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Resource Public Key Infrastructure (RPKI) Validation Reconsidered

 


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Internet Engineering Task Force (IETF)                         G. Huston
Request for Comments: 8360                                 G. Michaelson
Category: Standards Track                                          APNIC
ISSN: 2070-1721                                              C. Martinez
                                                                  LACNIC
                                                          T. Bruijnzeels
                                                                RIPE NCC
                                                               A. Newton
                                                                    ARIN
                                                                 D. Shaw
                                                                 AFRINIC
                                                              April 2018


   Resource Public Key Infrastructure (RPKI) Validation Reconsidered

Abstract

   This document specifies an alternative to the certificate validation
   procedure specified in RFC 6487 that reduces aspects of operational
   fragility in the management of certificates in the Resource Public
   Key Infrastructure (RPKI), while retaining essential security
   features.

   The procedure specified in RFC 6487 requires that Resource
   Certificates are rejected entirely if they are found to overclaim any
   resources not contained on the issuing certificate, whereas the
   validation process defined here allows an issuing Certification
   Authority (CA) to chose to communicate that such Resource
   Certificates should be accepted for the intersection of their
   resources and the issuing certificate.

   It should be noted that the validation process defined here considers
   validation under a single trust anchor (TA) only.  In particular,
   concerns regarding overclaims where multiple configured TAs claim
   overlapping resources are considered out of scope for this document.

   This choice is signaled by a set of alternative Object Identifiers
   (OIDs) per "X.509 Extensions for IP Addresses and AS Identifiers"
   (RFC 3779) and "Certificate Policy (CP) for the Resource Public Key
   Infrastructure (RPKI)" (RFC 6484).  It should be noted that in case
   these OIDs are not used for any certificate under a trust anchor, the
   validation procedure defined here has the same outcome as the
   procedure defined in RFC 6487.

   Furthermore, this document provides an alternative to Route Origin
   Authorization (ROA) (RFC 6482) and BGPsec Router Certificate (BGPsec
   PKI Profiles -- publication requested) validation.

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Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8360.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Notation . . . . . . . . . . . . . . . . . .   4
   2.  Certificate Validation in the RPKI  . . . . . . . . . . . . .   4
   3.  Operational Considerations  . . . . . . . . . . . . . . . . .   5
   4.  An Amended RPKI Certification Validation Process  . . . . . .   7
     4.1.  Verified Resource Sets  . . . . . . . . . . . . . . . . .   7
     4.2.  Differences with Existing Standards . . . . . . . . . . .   7
       4.2.1.  Certificate Policy (CP) for Use with Validation
               Reconsidered in the RPKI  . . . . . . . . . . . . . .   7
       4.2.2.  An Alternative to X.509 Extensions for IP Addresses
               and AS Identifiers (RFC 3779) . . . . . . . . . . . .   8
       4.2.3.  Addendum to RFC 6268  . . . . . . . . . . . . . . . .  12
       4.2.4.  An Alternative to the Profile for X.509 PKIX Resource
               Certificates  . . . . . . . . . . . . . . . . . . . .  14
       4.2.5.  An Alternative ROA Validation . . . . . . . . . . . .  18
       4.2.6.  An Alternative to BGPsec Router Certificate
               Validation  . . . . . . . . . . . . . . . . . . . . .  18
   5.  Validation Examples . . . . . . . . . . . . . . . . . . . . .  19
     5.1.  Example 1 -- An RPKI Tree Using the Old OIDs Only . . . .  19
     5.2.  Example 2 -- An RPKI Tree Using the New OIDs Only . . . .  21
     5.3.  Example 3 -- An RPKI Tree Using a Mix of Old and New OIDs  23
   6.  Deployment Considerations . . . . . . . . . . . . . . . . . .  25
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  28
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

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1.  Overview

   This document specifies an alternative to the certificate validation
   procedure specified in RFC 6487.  Where the procedure specified in
   RFC 6487 will require that Resource Certificates be rejected entirely
   if they are found to overclaim any resources not contained on the
   issuing certificate, the procedure defined here dictates that these
   Resource Certificates be accepted for the intersection of their
   resources and the issuing certificate only.

   The outcome of both procedures is the same as long as no overclaims
   occur.  Furthermore, the new procedure can never lead to the
   acceptance of resources that are not validly held on the path of
   issuing certificates.

   However, the procedure defined here will limit the impact in case
   resources are no longer validly held on the path of issuing
   certificates to attestations, such as Route Origin Authorizations
   [RFC6482] that refer to these resources only.

1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Certificate Validation in the RPKI

   As currently defined in Section 7.2 of [RFC6487], validation of PKIX
   certificates that conform to the RPKI profile relies on the use of a
   path validation process where each certificate in the validation path
   is required to meet the certificate validation criteria.

   These criteria require, in particular, that the Internet Number
   Resources (INRs) of each certificate in the validation path are
   "encompassed" by INRs on the issuing certificate.  The first
   certificate in the path is required to be a trust anchor, and its
   resources are considered valid by definition.

