Trusted Path Routing
draft-voit-rats-trustworthy-path-routing-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
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|
|---|---|---|---|
| Author | Eric Voit | ||
| Last updated | 2020-10-02 | ||
| Replaces | draft-voit-rats-trusted-path-routing | ||
| RFC stream | (None) | ||
| Formats | |||
| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-voit-rats-trustworthy-path-routing-01
RATS Working Group E. Voit
Internet-Draft Cisco
Intended status: Standards Track October 02, 2020
Expires: April 5, 2021
Trusted Path Routing
draft-voit-rats-trustworthy-path-routing-01
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 April 5, 2021.
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. Protocol Independent Definitions . . . . . . . . . . . . . . 4
3.1. Trusted Path Routing Service . . . . . . . . . . . . . . 4
3.2. Network Topology Assembly . . . . . . . . . . . . . . . . 5
3.3. Link Appraisal . . . . . . . . . . . . . . . . . . . . . 5
3.4. Trustworthiness Vector . . . . . . . . . . . . . . . . . 6
3.5. Attestation Results . . . . . . . . . . . . . . . . . . . 8
3.6. Stamped Passport . . . . . . . . . . . . . . . . . . . . 9
3.7. Appraising the Stamped Passport . . . . . . . . . . . . . 11
4. Implementable Solution . . . . . . . . . . . . . . . . . . . 13
4.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Protocol Bindings . . . . . . . . . . . . . . . . . . . . 14
5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.1. Normative References . . . . . . . . . . . . . . . . . . 23
7.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 25
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 25
Appendix C. Open Questions . . . . . . . . . . . . . . . . . . . 26
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26
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 provides a method of establishing Trusted
Topologies which only include trust-verified network devices.
Membership in a Trusted Topology is established and maintained via an
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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 this Trusted
Topology. Routing protocols like [I-D.ietf-lsr-flex-algo] can then
used to propagate topology state throughout a network. IP Packets to
and from end-user designated Sensitive Subnets are then forwarded
into this Trusted Topology at each network boundary.
The specification works under the following assumptions:
o A set of network devices supporting the TPM remote attestation
profile as laid out in [RATS-Device] are connected within a
network domain.
o A routing protocol capable of maintaining multiple forwarding
topologies connects these network devices.
o One or more Verifiers continuously appraise each of network
devices, and these Verifiers can return the Attestation Results
back to the attesting network device.
2. Terminology
2.1. Terms
The following terms are imported from [RATS-Arch]: Attester,
Evidence, Passport, Relying Party, and Verifier.
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 desire confidentially guarantees beyond those of non-
identified subnets. In practice, flows to or from a Sensitive
Subnet must only have their IP headers and encapsulated payloads
accessible/visible only by Attested Devices supporting one or more
Trustworthiness Vectors.
Transparently-Transited Device - a network device within an network
domain where any packets originally passed into that network
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domain are completely opaque on that network device 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. Protocol Independent Definitions
3.1. Trusted Path Routing Service
An end user identifies sensitive IP subnets where flows with
applications using these IP subnets need enhanced privacy guarantees.
Trusted Path Routing passes flows to/from these Sensitive Subnets
over a Trusted Topology able to meet these guarantees. The Trusted
Topology itself consists of the interconnection of network devices
where each potentially transited device has passed a recent
trustworthiness appraisal.
Different guarantees of end-to-end trustworthiness appraisal may be
offered to network users. These guarantees are network operator
specific, but might include options such as:
o all transited devices are currently boot integrity verified
o all transited devices are from a specific set of vendors and are
running known software containing the latest patches
o no guarantees provided
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3.2. Network Topology Assembly
To be included in a Trusted Topology, Evidence of trustworthiness is
shared between network device peers (such as routers). Upon
receiving and appraising this Evidence as part of link layer
authentication, the network device peer decides if this link should
be added as an active adjacency for the Trusted Topology.
When enough links have been successfully added, a Trusted Topology
will come into existence as routing protocols flood the adjacency
information across the network domain.
