RATS Working Group E. Voit
Internet-Draft C. Gaddam
Intended status: Standards Track Cisco
Expires: November 14, 2021 G. Fedorkow
Juniper
H. Birkholz
Fraunhofer SIT
May 13, 2021
Trusted Path Routing
draft-voit-rats-trustworthy-path-routing-03
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 for
trustworthiness. 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
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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 November 14, 2021.
Copyright Notice
Copyright (c) 2021 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Notation . . . . . . . . . . . . . . . . . . 4
3. Implementation Prerequisites . . . . . . . . . . . . . . . . 4
4. End-to-end Solution . . . . . . . . . . . . . . . . . . . . . 5
4.1. Network Topology Assembly . . . . . . . . . . . . . . . . 5
4.2. Attestation Information Flows . . . . . . . . . . . . . . 6
4.2.1. Step 1 . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.2. Step 2 . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.3. Step 3 . . . . . . . . . . . . . . . . . . . . . . . 11
4.2.4. Step 4 . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.5. Step 5 . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.6. Step 6 . . . . . . . . . . . . . . . . . . . . . . . 15
5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 24
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1. Normative References . . . . . . . . . . . . . . . . . . 24
7.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 26
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 26
Appendix C. Open Questions . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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.
By using a router's embedded TPM based cryptoprocessors in
conjunction with the Remote Attestation context established by
[attestation-results], a network provider can identify potentially
compromised devices as well as potentially exploitable (or even
exploited) vulnerabilities. Using this knowledge, it is then
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possible to redirect sensitive flows around these devices while other
remediations are potentially considered by Network Operations.
Trusted Path Routing allows the establishing Trusted Topologies which
only include trust-verified network devices. 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 Claims, the links are
then included as members of this Trusted Topology. Routing protocols
are 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. This
is done by an end user identifying 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 been verified as achieving a specific set of
Trustworthiness Claims during its most recent trustworthiness
appraisal. Interesting sets of Trustworthiness Claims might be
marketed to end-users in the following ways:
o all transited devices have booted with known hardware and firmware
o all transited devices are from a specific set of vendors and are
running known software containing the latest patches
o no guarantees provided
2. Terminology
2.1. Terms
The following terms are imported from [RATS-Arch]: Attester,
Evidence, Passport, Relying Party, and Verifier.
The following terms are impored from [attestation-results]:
Trustworthiness Claim, Trustworthiness Vector, AR-augmented Evidence
Newly defined terms for this document:
Attested Device - a network connected Attester where a Verifier's
most recent appraisal of Evidence has returned a Trustworthiness
Vector.
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Stamped Passport - AR-augmented Evidence which can take two forms.
First if the Attester uses a TPM2, the the Verifier Proof-of-
Freshness includes the <clock>, <reset-counter>, <restart-counter>
and <safe> objects from a recent TPM2 quote made by that Attester,
and the Relying Party Proof-of-Freshness is returned along with
the timeticks as objects embedded within the most recent TPM quote
signed by the same TPM2. Second, if the Attester uses a TPM1.2:
the Verifier Proof-of-Freshness includes a global timestamp from
that Verifier, and the Relying Party Proof-of-Freshness is
embedded within a more recent TPM quote signed by the same TPM
Attesting Environment.
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
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.
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. Implementation Prerequisites
The specification is a valid instance of [attestation-results]. This
specification works under the following protocol and preconfiguration
prerequisite assumptions:
o All Attested Devices support the TPM remote attestation profile as
laid out in [RATS-Device].
o One or more Verifier A's as defined in [attestation-results]
'Interaction Model' continuously appraise each of the Attested
Devices in a network domain, and these Verifiers return the
Attestation Results back to each originating Attested Device.
