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12 13 RFC 6480
Secure Inter-Domain Routing M. Lepinski
Working Group S. Kent
Internet Draft BBN Technologies
Intended status: Informational November 3, 2008
Expires: May 3, 2009
An Infrastructure to Support Secure Internet Routing
draft-ietf-sidr-arch-04.txt
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Abstract
This document describes an architecture for an infrastructure to
support improved security of Internet routing. The foundation of this
architecture is a public key infrastructure (PKI) that represents the
allocation hierarchy of IP address space and Autonomous System
Numbers; and a distributed repository system for storing and
disseminating the data objects that comprise the PKI, as well as
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other signed objects necessary for improved routing security. As an
initial application of this architecture, the document describes how
a holder of IP address space can explicitly and verifiably authorize
one or more ASes to originate routes to that address space. Such
verifiable authorizations could be used, for example, to more
securely construct BGP route filters.
Table of Contents
1. Introduction...................................................3
2. PKI for Internet Number Resources..............................4
2.1. Role in the overall architecture..........................5
2.2. CA Certificates...........................................5
2.3. End-Entity (EE) Certificates..............................7
2.4. Trust Anchors.............................................8
2.5. Default Trust Anchor Considerations.......................8
2.6. Representing Early-Registration Transfers (ERX)..........10
3. Route Origination Authorizations..............................10
3.1. Role in the overall architecture.........................11
3.2. Syntax and semantics.....................................11
4. Repositories..................................................13
4.1. Role in the overall architecture.........................14
4.2. Contents and structure...................................14
4.3. Access protocols.........................................16
4.4. Access control...........................................16
5. Manifests.....................................................17
5.1. Syntax and semantics.....................................17
6. Local Cache Maintenance.......................................18
7. Common Operations.............................................18
7.1. Certificate issuance.....................................19
7.2. ROA management...........................................20
7.2.1. Single-homed subscribers (without portable allocations)
...........................................................20
7.2.2. Multi-homed subscribers.............................21
7.2.3. Portable allocations................................21
7.3. Route filter construction................................22
8. Security Considerations.......................................23
9. IANA Considerations...........................................24
10. Acknowledgments..............................................24
11. References...................................................25
11.1. Normative References....................................25
11.2. Informative References..................................25
Authors' Addresses...............................................26
Intellectual Property Statement..................................26
Disclaimer of Validity...........................................27
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1. Introduction
This document describes an architecture for an infrastructure to
support improved security for BGP routing [2] for the Internet. The
architecture encompasses three principle elements:
. a public key infrastructure (PKI)
. digitally-signed routing objects to support routing security
. a distributed repository system to hold the PKI objects and the
signed routing objects
The architecture described by this document enables an entity to
verifiably assert that it is the legitimate holder of a set of IP
addresses or a set of Autonomous System (AS) numbers. As an initial
application of this architecture, the document describes how a holder
of IP address space can explicitly and verifiably authorize one or
more ASes to originate routes to that address space. Such verifiable
authorizations could be used, for example, to more securely construct
BGP route filters. In addition to this initial application, the
infrastructure defined by this architecture also is intended to
provide future support for security protocols such as S-BGP [10] or
soBGP [11]. This architecture is applicable to the routing of both
IPv4 and IPv6 datagrams. IPv4 and IPv6 are currently the only address
families supported by this architecture. Thus, for example, use of
this architecture with MPLS labels is beyond the scope of this
document.
In order to facilitate deployment, the architecture takes advantage
of existing technologies and practices. The structure of the PKI
element of the architecture corresponds to the existing resource
allocation structure. Thus management of this PKI is a natural
extension of the resource-management functions of the organizations
that are already responsible for IP address and AS number resource
allocation. Likewise, existing resource allocation and revocation
practices have well-defined correspondents in this architecture. To
ease implementation, existing IETF standards are used wherever
possible; for example, extensive use is made of the X.509 certificate
profile defined by PKIX [3] and the extensions for IP Addresses and
AS numbers representation defined in RFC 3779 [5]. Also CMS [4] is
used as the syntax for the newly-defined signed objects required by
this infrastructure.
As noted above, the infrastructure is comprised of three main
components: an X.509 PKI in which certificates attest to holdings of
IP address space and AS numbers; non-certificate/CRL signed objects
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(including route origination authorizations and manifests) used by
the infrastructure; and a distributed repository system that makes
all of these signed objects available for use by ISPs in making
routing decisions. These three basic components enable several
security functions; this document describes how they can be used to
improve route filter generation, and to perform several other common
operations in such a way as to make them cryptographically
verifiable.
1.1. Terminology
It is assumed that the reader is familiar with the terms and concepts
described in "Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile" [3], and "X.509
Extensions for IP Addresses and AS Identifiers" [5].
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 RFC-2119 [1].
2. PKI for Internet Number Resources
Because the holder of a block IP address space is entitled to define
the topological destination of IP datagrams whose destinations fall
within that block, decisions about inter-domain routing are
inherently based on knowledge the allocation of the IP address space.
Thus, a basic function of this architecture is to provide
cryptographically verifiable attestations as to these allocations. In
current practice, the allocation of IP address is hierarchic. The
root of the hierarchy is IANA. Below IANA are five Regional Internet
Registries (RIRs), each of which manages address and AS number
allocation within a defined geopolitical region. In some regions the
third tier of the hierarchy includes National Internet Registries and
(NIRs) as well as Local Internet Registries (LIRs) and subscribers
with so-called ''portable'' (provider-independent) allocations. (The
term LIR is used in some regions to refer to what other regions
define as an ISP. Throughout the rest of this document we will use
the term LIR/ISP to simplify references to these entities.) In other
regions the third tier consists only of LIRs/ISPs and subscribers
with portable allocations.
