Internet DRAFT - draft-kwvanhove-sidrops-rpki-tree-hints
draft-kwvanhove-sidrops-rpki-tree-hints
Internet Engineering Task Force K.W. van Hove
Internet-Draft University of Twente
Intended status: Standards Track 13 December 2021
Expires: 16 June 2022
Tree Hints for the Resource Public Key Infrastructure (RPKI)
draft-kwvanhove-sidrops-rpki-tree-hints-01
Abstract
In the Resource Public Key Infrastructure (RPKI), holders of IP
address space can become a Certification Authority (CA), optionally
hosting their repository. They can also delegate (part of) their
resources to subordinate CAs, who in turn may do the same. This CA
hierarchy forms a tree structure. Relying Party (RP) software walks
this tree and determines the current valid objects. An underlying
assumption is that this tree is a reasonable size, and that the
information can be processed within reasonable time. This assumption
is not guaranteed to hold. This document describes two new
extensions, "maxDescendants" and "maxVrps", that add constraints for
use in RP processing that ensure this assumption holds.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 16 June 2022.
Copyright Notice
Copyright (c) 2021 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.
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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 Revised BSD License text as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Resource Certificate Extensions . . . . . . . . . . . . . . . 4
3.1. maxDescendants . . . . . . . . . . . . . . . . . . . . . 4
3.2. maxVrps . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Validation . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Example Resource Certificate . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
In the RPKI, holders of IP address space can host their own
repositories and act as their own CA. They have full control over
that repository and any objects signed by their CA. They may, for
example, sign one or more certificates that hold a subset of the
resources from the parent certificate. These certificates may
reference publication points in the same repository or different
ones. These new certificates can, in turn, do the same, ad
infinitum. The nested structure of CAs forms a tree structure. The
root of these trees are defined by the Trust Anchor Locators (TALs)
[RFC8630]. RP software is assumed to walk this tree, visit every
node, and retrieve all objects (e.g. Manifests [RFC6486], Route
Origin Authorizations [RFC6482], Ghostbuster records [RFC6493], other
certificates [RFC6481], etc.). RP software collects all information
from the objects and processes it. It is important to note that RP
software needs to visit every repository and consider every object
CAs put on manifests. If it would exclude any repository or CA, then
a BGP advertisement that should be valid can become invalid. For
example, if a ROA for the prefix 2001:DB8::/32 and AS64496 is
included, but the ROA for 2001:DB8:123::/48 and AS64497 (from another
CA) is not, then a BGP speaker performing ROV validation may falsely
reject the latter, more specific, announcement.
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For RP software to fully walk the tree, the tree needs to be finite
and reasonably sized. However, the size of the tree can only be
determined while traversing the tree - RP software cannot verify
these properties in advance. A malicious CA could, for example,
create its children in an ad-hoc fashion while RP software is
discovering it, thereby violating the implicit assumption that the
tree is finite. That specific behaviour can be countered by RP
software by setting a maximum depth for a certificate chain.
However, at 10 children per child, the number of repositories would
already reach 1111111111 (10^0 + 10^1 + ... + 10^9) after a modest 10
levels. With other strategies, such as serving gigabytes of data and
simulating a very low bandwidth, a malicious repository can violate
our second assumption that the tree is reasonably sized. Using
malicious repository content, any CA can cause the process to take so
unreasonably long that RP software does not finish processing in a
reasonable amount of time (possibly years). The size and structure
of nodes in the RPKI tree varies. For example, a NIR may have a
legitimate need for hundreds of child-CAs, while a regular CA under
the same parent does not. This diversity makes heuristics unsuitable
for detecting this issue adequately, only discarding the malicious
repository and its children, without heavily restricting the freedom
of the structure of RPKI or causing false positives capping future
growth.
Likewise, there may be valid reasons for splitting a prefix into many
subprefixes, or authorising subprefixes for many autonomous system
numbers (ASNs), but allowing any party to add limitless prefix-ASN
pairs may overflow BGP Origin Validation tables. Setting a fixed
limit may be problematic in these cases.
The new certificate extensions, "maxDescendants" and "maxVrps", are
added to mitigate this issue by providing RP software prior knowledge
about the tree limits before walking the tree.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Scope
The scope of "maxDescendants" and "maxVrps" is to provide guidance
for RP software regarding the expected structure of the tree, as well
as impose requirements on other aspects of the CA and its repository.
Following the information in "maxDescendants" and "maxVrps" is
RECOMMENDED. However, local policy MAY prevail.
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3. Resource Certificate Extensions
These extensions extend the already defined extensions for PKIX
Resource Certificates as defined in RFC 6487 section 4.8 [RFC6487].