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o The Attested Devices are connected via link layer protocols such
as [MACSEC] or [IEEE-802.1X].
o Each Attester can pass a Stamped Passport to a Relying Party /
Verifier B as defined in [attestation-results] 'Interaction Model'
within [RFC3748] over that link layer protocol.
o A Trusted Topology such as [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 Attested Devices which
currently meet at a defined set of Trustworthiness Vectors.
o A Relying Party is able to use mechanisms such as
[I-D.ietf-lsr-flex-algo]'s affinity to include/exclude links as
part of the Trusted Topology based on the appraisal of a Stamped
Passport.
o Customer designated Sensitive Subnets and their requested
Trustworthiness Vectors have been identified and associated with
external interfaces to/from Attested Devices at the edge of a
network. Traffic to a Sensitive Subnet can be passed into the
Trusted Topology by the Attested Device.
o Relying Party/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.
4. End-to-end Solution
4.1. Network Topology Assembly
To be included in a Trusted Topology, Stamped Passports are shared
between Attested Devices (such as routers). Upon receiving and
appraising the Stamped Passport as part of link layer authentication,
the Relying Party Attested Device decides if this link should be
added as an active adjacency for a particular Trusted Topology. In
Figure 1 below, this might be done by applying an Appraisal Policy
for Attestation Results which requires any Attesting Device be most
recently appraised with the Trustworthiness Claim 'hw-authentic'. If
Attested Device 'x' has been appraised with 'hw-verification-fail' is
would not become part of the Trustworthy Topology.
When enough links have been successfully added, the Trusted Topology
will support edge-to-edge forwarding as routing protocols flood the
adjacency information across the network domain.
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.------------. .----------.
| Attested | | Edge |
.----------. | Device 'x' | | Attested |
| Attested | | | | Device |
| Device | | | | |
| | | trust>---------------<no_trust |
| no_trust>--<trust | .----------. | |---Sensitive
| | '------------' | trust>==<trust | Subnet
| trust>==================<trust | | |
'----------' | | '----------'
| Attested |
| Device |
'----------'
Figure 1: Trusted Path Topology Assembly
As the process described above repeats over time 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. Traffic exchanged with Sensitive Subnets can then be
forwarded across that Trusted Topology from all edges of the network
domain.
4.2. Attestation Information Flows
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. A Stamped Passport is a valid
type of AR-augmented evidence as described in [attestation-results].
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.
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]. This figure is also a
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valid embodiment of the "Interaction Model" described within
[attestation-results]. (Note that the Relying Party must also be an
Attested Device in order to attract Sensitive Subnet traffic which
may flow from the Attester.)
.------------------.
| Attester |
| |
| (Attested Device |
| / Router) | .------------------.
| .-------------. | | Relying Party |
| | TPM based | | | / Verifier B |
| | Attesting | | .----------. | |
| | Environment | | | Verifier | | (Attested Device |
| '-------------' | | A | | / Router) |
'------------------' '----------' '------------------'
time(VG) | |
|<------nonce--------------time(NS) |
| | |
time(EG)(1)------Evidence------------>| |
| time(RG) |
|<------Attestation Results-(2) |
~ ~ ~
time(VG')? | |
~ ~ ~
|<------nonce---------------------------------(3)time(NS')
| | |
time(EG')(4)------Stamped Passport---------------------->|
| | time(RG',RA')(5)
(6)
~
time(RX')
Figure 2: Trusted Path Timing
To summarize Figure 2 above, Evidence about a specific Attester is
generated. Some subset of this evidence will be in the form of PCR
quotes which are signed by a TPM that exists as the Attester's
Attesting Environment. This Evidence will be delibered to and
appraised by Verifier A. Verifier A will then appraise the Attester
and give it a Trustworthiness Vector. This Trustworthiness Vector is
then signed by Verifier A and be returned as Attestation Results to
the Attester. Later, when a request comes in from a Relying Party,
the Attester assembles and returns a Stamped Passport. The Stamped
Passport contains all the information necessary for Verifier B to
appraise the most recent Trustworthiness Vector of the Attester.
Based on the Verifier B appraisal, the link will be included or not
in a Trusted Topology maintained on the Relying Party.
