Internet DRAFT - draft-harrison-sidrops-manifest-numbers
draft-harrison-sidrops-manifest-numbers
Internet Engineering Task Force T. Harrison
Internet-Draft G. Michaelson
Updates: RFC9286 (if approved) APNIC
Intended status: Standards Track J. Snijders
Expires: 5 September 2024 Fastly
4 March 2024
RPKI Manifest Number Handling
draft-harrison-sidrops-manifest-numbers-01
Abstract
The Resource Public Key Infrastructure (RPKI) makes use of signed
objects called manifests. A manifest lists each file that a
publisher intends to include within an RPKI repository, and can be
used to detect certain forms of attack against a repository.
Manifests include a "manifest number" (manifestNumber), which the
publisher must increment whenever it issues a new manifest, and
Relying Parties (RPs) are required to verify that a newly-retrieved
manifest for a given Certification Authority (CA) has a higher
manifestNumber than the previously-validated manifest. However, the
manifestNumber field is 20 octets in length (i.e. not unbounded), and
no behaviour is specified for when a manifestNumber reaches the
largest possible value. This document specifies publisher and RP
behaviour for this scenario.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 5 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Manifest Number Handling . . . . . . . . . . . . . . . . . . 4
3. Operational Considerations . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Implementation status . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Serial Number Arithmetic . . . . . . . . . . . . . . 6
Appendix B. Walkthrough of the rpki-client implementation . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Resource Public Key Infrastructure (RPKI) [RFC6480] makes use of
signed objects [RFC6488] called manifests [RFC9286]. A manifest
lists each file that a publisher intends to include within an RPKI
repository [RFC6481], and can be used to detect certain forms of
attack against a repository. Manifests include a "manifest number"
(manifestNumber), which the publisher must increment whenever it
issues a new manifest, and Relying Parties (RPs) are required to
verify that a newly-retrieved manifest for a given Certification
Authority (CA) has a higher manifestNumber than the previously-
validated manifest (see section 4.2.1 of [RFC9286]).
However, the manifestNumber field is 20 octets in length (i.e. not
unbounded), and no behaviour is specified for when a manifestNumber
reaches the largest possible value, which means that a publisher can
no longer make use of a given CA certificate when that value is
reached. (For the purposes of [RFC9286], a "CA" is represented by a
CA certificate with a stable location and a stable private key.
Reissuing a CA certificate with changed resources or a changed expiry
date does not change the identity of the CA such that the stored
manifestNumber for the CA is reset, for example.)
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While it is practically impossible for a publisher to reach the
largest possible value under normal operating conditions (it would
require that the publisher issue one manifest per second for
46,343,912,903,694,283,301,740 quintillion years), there is a chance
that it could be reached due to bugs in the issuance or publication
systems or incorrect/inadvertent use of those systems. For example:
occur:
Incrementing by large values when issuing manifests, such that the
time to reach that largest value is reduced.
Reissuing new manifests in an infinite delay-free loop, such that
the manifestNumber increases by a large value in a comparatively
short period of time.
Inadvertently setting the manifestNumber to the largest possible
value, such that the publisher will no longer be able to publish
usable manifests for that repository.
These scenarios might also arise in combination and be more severe as
a result: for example, a large manifest number increment bug in
conjunction with a manifest reissuance loop problem.
For a subordinate CA, the risk of repository invalidation due to this
problem can be addressed by the publisher simply using the key
rollover process ([RFC6489]) to get a new Certification Authority
(CA) certificate. RPs will treat this new certificate as though it
represents a distinct CA, and the manifestNumber can be reset at that
point.
However, this option is not available for RPKI Trust Anchors (TAs).
If a TA publishes a manifest with the largest-possible manifestNumber
value, then it is not possible to make use of the TA after that
point, because the certificate location (stored in the associated
Trust Anchor Locator (TAL) [RFC8630]) and its private key cannot be
changed. Issuing a new TA and distributing the associated TAL to
clients would involve a large amount of work for TA operators and
RPs, and there would be a limited degree of RPKI protection by way of
that TA for the time between the issuance of the problematic manifest
and the installation of the new TAL for a given client.
In order to avoid these problems, this document defines how
publishers and RPs can handle this scenario in order to facilitate
ongoing use of an affected repository.
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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 [RFC2119] [RFC8174].
