Internet DRAFT - draft-voit-rats-trusted-path-routing
draft-voit-rats-trusted-path-routing
RATS Working Group E. Voit
Internet-Draft Cisco
Intended status: Standards Track June 10, 2020
Expires: December 12, 2020
Trusted Path Routing
draft-voit-rats-trusted-path-routing-02
Abstract
There are end-users who believe encryption technologies like IPSec
alone are insufficient to protect the confidentiality of their highly
sensitive traffic flows. These end-users want their flows to
traverse devices which have been freshly appraised and verified.
This specification describes Trusted Path Routing. Trusted Path
Routing protects sensitive flows as they transit a network by
forwarding traffic to/from sensitive subnets across network devices
recently appraised as trustworthy.
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 December 12, 2020.
Copyright Notice
Copyright (c) 2020 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
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Notation . . . . . . . . . . . . . . . . . . 4
3. Distributed Trusted Path Routing . . . . . . . . . . . . . . 4
3.1. Trusted Topology . . . . . . . . . . . . . . . . . . . . 4
3.2. Trustworthiness Vector . . . . . . . . . . . . . . . . . 5
3.3. Stamped Passport . . . . . . . . . . . . . . . . . . . . 7
3.4. Passport Protocol Bindings . . . . . . . . . . . . . . . 11
3.5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 13
4. Security Considerations . . . . . . . . . . . . . . . . . . . 16
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1. Normative References . . . . . . . . . . . . . . . . . . 17
5.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Centralized Trusted Path Routing . . . . . . . . . . 18
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 20
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 20
Appendix D. Open Questions . . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
There are end-users who believe encryption technologies like IPSec
alone are insufficient to protect the confidentiality of their highly
sensitive traffic flows. These customers want their highly sensitive
flows to be transported over only network devices recently verified
as trustworthy.
With the inclusion of TPM based cryptoprocessors into network
devices, it is now possible for network providers to identify
potentially compromised devices as well as potentially exploitable
(or even exploited) vulnerabilities. Using this knowledge, it then
becomes possible to redirect sensitive flows around these devices.
Trusted Path Routing (TPR) provides a method of establishing Trusted
Topologies which only include trust-verified network devices. This
specification describes a distributed variant of TPR. With this
variant, membership in a Trusted Topology is established and
maintained via an exchange of Stamped Passports at the link layer
between peering network devices. As links to Attesting Devices are
appraised as meeting at least a minimum set of formally defined
Trustworthiness Levels, the links are then included as members of
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this Trusted Topology. [I-D.ietf-lsr-flex-algo] is then used to
propogate topology state throughout an IGP domain. IP Packets to and
from end-user designated Sensitive Subnets are then forwarded into
this Trusted Topology at each IGP boundary.
The specification works under the following assumptions:
1. All network devices supports the TPM remote attestation profile
as laid out in [RATS-Device]
2. A [I-D.ietf-lsr-flex-algo] topology spans network devices within
an IGP domain.
3. One or more Verifiers continuously appraise the set of network
devices in the IGP domain, and the Verifiers canse return the
Attestation Results back to the attesting network device.
4. 802.1x or MACSEC is used to communicate EAP credentials
containing a Stamped Passport between network peers.
Beyond the distributed variant of TPR, there is another method to
accomplish Trusted Path Routing. A controller-based TPR variant is
described in the appendicies.
2. Terminology
2.1. Terms
The following terms are imported from [RATS-Arch]: Attester,
Evidence, Passport, Relying Party, and Verifier.
The following terms at imported from [RFC8639]: Event Stream.
Newly defined terms for this document:
Attested Device - a device where a Verifier's most recent appraisal
of Evidence has returned a Trustworthiness Vector.
Stamped Passport - a bundle of Evidence which includes at least
signed Attestation Results from a Verifier, and two independent
TPM quotes from an Attester.
Sensitive Subnet - an IP address range where IP packets to or from
that range must only have their IP headers and encapsulated
payloads accessible/visible only by Attested Devices.