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More details on the mechanisms used in the construction,
verification, and transmitting of the Stamped Passport are listed
below. These numbers match to both the numbered steps of Figure 2
and numbered steps described in Section 3 of [attestation-results]:
4.2.1. Step 1
Evidence about and Attester is generated. A portion of this Evidence
will include a PCR quote signed by a TPM private LDevID key that
exists within the Attester's TPM based Attesting Environment. The
Attester sends a signed TPM Quote which includes PCR measurements to
Verifier A at time(EG).
There are two alternatives for Verifier A to acquire this signed
Evidence:
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 Periodic polling of RPC <tpm20-challenge-response-attestation> or
the RPC <tpm12-challenge-response-attestation> which are defined
in [RATS-YANG].
4.2.2. Step 2
Verifier A appraises the Evidence from Step 1. A portion of this
appraisal process will follow the appraisal process flow described
below. This appraisal process MUST be able to set at least the
following set of Trustworthiness Claims from [attestation-results]:
'hw-authentic', 'hw-verification-fail', 'tee-identity-verified',
'tee-identity-fail', 'executables-verified', and 'executables-fail'.
The establishment of a Trustworthiness Vector uses the following
Figure 3 logic on the Verifier:
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Start: TPM Quote Received, log received, or appraisal timer expired
for the the Attesting network device.
Appraisal 0: set Trustworthiness Vector = Null
Appraisal 1: Is there sufficient fresh signed evidence to appraise?
yes - No action
no - Go to End
Appraisal 2: Appraise Hardware Integrity
if not evaluated, or insufficient data to conclude: take no action
else if (hw-authentic) - push onto vector
else (if hw-verification-fail) - push onto vector, go to End
Appraisal 3: Appraise attester identity
if not evaluated, or insufficient data to conclude: take no action
else if (tee-identity-verified) - push onto vector
else if (tee-identity-fail) - push onto vector
Appraisal 4: Appraise executable loaded
if not evaluated, or insufficient data to conclude: take no action
else if (executables-verified) - push onto vector
else (if executables-fail) - push onto vector, go to End
Appraisal 5: a Verifier has the option of appraising and asserting
additional non-standard Trustworthiness Claims. It can do so here.
End
Figure 3: Verifier A Appraisal Flow
After the appraisal and generation of the Trustworthiness Vector, the
following are assembled as the set of Attestation Results from this
particular appraisal cycle:
(2.1) the Public Attestation Key which was used to validate the TPM
Quote of Step 1. This is encoded by <public-key>, <public-key-
format>, and <public-key-algorithm-type>.
(2.2) the appraised Trustworthiness Vector of the Attester as
calculated in Figure 3
(2.3) the PCR state information from the TPM Quote of (1) plus the
time information associated with the TPM Quote of (1). Specifically
if the Attester has a TPM2, then the values of the TPM PCRs are
included (i.e., <TPM2B_DIGEST>, <tpm20-hash-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
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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.
(2.4) a Verifier A signature across (2.1) though (2.3). This
signature is encoded by <verifier-signature>, <verifier-key-
algorithm-type>, and <verifier-signature-key-name>.
Immediately subsequent to each Verifier appraisal cycle of an
Attester, these Attestation Results MUST be pushed to the Attesting
Router. This is done via a daatstore write to the following YANG
model on the Attester. A YANG tree showing the relevant YANG objects
is below. The YANG model describing each of these objects is
described later in the document. Note however that although the YANG
model shows the specific objects which are needed, the specific set
of objects needs to be encoded in CDDL. This makes the payload going
over TLS more efficient. Look for this encoding in a new version of
the draft which is coming shortly.
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module: ietf-trustworthiness-claims
+--rw attestation-results!
+--rw (tpm-specification-version)?
