Internet DRAFT - draft-ietf-sidrops-cms-signing-time
draft-ietf-sidrops-cms-signing-time
SIDROPS J. Snijders
Internet-Draft Fastly
Updates: 6488 (if approved) T. Harrison
Intended status: Standards Track APNIC
Expires: 13 August 2024 10 February 2024
On the use of the CMS signing-time attribute in RPKI Signed Objects
draft-ietf-sidrops-cms-signing-time-06
Abstract
In the Resource Public Key Infrastructure (RPKI), Signed Objects are
defined as Cryptographic Message Syntax (CMS) protected content types
by way of a standard template (RFC 6488). That template includes an
optional CMS signing-time attribute, representing the purported time
at which the object was signed by its issuer. At the time when the
standard template was defined, rsync was the only distribution
mechanism for RPKI repositories.
Since the publication of the standard template, a new, additional
protocol for distribution of RPKI repositories has been developed:
the RPKI Repository Delta Protocol (RRDP). While RPKI repository
operators must provide rsync service, RRDP is typically deployed
alongside it as well, and preferred by default by most Relying Party
(RP) implementations. However, RP implementations also support
fallback to rsync in the event of problems with the RRDP service. As
deployment experience with RRDP has increased, the usefulness of
optimizing switchovers by RPs from one mechanism to the other has
become apparent.
This document describes how Publishers and RPs can use the CMS
signing-time attribute to minimize the burden of switching over from
RRDP to rsync. Additionally, this document updates RFC 6488 by
mandating the presence of the CMS signing-time attribute and
disallowing the use of 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.
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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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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on 13 August 2024.
Copyright Notice
Copyright (c) 2024 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Optimized switchover from RRDP to rsync . . . . . . . . . . . 3
2.1. Guidance for Publishers . . . . . . . . . . . . . . . . . 4
2.2. Guidance for Relying Parties . . . . . . . . . . . . . . 4
3. Presence of the CMS signing-time attribute in public
repositories . . . . . . . . . . . . . . . . . . . . . . 5
4. Update to RFC 6488 . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Considerations and Alternative Approaches . . . . . 9
Appendix B. Implementation status . . . . . . . . . . . . . . . 10
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
In the Resource Public Key Infrastructure (RPKI) [RFC6480], Signed
Objects are defined as Cryptographic Message Syntax (CMS) [RFC5652]
[RFC6268] protected content types by way of a standard template
[RFC6488]. That template includes an optional CMS signing-time
attribute, representing the time at which the object was signed by
its issuer. At the time when the standard template was defined,
rsync was the only distribution mechanism for RPKI repositories.
Since the publication of the standard template, a new, additional
protocol for distribution of RPKI repositories has been developed:
the RPKI Repository Delta Protocol (RRDP) [RFC8182]. While RPKI
repository operators must provide rsync service, RRDP is typically
deployed alongside it as well, and preferred by default by most RP
implementations. However, RP implementations also support fallback
to rsync in the event of problems with the RRDP service. As
deployment experience with RRDP has increased, the usefulness of
optimizing switchovers by RPs from one mechanism to the other has
become apparent.
This document describes how Publishers and RPs can use the CMS
signing-time attribute to minimize the burden of switching over from
RRDP to rsync. Additionally, this document updates [RFC6488] by
mandating the presence of the CMS signing-time attribute and
disallowing the use of the binary-signing-time attribute.
2. Optimized switchover 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. When the content of a file is unchanged,
Publishers SHOULD ensure that the last modification timestamp of the
file remains unchanged as well.
This document advances the aforementioned concept by describing a
synchronization strategy through which needless transfers are also
avoided upon first use of rsync, by leveraging data previously
fetched via RRDP.
As described in [I-D.ietf-sidrops-prefer-rrdp], all modern RP
implementations will first attempt synchronization via RRDP. If
synchronization via RRDP fails for some reason (e.g. malformed XML,
expired TLS certificate, HTTP connection timeout), the RP will
attempt to synchronize via rsync instead.
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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
the original rsync implementation [rsync] and the OpenBSD
implementation [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 will be
omitted from the list of files to be transferred. Ensuring
consistency with respect to mod-time for both senders and receivers
helps to reduce the burden of rsync synchronization in terms of
network bandwidth, disk I/O operations, and CPU usage.
In order to reduce the burden of the rsync synchronization (following
an RRDP failure), Publishers and RPs SHOULD adhere to the following
guidelines.
2.1. Guidance for Publishers
When serializing RPKI Signed Objects to a filesystem hierarchy for
publication via rsync, the mod-time of the file containing the Signed
Object SHOULD be set to the value of the CMS signing-time attribute
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 SHOULD be set to the value of the CMS signing-time attribute
contained within the Signed Object.
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
can synchronize to a new (empty) directory using the _--compare-
dest=DIR_ rsync feature, in order to avoid retrieving files that are
already available by way of the synthesized filesystem hierarchy
stemming from previous RRDP fetches. The _DIR_ component is to be
substituted with the name of the directory containing previously
fetched and validated RPKI data (in its original DER-encoded form, to
ensure the filesize parameter matches).
From the [rsync] man page for _--compare-dest=DIR_:
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
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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.
From the [openrsync] man page for _--compare-dest=directory_:
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 the CMS signing-time attribute in public repositories
Analysing the [rpkiviews] archives containing millions of RPKI Signed
Objects discovered via the five Regional Internet Registry (RIR)
Trust Anchors (TAs) from June 6th, 2022 until January 29th, 2024,
each Signed Object contained a CMS signing-time attribute.
