This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.
The following 'Verified' errata have been incorporated in this document:
EID 5638, EID 5870
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.
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.
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
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.
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.
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.
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.
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 }
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 }
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
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
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)}
-- 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-v2 OBJECT IDENTIFIER ::= { id-pe 29 }
EID 5870 (Verified) is as follows:Section: 4.2.3
Original Text:
ext-pe-autonomousSysIds-v2 EXTENSION ::= {
SYNTAX ASIdentifiers
IDENTIFIED BY id-pe-autonomousSysIds-v2
}
id-pe-autonomousSysIds OBJECT IDENTIFIER ::= { id-pe 29 }
Corrected Text:
ext-pe-autonomousSysIds-v2 EXTENSION ::= {
SYNTAX ASIdentifiers
IDENTIFIED BY id-pe-autonomousSysIds-v2
}
id-pe-autonomousSysIds-v2 OBJECT IDENTIFIER ::= { id-pe 29 }
Notes:
The "-v2" is missing from the identifier. It is needed for the ASN.1 module to compile properly.
-- 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.
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
EID 5638 (Verified) is as follows:Section: 4.2.4.4
Original Text:
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 (...)
* If the IP Address Delegation extension (...)
* 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 (...)
* If the AS Identifier Delegation extension (...)
Corrected Text:
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 (...)
* If the IP Address Delegation extension (...)
* If the AS Identifier Delegation extension is present in
certificate x and x=1, set the VRS-AS to the resources found
in this extension.
* If the AS Identifier Delegation extension (...)
* If the AS Identifier Delegation extension (...)
Notes:
There seems to be a copy-paste error.
There are two bullet points explaining the initialization of VRS-IP, and none explaining the initialization of VRS-AS.
All the evidence suggests that the two extensions (IP Address Delegation and AS Identifier Delegation) are meant to be handled similarly, so I believe that the last three bullet points are supposed to perfectly mirror the first three.
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.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
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
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>.
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
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