+--:(tpm20-attestation-results-cddl) {taa:tpm20}?
| +--rw trustworthiness-vector* identityref
| +--rw tpm20-pcr-selection* [tpm20-hash-algo]
| | +--rw tpm20-hash-algo identityref
| | +--rw pcr-index* tpm:pcr
| +--rw TPM2B_DIGEST binary
| +--rw clock uint64
| +--rw reset-counter uint32
| +--rw restart-counter uint32
| +--rw safe boolean
| +--rw appraisal-timestamp
| | yang:date-and-time
| +--rw verifier-algorithm-type identityref
| +--rw verifier-signature binary
| +--rw verifier-certificate-keystore-ref
| tpm:certificate-name-ref
+--:(tpm12-attestation-results-cddl) {taa:TPM12}?
+--rw trustworthiness-vector* identityref
+--rw pcr-index* pcr
+--rw tpm12-pcr-value* binary
+--rw TPM12-quote-timestamp
| yang:date-and-time
+--rw appraisal-timestamp
| yang:date-and-time
+--rw verifier-algorithm-type identityref
+--rw verifier-signature binary
+--rw verifier-certificate-keystore-ref
tpm:certificate-name-ref
(Do we want the Verifier signature across the keystore-ref?)
Figure 4: Attestation Results Tree
4.2.3. Step 3
At time(NS') some form of time-based freshness (such as a nonce or
Epoch Handle [RATS-Interactions]) will be generated in a way which
makes it available to the Relying Party. Soon after time(NS'), a
Relying Party will make a Link Layer authentication request to an
Attester via a either [MACSEC] or [IEEE-802.1X]. This connection
request MUST expect the return of [RFC3748] credentials from the
Attester.
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4.2.4. Step 4
Upon receipt of the Link Layer request from Step 3, a Stamped
Passport is generated and sent to the Relying Party. The Stamped
Passport MUST include the following:
(4.1) The Attestation Results from Step 2
(4.2) New signed, verifiably fresh PCR measurements based on a TPM
quote at time(EG') which incorporates the freshness information known
by the Relying Party from Step 3. If it is a nonce, the freshness
information will have been delivered as part of the link layer
connection request in Steps 3.
Stamped Passports contain following objects, defined in this document
via YANG. A subsequent draft will convert the objects below into
CDDL format so that the objects can efficiently be passed over EAP.
If an Attester includes a TPM2, these YANG objects are:
+---n tpm20-stamped-passport
+--ro attestation-results
| +--ro trustworthiness-vector* identityref
| +--ro tpm20-pcr-selection* [tpm20-hash-algo]
| | +--ro tpm20-hash-algo identityref
| | +--ro pcr-index* tpm:pcr
| +--ro TPM2B_DIGEST binary
| +--ro clock uint64
| +--ro reset-counter uint32
| +--ro restart-counter uint32
| +--ro safe boolean
| +--ro appraisal-timestamp
| | yang:date-and-time
| +--ro verifier-algorithm-type identityref
| +--ro verifier-signature binary
| +--ro verifier-certificate-keystore-ref
| tpm:certificate-name-ref
+--ro tpm20-quote
+--ro TPMS_QUOTE_INFO binary
+--ro quote-signature? binary
+--ro certificate-name certificate-name-ref
Figure 5: YANG Tree for a TPM2 Stamped Passport
Note that where a TPM2.0 is used, the PCR numbers and hash algorithms
quoted in Step 1 MUST match the PCR numbers and hash algorithms
quoted in this step.
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And if the Attester is a TPM1.2, the YANG object are:
+---n tpm12-stamped-passport
+--ro attestation-results
| +--ro trustworthiness-vector* identityref
| +--ro pcr-index* pcr
| +--ro tpm12-pcr-value* binary
| +--ro TPM12-quote-timestamp
| | yang:date-and-time
| +--ro appraisal-timestamp
| | yang:date-and-time
| +--ro verifier-algorithm-type identityref
| +--ro verifier-signature binary
| +--ro verifier-certificate-keystore-ref
| tpm:certificate-name-ref
+--ro tpm12-quote
+--ro TPM_QUOTE2? binary
+--ro certificate-name certificate-name-ref
Figure 6: YANG Tree for a TPM1.2 Stamped Passport
With either of these passport formats, if the TPM quote is verifiably
fresh, then the state of the Attester can be appraised by a network
peer.