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Transparently-Transited Device - a network device within an IGP
domain where any packets passed into that IGP domain are
completely opaque at Layer 3 and above.
Trusted Topology - A topology which includes only Attested Devices
and Transparently-Transited Devices.
Trustworthiness Level - a specific quanta of trustworthiness which
can be assigned by a Verifier.
Trustworthiness Vector - a set of Trustworthiness Levels assigned
during a single assessment cycle by a Verfier using Evidence and
Claims related to an Attested Device. The vector is included
within Attestation Results.
2.2. 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.
3. Distributed Trusted Path Routing
3.1. Trusted Topology
To be included in a Trusted Topology, a Stamped Passport Section 3.3
is assembled by an Attested Device. This Stamped Passport will
include the most recent Verifier provided Trustworthiness Vector
Section 3.2 for that Attested Device. Upon receiving and appraising
this Stamped Passport as part of link layer authentication, the
Relying Party decides if this link should be added to a Trusted
Topology.
When enough links on enough Relying Parties have been so appraised, a
Trusted Topology will now exist within an IGP domain. And traffic
exchanged with Sensitive Subnets can be forwarded into that Trusted
Topology from all edges of an IGP domain.
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.--------. .---------.
| Hacked | | Edge |
.---------. | Router | | Router |
| Router | | | | |
| | | trust>-------------<no_trust |
| no_trust>--<trust | .--------. | |----Sensitive
| | '--------' | trust>==<trust | Subnet
| trust>=============<trust | | |
'---------' | | '---------'
| Router |
'--------'
Figure 1: Distributed Trusted Path Topology Assembly
3.2. Trustworthiness Vector
For distributed TPR to operate, specific Appraisal Results need to be
consistently interpreted by Relying Party network devices. The
following set of Trustworthiness Levels are defined for this purpose:
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+------------------------+------------------------------------------+
| Trustworthiness Level | Definition |
+------------------------+------------------------------------------+
| hw-authentic | A Verifier has appraised an Attester as |
| | having authentic hardware |
| | |
| fw-authentic | A Verifier has appraised an Attester as |
| | having authentic firmware |
| | |
| hw-verification-fail | A Verifier has appraised an Attester has |
| | failed its hardware or firmware |
| | verification |
| | |
| identity-verified | A Verifier has appraised and verified an |
| | Attester's unique identity |
| | |
| identity-fail | A Verifier has been unable to assess or |
| | verify an Attester's unique identity |
| | |
| boot-verified | A Verifier has appraised an Attester as |
| | Boot Integrity Verified |
| | |
| boot-verification-fail | A Verifier has appraised an Attester has |
| | failed its Boot Integrity verification |
| | |
| files-verified | A Verifier has appraised an Attester's |
| | file system, and asserts that it |
| | recognizes relevant files |
| | |
| file-blacklisted | A Verifier has found a file on an |
| | Attester which should not be present |
+------------------------+------------------------------------------+
More that one Trustworthiness Level may be contained within Appraisal
Results. As a result, a single Trustworthiness Vector which contains
a sequenced list of Trustworthiness Levels MUST be returned within
the Attestation Results. The establishment of this Vector follows
the following logic on the Verifier.
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Start: TPM Quote Received, log recevied, or appraisal timer expired
Step 0: set Trustworthiness Vector = Null
Step 1: Is there sufficient fresh signed evidence to appraise?
(yes) - No Action
(no) - Goto Step 6
Step 2: Appraise Hardware Integrity
(if hw-verification-fail) - push onto vector, Goto Step 6
(if hw-authentic) - push onto vector
(if fw-authentic) - push onto vector
(if not evaluated, or insufficient data to conclude: take no action)
Step 3: Appraise attester identity
(if identity-verified) - push onto vector
(if identity-fail) - push onto vector
(if not evaluated, or insufficient data to conclude: take no action)
Step 4: Appraise boot integrity
(if boot-verified) - push onto vector
(if boot-verification-fail) - push onto vector
(if not evaluated, or insufficient data to conclude: take no action)
Step 5: Appraise filesystem integrity
(if files-verified) - push onto vector
(if file-blacklisted) - push onto vector
(if not evaluated, or insufficient data to conclude: take no action)
Step 6: Assemble Attestation Results, and push to Attester
End
3.3. Stamped Passport
Critical to the establishment and maintenance of a Trusted Topology
is the Stamped Passport. Such passports are continuously exchanged
between peering network devices over a link layer protocol like
802.1x. Section 3.3 provides a protocol independent process for
Stamped Passport generation and evaluation. Section 3.4 later in the
document binds the Stamped Passport to specific link layer protocols,
YANG models, and authentication methods.
