RATS Working Group H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Standards Track T. Fossati
Expires: 5 November 2022 Arm Limited
W. Pan
Huawei Technologies
C. Bormann
Universität Bremen TZI
4 May 2022
Epoch Markers
draft-birkholz-rats-epoch-markers-01
Abstract
Abstract Text
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-birkholz-rats-epoch-markers/.
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https://github.com/ietf-rats/draft-birkholz-rats-epoch-marker.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3
2. Epoch IDs . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Interaction Models . . . . . . . . . . . . . . . . . . . . . 4
4. Epoch Marker CDDL . . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. RFC 3161 TSTInfo . . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Systems that are required to interact via secure interactions often
require a shared understanding of the freshness of conveyed
information, especially in the domain of remote attestation
procedures. Establishing a notion of freshness between various
involved entities taking on roles that rely on information that is
not outdated is not simple. In general, establishing a shared
understanding of freshness in a secure manner is not simple. The
RATS architecture [I-D.ietf-rats-architecture] dedicates an extensive
appendix solely on the topic of freshness considerations and that
fact alone should be considered a telltale sign on how necessary yet
complex establishing a trusted and shared understanding of freshness
between systems actually is.
This document provides a prominent way to establish a notion of
freshness between systems: Epoch Markers. Epoch Markers are messages
that are like time ticks produced and conveyed by a system in a
freshness domain: the Epoch Bell. Systems that receive Epoch Markers
do not have to track freshness with their own local understanding of
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time (e.g., a local real time clock). Instead, each reception of a
specific Epoch Marker rings in a new age of freshness that is shared
between all recipients. In essence, the emissions and corresponding
receptions of Epoch Markers are like the ticks of a clock where the
ticks are conveyed by the Internet.
The layout of the freshness domain in which Epoch Markers are
conveyed like the ticks of a clock, introduces a domain-specific
latency -- and therefore a certain uncertainty about tick accuracy.
While all Epoch Markers share the common characteristic of being like
clock ticks in a freshness domain, there are various payload types
that can make up the content of an Epoch Marker. These different
types of Epoch Marker payloads address several specific use cases and
are laid out in this document. While Epoch Markers are encoded in
CBOR and many of the payload types are encoded in CBOR as well, a
prominent payload is the Time Stamp Token content as defined by
[RFC3161]: a DER-encoded TSTInfo value. Time Stamp Tokens (TST)
produced by Time Stamp Authorities (TSA) are conveyed by the Time
Stamp Protocol (TSP). At the time of writing, TSAs are the most
common world-wide implemented secure timestamp token systems.
Reusing the essential TST payload structure as a payload type for
CBOR encoded Epoch Markers makes sense with respect to migration
paths and general interoperability. But there is more than one way
to represent a signed timestamp and other kinds of freshness ticks
that can be used for Epoch Markers.
In this document, basic interaction models on how to convey Epoch
Marchers are illustrated as they impact the message design of a
generic Epoch Marker. Then, the structure of Epoch Markers is
specified using CDDL and the corresponding payload types are
introduced and elaborated on. To increase the level of
trustworthiness in the Epoch Bell and the system that produces them,
Epoch Markers also provide the option to include (concise) remote
attestation evidence or corresponding remote attestation results.
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.
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2. Epoch IDs
The RATS architecture introduces the concept of Epoch IDs that mark
certain events during remote attestation procedures ranging from
simple handshakes to rather complex interactions including elaborate
freshness proofs. The Epoch Markers defined in this document are a
solution that includes the lessons learned from TSAs, the concept of
Epoch IDs and provides several means to identify a new freshness
epoch. Some of these methods are introduced and discussed in
Section 10.3 of [I-D.ietf-rats-architecture].