Note that with [MACSEC] or [IEEE-802.1X], Step 3 plus Step 4 will
repeat periodically independently of any subsequent iteration Steps 1
and Step 2. This allows for periodic reauthentication of the link
layer in a way not bound to the updating of Verifier A's Attestation
Results.
4.2.5. Step 5
Upon receipt of the Stamped Passport generated in Step 4, the Relying
Party appraises this Stamped Passport as per its Appraisal Policy for
Attestation Results. The result of this application will determine
how the Stamped Passport will impact adjacencies within a Trusted
Topology. The decision process is as follows:
(5.1) Verify that (4.2) includes the freshness context from Step 3.
(5.2) Use a local certificate to validate the signature (4.1).
(5.3) Verify that the hash from (4.2) matches (4.1)
(5.4) Use the identity of (2.1) to validate the signature of (4.2).
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(5.5) Failure of any steps (5.1) through (5.4) means the link does
not meet minimum validation criteria, therefore appraise the link as
having a null Verifier B Trustworthiness Vector. Jump to Step 6.
(5.6) Compare the time(EG) TPM state to the time(EG') TPM state
o If TPM2.0
1. If the <TPM2B_DIGEST>, <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.
2. 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.)
3. Assign the link a null Trustworthiness Vector.
o If TPM1.2
1. 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).
2. 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.)
3. Assign the link a null Trustworthiness Vector.
(5.7) Assemble the Verifier B Trustworthiness Vector
1. Copy Verifier A Trustworthiness Vector to Verifier B
Trustworthiness Vector
2. Prune any Trustworthiness Claims the Relying Party doesn't accept
from this Verifier.
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4.2.6. Step 6
After the Trustworthiness Vector has been validated or reset, based
on the link's Trustworthiness Vector, the Relying Party adjusts 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.
5. YANG Module
This YANG module imports modules from [RATS-YANG], [crypto-types] and
[RFC6021].
<CODE BEGINS> ietf-trustworthiness-claims@2021-05-12.yang
module ietf-trustworthiness-claims {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-trustworthiness-claims";
prefix tc;
import ietf-yang-types {
prefix yang;
}
import ietf-tcg-algs {
prefix taa;
reference
"draft-ietf-rats-yang-tpm-charra";
}
import ietf-keystore {
prefix ks;
}
import ietf-tpm-remote-attestation {
prefix tpm;
reference
"draft-ietf-rats-yang-tpm-charra";
}
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
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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 2021-05-12 {
description
"Initial version.";
reference
"draft-voit-rats-trustworthy-path-routing";
}
/*
* IDENTITIES
*/
identity trustworthiness-claim {
base trustworthiness-claim;
description
"Base identity for a Verifier that uses its Appraisal Policy for
Evidence to establish a trustworthiness level.";
}
identity trustworthiness-pass {
base trustworthiness-claim;
description
"A trustworthiness-claim which successfully meets an Appraisal
Policy for Evidence.";
}
identity trustworthiness-fail {
description
"A trustworthiness-claim 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-claim.";
}
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identity hw-authentic {
base trustworthiness-pass;
description
"A Verifier has appraised an Attester as having authentic
hardware, as well as authentic firmwhere where that can be
verified.";
}
identity hw-verification-fail {
base trustworthiness-fail;
description
"A Verifier has appraised an Attester has failed its hardware or
firmware verification.";
}
identity tee-identity-verified {
base trustworthiness-pass;
description
"A Verifier has appraised and verified an Attester's unique
identity stored within the hardware of a Trusted Execution
Environment.";
}
identity tee-identity-fail {
base trustworthiness-fail;
description
"A Verifier has been unable to assess or verify an Attester's
unique identity";
}
identity executables-verified {
base trustworthiness-pass;
description
"A Verifier has appraised the executables loaded on Attester's,
and asserts that it recognizes and approves of all relevant
executiable files loaded.";
}
identity executables-fail {
base trustworthiness-fail;
description