The composite nature of the Stamped Passport exposes multiple
dimensions of an attesting router's security posture to a network
peer. Specifically, using capabilities defined within [RATS-YANG]
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and [stream-subscription], the following can be established about the
Attester:
o its hardware-based identity,
o the Trustworthiness Vector according to its most recent Verifier
appraisal,
o the amount of time which has passed since the Attester has been
assigned the Trustworthiness Vector, and
o if the PCRs haven't changed, the Attester's current
Trustworthiness Vector
With this information, the Relying Party peer can make nuanced
decisions. For example, when the Attester's legitimate hardware
identity credentials can be verified, it might choose to accept link
layer connections and forward generic Internet traffic.
Additionally, if the Attester's Trustworthiness Vector is acceptable
to the Relying Party, and it hasn't been too long since the Verifier
has provided a passport, the Relying Party can include that link in a
Trusted Topology.
As the process described above repeats across the set of links within
the IGP domain, Trusted Topologies can be extended and maintained.
Traffic to and from Sensitive Subnets is then identified at the edges
of the IGP domain and passed into this Trusted Topology.
The prerequisites for this solution to work are:
o Customer designated Sensitive Subnets and their requested
Trustworthiness Vectors have been identified and associated with
external interfaces to/from the edge of an IGP domain.
o A Trusted Topology such as one established by
[I-D.ietf-lsr-flex-algo] exists in an IGP domain for the
forwarding of Sensitive Subnet traffic. This Topology will carry
traffic across a set of devices which currently meet at least
minimum Trustworthiness Vectors.
o Verifiers A and B (in the figure below) are able to verify
[TPM1.2] or [TPM2.0] signatures of an Attester.
o Verifier A can establish the Trustworthiness Vector of an Attester
and return a signed result to that Attester.
o An Attester can assemble a Stamped Passport for Verifier B.
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o Verifier B trusts the Attestation Results and can verify
signatures made by Verifier A.
o Within an IGP domain, a Relying Party is able to use affinity to
include/exclude links as part of the Trusted Topology based on
this appraisal.
o Traffic to a Sensitive Subnet can be passed into the Trusted
Topology.
.--------------.
| Verifier A |
'--------------'
^ (2)
| Verifier A signed Trustworthiness Vector
Evidence |
(1) V
.-------------. .---------------.
| Attester | | Relying Party |
| (Router) |<------------------nonce(3)| / Verifier B |
| .-----. | | (Router) |
| | TPM | |(4)-Stamped Passport------>| |
| '-----' | | (5) |
'-------------' '---------------'
Figure 2: Stamped Passport Generation and Appraisal
In Figure 2 above, Evidence from a TPM1.2 or TPM2.0 is generated and
signed by that TPM. This Evidence is appraised by Verifier A, and
the Attester is given a Trustworthiness Vector which is signed and
returned as Attestation Results to the Attester. Later, when a
request comes in from a Relying Party, the Attester assembles and
returns three independently signed elements of Evidence. These three
comprise the Stamped Passport which when taken together allow
Verifier B to appraise and set the current Trustworthiness Vector of
the Attester.
More details on the mechanisms used in the construction and
verification of the Stamped Passport match to the numbered steps of
Figure 2:
1. An Attester sends a signed TPM Quote which includes PCR
measurements to Verifier A at time(x).