In general, the holder of a set of IP addresses may sub-allocate
portions of that set, either to itself (e.g., to a particular unit of
the same organization), or to another organization, subject to
contractual constraints established by the registries. Because of
this structure, IP address allocations can be described naturally by
a hierarchic public-key infrastructure, in which each certificate
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attests to an allocation of IP addresses, and issuance of subordinate
certificates corresponds to sub-allocation of IP addresses. The
above reasoning holds true for AS number resources as well, with the
difference that, by convention, AS numbers may not be sub-allocated
except by regional or national registries. Thus allocations of both
IP addresses and AS numbers can be expressed by the same PKI. Such a
PKI is a central component of this architecture.
2.1. Role in the overall architecture
Certificates in this PKI are called Resource Certificates, and
conform to the certificate profile for such certificates [6].
Resource certificates attest to the allocation by the (certificate)
issuer of IP addresses or AS numbers to the subject. They do this by
binding the public key contained in the Resource Certificate to the
IP addresses or AS numbers included in the certificate's IP Address
Delegation or AS Identifier Delegation Extensions, respectively, as
defined in RFC 3779 [5].
An important property of this PKI is that certificates do not attest
to the identity of the subject. Therefore, the subject names used in
certificates are not intended to be ''descriptive.'' That is, this
PKI is intended to provide authorization, but not authentication.
This is in contrast to most PKIs where the issuer ensures that the
descriptive subject name in a certificate is properly associated with
the entity that holds the private key corresponding to the public key
in the certificate. Because issuers need not verify the right of an
entity to use a subject name in a certificate, they avoid the costs
and liabilities of such verification. This makes it easier for these
entities to take on the additional role of CA.
Most of the certificates in the PKI assert the basic facts on which
the rest of the infrastructure operates. CA certificates within the
PKI attest to IP address space and AS number holdings. End-entity
(EE) certificates are issued by resource holder CAs to delegate the
authority attested by their allocation certificates. The primary use
for EE certificates is the validation of Route Origination
Authorizations (ROAs). Additionally, signed objects called manifests
will be used to help ensure the integrity of the repository system,
and the signature on each manifest will be verified via an EE
certificate.
2.2. CA Certificates
Any holder of Internet resources who is authorized to sub-allocate
them must be able to issue Resource Certificates to correspond to
these sub-allocations. Thus, for example, CA certificates will be
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associated with IANA and each of the RIRs, NIRs, and LIRs/ISPs. A CA
certificate also is required to enable a resource holder to issue
ROAs, because it must issue the corresponding end-entity certificate
used to validate each ROA. Thus some subscribers also will need to
have CA certificates for their allocations, e.g., subscribers with
portable allocations, to enable them to issue ROAs. (A subscriber who
is not multi-homed, whose allocation comes from an LIR/ISP, and who
has not moved to a different LIR/ISP, need not be represented in the
PKI. Moreover, a multi-homed subscriber with an allocation from an
LIR/ISP may or may not need to be explicitly represented, as
discussed in Section 6.2.2)
Unlike in most PKIs, the distinguished name of the subject in a CA
certificate is chosen by the certificate issuer. If the subject of a
certificate is an RIR or IANA, then the distinguished name of the
subject will be chosen to convey the identity of the registry and
should consist of (a subset of) the following attributes: country,
organization, organizational unit, and common name. For example, an
appropriate subject name for the APNIC RIR might be:
. Country: AU
. Organization: Asia Pacific Network Information Centre
. Common Name: APNIC Resource Certification Authority
If the subject of a certificate is not an RIR or IANA, (e.g., the
subject is a NIR, or LIR/ISP) the distinguished name MUST consist
only of the common name attribute and must not attempt to convey the
identity of the subject in a descriptive fashion. Additionally, the
subject's distinguished name must be unique among all certificates
issued by a given authority. In this PKI, the certificate issuer,
being an internet registry or LIR/ISP, is not in the business of
verifying the legal right of the subject to assert a particular
identity. Therefore, selecting a distinguished name that does not
convey the identity of the subject in a descriptive fashion minimizes
the opportunity for the subject to misuse the certificate to assert
an identity, and thus minimizes the legal liability of the issuer.
Since all CA certificates are issued to subjects with whom the issuer
has an existing relationship, it is recommended that the issuer
select a subject name that enables the issuer to easily link the
certificate to existing database records associated with the subject.
For example, an authority may use internal database keys or
subscriber IDs as the subject common name in issued certificates.
Each Resource Certificate attests to an allocation of resources to
its holder, so entities that have allocations from multiple sources
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will have multiple CA certificates. A CA also may issue distinct
certificates for each distinct allocation to the same entity, if the
CA and the resource holder agree that such an arrangement will
facilitate management and use of the certificates. For example, an
LIR/ISP may have several certificates issued to it by one registry,
each describing a distinct set of address blocks, because the LIR/ISP
desires to treat the allocations as separate.
2.3. End-Entity (EE) Certificates
The private key corresponding to public key contained in an EE
certificate is not used to sign other certificates in a PKI. The
primary function of end-entity certificates in this PKI is the
verification of signed objects that relate to the usage of the
resources described in the certificate, e.g., ROAs and manifests.
