and hence the PKCS#10 request may be generated by
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the router or by the operator.
5.1. Router-Generated Keys
In the router-generated method, once the protected session is
established and the initial Set-Up (Section 4) performed, the
operator issues a command or commands for the router to generate the
public/private key pair, to generate the PKCS#10 request, and to sign
the PKCS#10 with the private key. Once generated, the PKCS#10 is
returned to the operator over the protected channel.
If a router was to communicate directly with a CA to have the CA
certify the PKCS#10, there would be no way for the CA to authenticate
the router. As the operator knows the authenticity of the router,
the operator must mediate the communication with the CA.
The operator adds the chosen AS number and the RouterID to send to
the RPKI CA for the CA to certify.
5.2. Operator-Generated Keys
In the operator-generated method, the operator generates the public/
private key pair on a management station and installs the private key
into the router over the protected channel. Beware that experience
has shown that copy and paste from a management station to a router
can be unreliable for long texts.
Alternatively, the private key may be encapsulated in a PKCS #8
[RFC5958], the PKCS#8 is further encapsulated in Cryptographic
Message Syntax (CMS) SignedData [RFC5652], and signed by the AS's End
Entity (EE) certificate.
The router SHOULD verify the signature of the encapsulated PKCS#8 to
ensure the returned private key did in fact come from the operator,
but this requires that the operator also provision via the CLI or
include in the SignedData the RPKI CA certificate and relevant AS's
EE certificate(s). The router should inform the operator whether or
not the signature validates to a trust anchor; this notification
mechanism is out of scope.
The operator then creates and signs the PKCS#10 with the private key,
and adds the chosen AS number and RouterID to be sent to the RPKI CA
for the CA to certify.
6. Installing Signed Keys
The operator uses RPKI management tools to communicate with the
global RPKI system to have the appropriate CA validate the PKCS#10
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request, sign the key in the PKCS#10 and generated PKCS#7 response,
as well as publishing the certificate in the Global RPKI. External
network connectivity may be needed if the certificate is to be
published in the Global RPKI.
After the CA certifies the key, it does two things:
1. Publishes the certificate in the Global RPKI. The CA must have
connectivity to the relevant publication point, which in turn
must have external network connectivity as it is part of the
Global RPKI.
2. Returns the certificate to the operator's management station,
packaged in a PKCS#7, using the corresponding method by which it
received the certificate request. It SHOULD include the
certificate chain below the TA Certificate so that the router can
validate the router certificate.
In the operator-generated method, the operator SHOULD extract the
certificate from the PKCS#7, and verify that the private key it holds
corresponds to the returned public key.
In the operator-generated method, the operator has already installed
the private key in the router (see Section 5.2).
The operator provisions the PKCS#7 into the router over the secure
channel.
The router SHOULD extract the certificate from the PKCS#7 and verify
that the private key corresponds to the returned public key. The
router SHOULD inform the operator whether it successfully received
the certificate and whether or not the keys correspond; the mechanism
is out of scope.
The router SHOULD also verify that the returned certificate validates
back to the installed TA Certificate, i.e., the entire chain from the
installed TA Certificate through subordinate CAs to the BGPsec
certificate validate. To perform this verification the CA
certificate chain needs to be returned along with the router's
certificate in the PKCS#7. The router SHOULD inform the operator
whether or not the signature validates to a trust anchor; this
notification mechanism is out of scope.
Note: The signature on the PKCS#8 and Certificate need not be made by
the same entity. Signing the PKCS#8, permits more advanced
configurations where the entity that generates the keys is not the
direct CA.
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Even if the operator cannot extract the private key from the router,
this signature still provides a linkage between a private key and a
router. That is the server can verify the proof of possession (POP),
as required by [RFC6484].
7. Key Management
An operator's responsibilities do not end after key generation, key
provisioning, certificate issuance, and certificate distribution.
They persist for as long as the operator wishes to operate the
BGPsec-speaking router.
7.1. Key Validity
It is critical that a BGPsec speaking router ensures that it is
signing with a valid certificate at all times. To this end, the
operator needs to ensure the router always has a non-expired
certificate. I.e. the key used to sign BGPsec announcements always
has an associated certificate whose expiry time is after the current
time.
Ensuring this is not terribly difficult but requires that either:
1. The router has a mechanism to notify the operator that the
certificate has an impending expiration, and/or
2. The operator notes the expiry time of the certificate and uses a
calendaring program to remind them of the expiry time, and/or
3. The RPKI CA warns the operator of pending expiration, and/or
4. Use some other kind of automated process to search for and track
the expiry times of router certificates.
It is advisable that expiration warnings happen well in advance of
the actual expiry time.