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   For example, in the following sequence:

   Certificate 1 (trust anchor):
   Issuer TA,
   Subject TA,
   Resources 192.0.2.0/24, 198.51.100.0/24,
         2001:db8::/32, AS64496-AS64500

   Certificate 2:
   Issuer TA,
   Subject CA1,
   Resources 192.0.2.0/24, 198.51.100.0/24, 2001:db8::/32

   Certificate 3:
   Issuer CA1,
   Subject CA2,
   Resources 192.0.2.0/24, 198.51.100.0/24, 2001:db8::/32

   ROA 1:
   Embedded Certificate 4 (EE certificate):
   Issuer CA2,
   Subject R1,
   Resources 192.0.2.0/24

   Prefix 192.0.2.0/24, Max Length 24, ASN 64496

   All certificates in this scenario are considered valid since the INRs
   of each certificate are encompassed by those of the issuing
   certificate.  ROA1 is valid because the specified prefix is
   encompassed by the embedded end entity (EE) certificate, as required
   by [RFC6482].

3.  Operational Considerations

   The allocations recorded in the RPKI change as a result of resource
   transfers.  For example, the CAs involved in transfer might choose to
   modify CA certificates in an order that causes some of these
   certificates to "overclaim" temporarily.  A certificate is said to
   "overclaim" if it includes INRs not contained in the INRs of the CA
   that issued the certificate in question.

   It may also happen that a child CA does not voluntarily request a
   shrunk Resource Certificate when resources are being transferred or
   reclaimed by the parent.  Furthermore, operational errors that may
   occur during management of RPKI databases also may create CA
   certificates that, temporarily, no longer encompass all of the INRs
   of subordinate certificates.

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   Consider the following sequence:

   Certificate 1 (trust anchor):
   Issuer TA,
   Subject TA,
   Resources 192.0.2.0/24, 198.51.100.0/24,
        2001:db8::/32, AS64496-AS64500

   Certificate 2:
   Issuer TA,
   Subject CA1,
   Resources 192.0.2.0/24, 2001:db8::/32

   Certificate 3 (invalid):
   Issuer CA1,
   Subject CA2,
   Resources 192.0.2.0/24, 198.51.100.0/24, 2001:db8::/32

   ROA 1 (invalid):
   Embedded Certificate 4 (EE certificate, invalid):
   Issuer CA2,
   Subject R1,
   Resources 192.0.2.0/24

   Prefix 192.0.2.0/24, Max Length 24, ASN 64496

   Here, Certificate 2 from the previous example was reissued by TA to
   CA1, and the prefix 198.51.100.0/24 was removed.  However, CA1 failed
   to reissue a new Certificate 3 to CA2.  As a result, Certificate 3 is
   now overclaiming and considered invalid; by recursion, the embedded
   Certificate 4 used for ROA1 is also invalid.  And ROA1 is invalid
   because the specified prefix contained in the ROA is no longer
   encompassed by a valid embedded EE certificate, as required by
   [RFC6482].

   However, it should be noted that ROA1 does not make use of any of the
   address resources that were removed from CA1's certificate; thus, it
   would be desirable if ROA1 could still be viewed as valid.
   Technically, CA1 should reissue a Certificate 3 to CA2 without
   198.51.100.0/24, and then ROA1 would be considered valid according to
   [RFC6482].  But as long as CA1 does not take this action, ROA1
   remains invalid.  It would be preferable if ROA1 could be considered
   valid, since the assertion it makes was not affected by the reduced
   scope of CA1's certificate.

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4.  An Amended RPKI Certification Validation Process

4.1.  Verified Resource Sets

   The problem described above can be considered a low probability
   problem today.  However, the potential impact on routing security
   would be high if an overclaiming occurred near the apex of the RPKI
   hierarchy, as this would invalidate the entirety of the subtree
   located below this point.

   The changes specified here to the validation procedure in [RFC6487]
   do not change the probability of this problem, but they do limit the
   impact to just the overclaimed resources.  This revised validation
   algorithm is intended to avoid causing CA certificates to be treated
   as completely invalid as a result of overclaims.  However, these
   changes are designed to not degrade the security offered by the RPKI.
   Specifically, ROAs and router certificates will be treated as valid
   only if all of the resources contained in them are encompassed by all
   superior certificates along a path to a trust anchor.

   The way this is achieved conceptually is by maintaining a Verified
   Resource Set (VRS) for each certificate that is separate from the
   INRs found in the resource extension [RFC3779] in the certificate.

4.2.  Differences with Existing Standards

4.2.1.  Certificate Policy (CP) for Use with Validation Reconsidered in
        the RPKI

   Note that Section 1.2 of [RFC6484] defines the "Certificate Policy
   (CP) for the Resource PKI (RPKI)" with the following OID:

   id-cp-ipAddr-asNumber OBJECT IDENTIFIER ::= { iso(1)
           identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) cp(14) 2 }

   Per this document, a new OID for an alternative "Certificate Policy
   (CP) for use with validation reconsidered in the Resource PKI (RPKI)"
   has been assigned as follows:

   id-cp-ipAddr-asNumber-v2 OBJECT IDENTIFIER ::= { iso(1)
           identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) cp(14) 3 }

   This alternative Certificate Policy is the same as the Certificate
   Policy described in [RFC6484], except that it is used to drive the
   decision in Step 8 of the validation procedure described in
   Section 4.2.4.4.

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4.2.2.  An Alternative to X.509 Extensions for IP Addresses and AS
        Identifiers (RFC 3779)

   This document defines an alternative to [RFC3779].  All
   specifications and procedures described in [RFC3779] apply, with the
   notable exceptions described in the following subsections.

4.2.2.1.  OID for id-pe-ipAddrBlocks-v2

   Per this document, an OID has been assigned for the extension
   id-pe-ipAddrBlocks-v2 (id-pe 28).  This OID MUST only be used in
   conjunction with the alternative Certificate Policy OID defined in
   Section 4.2.1.