For ROAs and manifests there will be a one-to-one correspondence
between end-entity certificates and signed objects, i.e., the private
key corresponding to each end-entity certificate is used to sign
exactly one object, and each object is signed with only one key.
This property allows the PKI to be used to revoke these signed
objects, rather than creating a new revocation mechanism. When the
end-entity certificate used to sign an object has been revoked, the
signature on that object (and any corresponding assertions) will be
considered invalid, so a signed object can be effectively revoked by
revoking the end-entity certificate used to sign it.
A secondary advantage to this one-to-one correspondence is that the
private key corresponding to the public key in a certificate is used
exactly once in its lifetime, and thus can be destroyed after it has
been used to sign its one object. This fact should simplify key
management, since there is no requirement to protect these private
keys for an extended period of time.
Although this document describes only two uses for end-entity
certificates, additional uses will likely be defined in the future.
For example, end-entity certificates could be used as a more general
authorization for their subjects to act on behalf of the holder of
the specified resources. This could facilitate authentication of
inter-ISP interactions, or authentication of interactions with the
repository system. These additional uses for end-entity certificates
may require retention of the corresponding private keys, even though
this is not required for the private keys associated with end-entity
certificates keys used for verification of ROAs and manifests, as
described above.
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2.4. Trust Anchors
In any PKI, each relying party (RP) is free to choose its own set of
trust anchors. This general property of PKIs applies here as well.
There is an extant IP address space and AS number allocation
hierarchy. IANA is the obvious candidate to be the TA, but
operational considerations may argue for a multi-TA PKI, e.g., one in
which both IANA and the RIRs form a default set of trust anchors.
Nonetheless, every relying party is free to choose a different set of
trust anchors to use for certificate validation operations.
For example, an RP (e.g., an LIR/ISP) could create a trust anchor to
which all address space and/or all AS numbers are assigned, and for
which the RP knows the corresponding private key. The RP could then
issue certificates under this trust anchor to whatever entities in
the PKI it wishes, with the result that the certificate paths
terminating at this locally-installed trust anchor will satisfy the
RFC 3779 validation requirements.
An RP who elects to create and manage its own set of trust anchors
may fail to detect allocation errors that arise under such
circumstances, but the resulting vulnerability is local to the RP.
2.5. Default Trust Anchors
The profile for resource certificates [6] specifies a format for a
putative trust anchor to distribute to relying parties trust anchor
material consisting of both a self-signed certificate (which would
form the root of certification paths in the PKI) along with an
additional 'trust anchor' certificate used to validate the self-
signed certificate. Any entity claiming authoritative information
regarding the allocation of a portion of IP address space may offer
itself up in the role of a putative trust anchor by distributing such
material (in an out-of-band fashion). Given the extant IP address
space and AS number allocation hierarchy, it is envisioned that IANA
and the five RIRs will provide trust anchor information to relying
parties and that relying parties will generally accept trust anchors
from this set.
IANA forms the root of the extant IP address space and AS number
allocation hierarchy. Therefore, it is expected that IANA will
provide to relying parties trust anchor material whose self-signed
certificate has RFC 3779 extensions corresponding either to the
entirety of IP address space, or alternatively that portion of IP
address space that has not been sub-allocated to any of the five
RIRs.
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As an example of the use of IANA as a trust anchor, consider the use
of private IP address space (i.e., 10/8, 172.16/12, and 192.168/16 in
IPv4 and FC00::/7 in IPv6). IANA could issue a CA certificate for
these blocks of private address space and then destroy the private
key corresponding to the public key in the certificate. In this way,
any relying party who configured IANA as their sole trust anchor
would automatically reject any ROA containing private addresses,
appropriate behavior with regard to routing in the public Internet.
On the other hand, such an approach would not interfere with an
organization that wishes to use private address space in conjunction
with BGP and this PKI technology. Such an organization could
configure its relying parties with an additional, local trust anchor
that issues certificates for private addresses used within the
organization. In this manner, BGP advertisements for these private
addresses would be accepted within the organization but would be
rejected if mistakenly sent outside the private address space context
in question.
In the DNSSEC context, IANA (as the root of the DNS) is already
experimenting with the operational procedures needed to digitally
sign the root zone. This is very much analogous to the role it would
play if it were to act as the default trust anchor for the RPKI, even
though DNSSEC does not make use of X.509 certificates. Nonetheless,
it is appropriate consider alternative default trust anchor models,
if IANA does not act in this capacity. This motivates the
consideration of alternative default trust anchor options for RPKI
relying parties.
Essentially all allocated IP address and AS number resources are sub-
allocated by IANA to one of the five RIRs. Therefore, it is expected
that each of the five RIRs will provide trust anchor material provide
to relying parties trust anchor material whose self-signed
certificate has RFC 3779 extensions corresponding to the IP address
and AS number resources that they manage.
One issue that the RIRs will need to consider when providing trust
anchor material is how to handle the approximately 49 /8 prefixes
containing legacy IPv4 allocations that are not each allocated to a
single RIR. Currently, for the purpose of administering reverse DNS
zones, each of these prefixes is administered by a single RIR who
delegates authority for allocations within the prefix as appropriate.
This existing arrangement could be used as the template for the
assignment of administrative responsibility for the certification of
these address blocks in the RPKI. Such an arrangement would in no way
alter the administrative arrangements and the associated policies
that apply to the individual legacy allocations that have been made
from these address blocks.
