Internet DRAFT - draft-spaghetti-sidrops-cms-signing-time
draft-spaghetti-sidrops-cms-signing-time
SIDROPS J. Snijders
Internet-Draft Fastly
Updates: 6488 (if approved) T. Harrison
Intended status: Standards Track APNIC
Expires: 9 December 2023 7 June 2023
On the use of the CMS signing-time attribute in RPKI Signed Objects
draft-spaghetti-sidrops-cms-signing-time-01
Abstract
RFC 6488 standardized a template for specifying Signed Objects that
can be validated using the RPKI. Since the publication of that
document, a new additional protocol for distribution of RPKI
repositories was developed (RFC 8182), and new insights arose with
respect to querying and combining the different distribution
mechanisms. This document describes how Publishers and Relying
Parties can use the CMS signing-time attribute to optimize seamless
transitions from RRDP to RSYNC. Additionally, this document updates
RFC 6488 by mandating the presence of the CMS signing-time attribute
and disallowing the binary-signing-time attribute.
Requirements Language
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.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 9 December 2023.
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Copyright Notice
Copyright (c) 2023 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 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
2. Optimizing Seamless transitions from RRDP to RSYNC . . . . . 3
2.1. Guidance for Publishers . . . . . . . . . . . . . . . . . 3
2.2. Guidance for Relying Parties . . . . . . . . . . . . . . 3
3. Presence of CMS signing-time attribute in the field . . . . . 4
4. Considerations and Alternative Approaches . . . . . . . . . . 5
5. Update to RFC 6488 . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[RFC6488] standardized a template for specifying Signed Objects that
can be validated using the RPKI. Since the publication of that
document, a new additional protocol for distribution of RPKI
repositories was developed [RFC8182], and new insights arose with
respect to querying and combining the different distribution
mechanisms. This document describes how Publishers and Relying
Parties can use the CMS signing-time [RFC5652] attribute to optimize
seamless transitions from RRDP to RSYNC. Additionally, this document
updates [RFC6488] by mandating the presence of the CMS signing-time
attribute and disallowing the binary-signing-time attribute.
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2. Optimizing Seamless transitions from RRDP to RSYNC
To avoid needless re-transfers of unchanged files in consecutive
RSYNC synchronizations, [I-D.timbru-sidrops-publication-server-bcp]
recommends the use of so-called 'deterministic' (normalized)
timestamps for files: as long as a file's contents are unchanged,
Publishers SHOULD ensure the file's last modification timestamp also
doesn't change. This document advances the aforementioned concept by
describing a synchronization strategy through which needless
transfers are also avoided when RSYNC is used for the first time, in
instances where previous retrieval via RRDP has occurred, by
leveraging that RRDP data.
As described in [I-D.ietf-sidrops-prefer-rrdp], RP implementations
are expected to first try synchronization via RRDP, and if and only
if that fails - for some reason (malformed XML, expired TLS
certificate, TCP connection timeout, etc.) - attempt to synchronize
via RSYNC instead.
In the RSYNC synchronization protocol, a file's last modification
timestamp (from here on 'mod-time') and filesize are used to
determine whether the general-purpose RSYNC synchronization algorithm
needs to be executed for the file. This is the default mode for both
GPL [rsync] and [openrsync]. If the sender's copy of the file and
the receiver's copy of the file both have the same mod-time and
filesize, the files are assumed to contain the same content, and are
skipped for the purposes of synchronization. Ensuring consistency
with respect to mod-time for both senders and receivers helps to
reduce the cost of RSYNC retrieval, in terms of bandwidth, disk
operations, and CPU instructions.
In order to reduce the burden of the RSYNC synchronization (following
a RRDP failure), Publishers and Relying Parties SHOULD adhere to the
following guidelines.
2.1. Guidance for Publishers
When serializing RPKI Signed Objects to a filesystem hierarchy for
RSYNC consumption, the mod-time of the file containing the Signed
Object MUST be set to the CMS signing-time contained within the
Signed Object.
2.2. Guidance for Relying Parties
When serializing RPKI Signed Objects retrieved via RRDP to a
filesystem hierarchy, the mod-time of the file containing the Signed
Object MUST be set to the CMS signing-time contained within the
Signed Object.