"A Verifier has appraised the executables loaded on Attester's,
and has not been able to recognize or does not approved of all
the executible files which have been loaded.";
}
identity file-system-anomaly {
base trustworthiness-fail;
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description
"A Verifier has found a file on an Attester which should not be
present.";
}
/*
* GROUPINGS
*/
grouping trustworthiness-vector {
leaf-list trustworthiness-vector {
type identityref {
base trustworthiness-claim;
}
ordered-by system;
description
"One or more Trustworthiness Claims assigned which expose the
Verifiers evaluation of the Evidence associated with the
AIK which signed as associated TPM Quote.";
}
}
grouping tpm-signature {
leaf aik-algorithm-type {
type identityref {
base taa:asymmetric;
}
mandatory true;
description
"Platform asymmetric algorithm used in the Attester signature
process.";
}
leaf aik-signature {
type binary;
mandatory true;
description
"Signature of the Attester across a TPM Quote.";
}
uses tpm:certificate-name-ref;
}
grouping verifier-evidence {
description
"Evidence generated by the Verifier.";
leaf appraisal-timestamp {
type yang:date-and-time;
mandatory true;
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description
"The timestamp of the Verifier's appraisal. This can be used
by a Relying Party to determine the freshness of the
attestation results.";
}
leaf verifier-algorithm-type {
type identityref {
base taa:asymmetric;
}
mandatory true;
description
"Platform asymmetric algorithm used in the Verifier signature
process.";
}
leaf verifier-signature {
type binary;
mandatory true;
description
"Signature of the Verifier across all the current objects in
the attestation-results container except for 'verifier-
signature' and 'verifier-certificate-keystore-ref'.
This assumes CDDL encoding of the objects in the current
order of this YANG model.";
}
leaf verifier-certificate-keystore-ref {
type tpm:certificate-name-ref;
mandatory true;
description
"A reference to a specific certificate to an asymmetric key
in the Keystore for the Verifier which can be used to validate
the 'verifier-signature'. Note that the
'name' reference must be globally unique so that it can be
read by the Relying Party in a way which identifies a
specific Verifier.";
}
}
grouping tpm20-cddl-attestation-results {
description
"Elements combined into a CDDL representation for TPM2.0.";
uses trustworthiness-vector;
list tpm20-pcr-selection {
key "tpm20-hash-algo";
description
"Specifies the list of PCRs and Hash Algorithms used by the
Verifier.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
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TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.9.7";
uses tpm:tpm20-hash-algo;
leaf-list pcr-index {
type tpm:pcr;
description
"The numbers of the PCRs associated with the TPM2B_DIGEST.";
}
}
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";
}
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
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"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";
}
uses tpm-aik-certificate;
uses verifier-evidence;
}
grouping tpm12-cddl-attestation-results {
description
"Elements combined into a CDDL representation for TPM1.2.";
uses trustworthiness-vector;
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 TPM12-quote-timestamp {
type yang:date-and-time;
mandatory true;
description
"The timestamp for when the indicator of freshness (such as a
nonce) was generated. This is the indicator of freshness
which was used in the generation of the TPM1.2 quote. This
timestamp can be used by a Relying Party to determine the
freshness of the attestation results.";
}
uses tpm-aik-certificate;
uses verifier-evidence;
}
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/*
* NOTIFICATIONS
*/
notification tpm20-stamped-passport {
description
"The augmentation of the most recent Attestation Results
delivered from a Verifier with a TPM2.0 Quote.";
container attestation-results {
description
"The latest Verifier delivered Attestation Results.";
uses tpm20-cddl-attestation-results;
}
container tpm20-quote {
description
"The TPM2.0 quote delivered in response to a connectivity
request.";
leaf TPMS_QUOTE_INFO {
type binary;
mandatory true;
description
"A hash of the latest PCR values (and the hash algorithm
used) which have been returned from a Verifier for the