2. Verifier A appraises (1), then sends the following items back to
that Attester as Attestation Results:
1. the Trustworthiness Vector of an Attester,
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2. the signature from the TPM Quote of (1),
3. a Verifier signature across (2.1) and (2.2).
3. A nonce known to the Relying Party is received by the Attester at
time(y).
4. The Attester generates and sends a Stamped Passport. This
passport includes:
1. (1)
2. (2)
3. New signed, verifiably fresh PCR measurements at time(y),
which incorporates the nonce from (3).
5. On receipt of (4), the Relying Party makes its determination of
how the Stamped Passport will impact adjacencies within a Trusted
Topology. The decision process is:
1. Verify that (4.3) includes the nonce from (3).
2. Verify the TPM signature within (4.2) matches the signature
of (4.1).
3. Validate the signatures of (4.1), (4.2), (4.3).
4. Failure of (5.1), (5.2), or (5.3) means the link does not
meet minimum criteria, appraise the link as having a null
Trustworthiness Vector, and additionally jump to step (5.8).
5. If selected PCR values of (1) match (4.3), then Relying Party
can accept (2.1) as the link's Trustworthiness Vector.
6. When the PCR values are different, and not much time has
passed between time(x) and time(y), the Relying Party can
either accept any previous Trustworthiness Vector, or attempt
to acquire a new Stamped Passport. Where
[stream-subscription] is used, it should only be a few
seconds before a new Attestation Results should be delivered
to an Attester via (2).
7. When the PCR values are different, but there is a large time
gap between time(x) and time(y), the link should be assigned
a null Trustworthiness Vector.
8. Based on the link's Trustworthiness Vector:
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1. include it within any Trusted Topology which accepts that
Trustworthiness Vector.
2. remove it from any Trusted Topology which does not accept
that Trustworthiness Vector.
3.4. Passport Protocol Bindings
This section provides details of how a Stamped Passport described in
Section 3.3 interacts with link layer protocols like [MACSEC] or
[IEEE-802.1X], YANG subscriptions [RFC8639], and [RFC3748] methods.
Additional linkages to the YANG module defined in Section 3.5 are
described.
.--------------.
| Verifier A |
'--------------'
^ (2)
| Verifier A signed Attestation Results @time(x) (
Evidence( | Trustworthiness Level,
TpmQuote | signature from TpmQuote@time(x) )
@time(x)) |
(1) V
.-------------. .---------------.
| Attester |<------nonce @time(y)---(3)| Relying Party |
| .-----. | | / Verifier B |
| | Tpm | |(4)-Stamped Passport ( --->| (Router) |
| '-----' | TpmQuote@time(y), | (5) |
'-------------' TpmQuote@time(x), '---------------'
Verifier A signed Attestation Results @time(x) )
Figure 3: Details of Stamped Passport Generation
Figure 3 above expands upon the previously described Figure 2. The
numbering in both figures is the same.
Step (1)
Verifier A acquires Evidence including a TPM Quote from the attester
via [RATS-YANG] and/or [stream-subscription].
Step (2)
As the Evidence changes, Verifier A evaluates the totality of the
Evidence received. Verifier A then sets the Trustworthiness Vector
of the Attester. Subsequently it sends back a signed Attestation
Result which includes the Trustworthiness Vector and the signature
sent as part of (1) from the Attester. It is this signature which
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allows the Trustworthiness Vector to be later provably associated
with a recent TPM Quote.
The delivery of Attestation Results back to the Attester can be done
via a YANG operational datastore write of the following objects:
+--rw attestation-results! {passport}?
+--rw trustworthiness-vector* identityref
+--rw timestamp yang:date-and-time
+--rw tpmt-signature? binary
+--rw verifier-signature? binary
+--rw verifier-signature-key-name? binary
Figure 4: Attestation Results Tree
Step (3)
At time(y) a Relying Party makes a Link Layer connection request to
an Attester via a protocol such as [MACSEC] or [IEEE-802.1X]. This
connection request must include [RFC3748] credentials. Specifics of
the EAP credentials are TBD. If there is no central distribution of
time via [I-D.birkholz-rats-tuda] a nonce must be included to ensure
freshness of a response.