The above means that all of the commonly-used TAs and their
subordinate Certification Authorities (CAs) produce Signed Objects
that contain a CMS signing-time attribute. This means that making
the CMS signing-time attribute mandatory would not cause any existing
commonly-used TA or CA to become non-compliant.
As of January 29th, 2024, for 83.8% of Signed Objects the CMS
signing-time timestamp 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.
In the above-mentioned period of time, no Signed Objects were
discovered with a CMS binary-signing-time [RFC6019] attribute in the
specified repositories. Therefore, disallowing the use of the CMS
binary-signing-time attribute would not cause any existing commonly-
used TA or CA to become non-compliant.
4. Update to RFC 6488
This section updates [RFC6488] to make the CMS signing-time attribute
mandatory and to 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:
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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.
In section 2.1.6.4.3, the sentence "Note that the presence or absence
of the signing-time attribute MUST NOT affect the validity of the
signed object (as specified in Section 3)." is removed.
Section 2.1.6.4.4 is removed in its entirety.
In section 3, the paragraph starting with "The signedAttrs field in
the SignerInfo object is present ..." (1.f) is replaced with the
following text:
The signedAttrs field in the SignerInfo object is present and
contains the content-type attribute (OID 1.2.840.113549.1.9.3),
the message-digest attribute (OID 1.2.840.113549.1.9.4), and the
signing-time attribute (1.2.840.113549.1.9.5).
In section 3, the paragraph starting with "The signedAttrs field in
the SignerInfo object does not ..." (1.g) is replaced with the
following text:
The signedAttrs field in the SignerInfo object does not contain
any attributes other than the following three: the content-type
attribute (OID 1.2.840.113549.1.9.3), the message-digest attribute
(OID 1.2.840.113549.1.9.4), and the signing-time attribute (OID
1.2.840.113549.1.9.5).
In section 9 ("Informative References"), [RFC6019] is removed from
the list.
5. Security Considerations
No requirement is imposed concerning the correctness of the signing
time attribute. It does not provide reliable information on the time
the signature was produced and it bears no relevance for seamless
switchover between RRDP and rsync.
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While the Security Considerations in [RFC6019] mandate that the
signing-time and binary-signing-time attributes, if both present,
MUST provide the same date and time; a potential for ambiguity is
removed by restricting the RPKI Signed Object profile to have only
one field to store the purported signing time.
6. IANA Considerations
This document has no IANA actions.
7. Acknowledgements
The authors would like to thank Ties de Kock, Niels Bakker, Mikael
Abrahamsson, and Russ Housley for their helpful review of this
document.
8. References
8.1. 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>.
[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>.
[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>.
[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>.
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[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>.
8.2. Informative References
[apnicrepository]
APNIC, "APNIC Repository", 2023,
<https://rpki.apnic.net/>.
[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., de Kock, T., Hill, F., and T. Harrison,
"RPKI Publication Server Best Current Practices", Work in
Progress, Internet-Draft, draft-timbru-sidrops-
publication-server-bcp-02, 18 January 2024,
<https://datatracker.ietf.org/doc/html/draft-timbru-
sidrops-publication-server-bcp-02>.
[krill-sync]
NLNet Labs, "krill-sync - 0.3.0 development branch",
December 2023, <https://github.com/NLnetLabs/krill-sync/
commit/1df59eac3112384e11b44c2da3010f63925ec50e>.
[ls] IEEE and The Open Group, "ls - The Open Group Base
Specifications Issue 7", 2018,
<https://pubs.opengroup.org/onlinepubs/9699919799/
utilities/ls.html>.
[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>.
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[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/>.
[rpki-rrdp-tools-py]
Kock, T. D., "rpki-rrdp-tools-py", November 2023,
<https://github.com/ties/rpki-rrdp-tools-py/>.
[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/>.
[rsyncit] RIPE NCC, "rsyncit", November 2023,
<https://github.com/RIPE-NCC/rsyncit/>.
Appendix A. Considerations and Alternative Approaches
This section is to be removed before publishing as an RFC.
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 this approach is that
objects from CAs not using one-time use EE certificates, per section
5.1.1 of [RFC9286] would result in multiple objects signed at
different points in time with the same mod-times.
Additionally, 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 for contractual reasons. Setting
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the mod-time of a file to a future date may be unintuitive for users,
and some programs (e.g. GNU 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.
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 rsync's _--checksum_ feature.
Appendix B. Implementation status
This section is to be removed before publishing as an RFC.
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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
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".
* [rpkitouch] - a timestamp setter utility for both rsync servers
and RRDP clients by Job Snijders in C.
* [rpki-client] - a Relying Party implementation by OpenBSD in C, a
client side implementation.
* [rsyncit] - a RRDP-to-rsync sync tool by RIPE NCC in Java, run on
the server side.
* [apnicrepository] - the public APNIC RPKI repository - the APNIC
rsync server normalizes timestamps.
* [rpki-rrdp-tools-py] - a number of client-side RRDP utilities by
Ties de Kock in Python.
* [krill-sync] - a RRDP-to-rsync sync tool by NLNet Labs in Rust,
run on the server side.
Authors' Addresses
Job Snijders
Fastly
Amsterdam
Netherlands
Email: job@fastly.com
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Tom Harrison
Asia Pacific Network Information Centre
6 Cordelia St
South Brisbane QLD 4101
Australia
Email: tomh@apnic.net
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