   The following is an amended specification to be used as an
   alternative to the specification in Section 2.2.1 of [RFC3779].

   The OID for this extension is id-pe-ipAddrBlocks-v2.

   id-pe-ipAddrBlocks-v2  OBJECT IDENTIFIER ::= { id-pe 28 }

   where [RFC5280] defines:

   id-pkix  OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
          dod(6) internet(1) security(5) mechanisms(5) pkix(7) }

   id-pe    OBJECT IDENTIFIER ::= { id-pkix 1 }

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4.2.2.2.  Syntax for id-pe-ipAddrBlocks-v2

   id-pe-ipAddrBlocks-v2      OBJECT IDENTIFIER ::= { id-pe 28 }

   IPAddrBlocks        ::= SEQUENCE OF IPAddressFamily

   IPAddressFamily     ::= SEQUENCE {    -- AFI & optional SAFI --
   addressFamily        OCTET STRING (SIZE (2..3)),
   ipAddressChoice      IPAddressChoice }

   IPAddressChoice     ::= CHOICE {
   inherit              NULL, -- inherit from issuer --
   addressesOrRanges    SEQUENCE OF IPAddressOrRange }

   IPAddressOrRange    ::= CHOICE {
   addressPrefix        IPAddress,
   addressRange         IPAddressRange }

   IPAddressRange      ::= SEQUENCE {
   min                  IPAddress,
   max                  IPAddress }

   IPAddress           ::= BIT STRING

   Note that the descriptions of objects referenced in the syntax above
   are defined in Sections 2.2.3.1 through 2.2.3.9 of [RFC3779].

4.2.2.3.  OID for id-pe-autonomousSysIds-v2

   Per this document, an OID has been assigned for the extension id-pe-
   autonomousSysIds-v2 (id-pe 29).  This OID MUST only be used in
   conjunction with the alternative Certificate Policy OID defined in
   Section 4.2.1.

   The following is an amended specification to be used as an
   alternative to the specification in Section 3.2.1 of [RFC3779].

   The OID for this extension is id-pe-autonomousSysIds-v2.

   id-pe-autonomousSysIds-v2  OBJECT IDENTIFIER ::= { id-pe 29 }

   where [RFC5280] defines:

   id-pkix  OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
          dod(6) internet(1) security(5) mechanisms(5) pkix(7) }

   id-pe    OBJECT IDENTIFIER ::= { id-pkix 1 }

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4.2.2.4.  Syntax for id-pe-autonomousSysIds-v2

   id-pe-autonomousSysIds-v2  OBJECT IDENTIFIER ::= { id-pe 29 }

   ASIdentifiers       ::= SEQUENCE {
   asnum               [0] EXPLICIT ASIdentifierChoice OPTIONAL,
   rdi                 [1] EXPLICIT ASIdentifierChoice OPTIONAL}

   ASIdentifierChoice  ::= CHOICE {
   inherit              NULL, -- inherit from issuer --
   asIdsOrRanges        SEQUENCE OF ASIdOrRange }

   ASIdOrRange         ::= CHOICE {
   id                  ASId,
   range               ASRange }

   ASRange             ::= SEQUENCE {
   min                 ASId,
   max                 ASId }

   ASId                ::= INTEGER

4.2.2.5.  Amended IP Address Delegation Extension Certification Path
          Validation

   Certificate path validation is performed as specified in
   Section 4.2.4.4.

4.2.2.6.  Amended Autonomous System Identifier Delegation Extension
          Certification Path Validation

   Certificate path validation is performed as specified in
   Section 4.2.4.4.

4.2.2.7.  Amended ASN.1 Module

   Per this document, an OID has been assigned for
   id-mod-ip-addr-and-as-ident-v2, as follows:

   IPAddrAndASCertExtn-v2 { iso(1) identified-organization(3) dod(6)
      internet(1) security(5) mechanisms(5) pkix(7) mod(0)
      id-mod-ip-addr-and-as-ident-v2(90) }

   The following is an amended specification to be used as an
   alternative to the specification in Appendix A of [RFC3779].

   This normative appendix describes the extensions for IP address and
   AS identifier delegation used by conforming PKI components in ASN.1

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   syntax.

   IPAddrAndASCertExtn-v2 { iso(1) identified-organization(3) dod(6)
      internet(1) security(5) mechanisms(5) pkix(7) mod(0)
      id-mod-ip-addr-and-as-ident-v2(90) }

   DEFINITIONS EXPLICIT TAGS ::=

   BEGIN

   -- EXPORTS ALL --

   IMPORTS

   -- PKIX specific OIDs and arcs --

   id-pe FROM PKIX1Explicit88 { iso(1) identified-organization(3)
        dod(6) internet(1) security(5) mechanisms(5) pkix(7)
        id-mod(0) id-pkix1-explicit(18) }

   -- IP Address Block and AS Identifiers Syntax --

   IPAddrBlocks, ASIdentifiers FROM  IPAddrAndASCertExtn { iso(1)
      identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) mod(0) id-mod-ip-addr-and-as-ident(30) }
   ;

   -- Validation Reconsidered IP Address Delegation Extension OID --

   id-pe-ipAddrBlocks-v2  OBJECT IDENTIFIER ::= { id-pe 28 }

   -- Validation Reconsidered IP Address Delegation Extension Syntax --
   -- Syntax is imported from RFC 3779 --