Regardless of the technique used to track router certificate expiry
times, it is advisable to notify additional operators in the same
organization as the expiry time approaches thereby ensuring that the
forgetfulness of one operator does not affect the entire
organization.
Depending on inter-operator relationship, it may be helpful to notify
a peer operator that one or more of their certificates are about to
expire.
7.2. Key Roll-Over
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Routers that support multiple private keys also greatly increase the
chance that routers can continuously speak BGPsec because the new
private key and certificate can be obtained and distributed prior to
expiration of the operational key. Obviously, the router needs to
know when to start using the new key. Once the new key is being
used, having the already distributed certificate ensures continuous
operation.
Whether the certificate is re-keyed (i.e., different key in the
certificate with a new expiry time) or renewed (i.e., the same key in
the certificate with a new expiry time) depends on the key's lifetime
and operational use. Arguably, re-keying the router's BGPsec
certificate every time the certificate expires is more secure than
renewal because it limits the private key's exposure. However, if
the key is not compromised the certificate could be renewed as many
times as allowed by the operator's security policy. Routers that
support only one key can use renewal to ensure continuous operation,
assuming the certificate is renewed and distributed well in advance
of the operational certificate's expiry time.
7.3. Key Revocation
Certain unfortunate circumstances may occur causing a need to revoke
a router's BGPsec certificate. When this occurs, the operator needs
to use the RPKI CA system to revoke the certificate by placing the
router's BGPsec certificate on the Certificate Revocation List (CRL)
as well as re-keying the router's certificate.
When an active router key is to be revoked, the process of requesting
the CA to revoke, the process of the CA actually revoking the
router's certificate, and then the process of re-keying/renewing the
router's certificate, (possibly distributing a new key and
certificate to the router), and distributing the status takes time
during which the operator must decide how they wish to maintain
continuity of operations, with or without the compromised private
key, or whether they wish to bring the router offline to address the
compromise.
Keeping the router operational and BGPsec-speaking is the ideal goal,
but if operational practices do not allow this then reconfiguring the
router to disabling BGPsec is likely preferred to bringing the router
offline.
Routers which support more than one private key, where one is
operational and other(s) are soon-to-be-operational, facilitate
revocation events because the operator can configure the router to
make a soon-to-be-operational key operational, request revocation of
the compromised key, and then make a next generation soon-to-be-
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operational key, all hopefully without needing to take offline or
reboot the router. For routers which support only one operational
key, the operators should create or install the new private key, and
then request revocation of the compromised private key.
7.4. Router Replacement
Currently routers often generate private keys for uses such as SSH,
and the private keys may not be seen or off-loaded from the router.
While this is good security, it creates difficulties when a routing
engine or whole router must be replaced in the field and all software
which accesses the router must be updated with the new keys. Also,
any network based initial contact with a new routing engine requires
trust in the public key presented on first contact.
To allow operators to quickly replace routers without requiring
update and distribution of the corresponding public keys in the RPKI,
routers SHOULD allow the private BGPsec key to be off-loaded via a
protected session, e.g. SSH, NetConf (see [RFC6470]), SNMP, etc.
This lets the operator upload the old private key via the mechanism
used for operator-generated keys, see Section 5.2.
8. Security Considerations
The router's manual will describe whether the router supports one,
the other, or both of the key generation options discussed in the
earlier sections of this draft as well as other important security-
related information (e.g., how to SSH to the router). After
familiarizing one's self with the capabilities of the router,
operators are encouraged to ensure that the router is patched with
the latest software updates available from the manufacturer.
This document defines no protocols so in some sense introduces no new
security considerations. However, it relies on many others and the
security considerations in the referenced documents should be
consulted; notably, those document listed in Section 1 should be
consulted first. PKI-relying protocols, of which BGPsec is one, have
many issues to consider so many in fact entire books have been
written to address them; so listing all PKI-related security
considerations is neither useful nor helpful; regardless, some boot-
strapping-related issues are listed here that are worth repeating:
Public-Private key pair generation: Mistakes here are for all
practical purposes catastrophic because PKIs rely on the pairing
of a difficult to generate public-private key pair with a signer;
all key pairs MUST be generated from a good source of non-
deterministic random input [RFC4086].
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Private key protection at rest: Mistakes here are for all practical
purposes catastrophic because disclosure of the private key allows
another entity to masquerade as (i.e., impersonate) the signer;
all private keys MUST be protected when at rest in a secure
fashion. Obviously, how each router protects private keys is
implementation specific. Likewise, the local storage format for
the private key is just that, a local matter.
