Secure Inter-Domain Routing M. Lepinski
Working Group S. Kent
Internet Draft R. Barnes
Intended status: Informational BBN Technologies
Expires: January 2008 July 8, 2007
An Infrastructure to Support Secure Internet Routing
draft-ietf-sidr-arch-01.txt
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Abstract
This document describes an architecture for an infrastructure to
support secure 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;
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certificates from this PKI are used to verify signed objects that
authorize autonomous systems to originate routes for specified IP
address prefixes. The data objects that comprise the PKI, as well as
other signed objects necessary for secure routing, are stored and
disseminated through a distributed repository system. This document
also describes at a high level how this architecture can be used to
add security features to common operations such as IP address space
allocation and route filter construction.
Conventions used in this document
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
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].
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.............................................7
2.5. Default Trust Anchor Considerations.......................8
2.6. Representing Early-Registration Transfers (ERX)...........9
3. Route Origination Authorizations..............................10
3.1. Role in the overall architecture.........................10
3.2. Syntax and semantics.....................................11
4. Repositories and Manifests....................................13
4.1. Role in the overall architecture.........................13
4.2. Contents and structure...................................13
4.3. Manifests................................................15
4.4. Access protocols.........................................16
4.5. Access control...........................................17
5. Local Cache Maintenance.......................................17
6. Common Operations.............................................18
6.1. Certificate issuance.....................................18
6.2. ROA management...........................................19
6.2.1. Single-homed subscribers (without portable allocations)
...........................................................20
6.2.2. Multi-homed subscribers.............................20
6.2.3. Portable allocations................................21
6.3. Route filter construction................................21
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7. Security Considerations.......................................22
8. IANA Considerations...........................................23
9. Acknowledgments...............................................23
10. References...................................................24
10.1. Normative References....................................24
10.2. Informative References..................................24
Author's Addresses...............................................25
Intellectual Property Statement..................................25
Disclaimer of Validity...........................................26
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 supports, at a minimum,
two aspects of routing security; it enables an entity to verifiably
assert that it is the legitimate holder of a set IP addresses or a
set of Autonomous System (AS) numbers, and it allows the holder of IP
address space to explicitly and verifiably authorize one or more ASes
to originate routes to that address space. In addition to these
initial applications, the infrastructure defined by this architecture
also is intended to be able to support security protocols such as S-
BGP [8] or soBGP [9]. This architecture is applicable to routing of
both IPv4 and IPv6 datagrams.
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
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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
(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.
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
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
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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
associated with 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
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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, 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, (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
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,
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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 defines 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.
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
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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 self-signed
certificate 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 Anchor Considerations
IANA forms the root of the extant IP address space and AS number
allocation hierarchy. Therefore, it is natural to consider a model in
which most relying parties have as their single trust anchor a self-
signed IANA certificate whose RFC 3779 extensions specify the
entirety of the AS number and IP address and spaces. However, IANA
has not traditionally acted in an operational capacity as the root of
the resource allocation hierarchy, much less managed certificates and
their associated private keys. Therefore it is unclear whether IANA
is willing to undertake this role as the default trust anchor for the
PKI. This has prompted the consideration of alternative approaches
for recommending trust anchors to potential relying parties.
Essentially all allocated IP address and AS number resources are sub-
allocated by IANA to one of the five RIRs. Therefore, one could
consider a model in which the default trust anchors are a set of five
self-signed certificates, one for each RIR. There are two
difficulties that such an approach must overcome.
The first difficulty is that IANA retains authority for 44 /8
prefixes in IPv4 and a /26 prefix in IPv6. Therefore, any approach
that recommends the RIRs as default trust anchors will also require
as a default trust anchor an IANA certificate who's RFC 3779
extensions correspond to this address space. Additionally, there are
about 49 /8 prefixes containing legacy 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
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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.
The second difficulty is that the resource allocations of the RIRs
may change several times a year. Typically in a PKI, trust anchors
are quite long-lived and distributed to relying parties via some out-
of-band mechanism. However, such out-of-band distribution of new
trust anchors is not feasible if the allocations change every few
months. Therefore, any approach that recommends the RIRs as default
trust anchors must provide an in-band mechanism for managing the
changes that will occur in the RIR allocations (as expressed via RFC
3779 extensions).
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
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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
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
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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. Syntactically, a ROA is a CMS signed-data object
whose content is defined as follows:
RouteOriginAttestation ::= SEQUENCE {
version [0] INTEGER DEFAULT 0,
asID ASID,
exactMatch BOOLEAN,
ipAddrBlocks ROAIPAddrBlocks }
ASID ::= INTEGER
ROAIPAddrBlocks ::= SEQUENCE of ROAIPAddressFamily
ROAIPAddressFamily ::= SEQUENCE {
addressFamily OCTET STRING (SIZE (2..3)),
addresses SEQUENCE OF IPAddress }
-- Only two address families are allowed: IPv4 and IPv6
IPAddress ::= BIT STRING
That is, the signed data within the ROA consists of a version number,
the AS number that is being authorized, and a list of IP prefixes to
which the AS is authorized to originate routes. If the exactMatch
flag is set to TRUE, then the AS is authorized to originate only
routes for the exact prefix(es) indicated in the ROA. Otherwise, if
the exactMatch flag is set to FALSE, the AS is authorized to
originate routes to the prefix(es) in the ROA as well as any longer
(more specific) prefixes.