   -- Validation Reconsidered Autonomous System Identifier --
   --     Delegation Extension OID                         --

   id-pe-autonomousSysIds-v2  OBJECT IDENTIFIER ::= { id-pe 29 }

   -- Validation Reconsidered Autonomous System Identifier --
   --     Delegation Extension Syntax                      --

   -- Syntax is imported from RFC 3779 --

   END

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4.2.3.  Addendum to RFC 6268

   Per this document, an OID has been assigned for
   id-mod-ip-addr-and-as-ident-2v2 as follows:

   IPAddrAndASCertExtn-2010v2 { iso(1) identified-organization(3) dod(6)
            internet(1) security(5) mechanisms(5) pkix(7) mod(0)
            id-mod-ip-addr-and-as-ident-2v2(91) }

   [RFC6268] is an informational RFC that updates some auxiliary ASN.1
   modules to conform to the 2008 version of ASN.1; the 1988 ASN.1
   modules in Section 4.2.2.7 remain the normative version.

   The following is an additional module conforming to the 2008 version
   of ASN.1 to be used with the extensions defined in Sections 4.2.2.1
   and 4.2.2.3.

  IPAddrAndASCertExtn-2010v2 { iso(1) identified-organization(3) dod(6)
           internet(1) security(5) mechanisms(5) pkix(7) mod(0)
           id-mod-ip-addr-and-as-ident-2v2(91) }

    DEFINITIONS EXPLICIT TAGS ::=

    BEGIN

       EXPORTS ALL;
       IMPORTS

       -- PKIX specific OIDs and arcs --

       id-pe
       FROM PKIX1Explicit-2009
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-pkix1-explicit-02(51)}

       EXTENSION
       FROM PKIX-CommonTypes-2009
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-pkixCommon-02(57)}

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    -- IP Address Block and AS Identifiers Syntax --

       IPAddrBlocks, ASIdentifiers
       FROM IPAddrAndASCertExtn-2010
          { iso(1) identified-organization(3) dod(6)
            internet(1) security(5) mechanisms(5) pkix(7) mod(0)
            id-mod-ip-addr-and-as-ident-2(72) }
       ;

       --
       -- Extensions contain the set of extensions defined in this
       -- module
       --
       -- These are intended to be placed in public key certificates
       -- and thus should be added to the CertExtensions extension
       -- set in PKIXImplicit-2009 defined for RFC 5280
       --

       Extensions EXTENSION ::= {
          ext-pe-ipAddrBlocks-v2 | ext-pe-autonomousSysIds-v2
       }

       -- Validation Reconsidered IP Address Delegation Extension OID --

       ext-pe-ipAddrBlocks-v2 EXTENSION ::= {
         SYNTAX IPAddrBlocks
         IDENTIFIED BY id-pe-ipAddrBlocks-v2
       }

       id-pe-ipAddrBlocks-v2  OBJECT IDENTIFIER ::= { id-pe 28 }

       -- Validation Reconsidered IP Address Delegation --
       --      Extension Syntax                         --

       -- Syntax is imported from RFC 6268 --

       -- Validation Reconsidered Autonomous System Identifier --
       --      Delegation Extension OID                        --

       ext-pe-autonomousSysIds-v2 EXTENSION ::= {
         SYNTAX ASIdentifiers
         IDENTIFIED BY id-pe-autonomousSysIds-v2
       }

       id-pe-autonomousSysIds OBJECT IDENTIFIER ::= { id-pe 29 }

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    -- Validation Reconsidered Autonomous System Identifier --
    --      Delegation Extension Syntax                     --

    -- Syntax is imported from RFC 6268 --

    END

4.2.4.  An Alternative to the Profile for X.509 PKIX Resource
        Certificates

   This document defines an alternative profile for X.509 PKIX Resource
   Certificates.  This profile follows all definitions and procedures
   described in [RFC6487] with the following notable exceptions.

4.2.4.1.  Amended Certificate Policies

   The following is an amended specification to be used in this profile,
   in place of Section 4.8.9 of [RFC6487].

   This extension MUST be present and MUST be marked critical.  It MUST
   include exactly one policy of type id-cp-ipAddr-asNumber-v2, as
   specified in the updated RPKI CP in Section 4.2.1.

4.2.4.2.  Amended IP Resources

   The following is an amended specification to be used in this profile,
   in place of Section 4.8.10 of [RFC6487].

   Either the IP resources extension or the AS resources extension, or
   both, MUST be present in all RPKI certificates and MUST be marked
   critical.

   This extension contains the list of IP address resources as per
   Section 4.2.2.1.  The value may specify the "inherit" element for a
   particular Address Family Identifier (AFI) value.  In the context of
   Resource Certificates describing public number resources for use in
   the public Internet, the Subsequent AFI (SAFI) value MUST NOT be
   used.

   This extension MUST either specify a non-empty set of IP address
   records or use the "inherit" setting to indicate that the IP address
   resource set of this certificate is inherited from that of the
   certificate's issuer.

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4.2.4.3.  Amended AS Resources

   The following is an amended specification to be used in this profile,
   in place of Section 4.8.11 of [RFC6487].

   Either the AS resources extension or the IP resources extension, or
   both, MUST be present in all RPKI certificates and MUST be marked
   critical.

   This extension contains the list of AS number resources as per
   Section 4.2.2.3, or it may specify the "inherit" element.  Routing
   Domain Identifier (RDI) values are NOT supported in this profile and
   MUST NOT be used.