3. Interaction Models
The interaction models illustrated in this section are derived from
the RATS Reference Interaction Models. In general there are three of
them:
* ad-hoc requests (e.g., via challenge-response requests addressed
at Epoch Bells), corresponding to Section 7.1 in
[I-D.ietf-rats-reference-interaction-models]
* unsolicited distribution (e.g., via uni-directional methods, such
as broad- or multicasting from Epoch Bells), corresponding to
Section 7.2 in [I-D.ietf-rats-reference-interaction-models]
* solicited distribution (e.g., via a subscription to Epoch Bells),
corresponding to Section 7.3 in
[I-D.ietf-rats-reference-interaction-models]
4. Epoch Marker CDDL
epoch-marker = [
header,
$payload,
]
header = {
? challenge-response-nonce,
? remote-attestation-evidence, ; could be EAT or Concise Evidence
? remote-attestation-results, ; hopefully EAT with AR4SI Claims
}
challenge-response-nonce = (1: "PLEASE DEFINE")
remote-attestation-evidence = (2: "PLEASE DEFINE")
remote-attestation-results = (3: "PLEASE DEFINE")
;payload types independent on interaction model
$payload /= native-rfc3161-TST-info
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$payload /= TST-info-based-on-CBOR-time-tag
$payload /= CBOR-time-tag
$payload /= multi-nonce
$payload /= multi-nonce-list
$payload /= strictly-monotonically-increasing-counter
native-rfc3161-TST-info = bytes ; DER-encoded value of TSTInfo
; ~~~
; ~~~ translation with a few poetic licenses of ASN.1 TSTInfo into CDDL
; ~~~
TST-info-based-on-CBOR-time-tag = {
&(version : 0) => int .default 1 ; obsolete?
&(policy : 1) => oid
&(messageImprint : 2) => MessageImprint
&(serialNumber : 3) => int
&(eTime : 4) => profiled-etime
? &(accuracy : 5) => rfc3161-accuracy
&(ordering : 6) => bool .default false
? &(nonce : 7) => int
? &(tsa : 8) => GeneralName
* $$TSTInfoExtensions
}
; based on COSE_Hash_Find (draft-ietf-cose-hash-algs)
MessageImprint = [
hashAlg : int
hashValue : bstr
]
rfc3161-accuracy = non-empty<{
? &(seconds : 0) => int
? &(millis: 1) => 1..999
? &(micros: 2) => 1..999
}>
; timeMap profiles etime from https://datatracker.ietf.org/doc/html/draft-ietf-cbor-time-tag
profiled-etime = #6.1001(timeMap)
timeMap = {
1 => #6.1(int / float) ; TIME_T
* int => any
}
; Section 11.8 of I-D.ietf-cose-cbor-encoded-cert
GeneralName = [ GeneralNameType : int, GeneralNameValue : any ]
; stuff
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oid = #6.111(bstr)
non-empty<M> = (M) .and ({ + any => any })
CBOR-time-tag = [
time-tag,
? nonce
]
time-tag = "PLEASE DEFINE"
nonce = "PLEASE DEFINE"
multi-nonce = tstr / bstr / int
multi-nonce-list = [+ multi-nonce]
strictly-monotonically-increasing-counter = uint ; counter context? per issuer? per indicator?
5. References
5.1. 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>.
[RFC3161] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, DOI 10.17487/RFC3161, August
2001, <https://www.rfc-editor.org/info/rfc3161>.
[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>.
5.2. Informative References
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture", Work
in Progress, Internet-Draft, draft-ietf-rats-architecture-
15, 8 February 2022, <https://www.ietf.org/archive/id/
draft-ietf-rats-architecture-15.txt>.
[I-D.ietf-rats-reference-interaction-models]
Birkholz, H., Eckel, M., Pan, W., and E. Voit, "Reference
Interaction Models for Remote Attestation Procedures",
Work in Progress, Internet-Draft, draft-ietf-rats-
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reference-interaction-models-05, 26 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-rats-
reference-interaction-models-05.txt>.
Appendix A. RFC 3161 TSTInfo
As a reference for the definition of TST-info-based-on-CBOR-time-tag
the code block below depicts the original layout of the TSTInfo
structure from [RFC3161].
TSTInfo ::= SEQUENCE {
version INTEGER { v1(1) },
policy TSAPolicyId,
messageImprint MessageImprint,
-- MUST have the same value as the similar field in
-- TimeStampReq
serialNumber INTEGER,
-- Time-Stamping users MUST be ready to accommodate integers
-- up to 160 bits.
genTime GeneralizedTime,
accuracy Accuracy OPTIONAL,
ordering BOOLEAN DEFAULT FALSE,
nonce INTEGER OPTIONAL,
-- MUST be present if the similar field was present
-- in TimeStampReq. In that case it MUST have the same value.
tsa [0] GeneralName OPTIONAL,
extensions [1] IMPLICIT Extensions OPTIONAL }
Acknowledgements
TBD
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@sit.fraunhofer.de
Thomas Fossati
Arm Limited
United Kingdom
Email: Thomas.Fossati@arm.com
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Wei Pan
Huawei Technologies
Email: william.panwei@huawei.com
Carsten Bormann
Universität Bremen TZI
Bibliothekstr. 1
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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