.-------------. .---------.
| Compromised | | Edge |
.---------. | Router | | Router |
| Router | | | | |
| | | trust>-------------<no_trust |
| no_trust>--<trust | .--------. | |----Sensitive
| | '-------------' | trust>==<trust | Subnet
| trust>==================<trust | | |
'---------' | | '---------'
| Router |
'--------'
Figure 1: Trusted Path Topology Assembly
Traffic exchanged with Sensitive Subnets can then be forwarded into
that Trusted Topology from all edges of the network domain.
3.3. Link Appraisal
Critical to the establishment and maintenance of a Trusted Topology
is the Stamped Passport. A Stamped Passport is comprised of Evidence
from both an Attester and a Verifier. Stamped Passports are
exchanged between adjacent network devices over a link layer
protocols like 802.1x or MACSEC. As both sides of a link may need
might need to appraise the other, independent Stamped Passports will
often be transmitted from either side of the link. Additionally, as
link layer protocols will continuously re-authenticate the link, this
allows for fresh Stamped Passports to be constantly appraised by
either side of the connection.
Each Stamped Passport will include the most recent Verifier provided
Attestation Results, as well as the most recent TPM Quote for that
Attester. Upon receiving this information as part of link layer
authentication, the Relying Party Router appraises the results and
decides if this link should be added to a Trusted Topology.
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Figure 2 describes this flow of information using the time
definitions described in [RATS-Arch], and the information flows
defined in Section 7 of [RATS-Interactions].
.----------. .----------. .---------------.
| Attester | | Verifier | | Relying Party |
| | | A | | / Verifier B |
| (Router) | | | | (Router) |
'----------' '----------' '---------------'
time(VG) | |
|<------nonce--------------time(NS) |
| | |
time(EG)(1)------Evidence------------>| |
| time(RG) |
|<------Attestation Result--(2) |
~ ~ ~
time(VG')? | |
~ ~ ~
|<------nonce---------------------------------(3)time(NS')
| | |
time(EG')(4)------Stamped Pat--------------------------->|
| | (5)time(RG',RA')
(6)
~
time(RX')
Figure 2: Trusted Path Timing
Specifics for each one of these information flows, including details
on what happens at the items numbered (1) through (5) are described
in Section 3.6.
3.4. Trustworthiness Vector
For Trusted Path Routing to operate, fresh Attestation Results need
to be communicated by a Verifier back to the Attester. These
Attestation Results must be encoded in a way which is known and
actionable.
To support this requirement, specific levels of appraised
trustworthiness have been defined. These are known as
Trustworthiness Levels. It is these Trustworthiness Levels which are
asserted as part of the Attestation Results by a Verifier. It is out
of the scope of this document for the Verifier to provide proof or
logic on how the assertion was derived.
Following are the set of available Trustworthiness Levels:
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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-repudiated | A Verifier has found a file on an |
| | Attester which should not be present |
+------------------------+------------------------------------------+
A quick look at the list above shows that multiple Trustworthiness
Level will often be applicable at single point in time. To support
this, the Attestation Results will include a single Trustworthiness
Vector consisting of a set of Trustworthiness Levels. The
establishment of this Trustworthiness Vector follows the following
logic on the Verifier:
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Start: TPM Quote Received, log received, 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, go to 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-repudiated) - push onto vector
(if not evaluated, or insufficient data to conclude: take no action)
Step 6: Assemble Attestation Results, and push to Attester
End
3.5. Attestation Results
As Evidence changes, a new Trustworthiness Vector needs to be
returned to the Attester as Attestation Results. But this
Trustworthiness Vector is not all that needs to be returned.
Following is a YANG tree for all the returned objects. Each of these
objects will later be used as Evidence by another Verifier which is
co-resident with the Relying Party.
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module: ietf-attestation-results-vector
+--rw attestation-results!