   This extension MUST either specify a non-empty set of AS number
   records or use the "inherit" setting to indicate that the AS number
   resource set of this certificate is inherited from that of the
   certificate's issuer.

4.2.4.4.  Amended Resource Certificate Path Validation

   The following is an amended specification for path validation to be
   used in place of Section 7.2 of [RFC6487], which allows for the
   validation of both certificates following the profile defined in
   [RFC6487], as well as certificates following the profile described
   above.

   The following algorithm is employed to validate CA and EE resource
   certificates.  It is modeled on the path validation algorithm from
   [RFC5280] but is modified to make use of the IP Address Delegation
   and AS Identifier Delegation extensions from [RFC3779].

   There are two inputs to the validation algorithm:

   1.  a trust anchor

   2.  a certificate to be validated

   The algorithm is initialized with two new variables for use in the
   RPKI: Verified Resource Set-IP (VRS-IP) and Verified Resource Set-AS
   (VRS-AS).  These sets are used to track the set of INRs (IP address
   space and AS numbers) that are considered valid for each CA
   certificate.  The VRS-IP and VRS-AS sets are initially set to the IP
   Address Delegation and AS Identifier Delegation values, respectively,
   from the trust anchor used to perform validation.

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   This path validation algorithm verifies, among other things, that a
   prospective certification path (a sequence of n certificates)
   satisfies the following conditions:

   a.  for all 'x' in {1, ..., n-1}, the subject of certificate 'x' is
       the issuer of certificate ('x' + 1);

   b.  certificate '1' is issued by a trust anchor;

   c.  certificate 'n' is the certificate to be validated; and

   d.  for all 'x' in {1, ..., n}, certificate 'x' is valid.

   Certificate validation requires verifying that all of the following
   conditions hold, in addition to the certification path validation
   criteria specified in Section 6 of [RFC5280].

   1.  The signature of certificate x (x>1) is verified using the public
       key of the issuer's certificate (x-1), using the signature
       algorithm specified for that public key (in certificate x-1).

   2.  The current time lies within the interval defined by the
       NotBefore and NotAfter values in the Validity field of
       certificate x.

   3.  The Version, Issuer, and Subject fields of certificate x satisfy
       the constraints established in Sections 4.1 to 4.7 of RFC 6487.

   4.  If certificate x uses the Certificate Policy defined in
       Section 4.8.9 of [RFC6487], then the certificate MUST contain all
       extensions defined in Section 4.8 of [RFC6487] that must be
       present.  The value(s) for each of these extensions MUST satisfy
       the constraints established for each extension in the respective
       sections.  Any extension not thus identified MUST NOT appear in
       certificate x.

   5.  If certificate x uses the Certificate Policy defined in
       Section 4.2.4.1, then all extensions defined in Section 4.8 of
       [RFC6487], except Sections 4.8.9, 4.8.10, and 4.8.11 MUST be
       present.  The certificate MUST contain an extension as defined in
       Sections 4.2.4.2 or 4.2.4.3, or both.  The value(s) for each of
       these extensions MUST satisfy the constraints established for
       each extension in the respective sections.  Any extension not
       thus identified MUST NOT appear in certificate x.

   6.  Certificate x MUST NOT have been revoked, i.e., it MUST NOT
       appear on a Certificate Revocation List (CRL) issued by the CA
       represented by certificate x-1.

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   7.  Compute the VRS-IP and VRS-AS set values as indicated below:

       *  If the IP Address Delegation extension is present in
          certificate x and x=1, set the VRS-IP to the resources found
          in this extension.

       *  If the IP Address Delegation extension is present in
          certificate x and x>1, set the VRS-IP to the intersection of
          the resources between this extension and the value of the
          VRS-IP computed for certificate x-1.

       *  If the IP Address Delegation extension is absent in
          certificate x, set the VRS-IP to NULL.

       *  If the IP Address Delegation extension is present in
          certificate x and x=1, set the VRS-IP to the resources found
          in this extension.

       *  If the AS Identifier Delegation extension is present in
          certificate x and x>1, set the VRS-AS to the intersection of
          the resources between this extension and the value of the
          VRS-AS computed for certificate x-1.

       *  If the AS Identifier Delegation extension is absent in
          certificate x, set the VRS-AS to NULL.

   8.  If there is any difference in resources in the VRS-IP and the IP
       Address Delegation extension on certificate x, or the VRS-AS and
       the AS Identifier Delegation extension on certificate x, then:

       *  If certificate x uses the Certificate Policy defined in
          Section 4.2.4.1, a warning listing the overclaiming resources
          for certificate x SHOULD be issued.

       *  If certificate x uses the Certificate Policy defined in
          Section 4.8.9 of [RFC6487], then certificate x MUST be
          rejected.

   These rules allow a CA certificate to contain resources that are not
   present in (all of) the certificates along the path from the trust
   anchor to the CA certificate.  If none of the resources in the CA
   certificate are present in all certificates along the path, no
   subordinate certificates could be valid.  However, the certificate is
   not immediately rejected as this may be a transient condition.  Not
   immediately rejecting the certificate does not result in a security
   problem because the associated VRS sets accurately reflect the
   resources validly associated with the certificate in question.

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4.2.5.  An Alternative ROA Validation

   Section 4 of [RFC6482] currently has the following text on the
   validation of resources on a ROA:

      The IP address delegation extension [RFC3779] is present in the
      end-entity (EE) certificate (contained within the ROA), and each
      IP address prefix(es) in the ROA is contained within the set of IP
      addresses specified by the EE certificate's IP address delegation
      extension.