Private key protection in transit: Mistakes here are for all
practical purposes catastrophic because disclosure of the private
key allows another entity to masquerade as (i.e., impersonate) the
signer; transport security is therefore strongly RECOMMENDED. The
level of security provided by the transport layer's security
mechanism SHOULD be commensurate with the strength of the BGPsec
key; there's no point in spending time and energy to generate an
excellent public-private key pair and then transmit the private
key in the clear or with a known-to-be-broken algorithm, as it
just undermines trust that the private key has been kept private.
Additionally, operators SHOULD ensure the transport security
mechanism is up to date, in order to addresses all known
implementation bugs.
SSH key management is known, in some cases, to be lax
[I-D.ylonen-sshkeybcp]; employees that no longer need access to
routers SHOULD be removed the router to ensure only those authorized
have access to a router.
Though the CA's certificate is installed on the router and used to
verify that the returned certificate is in fact signed by the CA, the
revocation status of the CA's certificate is rarely checked as the
router may not have global connectivity or CRL-aware software. The
operator MUST ensure that installed CA certificate is valid.
9. IANA Considerations
This document has no IANA Considerations.
10. References
10.1. Normative References
[I-D.ietf-sidr-bgpsec-algs]
Turner, S., "BGP Algorithms, Key Formats, & Signature
Formats", draft-ietf-sidr-bgpsec-algs (work in
progress), March 2013.
[I-D.ietf-sidr-bgpsec-pki-profiles]
Reynolds, M., Turner, S., and S. Kent, "A Profile for
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BGPSEC Router Certificates, Certificate Revocation Lists,
and Certification Requests", draft-ietf-sidr-bgpsec-pki-
profiles (work in progress), October 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, January 2006.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 5652, September 2009.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, August
2010.
10.2. Informative References
[I-D.ietf-sidr-bgpsec-overview]
Lepinski, M. and S. Turner, "An Overview of BGPSEC",
draft-ietf-sidr-bgpsec-overview (work in progress), May
2012.
[I-D.ietf-sidr-bgpsec-protocol]
Lepinski, M., "BGPSEC Protocol Specification", draft-ietf-
sidr-bgpsec-protocol (work in progress), February 2013.
[I-D.ylonen-sshkeybcp]
Ylonen, T. and G. Kent, "Managing SSH Keys for Automated
Access - Current Recommended Practice", draft-ylonen-
sshkeybcp (work in progress), April 2013.
[RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP",
RFC 2585, May 1999.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, April 2004.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, March 2009.
[RFC5647] Igoe, K. and J. Solinas, "AES Galois Counter Mode for the
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Secure Shell Transport Layer Protocol", RFC 5647, August
2009.
[RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm
Integration in the Secure Shell Transport Layer",
RFC 5656, December 2009.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
August 2010.
[RFC6187] Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure
Shell Authentication", RFC 6187, March 2011.
[RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF)
Base Notifications", RFC 6470, February 2012.
[RFC6484] Kent, S., Kong, D., Seo, K., and R. Watro, "Certificate
Policy (CP) for the Resource Public Key Infrastructure
(RPKI)", BCP 173, RFC 6484, February 2012.
[RFC6668] Bider, D. and M. Baushke, "SHA-2 Data Integrity
Verification for the Secure Shell (SSH) Transport Layer
Protocol", RFC 6668, July 2012.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
Appendix A. Management/Router Channel Security
Encryption, integrity, authentication, and key exchange algorithms
used by the secure communication channel SHOULD be of equal or
greater strength than the BGPsec keys they protect, which for the
algorithm specified in [I-D.ietf-sidr-bgpsec-algs] is 128-bit; see
[RFC5480] and by reference [SP800-57] for information about this
strength claim as well as [RFC3766] for "how to determine the length
of an asymmetric key as a function of a symmetric key strength
requirement." In other words, for the encryption algorithm, do not
use export grade crypto (40-56 bits of security), do not use Triple
DES (112 bits of security). Suggested minimum algorithms would be
AES-128: aes128-cbc [RFC4253] and AEAD_AES_128_GCM [RFC5647] for
encryption, hmac-sha2-256 [RFC6668] or AESAD_AES_128_GCM [RFC5647]
for integrity, ecdsa-sha2-nistp256 [RFC5656] for authentication, and
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ecdh-sha2-nistp256 [RFC5656] for key exchange.
Some routers support the use of public key certificates and SSH. The
certificates used for the SSH session are different than the
certificates used for BGPsec. The certificates used with SSH should
also enable a level of security commensurate with BGPsec keys;
x509v3-ecdsa-sha2-nistp256 [RFC6187] could be used for
authentication.
Authors' Addresses
Randy Bush
IIJ / Dragon Research Labs
5147 Crystal Springs
Bainbridge Island, Washington 98110
US
Email: randy@psg.com
Sean Turner
sn3rd
Email: sean@sn3rd.com
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: keyupate@cisco.com
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