+--rw trustworthiness-vector* identityref
+--rw (tpm-specification-version)?
| +--:(TPM2.0) {taa:TPM20}?
| | +--rw TPM2B_DIGEST binary
| | +--rw tpm20-pcr-bank* [TPM-hash-algo]
| | | +--rw TPM-hash-algo identityref
| | | +--rw pcr-index* tpm:pcr
| | +--rw clock uint64
| | +--rw reset-counter uint32
| | +--rw restart-counter uint32
| | +--rw safe boolean
| +--:(TPM1.2) {taa:TPM12}?
| +--rw pcr-index* pcr
| +--rw tpm12-pcr-value* binary
| +--rw timestamp yang:date-and-time
+--rw public-key-format identityref
+--rw public-key binary
+--rw public-key-algorithm-type identityref
+--rw verifier-signature-key-name? string
+--rw verifier-key-algorithm-type identityref
+--rw verifier-signature binary
Figure 3: Attestation Results Tree
Looking at the objects above, if the Attester has a TPM2, then the
values of the TPM PCRs are included (i.e., <TPM2B_DIGEST>,
<TPM2_Algo>, and <pcr-index>), as are the timing counters from the
TPM (i.e., <clock>, <reset-counter>, <restart-counter>, and <safe>).
Likewise if the Attester has a TPM1.2, the TPM PCR values of the
<pcr-index> and <pcr-value> are included. Timing information comes
from the Verifier itself via the <timestamp> object.
For both the TPM1.2 and the TPM2, there are other Attestation Results
which are sent. These are the Attester's TPM key (i.e., <public-
key>, <public-key-format>, and <public-key-algorithm-type>). This
key later will allow the Relying Party router to appraise a
subsequent TPM Quote. It is this signature which allows the
Trustworthiness Vector to be later provably associated with a recent
TPM Quote.
3.6. Stamped Passport
The Attestation Results are not the only item which a Relying Party
needs to consider during its appraisal. A provably recent TPM Quote
from the Attester must also be included. With these two items, the
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resulting Stamped Passports formats described below must be converted
to CDDL and passed over EAP. If an Attester includes a TPM2, the
objects are:
YANG structure for a TPM2 Stamped Passport
+--ro latest-tpm-quote
| +--ro quote binary
| +--ro quote-signature binary
+--ro latest-attestation-results
+--ro trustworthiness-vector* identityref
+--ro TPM2B_DIGEST binary
+--ro tpm20-pcr-bank* [TPM-hash-algo]
| +--ro TPM-hash-algo identityref
| +--ro pcr-index* tpm:pcr
+--ro clock uint64
+--ro reset-counter uint32
+--ro restart-counter uint32
+--ro safe boolean
+--ro public-key-format identityref
+--ro public-key binary
+--ro public-key-algorithm-type identityref
+--ro verifier-signature-key-name? string
+--ro verifier-signature binary
And if the Attester is a TPM1.2, the object are:
YANG structure for a TPM1.2 Stamped Passport
+--ro latest-tpm-quote
| +--ro version* []
| | +--ro major? uint8
| | +--ro minor? uint8
| | +--ro revMajor? uint8
| | +--ro revMinor? uint8
| +--ro digest-value? binary
+--ro latest-tpm12-attestation-results
+--ro trustworthiness-vector* identityref
+--ro pcr-index* pcr
+--ro tpm12-pcr-value* binary
+--ro timestamp yang:date-and-time
+--ro public-key-format identityref
+--ro public-key binary
+--ro public-key-algorithm-type identityref
+--ro verifier-signature-key-name? string
+--ro verifier-signature binary
With either of these passport formats, if the <latest-tpm-quote> is
verifiably fresh, then the state of the Attester can be appraised by
a network peer.
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3.7. Appraising the Stamped Passport
When it receives a Stamped Passport, a Verifier co-resident with the
Relying Party on a network peer can make nuanced decisions about how
to handle traffic coming from that link. For example, when the
Attester's TPM 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 Stamped Passport, the Relying Party can include that
link in a Trusted Topology.
As the process described above repeats across the set of links within
a network domain, Trusted Topologies can be extended and maintained.
Traffic to and from Sensitive Subnets is then identified at the edges
of the network domain and passed into this Trusted Topology.
.--------------.
| Verifier A |
'---------(2)--'
^ |
| Attestation Results
Evidence |
| V
.-(1)---------. .---------------.
| Attester | | Relying Party |
| (Router) |<--------------------nonce(3) / Verifier B |
| .-----. | | (Router) |
| | TPM | (4)-Stamped Passport-------->| |
| '-----' | | (5) & (6) |
'-------------' '---------------'
Figure 4: Stamped Passport Generation and Appraisal
In Figure 4 above, Evidence from a TPM 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 are listed below. These numbers
match to the numbered steps of Figure 4:
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1. An Attester sends a signed TPM Quote which includes PCR
measurements to Verifier A at time(EG).