Both maxDescendants and maxVrps SHOULD appear at least once in each
certificate chain. If these extensions are absent on a certificate,
it means that this certificate imposes no additional limits.
3.1. maxDescendants
This extension is a non-critical extension that defines the maximum
cumultative amount of descendants under this CA. BGPsec Router
Certificates [RFC8209] are not counted because they do not add child-
objects to the validation tree. At a value of 0, an RP SHOULD NOT
visit any of the child CAs listed on the manifest. At a value of N,
an RP SHOULD at most visit N descendants of this CA. This does not
affect the amount of EE certificates used for signing objects like
manifests and ROAs - those are not affected by this limit. This does
include children and children of children. If maxDescendants is
defined at multiple levels in the certificate chain, then the
strictest limit MUST prevail.
The maxDescendants extension contains the maximum amount of children
the CA may at most have. This number SHOULD be lower than the
effective maxDescendants value for this CA. A value higher than or
equal to the effective maxDescendants value will cause the children
to have an effective maxDescendants value equal to the effective
maxDescendants value of this CA minus one.
3.2. maxVrps
This extension is a non-critical extension that defines the maximum
cumultative amount of Validated ROA Payloads (VRPs) [RFC6811] under
this CA. At a value of 0, an RP SHOULD NOT accept any of the ROAs
under this CA. At a value of N, an RP SHOULD create most accept N
VRPs based on data from this CA and its descendants. This means that
at a limit of 25, one can create five ROAs with different ASNs with
each five prefixes, or one ROA with 25 prefixes, or any combination
that ensures the VRP count stays less or equal to maxVrps. This
includes data from ROAs at children and children of children. If
maxDescendants is defined at multiple levels in the certificate
chain, then the strictest limit MUST prevail.
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4. Validation
In order to validate the limits, RP software constructs the chain of
certificates from the current certificate up to the root. For each
limit, RP software should check for each certificate in this chain
whether that certificate defines a limit. Then the most strict limit
of all limits present in the chain should be used as limit. During
evaluation the RP software checks whether any limits have been
violated, and if so, stops processing below the violating branch of
the tree. If a limit is absent from the entire chain, a reasonable
default SHOULD be used. Root CAs SHOULD define all limits on
certificates for third-parties.
5. IANA Considerations
This document registers the following RPKI extensions:
Name: maxDescendants
OID: xxx
Reference: [RFCxxxx] (this document)
Name: maxVrps
OID: xxx
Reference: [RFCxxxx] (this document)
6. Security Considerations
This document contains security enhancements for the tree discovery
process in the RPKI protocol. maxDescendants and maxVrps can help
prevent a number of denial of service attacks against RP instances.
There may be maxDescendants and maxVrps extensions published at the
root level with very large allowances, thereby effectively negating
the protections offered. The same precautions described in [RFC8630]
apply here as well.
CAs should be careful with setting their maxDescendants limits. If
the maxDescendants value times the amount of children of a CA is
higher than the effective maxDescendants value of that CA, then one
or more children may cause the maximum amount of children to be
exceeded, even if none act malicious. This may cause routing data to
not be retrieved. For example, take a CA A with three children: AA,
AB, and AC. A has an effective maxDescendants of 10, and sets its
maxDescendants value to 5, which thus applies to AA, AB, and AC. If
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both AA and AB decide to fully use their five children, for example
by creating AAA, AAB, AAC, AACA, AACB, ABA, ABAA, ABAAA, ABAAAA, and
ABAAAAA, then RP software may no longer check AC, as AA and AB
together already hit the effective maxDescendants of A. Note that
the retrieval order is not defined, thus different RP software may
decide to first retrieve AA, AB, and AC, and exclude a different CA,
for example ABAAAAA. This also applies to maxVrps.
This may lead to RP software not retrieving data from certain CAs,
which can lead to partial data. The threat that comes with partial
data is that, for example, a BGP advertisement that should be valid,
may become invalid, as the ROA for the advertisement is missing, and
the less-specific prefix does have a ROA that was retrieved. When
choosing limits, careful consideration must be taken to ensure that
malicious actors cannot disrupt RPKI, whilst the data from valid
actors is still retrieved.
7. References
7.1. 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>.
[RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", RFC 6481,
DOI 10.17487/RFC6481, February 2012,
<https://www.rfc-editor.org/info/rfc6481>.
[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>.
[RFC6486] Austein, R., Huston, G., Kent, S., and M. Lepinski,
"Manifests for the Resource Public Key Infrastructure
(RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
<https://www.rfc-editor.org/info/rfc6486>.
[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>.
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[RFC6493] Bush, R., "The Resource Public Key Infrastructure (RPKI)
Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493,
February 2012, <https://www.rfc-editor.org/info/rfc6493>.