   If the end entity certificate uses the Certificate Policy defined in
   Section 4.2.4.1, then the following approach must be used instead.

      The amended IP Address Delegation extension described in
      Section 4.2.4.2 is present in the end entity (EE) certificate
      (contained within the ROA), and each IP address prefix(es) in the
      ROA is contained within the VRS-IP set that is specified as an
      outcome of EE certificate validation described in Section 4.2.4.4.

   Note that this ensures that ROAs can be valid only if all IP address
   prefixes in the ROA are encompassed by the VRS-IP of all certificates
   along the path to the trust anchor used to verify it.

   Operators MAY issue separate ROAs for each IP address prefix, so that
   the loss of one or more IP address prefixes from the VRS-IP of any
   certificate along the path to the trust anchor would not invalidate
   authorizations for other IP address prefixes.

4.2.6.  An Alternative to BGPsec Router Certificate Validation

   If a BGPsec Router Certificate [RFC8209] uses the Certificate Policy
   defined in Section 4.2.4.1, then in addition to the BGPsec Router
   Certificate Validation defined in Section 3.3 of [RFC8209], the
   following constraint MUST be met:

   o  The VRS-AS of BGPsec Router Certificates MUST encompass all
      Autonomous System Numbers (ASNs) in the AS Resource Identifier
      Delegation extension.

   Operators MAY issue separate BGPsec Router Certificates for different
   ASNs, so that the loss of an ASN from the VRS-AS of any certificate
   along the path to the trust anchor would not invalidate router keys
   for other ASNs.

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5.  Validation Examples

   In this section, we will demonstrate the outcome of RPKI validation
   performed using the algorithm and procedures described in Sections
   4.2.4.4, 4.2.5, and 4.2.6, under three deployment scenarios:

   o  An RPKI tree consisting of certificates using the old OIDs only

   o  An RPKI tree consisting of certificates using the new OIDs only

   o  An RPKI tree consisting of a mix of certificates using either the
      old or the new OIDs

   In this context, we refer to a certificate as using the 'old' OIDs,
   if the certificate uses a combination of the OIDs defined in
   Section 1.2 of [RFC6484], Section 2.2.1 of [RFC3779], and/or
   Section 3.2.1 of [RFC3779].  We refer to a certificate as using the
   'new' OIDS, if the certificate uses a combination of OIDs defined in
   Sections 4.2.4.1, 4.2.2.1, and/or Section 4.2.2.3.

5.1.  Example 1 -- An RPKI Tree Using the Old OIDs Only

   Consider the following example:

     Certificate 1 (trust anchor):
      Issuer: TA,
      Subject: TA,
      OIDs: OLD,
      Resources: 0/0, ::0, AS0-4294967295 (all resources)

       Verified Resource Set: 0/0, ::0, AS0-4294967295 (all resources)
       Warnings: none

     Certificate 2:
      Issuer: TA,
      Subject: CA1,
      OIDs: OLD,
      Resources: 192.0.2.0/24, 2001:db8::/32, AS64496

       Verified Resource Set: 192.0.2.0/24,
                              2001:db8::/32, AS64496
       Warnings: none

Top      ToC       Page 20 
     Certificate 3 (invalid):
      Issuer: CA1,
      Subject: CA2,
      OIDs: OLD,
      Resources: 192.0.2.0/24, 198.51.100.0/24, AS64496

       Verified Resource Set: 192.0.2.0/24, AS64496

       Certificate 3 is considered invalid because resources
       contains 198.51.100.0/24, which is not found in the
       Verified Resource Set.

     ROA 1 (invalid):
      Embedded Certificate 4 (EE certificate invalid):
       Issuer: CA2,
       Subject: R1,
       OIDs: OLD,
       Resources: 192.0.2.0/24
         Prefix 192.0.2.0/24, Max Length 24, ASN 64496

       ROA1 is considered invalid because Certificate 3 is invalid.

     ROA 2 (invalid):
      Embedded Certificate 5 (EE certificate invalid):
       Issuer: CA2,
       Subject: R2,
       OIDs: OLD,
       Resources: 198.51.100.0/24
        Prefix 198.51.100.0/24, Max Length 24, ASN 64496

       ROA2 is considered invalid because Certificate 3 is invalid.

     BGPsec Certificate 1 (invalid):
      Issuer: CA2,
      Subject: ROUTER-64496,
      OIDs: NEW,
      Resources: AS64496

       BGPsec Certificate 1 is invalid because Certificate 3 is invalid.

     BGPsec Certificate 2 (invalid):
      Issuer: CA2,
      Subject: ALL-ROUTERS,
      OIDs: NEW,
      Resources: AS64496-AS64497

       BGPsec Certificate 2 is invalid because Certificate 3 is invalid.