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2.6. Representing Early-Registration Transfers (ERX)
Currently, IANA allocates IPv4 address space to the RIRs at the level
of /8 prefixes. However, there exist allocations that cross these RIR
boundaries. For example, A LACNIC customer may have an allocation
that falls within a /8 prefix administered by ARIN. Therefore, the
resource PKI must be able to represent such transfers from one RIR to
another in a manner that permits the validation of certificates with
RFC 3779 extensions.
+-------------------------------+
| |
| LACNIC Administrative |
| Boundary |
| |
+--------+ | +--------+ | +--------+
| ARIN | | | LACNIC | | | RIPE |
| ROOT | | | ROOT | | | ROOT |
+--------+ | +--------+ | +--------+
\ | | /
------------ ------------
| \ / |
| +--------+ +--------+ |
| | LACNIC | | LACNIC | |
| | CA | | CA | |
| +--------+ +--------+ |
| |
+-------------------------------+
FIGURE 1: Representing EXR
To represent such transfers, RIRs will need to manage multiple CA
certificates, each with distinct public (and corresponding private)
keys. Each RIR will have a single ''root'' certificate (e.g., a self-
signed certificate or a certificate signed by IANA, see Section 2.5),
plus one additional CA certificate for each RIR from which it
receives a transfer. Each of these additional CA certificates will be
issued under the ''root'' certificate of the RIR from which the
transfer is received. This means that although the certificate is
bound to the RIR that receives the transfer, for the purposes of
certificate path construction and validation, it does not appear
under that RIR's ''root'' certificate (see Figure 1).
3. Route Origination Authorizations
The information on IP address allocation provided by the PKI is not,
in itself, sufficient to guide routing decisions. In particular, BGP
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is based on the assumption that the AS that originates routes for a
particular prefix is authorized to do so by the holder of that prefix
(or an address block encompassing the prefix); the PKI contains no
information about these authorizations. A Route Origination
Authorization (ROA) makes such authorization explicit, allowing a
holder of address space to create an object that explicitly and
verifiably asserts that an AS is authorized originate routes to
prefixes.
3.1. Role in the overall architecture
A ROA is an attestation that the holder of a set of prefixes has
authorized an autonomous system to originate routes for those
prefixes. A ROA is structured according to the format described in
[7]. The validity of this authorization depends on the signer of the
ROA being the holder of the prefix(es) in the ROA; this fact is
asserted by an end-entity certificate from the PKI, whose
corresponding private key is used to sign the ROA.
ROAs may be used by relying parties to verify that the AS that
originates a route for a given IP address prefix is authorized by the
holder of that prefix to originate such a route. For example, an ISP
might use ROAs as inputs to route filter construction for use by its
BGP routers. These filters would prevent importation of any route in
which the origin AS of the AS-PATH attribute is not an AS that is
authorized (via a valid ROA) to originate the route. (See Section 6.3
for more details.)
Initially, the repository system will be the primary mechanism for
disseminating ROAs, since these repositories will hold the
certificates and CRLs needed to verify ROAs. In addition, ROAs also
could be distributed in BGP UPDATE messages or via other
communication paths, if needed to meet timeliness requirements.
3.2. Syntax and semantics
A ROA constitutes an explicit authorization for a single AS to
originate routes to one or more prefixes, and is signed by the holder
of those prefixes. A detailed specification of the ROA syntax can be
found in [7] but, at a high level, a ROA consists of (1) an AS
number; (2) a list of IP address prefixes; and, optionally, (3) for
each prefix, the maximum length of more specific (longer) prefixes
that the AS is also authorized to advertise. (This last element
facilitates a compact authorization to advertise, for example, any
prefixes of length 20 to 24 contained within a given length 20
prefix.)
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Note that a ROA contains only a single AS number. Thus, if an ISP has
multiple AS numbers that will be authorized to originate routes to
the prefix(es) in the ROA, an address space holder will need to issue
multiple ROAs to authorize the ISP to originate routes from any of
these ASes.
A ROA is signed using the private key corresponding to the public key
in an end-entity certificate in the PKI. In order for a ROA to be
valid, its corresponding end-entity (EE) certificate must be valid
and the IP address prefixes of the ROA must exactly match the IP
address prefix(es) specified in the EE certificate's RFC 3779
extension. Therefore, the validity interval of the ROA is implicitly
the validity interval of its corresponding certificate. A ROA is
revoked by revoking the corresponding EE certificate. There is no
independent method of invoking a ROA. One might worry that this
revocation model could lead to long CRLs for the CA certification
that is signing the EE certificates. However, routing announcements
on the public internet are generally quite long lived. Therefore, as
long as the EE certificates used to verify a ROA are given a validity
interval of several months, the likelihood that many ROAs would need
to revoked within time that is quite low.
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--------- ---------
| RIR | | NIR |
| CA | | CA |
--------- ---------
| |
| |
| |
--------- ---------
| ISP | | ISP |
| CA 1 | | CA 2 |
--------- ---------
| \ |
| ----- |
| \ |
---------- ---------- ----------
| ISP | | ISP | | ISP |
| EE 1a | | EE 1b | | EE 2 |
---------- ---------- ----------
| | |
| | |
| | |
---------- ---------- ----------
| ROA 1a | | ROA 1b | | ROA 2 |
---------- ---------- ----------
FIGURE 2: This figure illustrates an ISP with allocations from two
sources (and RIR and an NIR). It needs two CA certificates due to RFC
3779 rules.