2. Verifier A appraises (1), then sends the following items back to
that Attester as Attestation Results:
1. the Trustworthiness Vector of an Attester,
2. the PCR state information from the TPM Quote of (1),
3. time information associated with the TPM Quote of (1),
4. the Public Attestation Key which it used to validate the TPM
Quote of (1), and
5. a Verifier signature across (2.1) though (2.4).
3. At time(EG') a nonce known to the Relying Party is sent to the
Attester .
4. The Attester generates and sends a Stamped Passport. This
Stamped Passport includes:
1. The Attestation Results from (2)
2. New signed, verifiably fresh PCR measurements from time(EG'),
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 (4.2) includes the nonce from (3).
2. Use a local certificate to validate the signature (4.1).
3. Use the Attestation Results provided public key info of (2.4)
to validate the signatures of (4.2).
4. Failure of (5.1) through (5.3) means the link does not meet
minimum validation criteria, therefore appraise the link as
having a null Trustworthiness Vector. Jump to step (6).
5. If all PCR values from (2.2) equal those (4.2), then Relying
Party can accept (2.1) as the link's Trustworthiness Vector.
Jump to step (6).
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6. If the PCR state information of (2.2) doesn't equal (4.2),
and not much time has passed between time(EG) and time(EG'),
the Relying Party accepts any previous Trustworthiness
Vector. (Note: rather than accepting, it is also viable to
attempt to acquire a new Stamped Passport. Where
[stream-subscription] is used, it should only be a few
seconds before a new Attestation Results are delivered to an
Attester via (2).)
7. When the PCR state information is different, and there is a
large or uncertain time gap between time(EG) and time(EG'),
the link should be assigned a null Trustworthiness Vector.
6. Take action based on Verifier B's appraised Trustworthiness
Vector:
1. Include the link within any Trusted Topology for which that
Trustworthiness Vector is qualified.
2. Remove the link from any Trusted Topology for which that
Trustworthiness Vector is not qualified.
4. Implementable Solution
This section defines one set of protocols which can be used for
Trusted Path Routing. The protocols include [MACSEC] or
[IEEE-802.1X], ISIS [I-D.ietf-lsr-flex-algo], YANG subscriptions
[RFC8639], and [RFC3748] methods. Other alternatives are also
viable.
4.1. Prerequisites
o A Trusted Topology such as one established by ISIS 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 a defined set of Trustworthiness Vectors.
o Customer designated Sensitive Subnets and their requested
Trustworthiness Vectors have been identified and associated with
external interfaces to/from the edge of a network. Traffic to a
Sensitive Subnet can be passed into the Trusted Topology.
o Verifiers A and B are able to verify [TPM1.2] or [TPM2.0]
signatures of an Attester.
o Verifier B trusts information signed by Verifier A. Verifier B
has also been pre-provisioned with certificates or public keys
necessary to confirm that Stamped Passports came from Verifier A
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o Within a network, a Relying Party is able to use affinity to
include/exclude links as part of the Trusted Topology based on
this appraisal.
4.2. Protocol Bindings
The numbering in below matches to the steps in Figure 4.
Step (1)
There are two alternatives for Verifier A to acquires Evidence
including a TPM Quote from the Attester:
o Subscription to the <attestation> stream defined in
[stream-subscription]. Note: this method is recommended as it
will minimize the interval between when a PCR change is made in a
TPM, and when the PCR change appraisal is incorporated within a
subsequent Stamped Passport.
o The RPCs <tpm20-challenge-response-attestation> or <tpm12-
challenge-response-attestation> defined in device [RATS-YANG]
Step (2)
The delivery of these Attestation Results back to the Attester MAY be
done via an operational datastore write to the YANG module <ietf-
attestation-results-vector>.
Step (3)
At time(NS') a Relying Party makes a Link Layer authentication
request to an Attester via a either [MACSEC] or [IEEE-802.1X]. This
connection request must include [RFC3748] credentials. Specifics of
the EAP mapping to the Stamped Passport is tbd.