selected PCRs and Hash Algorithms.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 10.12.1";
}
leaf quote-signature {
type binary;
description
"Quote signature returned by TPM Quote. The signature was
generated using the key associated with the
certificate 'name'.";
reference
"https://www.trustedcomputinggroup.org/wp-content/uploads/
TPM-Rev-2.0-Part-2-Structures-01.38.pdf Section 11.2.1";
}
uses tpm:certificate-name-ref;
}
}
notification tpm12-stamped-passport {
description
"The augmentation of the most recent Attestation Results
delivered from a Verifier with a TPM1.2 Quote.";
container attestation-results {
description
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"The latest Verifier delivered Attestation Results.";
uses tpm12-cddl-attestation-results;
}
container tpm12-quote {
description
"The TPM1.2 quote delivered in response to a connectivity
request.";
leaf TPM_QUOTE2 {
type binary;
description
"Result of a TPM1.2 Quote2 operation. This includes PCRs,
signatures, locality, the provided nonce and other data which
can be further parsed to appraise the Attester.";
reference
"TPM1.2 commands rev116 July 2007, Section 16.5";
}
uses tpm:certificate-name-ref;
}
}
/*
* DATA NODES
*/
container attestation-results {
presence
"Indicates that Verifier has appraised the security posture of
the Attester, and returned the results within this container.";
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.";
choice tpm-specification-version {
description
"Identifies the cryptoprocessor API set which drove the
Attestation Results.";
case tpm20-attestation-results-cddl {
if-feature "taa:tpm20";
description
"Attestation Results which are returned from the
evaluation of Evidence which includes a TPM2 quote.";
uses tpm20-cddl-attestation-results;
}
case tpm12-attestation-results-cddl {
if-feature "taa:TPM12";
description
"Attestation Results which are returned from the
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evaluation of Evidence which includes a TPM1.2 quote.";
uses tpm12-cddl-attestation-results;
}
}
}
}
<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 4 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
[attestation-results]
"Attestation Results for Connectivity", April 2021,
<https://tools.ietf.org/html/
draft-voit-rats-attestation-results-00>.
[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]
Cisco Systems, Juniper Networks, Cisco Systems, Cisco
Systems, and Edward Jones, "IGP Flexible Algorithm",
draft-ietf-lsr-flex-algo-15 (work in progress), April
2021.
[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
Peter Psenak, Shwetha Bhandari, Adwaith Gautham, Annu Singh, Sujal
Sheth, Nancy Cam Winget, and Ned Smith.
Appendix B. Change Log
[THIS SECTION TO BE REMOVED BY THE RFC EDITOR.]
v02-v03
o Integrated [attestation-results] as prerequisite context.
o Totally rearranged content. But there were not meaningful process
changes.
o Redid YANG model, and highlighted CDDL needs.
v01-v02
o Minor tweaks such as renaming and removal of a few
trustworthiness-claims
v00-v01
o Minor tweaks
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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
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 allow passport definition 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?
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Format of the reference to the 'verifier-certificate-name' based on
WG desire to include more information in the Stamped Passport. Also
we need to make sure that the keystore referenced names are globally
unique, else we will need to include a node name in the object set.
(3) Encoding of objects in CDDL. A Verifier will want to sign
encoded objects rather than YANG structures. It is most efficient to
encode the Attestation Results once on the Verifier, and push these
down via a YANG model to the Attester.
Authors' Addresses
Eric Voit
Cisco Systems, Inc.
8135 Maple Lawn Blvd
Fulton, Maryland 20759
USA
Email: evoit@cisco.com
Chennakesava Reddy Gaddam
Cisco Systems, Inc.
Cessna Business Park, Kadubeesanahalli
Bangalore, Karnataka 560103
India
Email: chgaddam@cisco.com
Guy C. Fedorkow
Juniper Networks
10 Technology Park Drive
Westford, Massachusetts 01886
USA
Email: gfedorkow@juniper.net
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
Darmstadt 64295
Germany
Email: henk.birkholz@sit.fraunhofer.de
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