2. Manifest Number Handling
For a given CA, an RP MUST NOT reject a new manifest issued by that
CA on the grounds of it not having a higher manifestNumber than a
previously validated manifest if the new manifest has a different
filename from that of the previously validated manifest. In other
words, an RP MUST reset its stored manifestNumber for a given CA if
the CA changes the filename of its manifest.
With this behaviour, it is possible for a CA to be configured such
that any time it issues a new manifest, it uses a new filename for
that manifest. If a CA were configured in this way, the
manifestNumber validation set out in section 4.2.1 of [RFC9286] would
have no purpose. To avoid this outcome, CAs SHOULD NOT use new
filenames for manifests except in situations where it is necessary to
ensure the ongoing validity of the CA or its repository. Similarly,
RP software SHOULD alert its operators when a manifest filename
changes for a given CA.
Note that this approach is different from that described in
Section 3.2.1 of [RFC8488].
3. Operational Considerations
CA software may opt to support this functionality in various ways.
For example, it could change the manifest filename when the
manifestNumber reaches a certain threshold, or it could alert the
operator in this scenario and request confirmation that the filename
should be changed.
4. IANA Considerations
N/A
5. Implementation status
This section is to be removed before publishing as an RFC.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
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assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
* OpenBSD [rpki-client]
6. Acknowledgements
N/A
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>.
[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>.
[RFC9286] Austein, R., Huston, G., Kent, S., and M. Lepinski,
"Manifests for the Resource Public Key Infrastructure
(RPKI)", RFC 9286, DOI 10.17487/RFC9286, June 2022,
<https://www.rfc-editor.org/info/rfc9286>.
7.2. Informative References
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
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[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/info/rfc6480>.
[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>.
[RFC6488] Lepinski, M., Chi, A., and S. Kent, "Signed Object
Template for the Resource Public Key Infrastructure
(RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
<https://www.rfc-editor.org/info/rfc6488>.
[RFC6489] Huston, G., Michaelson, G., and S. Kent, "Certification
Authority (CA) Key Rollover in the Resource Public Key
Infrastructure (RPKI)", BCP 174, RFC 6489,
DOI 10.17487/RFC6489, February 2012,
<https://www.rfc-editor.org/info/rfc6489>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[RFC8488] Muravskiy, O. and T. Bruijnzeels, "RIPE NCC's
Implementation of Resource Public Key Infrastructure
(RPKI) Certificate Tree Validation", RFC 8488,
DOI 10.17487/RFC8488, December 2018,
<https://www.rfc-editor.org/info/rfc8488>.
[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>.
[rpki-client]
OpenBSD Project, "rpki-client", January 2024,
<https://www.rpki-client.org/>.
Appendix A. Serial Number Arithmetic
Serial number arithmetic [RFC1982] is an approach that has been used
in the DNS context (among others) to permit the indefinite use of a
finite number space. At least in theory, it would be possible to use
a similar approach with the manifestNumber field as well.
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However, unlike the corresponding DNS context with SOA resource
records, an RPKI CA does not have visibility into or control over
RPKI RPs generally. This means that it is not possible to select
updated manifestNumber values or to manage the relevant state
transitions so as to definitively ensure that all RPs will have valid
state at the end of the process. The approach proposed in Section 2
does not have this problem.
Appendix B. Walkthrough of the rpki-client implementation
This section describes the [rpki-client] implementation with regard
to handling manifest numbers. The process is composed of multiple
stages:
1. Fetching the manifests and acquiring referenced files
2. Preprocessing of the manifests
3. Selecting the first candidate manifest
4. Matching file names and hashes
5. Optionally selecting the second candidate manifest
B.1. Stage: Fetching the Manifests and Acquiring Referenced Files
The RP follows _rpkiNotify_ or _caRepository_ pointers in the
_SubjectInfoAccess_ extension of valid CA certificates to queue up
synchronization tasks.
At the end of this stage the RP has zero, one, or two manifests for a
given _caRepository_. Depending on the validation status, the RP
stores files into two locations: _DIR_VALID_ or _DIR_TEMP_.
_DIR_VALID_ contains objects which were found to be valid (current,
not revoked, not expired) during the previous validation run, the
_DIR_TEMP_ location contains files retrieved via RRDP or rsync which
have not yet been validated, or were rejected by the validation
process.
If the remote publication point is unreachable on both RRDP and
rsync, no purported "new" manifest file will be stored in _DIR_TEMP_.
It is possible that the _DIR_VALID_ location contains a locally
cached version of the object from a previous validation run.