Because each ROA is associated with a single end-entity certificate,
the set of IP prefixes contained in a ROA must be drawn from an
allocation by a single source, i.e., a ROA cannot combine allocations
from multiple sources. Address space holders who have allocations
from multiple sources, and who wish to authorize an AS to originate
routes for these allocations, must issue multiple ROAs to the AS.
4. Repositories
Initially, an LIR/ISP will make use of the resource PKI by acquiring
and validating every ROA, to create a table of the prefixes for which
each AS is authorized to originate routes. To validate all ROAs, an
LIR/ISP needs to acquire all the certificates and CRLs. The primary
function of the distributed repository system described here is to
store these signed objects and to make them available for download by
LIRs/ISPs. Note that this repository system provides a mechanism by
which relying parties can pull fresh data at whatever frequency they
deem appropriate. However, it does not provide a mechanism for
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pushing fresh data to relying parties (e.g. by including resource PKI
objects in BGP or other protocol messages) and such a mechanism is
beyond the scope of the current document.
The digital signatures on all objects in the repository ensure that
unauthorized modification of valid objects is detectable by relying
parties. Additionally, the repository system uses manifests (see
Section 5) to ensure that relying parties can detect the deletion of
valid objects and the insertion of out of date, valid signed objects.
The repository system is also a point of enforcement for access
controls for the signed objects stored in it, e.g., ensuring that
records related to an allocation of resources can be manipulated only
by authorized parties. The use access controls prevents denial of
service attacks based on deletion of or tampering to repository
objects. Indeed, although relying parties can detect tampering with
objects in the repository, it is preferable that the repository
system prevent such unauthorized modifications to the greatest extent
possible.
4.1. Role in the overall architecture
The repository system is the central clearing-house for all signed
objects that must be globally accessible to relying parties. When
certificates and CRLs are created, they are uploaded to this
repository, and then downloaded for use by relying parties (primarily
LIRs/ISPs). ROAs and manifests are additional examples of such
objects, but other types of signed objects may be added to this
architecture in the future. This document briefly describes the way
signed objects (certificates, CRLs, ROAs and manifests) are managed
in the repository system. As other types of signed objects are added
to the repository system it will be necessary to modify the
description, but it is anticipated that most of the design principles
will still apply. The repository system is described in detail in
[9].
4.2. Contents and structure
Although there is a single repository system that is accessed by
relying parties, it is comprised of multiple databases. These
databases will be distributed among registries (RIRs, NIRs,
LIRs/ISPs). At a minimum, the database operated by each registry will
contain all CA and EE certificates, CRLs, and manifests signed by the
CA(s) associated with that registry. Repositories operated by
LIRs/ISPs also will contain ROAs. Registries are encouraged maintain
copies of repository data from their customers, and their customer's
customers (etc.), to facilitate retrieval of the whole repository
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contents by relying parties. Ideally, each RIR will hold PKI data
from all entities within its geopolitical scope.
For every certificate in the PKI, there will be a corresponding file
system directory in the repository that is the authoritative
publication point for all objects (certificates, CRLs, ROAs and
manifests) verifiable via this certificate. A certificate's Subject
Information Authority (SIA) extension provides a URI that references
this directory. Additionally, a certificate's Authority Information
Authority (AIA) extension contains a URI that references the
authoritative location for the CA certificate under which the given
certificate was issued. That is, if certificate A is used to verify
certificate B, then the AIA extension of certificate B points to
certificate A, and the SIA extension of certificate A points to a
directory containing certificate B (see Figure 2).
+--------+
+--------->| Cert A |<----+
| | CRLDP | | +---------+
| | AIA | | +-->| A's CRL |<-+
| +--------- SIA | | | +---------+ |
| | +--------+ | | |
| | | | |
| | +---+----+ |
| | | | |
| | +---------------|---|-----------------+ |
| | | | | | |
| +->| +--------+ | | +--------+ | |
| | | Cert B | | | | Cert C | | |
| | | CRLDP ----+ | | CRLDP -+--------+
+----------- AIA | +----- AIA | |
| | SIA | | SIA | |
| +--------+ +--------+ |
| |
+-------------------------------------+
FIGURE 3: In this example, certificates B and C are issued under
certificate A. Therefore, the AIA extensions of certificates B and C
point to A, and the SIA extension of certificate A points to the
directory containing certificates B and C.
If a CA certificate is reissued with the same public key, it should
not be necessary to reissue (with an updated AIA URI) all
certificates signed by the certificate being reissued. Therefore, a
certification authority SHOULD use a persistent URI naming scheme for
issued certificates. That is, reissued certificates should use the
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same publication point as previously issued certificates having the
same subject and public key, and should overwrite such certificates.
4.3. Access protocols
Repository operators will choose one or more access protocols that
relying parties can use to access the repository system. These
protocols will be used by numerous participants in the infrastructure
(e.g., all registries, ISPs, and multi-homed subscribers) to maintain
their respective portions of it. In order to support these
activities, certain basic functionality is required of the suite of
access protocols, as described below. No single access protocol need
implement all of these functions (although this may be the case), but
each function must be implemented by at least one access protocol.
Download: Access protocols MUST support the bulk download of
repository contents and subsequent download of changes to the
downloaded contents, since this will be the most common way in which
relying parties interact with the repository system. Other types of
download interactions (e.g., download of a single object) MAY also be
supported.
Upload/change/delete: Access protocols MUST also support mechanisms
for the issuers of certificates, CRLs, and other signed objects to
add them to the repository, and to remove them. Mechanisms for
modifying objects in the repository MAY also be provided. All access
protocols that allow modification to the repository (through
addition, deletion, or modification of its contents) MUST support
verification of the authorization of the entity performing the
modification, so that appropriate access controls can be applied (see
Section 4.4).