[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811,
DOI 10.17487/RFC6811, January 2013,
<https://www.rfc-editor.org/info/rfc6811>.
[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>.
[RFC8630] Huston, G., Weiler, S., Michaelson, G., Kent, S., and T.
Bruijnzeels, "Resource Public Key Infrastructure (RPKI)
Trust Anchor Locator", RFC 8630, DOI 10.17487/RFC8630,
August 2019, <https://www.rfc-editor.org/info/rfc8630>.
Appendix A. Example Resource Certificate
The following is the example resource certificate from RFC 6487
[RFC6487] adapted with maxDescendants and maxVrps.
Certificate Name: 9JfgAEcq7Q-47IwMC5CJIJr6EJs.cer
Data:
Version: 3 (0x2)
Serial: 1500 (0x5dc)
Signature Algorithm: SHA256WithRSAEncryption
Issuer: CN=APNIC Production-CVPQSgUkLy7pOXdNeVWGvnFX_0s
Validity
Not Before: Oct 25 12:50:00 2008 GMT
Not After : Jan 31 00:00:00 2010 GMT
Subject: CN=A91872ED
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
RSA Public Key: (2048 bit)
Modulus (2048 bit):
00:bb:fb:4a:af:a4:b9:dc:d0:fa:6f:67:cc:27:39:
34:d1:80:40:37:de:88:d1:64:a2:f1:b3:fa:c6:7f:
bb:51:df:e1:c7:13:92:c3:c8:a2:aa:8c:d1:11:b3:
aa:99:c0:ac:54:d3:65:83:c6:13:bf:0d:9f:33:2d:
39:9f:ab:5f:cd:a3:e9:a1:fb:80:7d:1d:d0:2b:48:
a5:55:e6:24:1f:06:41:35:1d:00:da:1f:99:85:13:
26:39:24:c5:9a:81:15:98:fb:5f:f9:84:38:e5:d6:
70:ce:5a:02:ca:dd:61:85:b3:43:2d:0b:35:d5:91:
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98:9d:da:1e:0f:c2:f6:97:b7:97:3e:e6:fc:c1:c4:
3f:30:c4:81:03:25:99:09:4c:e2:4a:85:e7:46:4b:
60:63:02:43:46:51:4d:ed:fd:a1:06:84:f1:4e:98:
32:da:27:ee:80:82:d4:6b:cf:31:ea:21:af:6f:bd:
70:34:e9:3f:d7:e4:24:cd:b8:e0:0f:8e:80:eb:11:
1f:bc:c5:7e:05:8e:5c:7b:96:26:f8:2c:17:30:7d:
08:9e:a4:72:66:f5:ca:23:2b:f2:ce:54:ec:4d:d9:
d9:81:72:80:19:95:57:da:91:00:d9:b1:e8:8c:33:
4a:9d:3c:4a:94:bf:74:4c:30:72:9b:1e:f5:8b:00:
4d:e3
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Subject Key Identifier:
F4:97:E0:00:47:2A:ED:0F:B8:EC:8C:0C:0B:90:89:
20:9A:FA:10:9B
X509v3 Authority Key Identifier:
keyid:09:53:D0:4A:05:24:2F:2E:E9:39:77:4D:79:
55:86:BE:71:57:FF:4B
X509v3 Key Usage: critical
Certificate Sign, CRL Sign
X509v3 Basic Constraints: critical
CA:TRUE
X509v3 CRL Distribution Points:
URI:rsync://rpki.apnic.net/repository/A3C38A24
D60311DCAB08F31979BDBE39/CVPQSgUkLy7pOXdNe
VWGvnFX_0s.crl
Authority Information Access:
CA Issuers - URI:rsync://rpki.apnic.net/repos
itory/8BDFC7DED5FD11DCB14CF4B1A703F9B7/CVP
QSgUkLy7pOXdNeVWGvnFX_0s.cer
X509v3 Certificate Policies: critical
Policy: 1.3.6.1.5.5.7.14.2
Subject Information Access:
CA Repository - URI:rsync://rpki.apnic.net/mem
ber_repository/A91872ED/06A83982887911DD81
3F432B2086D636/
Manifest - URI:rsync://rpki.apnic.net/member_r
epository/A91872ED/06A83982887911DD813F432
B2086D636/9JfgAEcq7Q-47IwMC5CJIJr6EJs.mft
sbgp-autonomousSysNum: critical
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Autonomous System Numbers:
24021
38610
131072
131074
sbgp-ipAddrBlock: critical
IPv4:
203.133.248.0/22
203.147.108.0/23
maxDescendants:
16
maxVrps:
2048
Author's Address
Koen van Hove
University of Twente
Email: koen@koenvh.nl
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