This step can repeat periodically independently of any subsequent
iteration (1) and (2). This allows for periodic reauthentication of
the link layer in a way not bound to the updating of Verifier A's
Attestation Results.
Step (4)
Upon receipt of (3), a Stamped Passport is generated as per
Section 3.3, and sent to the Relying Party.
Step (5)
Upon receipt of (4), the Relying Party verifies the Stamped Passport
as per Section 3.3. Most often, the relevant PCR values at time(x)
will be the same as the PCR values at time(y). In this case, the
Relying Party can simply accept the Trustworthiness Vector assigned
by the Verifier A. When the PCR values are different, and not much
time has passed between time(x) and time(y), the Relying Party can
either accept the previous Trustworthiness Vector, or attempt another
EAP request in a few seconds as new Attestation Results are delivered
by Step (2). When there is a large time gap between time(x) and
time(y) and the PCR values are different, the Attester should be
given a blank Trustworthiness Vector.
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Based on the link's Trustworthiness Vector, the Relying Party may
adjust the link affinity of the corresponding
[I-D.ietf-lsr-flex-algo] topology.
3.5. YANG Module
This YANG module imports modules from [RATS-YANG] and [RFC8639].
<CODE BEGINS> ietf-rats-attestation-results-vector@2020-06-03.yang
module ietf-rats-attestation-results-vector {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-rats-attestation-results-vector";
prefix arv;
import ietf-yang-types {
prefix yang;
}
organization "IETF";
contact
"WG Web: <http://tools.ietf.org/wg/rats/>
WG List: <mailto:rats@ietf.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>";
description
"This module contains conceptual YANG specifications for
subscribing to attestation streams being generated from TPM chips.
Copyright (c) 2020 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see the RFC
itself for full legal notices.";
revision 2020-06-03 {
description
"Initial version.";
reference
"draft-voit-rats-trusted-path-routing";
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}
/*
* IDENTITIES
*/
identity trustworthiness-level {
description
"Base identity for a verifier assessed trustworthiness level.";
}
identity trustworthiness-pass {
description
"Identity for a verifier assessed trustworthiness pass.";
}
identity trustworthiness-fail {
description
"Base identity for a verifier assessed trustworthiness fail.";
}
identity boot-verified {
base trustworthiness-pass;
description
"A Verifier has assessed an Attester as Boot Integrity Verified.";
}
identity boot-verification-fail {
base trustworthiness-fail;
description
"A Verifier has assessed an Attester has failed its Boot Integrity
verification.";
}
identity hw-authentic {
base trustworthiness-pass;
description
"A Verifier has assessed an Attester as having authentic hardware.";
}
identity fw-authentic {
base trustworthiness-pass;
description
"A Verifier has assessed an Attester as having authentic firmware.";
}
identity hw-verification-fail {
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base trustworthiness-fail;
description
"A Verifier has assessed an Attester has failed its hardware or
firmware verification.";
}
identity identity-verified {
base trustworthiness-pass;
description
"A Verifier has assessed and verified an Attester's unique identity.";
}
identity identity-fail {
base trustworthiness-fail;
description
"A Verifier has been unable to assess or verify an Attester's unique
identity";
}
identity files-verified {
base trustworthiness-pass;
description
"A Verifier has assessed an Attester's file system, and asserts that
it recognizes relevant files.";
}
identity file-blacklisted {
base trustworthiness-fail;
description
"A Verifier has found a file on an Attester which should not be
present.";
}
/*
* DATA NODES
*/
container attestation-results {
presence
"An attestation Verifier has appraised the security posture of the
device, and returned the results within this container.";
description
"Containes the latest Verifier appraisal of an Attester.";
leaf-list trustworthiness-vector {
type identityref {
base trustworthiness-level;
}
ordered-by system;
description
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"One or more Trustworthiness Levels assigned which expose the
Verifiers evaluation of the Evidence associated with the
'tpmt-signature'.";
}
leaf timestamp {
type yang:date-and-time;
mandatory true;
description
"The timestamp of the Verifier's appraisal.";
}
leaf tpmt-signature {
type binary;
description
"Must match a recent tpmt-signature sent in a notification to
a Verifier. This allows correlation of the Attestation Results to
a recent PCR change.";
}
leaf verifier-signature {
type binary;
mandatory true;
description
"Signature of the Verifier across all the current objects in the
attestation-results container.";
}
leaf verifier-signature-key-name {
type binary;
description
"Name of the key the Verifier used to sign the results.";
}
}
}
<CODE ENDS>
4. Security Considerations
Successful attacks on an IGP domain Verifier has the potential of
affecting traffic on the Trusted Topology.