Note that a ROA contains only a single AS number. Thus, in cases
where 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
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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 sign 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.
--------- ---------
| 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.
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4. Repositories and Manifests
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. 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 (described below) 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
[??].
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
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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
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.
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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
same publication point as previously issued certificates having the
same subject and public key, and should overwrite such certificates.
4.3. Manifests
A manifest is a signed object listing of all of the signed objects
issued by a particular authority that are present 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 whose
corresponding public key appears in an end-entity certificate signed
by the CA in question. Each such end-entity certificate is used to
sign a single manifest and the private key corresponding to such an
end-entity certificate may be deleted after it is used to sign that
manifest. To avoid needless CRL growth, the EE certificate used to
validate a manifest SHOULD expire at the same time that the manifest
expires, i.e., the notAfter value in the EE certificate should be the
same as the nextUpdate value in the manifest.
Syntactically, a manifest is a CMS signed-data object whose content
is defined as follows:
Manifest ::= SEQUENCE {
version INTEGER DEFAULT 0,
manifestNumber INTEGER,
thisUpdate GeneralizedTime,
nextUpdate GeneralizedTime,
fileHashAlg OBJECT IDENTIFIER,
fileList SEQUENCE OF FileAndHash
}
FileAndHash ::= SEQUENCE {
file IA5String
hash BIT STRING
}
The manifestNumber field is a sequence number that is incremented
each time a manifest is issued by a authority. The thisUpdate field
contains the time when the manifest was created and the nextUpdate
field contains the time at which the next scheduled manifest will be
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issued. If the authority alters any of its items in the repository,
then it MUST issue a new manifest before nextUpdate. In such a case,
when the authority issues the new manifest, it MUST also issue a new
CRL which includes the EE certificate corresponding to the old
manifest. A manifest is thus valid until the time specified in
nextUpdate or until a manifest is issued with a greater manifest
number, whichever comes first. The revoked EE certificate for the old
manifest will be removed from the CRL when it expires, thus this
procedure ought not yield large CRLs.
The fileHashAlg field contains the OID of the hash algorithm used to
hash the files that the authority has placed into the repository. The
mandatory to implement hash algorithm is SHA-256 and its OID is
2.16.840.1.101.3.4.2.1. [RFC 4055]
The fileList field contains a sequence of FileAndHash pairs, one for
each currently valid certificate, CRL and ROA that has been issued by
the authority. Each of the FileAndHash pairs contains the name of the
file in the repository that contains the object in question, and a
hash of the file's contents.
4.4. 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
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modification, so that appropriate access controls can be applied (see
Section 4.4).
Current efforts to implement a repository system use RSYNC [10] 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.
4.5. 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.
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. 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.
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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.
6. 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
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.
6.1. 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
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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
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.
6.2. 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.
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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.
6.2.1. 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
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.
6.2.2. 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.
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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.
6.2.3. 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
ROA is required because none of the ISP's existing ROAs authorize it
to originate routes to that portable allocation.
6.3. 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, which can be accomplished
with the following procedure:
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. (ROAs are
contained in files with a ".roa" suffix, so missing ROAs are
readily detected.)
4. Validate each ROA by verifying that it's signature is verifiable
by a valid end-entity certificate that matches the address
allocation in the ROA. (See [7] for more details.)
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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.
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 might have a daily
schedule to download updates from the repository, upload any
modifications it has made, and construct route filters.
It should be noted that the transition to 4-byte AS numbers (see RFC
4893 [10]) 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).
7. 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
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precautions should also be taken, both through replication and backup
of the constituent databases and through the physical security of
database servers
8. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC
9. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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10. References
10.1. 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] Housley, R., et al., "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile", RFC
3280, April 2002.
[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,
July 2007 (work in progress).
[7] Lepinski, M., Kent, S., and Kong, D., "A Profile for Route
Origin Authorizations (ROA)", draft-ietf-sidr-roa-format,
July 2008 (work in progress).
10.2. Informative References
[8] [S-BGP]
[9] [soBGP]
[10] [rsync]
[11] Vohra, Q., and Chen, E., "BGP Support for Four-octet AS Number
Space", RFC 4893, May 2007.
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Author's 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
Richard Barnes
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
Email: rbarnes@bbn.com
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Barnes & Kent Expires January 8, 2008 [Page 26]