Current efforts to implement a repository system use RSYNC [12] as
the single access protocol. RSYNC, as used in this implementation,
provides all of the above functionality. A document specifying the
conventions for use of RSYNC in the PKI will be prepared.
4.4. Access control
In order to maintain the integrity of information in the repository,
controls must be put in place to prevent addition, deletion, or
modification of objects in the repository by unauthorized parties.
The identities of parties attempting to make such changes can be
authenticated through the relevant access protocols. Although
specific access control policies are subject to the local control of
repository operators, it is recommended that repositories allow only
the issuers of signed objects to add, delete, or modify them.
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Alternatively, it may be advantageous in the future to define a
formal delegation mechanism to allow resource holders to authorize
other parties to act on their behalf, as suggested in Section 2.3
above.
5. Manifests
A manifest is a signed object listing of all of the signed objects
issued by an authority responsible for a publication in the
repository system. For each certificate, CRL, or ROA issued by the
authority, the manifest contains both the name of the file containing
the object, and a hash of the file content.
As with ROAs, a manifest is signed by a private key, for which the
corresponding public key appears in an end-entity certificate. This
EE certificate, in turn, is signed by the CA in question. The EE
certificate private key may be used to issue one for more manifests.
If the private key is used to sign only a single manifest, then the
manifest can be revoked by revoking the EE certificate. In such a
case, to avoid needless CRL growth, the EE certificate used to
validate a manifest SHOULD expire at the same time that the manifest
expires. If an EE certificate is used to issue multiple (sequential)
manifests for the CA in question, then there is no revocation
mechanism for these individual manifests.
Manifests may be used by relying parties when constructing a local
cache (see Section 6) to mitigate the risk of an attacker who deletes
files from a repository or replaces current signed objects with stale
versions of the same object. Such protection is needed because
although all objects in the repository system are signed, the
repository system itself is untrusted.
5.1. Syntax and semantics
A manifest constitutes a list of (the hashes of) all the files in a
repository point at a particular point in time. A detailed
specification of manifest syntax is provided in [8] but, at a high
level, a manifest consists of (1) a manifest number; (2) the time the
manifest was issued; (3) the time of the next planned update; and (4)
a list of filename and hash value pairs.
The manifest number is a sequence number that is incremented each
time a manifest is issued by the authority. An authority is required
to issue a new manifest any time it alters any of its items in the
repository, or when the specified time of the next update is reached.
A manifest is thus valid until the specified time of the next update
or until a manifest is issued with a greater manifest number,
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whichever comes first. (Note that when an EE certificate is used to
sign only a single manifest, whenever the authority issues the new
manifest, the CA MUST also issue a new CRL which includes the EE
certificate corresponding to the old manifest. The revoked EE
certificate for the old manifest will be removed from the CRL when it
expires, thus this procedure ought not result in significant CRLs
growth.)
6. Local Cache Maintenance
In order to utilize signed objects issued under this PKI (e.g. for
route filter construction, see Section 6.3), a relying party must
first obtain a local copy of the valid EE certificates for the PKI.
To do so, the relying party performs the following steps:
1. Query the registry system to obtain a copy of all certificates,
manifests and CRLs issued under the PKI.
2. For each CA certificate in the PKI, verify the signature on the
corresponding manifest. Additionally, verify that the current
time is earlier than the time indicated in the nextUpdate field
of the manifest.
3. For each manifest, verify that certificates and CRLs issued
under the corresponding CA certificate match the hash values
contained in the manifest. If the hash values do not match, use
an out-of-band mechanism to notify the appropriate repository
administrator that the repository data has been corrupted.
4. Validate each EE certificate by constructing and verifying a
certification path for the certificate (including checking
relevant CRLs) to the locally configured set of TAs. (See [6]
for more details.)
Note that when a relying party performs these operations regularly,
it is more efficient for the relying party to request from the
repository system only those objects that have changed since the
relying party last updated its local cache. Note also that by
checking all issued objects against the appropriate manifest, the
relying party can be certain that it is not missing an updated
version of any object.
7. Common Operations
Creating and maintaining the infrastructure described above will
entail additional operations as ''side effects'' of normal resource
allocation and routing authorization procedures. For example, a
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subscriber with ''portable'' address space who entes a relationship
with an ISP will need to issue one or more ROAs identifying that ISP,
in addition to conducting any other necessary technical or business
procedures. The current primary use of this infrastructure is for
route filter construction; using ROAs, route filters can be
constructed in an automated fashion with high assurance that the
holder of the advertised prefix has authorized the first-hop AS to
originate an advertised route.
7.1. Certificate issuance
There are several operational scenarios that require certificates to
be issued. Any allocation that may be sub-allocated requires a CA
certificate, e.g., so that certificates can be issued as necessary
for the sub-allocations. Holders of ''portable'' address allocations
also must have certificates, so that a ROA can be issued to each ISP
that is authorized to originate a route to the allocation (since the
allocation does not come from any ISP). Additionally, multi-homed
subscribers may require certificates for their allocations if they
intend to issue the ROAs for their allocations (see Section 6.2.2).
Other holders of resources need not be issued CA certificates within
the PKI.