Step (4)
Upon receipt of (3), a Stamped Passport is generated as per
Section 3.6, and sent to the Relying Party. Note that with [MACSEC]
or [IEEE-802.1X], steps (3) & (4) will 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 (5)
Upon receipt of (4), the Relying Party appraises the Stamped Passport
as per Section 3.6. Following are relevant mappings which replace
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generic steps from Section 3.6 with specific objects available with a
TPM1.2 or TPM2.0.
+-------------------------------------------------------------------+
| TPM2.0 - Bindings/details |
+-------------------------------------------------------------------+
| (5.5): If the <TPM2B_DIGEST>, <TPML_PCR_SELECTION>, <reset- |
| counter>, <restart-counter> and <safe> are equal between the |
| Attestation Results and the TPM Quote at time(EG') then Relying |
| Party can accept (2.1) as the link's Trustworthiness Vector. Jump |
| to step (6). |
| |
| (5.6): If the <reset-counter>, <restart-counter> and <safe> are |
| equal between the Attestation Results and the TPM Quote at |
| time(EG'), and the <clock> object from time(EG') has not |
| incremented by an unacceptable number of seconds since the |
| Attestation Result, then Relying Party can accept (2.1) as the |
| link's Trustworthiness Vector. Jump to step (6). |
| |
| (5.7): Assign the link a null Trustworthiness Vector. |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| TPM1.2 - Bindings/details |
+-------------------------------------------------------------------+
| (5.5): If the <pcr-index>'s and <tpm12-pcr-value>'s are equal |
| between the Attestation Results and the TPM Quote at time(EG'), |
| then Relying Party can accept (2.1) as the link's Trustworthiness |
| Vector. Jump to step (6). |
| |
| (5.6): If the time hasn't incremented an unacceptable number of |
| seconds from the Attestation Results <timestamp> and the system |
| clock of the Relying Party, then Relying Party can accept (2.1) |
| as the link's Trustworthiness Vector. Jump to step (6). |
| |
| (5.7): Assign the link a null Trustworthiness Vector. |
+-------------------------------------------------------------------+
Step (6)
After the Trustworthiness Vector has been validated or reset, based
on the link's Trustworthiness Vector, the Relying Party may adjust
the link affinity of the corresponding ISIS [I-D.ietf-lsr-flex-algo]
topology. ISIS will then replicate the link state across the IGP
domain. Traffic will then avoid links which do not have a qualifying
Trustworthiness Vector.
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5. YANG Module
This YANG module imports modules from [RATS-YANG], [crypto-types] and
[RFC6021].
<CODE BEGINS> ietf-attestation-results-vector@2020-09-17.yang
module ietf-attestation-results-vector {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-attestation-results-vector";
prefix arv;
import ietf-yang-types {
prefix yang;
}
import ietf-tpm-remote-attestation {
prefix tpm;
reference
"draft-ietf-rats-yang-tpm-charra";
}
import ietf-crypto-types {
prefix ct;
reference
"RFC XXXX: Common YANG Data Types for Cryptography
(currently draft-ietf-netconf-crypto-types)";
}
import ietf-tcg-algs {
prefix taa;
}
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
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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 2020-09-17 {
description
"Initial version.";
reference
"draft-voit-rats-trustworthy-path-routing";
}
/*
* IDENTITIES
*/
identity trustworthiness-level {
description
"Base identity for a Verifier that uses its Appraisal Policy for
Evidence to establish a trustworthiness level.";
}
identity trustworthiness-pass {
description
"A trustworthiness-level which successfully meets an Appraisal
Policy for Evidence.";
}
identity trustworthiness-fail {
description
"A trustworthiness-level which hit Appraisal Policy for Evidence
necessary to fail an evaluation. Note: this failure might or
might not consider whether sufficient Evidence has been provided.
