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

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   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",
   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)
         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

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

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

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

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. [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

   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

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

   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

   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

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

9. Acknowledgments

   This document was prepared using

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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

   [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


   Stephen Kent
   BBN Technologies
   10 Moulton St.
   Cambridge, MA 02138


   Richard Barnes
   BBN Technologies
   10 Moulton St.
   Cambridge, MA 02138


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