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If an RP uses RRDP to synthesize a filesystem hierarchy for the
repository, then synchronizing from the publisher to the
corresponding directory directly is an option. Alternatively, the RP
may synchronize to a new (empty) directory while using the '--
compare-dest=DIR' rsync feature, to avoid having to retrieve files
that are already available by way of the synthesized filesystem
hierarchy. The DIR variable SHOULD point at the directory containing
previously fetched and validated RPKI data (in its original form, to
ensure the filesize parameter matches).
Quoted from the GPL rsync man page:
This option instructs rsync to use DIR on the destination machine
as an additional hierarchy to compare destination files against
doing transfers (if the files are missing in the destination
directory). If a file is found in DIR that is identical to the
sender's file, the file will NOT be transferred to the destination
directory. This is useful for creating a sparse backup of just
files that have changed from an earlier backup.
Quoted from the openrsync man page:
Use directory as an alternate base directory to compare files
against on the destination machine. If file in directory is found
and identical to the sender's file, the file will not be
transferred.
3. Presence of CMS signing-time attribute in the field
Analysing an archive [rpkiviews] containing valid RPKI Signed Objects
discovered via the five RIR Trust Anchors in the last eight weeks
(2023-04-14 to 2023-06-06), 100% of Signed Objects contain a CMS
signing-time attribute. [NOTE: a job is running to analyse the
milions of objects going back to 2022-06-06 - might take a few more
days to parse all that data]
The above means that already today, all Certificate Authorities
produce Signed Objects which contain a CMS signing-time attribute.
Thus, making the CMS signing-time attribute mandatory would not make
any existing CA operations non-compliant.
As of 3 June, 2023, for 25.8% of Signed Objects the CMS signing-time
timestamp exactly matches the file's mod-time observed via RSYNC.
This means that it is already the case that RPs would see a
significant reduction in the amount of processing required in RSYNC
if they adopted the strategy outlined in Section 2.2.
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In the above-mentioned period of time, zero Signed Objects were
discovered with a CMS binary-signing-time [RFC6019] attribute.
Therefore, disallowing the CMS binary-signing-time attribute would
not make any existing CA operations non-compliant.
4. Considerations and Alternative Approaches
A slightly different approach that has been suggested is to normalize
file mod-times based on the Signed Object's embedded End-Entity (EE)
X.509 notBefore timestamp value. A downside of that approach is that
CAs might backdate the notBefore timestamp to increase the validity
window of the Signed Object, which in turn decreases insight for RPKI
operators as to when exactly the Signed Object purportedly came into
existence.
Along similar lines, the notBefore timestamp may be set in the
future. Setting the mod-time of a file to a future date may be
unintuitive for users, and some programs (e.g. make) will warn on
encountering files with such mod-times.
There is also an increased chance of two distinct objects published
to the same path having the same mod-time and filesize under this
approach, due to CAs setting the notBefore timestamp to some stable
value for a given object and reissuance often not changing the file
size (e.g. where a prefix or a max-length value is changed in a ROA).
In such a situation, if the receiver has the first copy of a file,
RSYNC retrieval will skip the second copy of the file, and the
synchronization operation for the associated repository will result
in a "failed fetch", per section 6.6 of [RFC9286], due to an
inconsistency between the file's hash and the hash listed in the
associated manifest. That in turn necessitates further retrieval
operations on the part of the receiver. The chance of two distinct
objects being issued with the same mod-time and filesize when CMS
signing-time is used to set the mod-time is much smaller, since it
requires that those distinct objects be issued in very close
succession.
Another downside of using notBefore is that Publishers would need to
deserialize both the CMS envelope and the X.509 EE certificate
contained therein to extract a timestamp, instead of merely parsing
the CMS envelope.
Ensuring the mod-time is set to the CMS signing-time gives RPKI
operators a headstart when using tools like [ls], in the sense that
the mod-time aligns with the purported time of object issuance.
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The CMS signing-time attribute has proven useful in researching and
tracking delays in various layers of the RPKI [PAM23]. Mandating the
CMS signing-time to be present might aid future researchers studying
the RPKI ecosystem.
The --checksum option to rsync disables the mod-time and filesize
comparison check in favour of a check based on a whole-file checksum.