In other words having insufficient evidence might not drive the
setting of this failing trustworthiness-level.";
}
identity boot-verified {
base trustworthiness-pass;
description
"A Verifier has appraised an Attester as Boot Integrity
Verified.";
}
identity boot-verification-fail {
base trustworthiness-fail;
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description
"A Verifier has appraised an Attester has failed its Boot
Integrity verification.";
}
identity hw-authentic {
base trustworthiness-pass;
description
"A Verifier has appraised an Attester as having authentic
hardware.";
}
identity fw-authentic {
base trustworthiness-pass;
description
"A Verifier has appraised an Attester as having authentic
firmware.";
}
identity hw-verification-fail {
base trustworthiness-fail;
description
"A Verifier has appraised an Attester has failed its hardware or
firmware verification.";
}
identity identity-verified {
base trustworthiness-pass;
description
"A Verifier has appraised 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 appraised an Attester's file system, and asserts
that it recognizes relevant files.";
}
identity file-repudiated {
base trustworthiness-fail;
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description
"A Verifier has found a file on an Attester which should not be
present.";
}
grouping TPM20-unsigned-internals {
description
"The unsigned extract of a TPM2 Quote.";
leaf TPM2B_DIGEST {
mandatory true;
type binary;
description
"A hash of the latest PCR values (and the hash algorithm used)
which have been returned from a Verifier for the selected PCRs
identified within TPML_PCR_SELECTION.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.12.1";
}
list tpm20-pcr-bank {
min-elements 1;
key "TPM-hash-algo";
description
"Specifies the list of PCRs and Hash Algorithms used for the
latest returned TPM2B_DIGEST. Identifying
this object simplifies Stamped Passport troubleshooting if the
same PCRs and Hash algorithms are not used when attempting to
correlate independent TPM2B_DIGESTs.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.9.7";
leaf TPM-hash-algo {
type identityref {
base taa:hash;
}
description
"The hash scheme actively being used to hash a PCRs.";
}
leaf-list pcr-index {
type tpm:pcr;
min-elements 1;
description
"Defines what TPM2 Banks are available. A bank is a set
of PCRs which are extended using a particular hash
algorithm.";
}
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}
leaf clock {
mandatory true;
type uint64;
description
"Clock is a monotonically increasing counter that advances
whenever power is applied to a TPM2. The value of Clock is
incremented each millisecond.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.11.2";
}
leaf reset-counter {
mandatory true;
type uint32;
description
"This counter increments on each TPM Reset. The most common
TPM Reset would be due to a hardware power cycle.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.11.3";
}
leaf restart-counter {
mandatory true;
type uint32;
description
"This counter shall increment by one for each TPM Restart or
TPM Resume. The restartCount shall be reset to zero on a TPM
Reset.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.11.4";
}
leaf safe {
mandatory true;
type boolean;
description
"This parameter is set to YES when the value reported in Clock
is guaranteed to be unique for the current Owner. It is set to
NO when the value of Clock may have been reported in a previous
attestation or access.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.11.5";
}
}
grouping TPM12-unsigned-internals-extended {
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description
"The unsigned extract of a TPM12 Quote, with extra content from
the Verifier specific to a TPM12.";
uses tpm:tpm12-pcr-selection;
leaf-list tpm12-pcr-value {
type binary;
description
"The list of TPM_PCRVALUEs from each PCR selected in sequence
of tpm12-pcr-selection.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf
Section 10.9.7";
}
leaf timestamp {
type yang:date-and-time;
mandatory true;
description
"The timestamp of the Verifier's appraisal. This can be used by
a Relying Party to determine the freshness of the attestation
results.";
}
}
/*
* DATA NODES
*/
container attestation-results {
presence
"Indicates that Verifier has appraised the security posture of the
Attester, and returned the results within this container. If the
Attester believes this information is no longer fresh, this
container should automatically be deleted.";
description
"Retains the most recent Attestation Results for this Attester.