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5.2.  Example 2 -- An RPKI Tree Using the New OIDs Only

   Consider the following example under the amended approach:

     Certificate 1 (trust anchor):
      Issuer: TA,
      Subject: TA,
      OIDs: NEW,
      Resources: 0/0, ::0, AS0-4294967295 (all resources)

       Verified Resource Set: 0/0, ::0, AS0-4294967295 (all resources)
       Warnings: none

     Certificate 2:
      Issuer: TA,
      Subject: CA1,
      OIDs: NEW,
      Resources: 192.0.2.0/24, 2001:db8::/32, AS64496

       Verified Resource Set: 192.0.2.0/24,
                              2001:db8::/32, AS64496
       Warnings: none

     Certificate 3:
      Issuer: CA1,
      Subject: CA2,
      OIDs: NEW,
      Resources: 192.0.2.0/24, 198.51.100.0/24, AS64496

       Verified Resource Set: 192.0.2.0/24, AS64496
       Warnings: overclaim for 198.51.100.0/24

     ROA 1 (valid):
      Embedded Certificate 4 (EE certificate):
       Issuer: CA2,
       Subject: R1,
       OIDs: NEW,
       Resources: 192.0.2.0/24
        Prefix 192.0.2.0/24, Max Length 24, ASN 64496

        Verified Resource Set: 192.0.2.0/24
        Warnings: none

       ROA1 is considered valid because the prefix matches the Verified
       Resource Set on the embedded EE certificate.

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     ROA 2 (invalid):
      Embedded Certificate 5 (EE certificate invalid):
       Issuer: CA2,
       Subject: R2,
       OIDs: NEW,
       Resources: 198.51.100.0/24
         Prefix 198.51.100.0/24, Max Length 24, ASN 64496

         Verified Resource Set: none (empty set)
         Warnings: 198.51.100.0/24

       ROA2 is considered invalid because the ROA prefix 198.51.100.0/24
       is not contained in the Verified Resource Set.

     BGPsec Certificate 1 (valid):
      Issuer: CA2,
      Subject: ROUTER-64496,
      OIDs: NEW,
      Resources: AS64496

       Verified Resource Set: AS64496
       Warnings: none

     BGPsec Certificate 2 (invalid):
      Issuer: CA2,
      Subject: ALL-ROUTERS,
      OIDs: NEW,
      Resources: AS64496-AS64497

        Verified Resource Set: AS64496

       BGPsec Certificate 2 is invalid because not all of its resources
       are contained in the Verified Resource Set.

       Note that this problem can be mitigated by issuing separate
       certificates for each AS number.

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5.3.  Example 3 -- An RPKI Tree Using a Mix of Old and New OIDs

   In the following example, new OIDs are used only for CA certificates
   where the issuing CA anticipates that an overclaim could occur and
   has a desire to limit the impact of this to just the overclaimed
   resources in question:

   Certificate 1 (trust anchor):
    Issuer: TA,
    Subject: TA,
    OIDs: OLD,
    Resources: 0/0, ::0, AS0-4294967295 (all resources)

     Verified Resource Set: 0/0, ::0, AS0-4294967295 (all resources)
     Warnings: none

     Note that a trust anchor certificate cannot be found to
     overclaim.  So, using the new OIDs here would not change
     anything with regards to the validity of this certificate.

   Certificate 2:
    Issuer: TA,
    Subject: CA1,
    OIDs: OLD,
    Resources: 192.0.2.0/24, 2001:db8::/32, AS64496

     Verified Resource Set: 192.0.2.0/24,
                            2001:db8::/32, AS64496
     Warnings: none

     Note that since the TA certificate claims all resources, it
     is impossible to issue a certificate below it that could be
     found to be overclaiming.  Therefore, there is no benefit
     in using the new OIDs for Certificate 2.

   Certificate 3:
    Issuer: CA1,
    Subject: CA2,
    OIDs: NEW,
    Resources: 192.0.2.0/24, 198.51.100.0/24, AS64496

     Verified Resource Set: 192.0.2.0/24, AS64496
     Warnings: overclaim for 198.51.100.0/24

     Note that CA1 anticipated that it might invalid Certificate 3
     issued to CA2, if its own resources on Certificate 2 were
     modified and old OIDs were used on Certificate 3.

Top      ToC       Page 24 
   ROA 1 (valid):
    Embedded Certificate 4 (EE certificate):
     Issuer: CA2,
     Subject: R1,
     OIDs: OLD,
     Resources: 192.0.2.0/24
      Prefix 192.0.2.0/24, Max Length 24, ASN 64496

      Verified Resource Set: 192.0.2.0/24
      Warnings: none

     ROA1 is considered valid because the prefix matches the Verified
     Resource Set on the embedded EE certificate.

   ROA 2 (invalid):
    Embedded Certificate 5 (EE certificate invalid):
     Issuer: CA2,
     Subject: R2,
     OIDs: OLD,
     Resources: 198.51.100.0/24
       Prefix 198.51.100.0/24, Max Length 24, ASN 64496

       Verified Resource Set: none (empty set)

     ROA2 is considered invalid because resources on its EE
     certificate contains 198.51.100.0/24, which is not contained
     in its Verified Resource Set.

     Note that if new OIDs were used here (as in example 2), ROA 2
     would be considered invalid because the prefix is not
     contained in the Verified Resource Set.

     So, if there is no difference in the validity outcome, one could
     argue that using old OIDs here is clearest, because any
     overclaim of ROA prefixes MUST result in it being considered
     invalid (as described in Section 4.2.5).

   BGPsec Certificate 1 (valid):
    Issuer: CA2,
    Subject: ROUTER-64496,
    OIDs: OLD,
    Resources: AS64496

     Verified Resource Set: AS64496
     Warnings: none

Top      ToC       Page 25 
   BGPsec Certificate 2 (invalid):
    Issuer: CA2,
    Subject: ALL-ROUTERS,
    OIDs: OLD,
    Resources: AS64496-AS64497

      Verified Resource Set: AS64496

     BGPsec Certificate 2 is considered invalid because resources
     contains AS64497, which is not contained in its Verified Resource
     Set.