For Distributed Trusted Path Routing, links which are part of the
FlexAlgo are visible across the entire IGP domain. Therefore a
compromised device will know when it is being bypassed.
Access control for the objects in Figure 4 should be tightly
controlled so that it becomes difficult for the Stamped Passport to
become a denial of service vector.
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5. References
5.1. Normative References
[RATS-Arch]
"Remote Attestation Procedures Architecture", July 2020,
<https://tools.ietf.org/html/draft-ietf-rats-architecture-
02>.
[RATS-YANG]
"A YANG Data Model for Challenge-Response-based Remote
Attestation Procedures using TPMs", January 2020,
<https://datatracker.ietf.org/doc/draft-ietf-rats-yang-
tpm-charra/>.
[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>.
[RFC8639] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Subscription to YANG Notifications",
RFC 8639, DOI 10.17487/RFC8639, September 2019,
<https://www.rfc-editor.org/info/rfc8639>.
[TPM1.2] TCG, ., "TPM 1.2 Main Specification", October 2003,
<https://trustedcomputinggroup.org/resource/tpm-main-
specification/>.
[TPM2.0] TCG, ., "TPM 2.0 Library Specification", March 2013,
<https://trustedcomputinggroup.org/resource/tpm-library-
specification/>.
5.2. Informative References
[I-D.birkholz-rats-tuda]
Fuchs, A., Birkholz, H., McDonald, I., and C. Bormann,
"Time-Based Uni-Directional Attestation", draft-birkholz-
rats-tuda-02 (work in progress), March 2020.
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[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Rosen, E., Jain, D., and S. Lin, "Advertising Segment
Routing Policies in BGP", draft-ietf-idr-segment-routing-
te-policy-09 (work in progress), May 2020.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-07 (work in progress), April 2020.
[IEEE-802.1X]
Parsons, G., "802.1AE: MAC Security (MACsec)", January
2020,
<https://standards.ieee.org/standard/802_1X-2010.html>.
[MACSEC] Seaman, M., "802.1AE: MAC Security (MACsec)", January
2006, <https://1.ieee802.org/security/802-1ae/>.
[RATS-Device]
Fedorkow, G., Voit, E., and J. Fitzgerald-McKay, "Network
Device Remote Integrity Verification", n.d.,
<https://tools.ietf.org/html/draft-ietf-rats-tpm-based-
network-device-attest-00>.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<https://www.rfc-editor.org/info/rfc3748>.
[stream-subscription]
"Attestation Event Stream Subscription", June 2020,
<https://tools.ietf.org/html/draft-birkholz-rats-network-
device-subscription-00>.
Appendix A. Centralized Trusted Path Routing
Trusted Path Routing does not require integration with Routing
protocols as is done with Distributed Trusted Path Routing. It is
also possible for a Controller to choose a path through a network.
This architural alternative is called Centralized Trusted Path
Routing.
With Centralized Trusted Path Routing, trusted end-to-end paths are
pre-assigned through a network provider domain. Along these paths,
Evidence of potentially transited components has been assessed. Each
path is guaranteed to only include devices which achieve at least a
minimum set of a formally defined Trustworthiness Levels.