It must only be written by a Verfier which is to be trusted by a
Relying Party.";
leaf-list trustworthiness-vector {
type identityref {
base trustworthiness-level;
}
ordered-by system;
description
"One or more Trustworthiness Levels assigned which expose the
Verifier's evaluation of the Evidence associated with the
'tpmt-signature'.";
}
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choice tpm-specification-version {
description
"Identifies the cryptoprocessor API set which drove the
Attestation Results.";
case TPM2.0 {
if-feature "taa:TPM20";
description
"The Attestation Results are from a TPM2.";
uses TPM20-unsigned-internals;
}
case TPM1.2 {
if-feature "taa:TPM12";
description
"The most recent Attestation Results from a TPM1.2.";
uses TPM12-unsigned-internals-extended;
}
}
uses ct:public-key-grouping {
description
"In order to avoid having to provision AIK certificates on a
Relying Party network device, it is possible to send the AIK
public key as from the Verifier as part of the passport. This
is safe because the key is signed by the Verifier (hence
vouching for its validity.) The two objects within this group
allow the Verifier to include this information as part of the
Attestation Results.";
}
leaf public-key-algorithm-type {
mandatory true;
type identityref {
base taa:asymmetric;
}
description
"Indicates what kind of algorithm is used with the Attester's
Public Key Value.";
}
leaf verifier-signature-key-name {
type string;
description
"Name of the key the Verifier used to sign the results.";
}
leaf verifier-key-algorithm-type {
mandatory true;
type identityref {
base taa:asymmetric;
}
description
"Indicates what kind of algorithm was used for the
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'verifier-signature'.";
}
leaf verifier-signature {
type binary;
mandatory true;
description
"Signature of the Verifier across all the other objects within
the attestation-results container. The signature will assume
the sequence of objects as defined in the YANG model schema.";
}
}
}
<CODE ENDS>
6. Security Considerations
Verifiers are limited to the Evidence available for appraisal from a
Router. Although the state of the art is improving, some exploits
may not be visible via Evidence.
Only security measurements which are placed into PCRs are capable of
being exposed via TPM Quote at time(EG').
Successful attacks on an Verifier have the potential of affecting
traffic on the Trusted Topology.
For 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 3 should be tightly
controlled so that it becomes difficult for the Stamped Passport to
become a denial of service vector.
7. References
7.1. Normative References
[crypto-types]
"Common YANG Data Types for Cryptography", May 2020,
<https://datatracker.ietf.org/doc/draft-ietf-netconf-
crypto-types/>.
[RATS-Arch]
"Remote Attestation Procedures Architecture", March 2020,
<https://tools.ietf.org/html/draft-ietf-rats-architecture-
02>.
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[RATS-YANG]
"A YANG Data Model for Challenge-Response-based Remote
Attestation Procedures using TPMs", June 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>.
[RFC6021] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6021, DOI 10.17487/RFC6021, October 2010,
<https://www.rfc-editor.org/info/rfc6021>.
[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/>.
7.2. Informative References
[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-11 (work in progress), September 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/>.
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[RATS-Device]
"Network Device Remote Integrity Verification", n.d.,
<https://datatracker.ietf.org/doc/draft-ietf-rats-tpm-
based-network-device-attest>.
[RATS-Interactions]
"Reference Interaction Models for Remote Attestation
Procedures", June 2020, <https://ietf-rats.github.io/
draft-birkholz-rats-reference-interaction-model/draft-
birkholz-rats-reference-interaction-model.html#section-7>.
[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://datatracker.ietf.org/doc/draft-birkholz-rats-
network-device-subscription>.
Appendix A. Acknowledgements
Shwetha Bhandari, Henk Birkholz, Chennakesava Reddy Gaddam, Sujal
Sheth, Peter Psenak, Adwaith Gautham, Annu Singh, Nancy Cam Winget,
Ned Smith, and Guy Fedorkow.
Appendix B. Change Log
[THIS SECTION TO BE REMOVED BY THE RFC EDITOR.]
v00-v01
o Minor tweaks
v02-v00 of draft-voit-rats-trustworthy-path-routing-00
o file rename was due to an IETF tool submission glitch
o The Attester's AIK is included within the Stamped Passport. This
eliminates the need to provision to AIK certificate on the Relying
Party.
o Removed Centralized variant
o Added timing diagram, and moved content around to match
v01-v02 of draft-voit-rats-trusted-path-routing
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o Extracted the attestation stream, and placed into draft-birkholz-
rats-network-device-subscription
o Introduced the Trustworthiness Vector
v00-v01 of draft-voit-rats-trusted-path-routing
o Move all FlexAlgo terminology to Section 4.2. This allows
Section 3.6 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 C. Open Questions
(1) When there is no available Trusted Topology?
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.
(2) Extension of the Stamped Passport?
We might move to 'verifier-certificate' and 'verifier-certificate-
name' based on WG desire to include more information in the Stamped
Passport. The format used could be extracted from ietf-
keystore.yang, grouping keystore-grouping.
Author's Address
Eric Voit
Cisco Systems, Inc.
Email: evoit@cisco.com
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