In the long run, a resource holder will not request resource
certificates, but rather receive a certificate as a side effect of
the allocation process for the resource. However, initial deployment
of the RPKI will entail issuance of certificates to existing resource
holders as an explicit event. Note that in all cases, the authority
issuing a CA certificate will be the entity who allocates resources
to the subject. This differs from most PKIs in which a subject can
request a certificate from any certification authority.
If a resource holder receives multiple allocations over time, it may
accrue a collection of resource certificates to attest to them. If a
resource holder receives multiple allocations from the same source,
the set of resource certificates may be combined into a single
resource certificate, if both the issuer and the resource holder
agree. This is effected by consolidating the IP Address Delegation
and AS Identifier Delegation Extensions into a single extension (of
each type) in a new certificate. However, if the certificates for
these allocations contain different validity intervals, creating a
certificate that combines them might create problems, and thus is NOT
RECOMMENDED.
If a resource holder's allocations come from different sources, they
will be signed by different CAs, and cannot be combined. When a set
of resources is no longer allocated to a resource holder, any
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certificates attesting to such an allocation MUST be revoked. A
resource holder SHOULD NOT to use the same public key in multiple CA
certificates that are issued by the same or differing authorities, as
reuse of a key pair complicates path construction. Note that since
the subject's distinguished name is chosen by the issuer, a subject
who receives allocations from two sources generally will receive
certificates with different subject names.
7.2. ROA management
Whenever a holder of IP address space wants to authorize an AS to
originate routes for a prefix within his holdings, he MUST issue an
end-entity certificate containing that prefix in an IP Address
Delegation extension. He then uses the corresponding private key to
sign a ROA containing the designated prefix and the AS number for the
AS. The resource holder MAY include more than one prefix in the EE
certificate and corresponding ROA if desired. As a prerequisite,
then, any address holder that issues ROAs for a prefix must have a
resource certificate for an allocation containing that prefix. The
standard procedure for issuing a ROA is as follows:
1. Create an end-entity certificate containing the prefix(es) to be
authorized in the ROA.
2. Construct the payload of the ROA, including the prefixes in the
end-entity certificate and the AS number to be authorized.
3. Sign the ROA using the private key corresponding to the end-
entity certificate (the ROA is comprised of the payload
encapsulated in a CMS signed message [7]).
4. Upload the end-entity certificate and the ROA to the repository
system.
The standard procedure for revoking a ROA is to revoke the
corresponding end-entity certificate by creating an appropriate CRL
and uploading it to the repository system. The revoked ROA and end-
entity certificate SHOULD BE removed from the repository system.
7.2.1. Single-homed subscribers (without portable allocations)
In BGP, a single-homed subscriber with a non-portable allocation does
not need to explicitly authorize routes to be originated for the
prefix(es) it is using, since its ISP will already advertise a more
general prefix and route traffic for the subscriber's prefix as an
internal function. Since no routes are originated specifically for
prefixes held by these subscribers, no ROAs need to be issued under
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their allocations; rather, the subscriber's ISP will issue any
necessary ROAs for its more general prefixes under resource
certificates its own allocation. Thus, a single-homed subscriber with
a non-portable allocation is not included in the RPKI, i.e., it does
not receive a CA certificate, nor issue EE certificates or ROAs.
7.2.2. Multi-homed subscribers
In order for multiple ASes to originate routers for prefixes held by
a multi-homed subscriber, each AS must have a ROA that explicitly
authorizes such route origination. There are two ways that this can
be accomplished.
One option is for the multi-homed subscriber to obtain a CA
certificate from the ISP who allocated the prefixes to the
subscriber. The multi-homed subscriber can then create a ROA (and
associated end-entity certificate) that authorizes a second ISP to
originate routes to the subscriber prefix(es). The ROA for the second
ISP generally SHOULD be set to require an exact match, if the intent
is to enable backup paths for the prefix. Note that the first ISP,
who allocated the prefixes, will want to advertise the more specific
prefix for this subscriber (vs. the encompassing prefix). Either the
subscriber or the first ISP will need to issue an EE certificate and
ROA for the (more specific) prefix, authorizing this ISP to advertise
this more specific prefix.
A second option is that the multi-homed subscriber can request that
the ISP that allocated the prefixes create a ROA that authorizes the
second ISP to originate routes to the subscriber's prefixes. (The ISP
also creates an EE certificate and ROA for its own advertisement of
the subscriber prefix, as above.) This option does not require that
the subscriber be issued a certificate or participate in ROA
management. Therefore, this option is simpler for the subscriber, and
is preferred if the option is supported by the ISP performing the
allocation.
7.2.3. Portable allocations
A resource holder is said to have a portable (provider independent)
allocation if the resource holder received its allocation from a
regional or national registry. Because the prefixes represented in
such allocations are not taken from an allocation held by an ISP,
there is no ISP that holds and advertises a more general prefix. A
holder of a portable allocation MUST authorize one or more ASes to
originate routes to these prefixes. Thus the resource holder MUST
generate one or more EE certificates and associated ROAs to enable
the AS(es) to originate routes for the prefix(es) in question. This
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ROA is required because none of the ISP's existing ROAs authorize it
to originate routes to that portable allocation.
7.3. Route filter construction
The goal of this architecture is to support improved routing
security. One way to do this is to use ROAs to construct route
filters that reject routes that conflict with the origination
authorizations asserted by current ROAs. The following is intended to
provide a high-level description of how the architecture might be
used to construct a route filter. Additional guidance on the use of
ROAs to derive inferences about the validity of BGP UPDATE messages
is provided in [14]. The guidance in [14] is particularly important
during a transition period where not all ISPs implement this
architecture (and thus the filter described below which naively
rejects all UPDATES without a corresponding ROA would incorrectly
reject valid routes originated by ISPs that do not yet implement this
architecture).