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In this alternative, a controller-based Verifier ensures
communications with Sensitive Subnets traverses a Trusted Topology
within the controller's routing domain. To do this, the Verifier
continuously acquires Evidence about each potentially transited
device. This access is done via the context established within
[RATS-Device]. The controller then appraises the Evidence and
decides on a Trustworthiness Vector for each device. The controller
then identifies end-to-end path(s) which avoid any devices which are
unable to meet the minimum Trustworthiness Levels. Finally, the
controller provisions network policy so that flows to and from
Sensitive Subnet to use just these end-to-end paths.
Evidence passed to the Verifier which are used to establish a
device's Trustworthiness Vector will include but is not limited to:
o An Attester's security measurements being extended into [TPM1.2]
or [TPM2.0] compliant Platform Configuration Registers (PCR).
o An Attester's current PCR measurements.
The prerequisites for this solution are:
1. Customer designated Sensitive Subnet ranges and their acceptable
Trustworthiness Vectors have been identified and associated with
external interfaces to/from the edge of a routing domain.
2. A Verifier which can continuously acquire Evidence and appraise
the Trustworthiness Levels of all network devices within the
routing domain.
3. A Verifier which continuously optimizes a set of network paths/
tunnels. These paths must traverse only Attested Devices or
Transparently-Transited Devices while on their way to an egress
interface for a routing Domain.
4. A Verifier which can provision and maintain the set of Sensitive
Subnets associated with specific network paths/tunnels.
Figure 5 provides a network diagram of where these four sit within a
network topology.
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.------------------------------------------------.
| Verifier + Relying Party (3) |
'------------------------------------------------'
(4) ^ ^ ^ ^ ^ (4)
| | (2) | | | |
| | .-------. | | (2) V
V (2) |Hacked | (2) (2) .--------.
.--------. |Router | .-------. .-------. | Edge |
| Edge | |(Attest| |Router | |Switch | | Router |
| Router | | =Fail)| |(Attest| |(Attest| | (Attest|
| | '-------' | =OK) | | =OK) | | =OK) |
(1) path==================================> (1)--- Sensitive
| <==================================path | Subnet
'--------' '-------' '-------' '--------'
Figure 5: Centralized Trusted Path Routing
The feature functionality describing how to achieve (1) - (4) are
outside the scope of this specification. The reasoning is that each
of these can be accomplished via technologies specified elsewhere.
For example, in step (4), it is possible for a Verifier to provision
each ingress device with the set of Sensitive Subnets for which
traffic would be placed into a specific
[I-D.ietf-idr-segment-routing-te-policy] tunnel. As another example,
consider prerequisite (2): network devices can stream changes in
Evidence to a Verifier by establishing an [RFC8639] subscription to
the <attestation> Event Stream as described in [stream-subscription].
Appendix B. Acknowledgements
Shwetha Bhandari, Henk Birkholz, Chennakesava Reddy Gaddam, Sujal
Sheth, Peter Psenak, Nancy Cam Winget, Ned Smith, Guy Fedorkow, Liang
Xia.
Appendix C. Change Log
[THIS SECTION TO BE REMOVED BY THE RFC EDITOR.]
v01-v02
o Extracted the attestation stream, and placed into draft-birkholz-
rats-network-device-subscription
o Introduced the Trustworthiness Vector
v00-v01
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o Move all FlexAlgo terminology to Section 3.4. This allows
Section 3.3 to be more generic.
o Edited Figure 1 so that (4) points to the egress router.
o Added text freshness mechanisms, and articulated configured
subscription support.
o Minor YANG model clarifications.
o Added a few open questions which Frank thinks interesting to work.
Appendix D. Open Questions
Do we need functional requirements on how to handle traffic to/from
Sensitive Subnets when no Trusted Topology exists between IGP edges?
The network typically can make this unnecessary. For example it is
possible to construct a local IPSec tunnel to make untrusted devices
appear as Transparently-Transited Devices. This way Secure Subnets
could be tunneled between FlexAlgo nodes where an end-to-end path
doesn't currently exist. However there still is a corner case where
all IGP egress points are not considered sufficiently trustworthy.
Author's Address
Eric Voit
Cisco Systems, Inc.
Email: evoit@cisco.com
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