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B.2. Stage: preprocessing of the manifests
Constructing the path and filename based on the _rpkiManifest_ of the
CA certificate, the RP attempts to open what purportedly are two
version of the same _.mft_ file in _DIR_TEMP_ and _DIR_VALID_,
respectively.
For brevity's sake, the version in _DIR_TEMP_ is associated with a
data structure named *mft1*, the version in _DIR_VALID_ is associated
with a data structure named *mft2*.
Assuming two files exist in the _DIR_TEMP_ and _DIR_VALID_ locations,
both files are run through a series of checks. If any check fails,
that file will be considered ineligible.
1. Can the file be opened?
2. Can the content of the file be DER-decoded
3. Can the DER-content be parsed as CMS ContentInfo?
4. Is the CMS self-signage correct?
5. Can exactly one CMS SignerInfo be extracted?
6. Is the ContentInfo of the right version?
7. Is the SignerInfo of the right version?
8. Does the SignerInfo have the correct signed attributes?
9. Does the SignerInfo have the correct digest and signature
algorithms?
10. Does the ContentInfo have the right type of embedded content?
11. Does the eContentType match the Content-Type?
12. Does the CMS contain zero CRLs?
13. Can exactly one X.509 cert be extracted from the SignerInfo?
14. Can the notBefore field be extracted from the X.509 cert?
15. Can the notAfter field be extracted from the X.509 cert?
16. Does the X.509 cert's SKI match the SignerInfo's
SignerIdentifier?
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17. Can the AIA be extracted from the X.509 EE?
18. Can the AKI be extracted from the X.509 EE?
19. Can the SIA be extracted from the X.509 EE?
20. Can the SKI be extracted from the X.509 EE?
21. Are the X509 EE's RFC 3779 extensions set to inherit?
22. Can the eContent be parsed according to the ASN.1 formal syntax?
23. Is the Manifest eContent of the right version?
24. Can the manifestNumber be extracted?
25. Is the CMS signing-time before the Manifest nextUpdate time?
26. Is 'now' not before the Manifest thisUpdate?
27. Is 'now' not after the Manifest nextUpdate?
28. Is the Manifest nextUpdate not before the Manifest thisUpdate?
29. Does a valid certification path from a TA to this EE cert exist?
Through the above checks, the *mft1* and *mft2* data structures are
populated, or marked ineligible.
B.3. Stage: selecting the first candidate manifest
Assuming both *mft1* and *mft2* successfully passed through stage 2
(Appendix B.2), a comparison can be made between *mft1* and *mft2* to
select the candidate mft for the next stage.
The RP checks whether the locally cached version *mft2* (from
_DIR_VALID_) is older in the sense that was issued earlier than
*mft1* (from _DIR_TEMP_) by comparing the Manifest _thisUpdate_
timestamp, and has a smaller _manifestNumber_. If both conditions are
true, the RP will select *mft1* as candidate for stage stage 4
(Appendix B.4).
If there was some kind of issue with *mft1*(such as it being older
than or has the same _thisUpdate_ as *mft2*, or it having a
_manifestNumber_ which is lower than or equal to *mft2*), the RP
proceeds with stage 5 (Appendix B.5).
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B.4. Stage: matching file names and hashes for mft1
The RP will now verify the hash value of each file listed in manifest
*mft1* matches the value obtained by hashing the file acquired from
the publication point. If the computed hash value of a file listed
on the manifest does not match the hash value contained in the
manifest, then a _failed fetch_ occurred and the RP proceeds to stage
5 (Appendix B.5).
If all the files and hashes matched, *mft1* and its associated files
are moved from _DIR_TEMP_ to _DIR_VALID_. The manifest handling
procedure now ends.
B.5. Optional Stage: matching file names and hashes for mft2
This stage is only reached if there was an issue with *mft1*.
The RP will now verify the hash value of each file listed in manifest
*mft2* matches the value obtained by hashing the file acquired from
the publication point. If the computed hash value of a file listed
on the manifest does not match the hash value contained in the
manifest, then the _caRepository_ is busted.
Authors' Addresses
Tom Harrison
Asia Pacific Network Information Centre
6 Cordelia St
South Brisbane QLD 4101
Australia
Email: tomh@apnic.net
George G. Michaelson
Asia-Pacific Network Information Centre
6 Cordelia St
South Brisbane QLD 4101
Australia
Email: ggm@apnic.net
Job Snijders
Fastly
Amsterdam
Netherlands
Email: job@fastly.com
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