     Note that if new OIDs were used here (as in example 2), BGPsec
     Certificate 2 would be considered invalid because the prefix is not
     contained in the Verified Resource Set.

     So, if there is no difference in the validity outcome, one could
     argue that using old OIDs here is the clearest, because any
     overclaim on this certificate MUST result in it being considered
     invalid (as described in Section 4.2.6).

     Also note that, as in example 2, this problem can be mitigated by
     issuing separate certificates for each AS number.

6.  Deployment Considerations

   This document defines an alternative RPKI validation algorithm, but
   it does not dictate how this algorithm will be deployed.  This should
   be discussed as a separate effort.  That said, the following
   observations may help this discussion.

   Because this document introduces new OIDs and an alternative to the
   profile for X.509 PKIX Resource Certificates described in [RFC6487],
   the use of such certificates in the global RPKI will lead to the
   rejection of such certificates by Relying Party tools that do not
   (yet) implement the alternative profile described in this document.

   For this reason, it is important that such tools are updated before
   Certification Authorities start to use this specification.

   However, because the OIDs are defined in each RPKI certificate, there
   is no strict requirement for all Certification Authorities, or even
   for all the certificates they issue, to migrate to the new OIDs at
   the same time.  The example in Section 5.3 illustrates a possible
   deployment where the new OIDs are used only in CA certificates where
   an accidental overclaim may occur.

Top      ToC       Page 26 
7.  Security Considerations

   The authors believe that the revised validation algorithm introduces
   no new security vulnerabilities into the RPKI, because it cannot lead
   to any ROA and/or router certificates to be accepted if they contain
   resources that are not held by the issuer.

8.  IANA Considerations

   IANA has added the following to the "SMI Security for PKIX
   Certificate Policies" registry:

         Decimal  Description                       References

           3     id-cp-ipAddr-asNumber-v2           Section 4.2.1

   IANA has added the following to the "SMI Security for PKIX
   Certificate Extension" registry:

         Decimal  Description                       References

           28     id-pe-ipAddrBlocks-v2             Section 4.2.2.1
           29     id-pe-autonomousSysIds-v2         Section 4.2.2.3

   IANA has added the following to the "SMI Security for PKIX Module
   Identifier" registry:

         Decimal  Description                       References

           90   id-mod-ip-addr-and-as-ident-v2      Section 4.2.2.7
           91   id-mod-ip-addr-and-as-ident-2v2     Section 4.2.3

Top      ToC       Page 27 
9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779,
              DOI 10.17487/RFC3779, June 2004,
              <https://www.rfc-editor.org/info/rfc3779>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <https://www.rfc-editor.org/info/rfc6482>.

   [RFC6484]  Kent, S., Kong, D., Seo, K., and R. Watro, "Certificate
              Policy (CP) for the Resource Public Key Infrastructure
              (RPKI)", BCP 173, RFC 6484, DOI 10.17487/RFC6484, February
              2012, <https://www.rfc-editor.org/info/rfc6484>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <https://www.rfc-editor.org/info/rfc6487>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8209]  Reynolds, M., Turner, S., and S. Kent, "A Profile for
              BGPsec Router Certificates, Certificate Revocation Lists,
              and Certification Requests", RFC 8209,
              DOI 10.17487/RFC8209, September 2017,
              <https://www.rfc-editor.org/info/rfc8209>.

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9.2.  Informative References

   [RFC6268]  Schaad, J. and S. Turner, "Additional New ASN.1 Modules
              for the Cryptographic Message Syntax (CMS) and the Public
              Key Infrastructure Using X.509 (PKIX)", RFC 6268,
              DOI 10.17487/RFC6268, July 2011,
              <https://www.rfc-editor.org/info/rfc6268>.

Acknowledgements

   The authors would like to thank Stephen Kent for reviewing and
   contributing to this document.  We would like to thank Rob Austein
   for suggesting that separate OIDs should be used to make the behavior
   of Relying Party tools deterministic, and we would like to thank Russ
   Housley, Sean Turner, and Tom Petch for their contributions on OID
   and ASN.1 updates.  Finally, we would like to thank Tom Harrison for
   a general review of this document.

Authors' Addresses

   Geoff Huston
   Asia Pacific Network Information Centre
   6 Cordelia St
   South Brisbane, QLD  4101
   Australia

   Phone: +61 7 3858 3100
   Email: gih@apnic.net


   George Michaelson
   Asia Pacific Network Information Centre
   6 Cordelia St
   South Brisbane, QLD  4101
   Australia

   Phone: +61 7 3858 3100
   Email: ggm@apnic.net


   Carlos M. Martinez
   Latin American and Caribbean Internet Address Registry
   Rambla Mexico 6125
   Montevideo  11400
   Uruguay

   Phone: +598 2604 2222
   Email: carlos@lacnic.net

Top      ToC       Page 29 
   Tim Bruijnzeels
   RIPE Network Coordination Centre
   Singel 258
   Amsterdam  1016 AB
   The Netherlands

   Email: tim@ripe.net


   Andrew Lee Newton
   American Registry for Internet Numbers
   3635 Concorde Parkway
   Chantilly, VA  20151
   United States of America

   Email: andy@arin.net


   Daniel Shaw
   African Network Information Centre (AFRINIC)
   11th Floor, Standard Chartered Tower
   Cybercity, Ebene
   Mauritius

   Phone: +230 403 51 00
   Email: daniel@afrinic.net