1. Obtain a local copy of all currently valid EE certificates, as
specified in Section 5.
2. Query the repository system to obtain a local copy of all ROAs
issued under the PKI.
3. Verify that the each ROA matches the hash value contained in the
manifest of the CA certificate used to verify the EE certificate
that issued the ROA and that no ROAs are missing.
4. Validate each ROA by verifying that its signature is verifiable
by a valid end-entity certificate that matches the address
allocation in the ROA. (See [7] for more details.)
5. Based on the validated ROAs, construct a table of prefixes and
corresponding authorized origin ASes (or vice versa).
A BGP speaker that applies such a filter is thus guaranteed that for
a given IP address prefix, all routes that the BGP speaker accepts
for that prefix were originated by an AS that is authorized by the
owner of the prefix to authorize routes to that prefix.
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The first three steps in the above procedure might incur a
substantial overhead if all objects in the repository system were
downloaded and validated every time a route filter was constructed.
Instead, it will be more efficient for users of the infrastructure to
initially download all of the signed objects and perform the
validation algorithm described above. Subsequently, a relying party
need only perform incremental downloads and validations on a regular
basis. A typical ISP using the infrastructure may choose any
frequency it desires for downloading updates from the repository,
uploading any modifications it has made, and constructing route
filters. However, an ISP might reasonably choose to perform these
actions on a daily schedule.
It should be noted that the transition to 4-byte AS numbers (see RFC
4893 [13]) weakens the security guarantees achieved by BGP speakers
who do not support 4-byte AS numbers (referred to as OLD BGP
speakers). RFC 4893 specifies that all 4-byte AS numbers (except
those whose first two bytes are entirely zero) be mapped to the
reserved value 23456 before being sent to a BGP speaker who does not
understand 4-byte AS numbers. Therefore, when an ISP creates a route
filter for use by an OLD BGP speaker, it must allow any 4-byte AS
number to advertise routes for an IP address prefix if there exists a
ROA that authorizes any 4-byte AS number to advertise routes to that
prefix. This means that if an OLD BGP speaker accepts a route that
was originated by an AS with a 4-byte AS number, there is no
guarantee that it was originated by an authorized 4-byte AS number
(unless the route was propagated by an intermediate NEW BGP speaker
who performed route filtering as described above).
8. Security Considerations
The focus of this document is security; hence security considerations
permeate this specification.
The security mechanisms provided by and enabled by this architecture
depend on the integrity and availability of the infrastructure it
describes. The integrity of objects within the infrastructure is
ensured by appropriate controls on the repository system, as
described in Section 4.4. Likewise, because the repository system is
structured as a distributed database, it should be inherently
resistant to denial of service attacks; nonetheless, appropriate
precautions should also be taken, both through replication and backup
of the constituent databases and through the physical security of
database servers
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9. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC
10. Acknowledgments
The architecture described in this draft is derived from the
collective ideas and work of a large group of individuals. This work
would not have been possible without the intellectual contributions
of George Michaelson, Robert Loomans, Sanjaya and Geoff Huston of
APNIC, Robert Kisteleki and Henk Uijterwaal of the RIPE NCC, Time
Christensen and Cathy Murphy of ARIN, Rob Austein of ISC and Randy
Bush of IIJ.
Although we are indebted to everyone who has contributed to this
architecture, we would like to especially thank Rob Austein for the
concept of a manifest, Geoff Huston for the concept of managing
object validity through single-use EE certificate key pairs, and
Richard Barnes for help in preparing an early version of this
document.
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11. References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4
(BGP-4)", RFC 4271, January 2006
[3] 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, May 2008.
[4] Housley, R., ''Cryptographic Message Syntax'', RFC 3852, July
2004.
[5] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[6] Huston, G., Michaelson, G., and Loomans, R., "A Profile for
X.509 PKIX Resource Certificates", draft-ietf-sidr-res-certs-
14, October 2008.
[7] Lepinski, M., Kent, S., and Kong, D., "A Profile for Route
Origin Authorizations (ROA)", draft-ietf-sidr-roa-format-04,
November 2008.
[8] Austein, R., et al., ''Manifests for the Resource Public Key
Infrastructure'', draft-ietf-sidr-rpki-manifests-04, October
2008.
11.2. Informative References
[9] Huston, G., Michaelson, G., and Loomans, R., ''A Profile for
Resource Certificate Repository Structure'', draft-ietf-sidr-
repos-struct-01, October 2008.
[10] Kent, S., Lynn, C., and Seo, K., "Secure Border Gateway
Protocol (Secure-BGP)'', IEEE Journal on Selected Areas in
Communications Vol. 18, No. 4, April 2000.
[11] White, R., "soBGP", May 2005, <ftp://ftp-
eng.cisco.com/sobgp/index.html>
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[12] Tridgell, A., "rsync", April 2006,
<http://samba.anu.edu.au/rsync/>
[13] Vohra, Q., and Chen, E., ''BGP Support for Four-octet AS Number
Space'', RFC 4893, May 2007.
[14] Huston, G., Michaelson, G., ''Validation of Route Origination
in BGP using the Resource Certificate PKI'', draft-ietf-sidr-
roa-validation-01, October 2008.
Authors' Addresses
Matt Lepinski
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
Email: mlepinski@bbn.com
Stephen Kent
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
Email: kent@bbn.com
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