This check is slower than the mod-time and filesize check, but (in
instances where the file content has not changed) faster than the
general-purpose RSYNC synchronization algorithm. Since ensuring
consistency between the mod-time and filesize on both sides of the
transaction is straightforward, there is no particular reason to
pursue an approach based on --checksum.
5. Update to RFC 6488
This section updates [RFC6488] to make the CMS signing-time attribute
mandatory and disallow the presence of the CMS binary-signing-time
attribute.
In section 2.1.6.4 the paragraph starting with "The signedAttrs
element MUST be present and ..." and ending in "Other signed
attributes MUST NOT be included." is replaced with the following
text:
The signedAttrs element MUST be present and MUST include the
content-type, message-digest, and signing-time attributes
[RFC5652]. Other signed attributes MUST NOT be included.
In section 2.1.6.4.3 the first sentence "The signing-time attribute
MAY be present." is replaced with the following text:
The signing-time attribute MUST be present.
Section 2.1.6.4.4 is removed in its entirety.
6. Security Considerations
This document has no Security Considerations.
7. IANA Considerations
This document has no IANA actions.
8. Acknowledgements
The authors would like to thank Ties de Kock for their helpful review
of this document.
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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>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[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>.
[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>.
[RFC8182] Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein,
"The RPKI Repository Delta Protocol (RRDP)", RFC 8182,
DOI 10.17487/RFC8182, July 2017,
<https://www.rfc-editor.org/info/rfc8182>.
9.2. Informative References
[I-D.ietf-sidrops-prefer-rrdp]
Bruijnzeels, T., Bush, R., and G. G. Michaelson, "Resource
Public Key Infrastructure (RPKI) Repository Requirements",
Work in Progress, Internet-Draft, draft-ietf-sidrops-
prefer-rrdp-02, 23 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-
prefer-rrdp-02>.
[I-D.timbru-sidrops-publication-server-bcp]
Bruijnzeels, T. and T. de Kock, "RPKI Publication Server
Best Current Practices", Work in Progress, Internet-Draft,
draft-timbru-sidrops-publication-server-bcp-00, 1 June
2023, <https://datatracker.ietf.org/doc/html/draft-timbru-
sidrops-publication-server-bcp-00>.
[ls] IEEE and The Open Group, "ls - The Open Group Base
Specifications Issue 7", 2018,
<https://pubs.opengroup.org/onlinepubs/9699919799/
utilities/ls.html>.
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[openrsync]
Jeker, C., Obser, F., and K. Dzonsons, "openrsync", 2023,
<https://www.openrsync.org/>.
[PAM23] Fontugne, R., Phokeer, A., Pelsser, C., Vermeulen, K., and
R. Bush, "RPKI Time-of-Flight: Tracking Delays in the
Management, Control, and Data Planes", February 2023,
<https://www.iijlab.net/en/members/romain/pdf/
romain_pam23.pdf>.
[RFC6019] Housley, R., "BinaryTime: An Alternate Format for
Representing Date and Time in ASN.1", RFC 6019,
DOI 10.17487/RFC6019, September 2010,
<https://www.rfc-editor.org/info/rfc6019>.
[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>.
[rpki-client]
Jeker, C., Snijders, J., Dzonsons, K., and T. Buehler,
"rpki-client", June 2023, <https://www.rpki-client.org/>.
[rpkitouch]
Snijders, J., "rpkitouch", June 2023,
<https://github.com/job/rpkitouch>.
[rpkiviews]
Snijders, J., "rpkiviews", June 2023,
<http://www.rpkiviews.org/>.
[rsync] Tridgell, A., Mackerras, P., and W. Davison, "rsync",
2022, <https://rsync.samba.org/>.
Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION
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 RFC 7942.
The description of implementations in this section is intended to
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
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features. Readers are advised to note that other implementations may
exist.
According to RFC 7942, "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".
* For the Publication side of the house: [rpkitouch]
* For the Relying Party side of the house: OpenBSD [rpki-client]
Authors' Addresses
Job Snijders
Fastly
Amsterdam
Netherlands
Email: job@fastly.com
Tom Harrison
Asia Pacific Network Information Centre
6 Cordelia St
South Brisbane QLD 4101
Australia
Email: tomh@apnic.net
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