TEEP H. Tschofenig
Internet-Draft Arm Ltd.
Intended status: Standards Track M. Pei
Expires: May 6, 2021 Broadcom
D. Wheeler
Intel
D. Thaler
Microsoft
A. Tsukamoto
AIST
November 2, 2020
Trusted Execution Environment Provisioning (TEEP) Protocol
draft-ietf-teep-protocol-04
Abstract
This document specifies a protocol that installs, updates, and
deletes Trusted Applications (TAs) in a device with a Trusted
Execution Environment (TEE). This specification defines an
interoperable protocol for managing the lifecycle of TAs.
The protocol name is pronounced teepee. This conjures an image of a
wedge-shaped protective covering for one's belongings, which sort of
matches the intent of this protocol.
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 http://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 May 6, 2021.
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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
(http://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
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Message Overview . . . . . . . . . . . . . . . . . . . . . . 4
4. Detailed Messages Specification . . . . . . . . . . . . . . . 6
4.1. Creating and Validating TEEP Messages . . . . . . . . . . 6
4.1.1. Creating a TEEP message . . . . . . . . . . . . . . . 6
4.1.2. Validating a TEEP Message . . . . . . . . . . . . . . 6
4.2. QueryRequest Message . . . . . . . . . . . . . . . . . . 7
4.3. QueryResponse Message . . . . . . . . . . . . . . . . . . 9
4.4. Install Message . . . . . . . . . . . . . . . . . . . . . 12
4.5. Delete Message . . . . . . . . . . . . . . . . . . . . . 13
4.6. Success Message . . . . . . . . . . . . . . . . . . . . . 14
4.7. Error Message . . . . . . . . . . . . . . . . . . . . . . 14
5. Mapping of TEEP Message Parameters to CBOR Labels . . . . . . 17
6. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8.1. Media Type Registration . . . . . . . . . . . . . . . . . 20
8.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 21
8.3. Ciphersuite Registry . . . . . . . . . . . . . . . . . . 21
8.4. CBOR Tag Registry . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . 22
9.2. Informative References . . . . . . . . . . . . . . . . . 23
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 24
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
C. Complete CDDL . . . . . . . . . . . . . . . . . . . . . . . . 24
D. Examples of Diagnostic Notation and Binary Representation . . 27
D.1. Some assumptions in examples . . . . . . . . . . . . . . 27
D.2. QueryRequest Message . . . . . . . . . . . . . . . . . . 28
D.2.1. CBOR Diagnostic Notation . . . . . . . . . . . . . . 28
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D.2.2. CBOR Binary Representation . . . . . . . . . . . . . 28
D.3. QueryResponse Message . . . . . . . . . . . . . . . . . . 29
D.3.1. CBOR Diagnostic Notation . . . . . . . . . . . . . . 29
D.3.2. CBOR Binary Representation . . . . . . . . . . . . . 29
D.4. Install Message . . . . . . . . . . . . . . . . . . . . . 29
D.4.1. CBOR Diagnostic Notation . . . . . . . . . . . . . . 29
D.4.2. CBOR Binary Representation . . . . . . . . . . . . . 30
D.5. Success Message (for Install) . . . . . . . . . . . . . . 30
D.5.1. CBOR Diagnostic Notation . . . . . . . . . . . . . . 30
D.5.2. CBOR Binary Representation . . . . . . . . . . . . . 30
D.6. Error Message (for Install) . . . . . . . . . . . . . . . 30
D.6.1. CBOR Diagnostic Notation . . . . . . . . . . . . . . 30
D.6.2. CBOR binary Representation . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
The Trusted Execution Environment (TEE) concept has been designed to
separate a regular operating system, also referred as a Rich
Execution Environment (REE), from security-sensitive applications.
In a TEE ecosystem, device vendors may use different operating
systems in the REE and may use different types of TEEs. When TA
Developers or Device Administrators use Trusted Application Managers
(TAMs) to install, update, and delete Trusted Applications (TAs) on a
wide range of devices with potentially different TEEs then an
interoperability need arises.
This document specifies the protocol for communicating between a TAM
and a TEEP Agent.
The Trusted Execution Environment Provisioning (TEEP) architecture
document [I-D.ietf-teep-architecture] provides design guidance and
introduces the necessary terminology.
2. Terminology
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.
This specification re-uses the terminology defined in
[I-D.ietf-teep-architecture].
As explained in Section 4.4 of that document, the TEEP protocol
treats each TA, any dependencies the TA has, and personalization data
as separate components that are expressed in SUIT manifests, and a
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SUIT manifest might contain or reference multiple binaries (see
[I-D.ietf-suit-manifest] for more details).
As such, the term Trusted Component in this document refers to a set
of binaries expressed in a SUIT manifest, to be installed in a TEE.
Note that a Trusted Component may include one or more TAs and/or
configuration data and keys needed by a TA to operate correctly.
Each Trusted Component is uniquely identified by a "component-id"
byte string, such as a 16-byte UUID [RFC4122]. If Concise Software
Identifiers [I-D.ietf-sacm-coswid] are used (e.g., in the suit-coswid
field of SUIT manifests), the component-id value is the CoSWID tag-id
value.
3. Message Overview
The TEEP protocol consists of messages exchanged between a TAM and a
TEEP Agent. The messages are encoded in CBOR and designed to provide
end-to-end security. TEEP protocol messages are signed by the
endpoints, i.e., the TAM and the TEEP Agent, but Trusted Applications
may also be encrypted and signed by a TA Developer or Device
Administrator. The TEEP protocol not only uses CBOR but also the
respective security wrapper, namely COSE [RFC8152]. Furthermore, for
software updates the SUIT manifest format [I-D.ietf-suit-manifest] is
used, and for attestation the Entity Attestation Token (EAT)
[I-D.ietf-rats-eat] format is supported although other attestation
formats are also permitted.
This specification defines six messages.
A TAM queries a device's current state with a QueryRequest message.
A TEEP Agent will, after authenticating and authorizing the request,
report attestation information, list all Trusted Components, and
provide information about supported algorithms and extensions in a
QueryResponse message. An error message is returned if the request
could not be processed. A TAM will process the QueryResponse message
and determine whether to initiate subsequent message exchanges to
install, update, or delete Trusted Applications.
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+------------+ +-------------+
| TAM | |TEEP Agent |
+------------+ +-------------+
QueryRequest ------->
QueryResponse
<------- or
Error
With the Install message a TAM can instruct a TEEP Agent to install a
Trusted Component. The TEEP Agent will process the message,
determine whether the TAM is authorized and whether the Trusted
Component has been signed by an authorized TA Signer. If the Install
message was processed successfully then a Success message is returned
to the TAM, or an Error message otherwise.
+------------+ +-------------+
| TAM | |TEEP Agent |
+------------+ +-------------+
Install ---->
Success
<---- or
Error
With the Delete message a TAM can instruct a TEEP Agent to delete one
or multiple Trusted Components. A Success message is returned when
the operation has been completed successfully, or an Error message
otherwise.
+------------+ +-------------+
| TAM | |TEEP Agent |
+------------+ +-------------+
Delete ---->
Success
<---- or
Error
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4. Detailed Messages Specification
TEEP messages are protected by the COSE_Sign1 structure. The TEEP
protocol messages are described in CDDL format [RFC8610] below.
{
teep-message => (query-request /
query-response /
install /
delete /
teep-success /
teep-error ),
}
4.1. Creating and Validating TEEP Messages
4.1.1. Creating a TEEP message
To create a TEEP message, the following steps are performed.
1. Create a TEEP message according to the description below and
populate it with the respective content.
2. Create a COSE Header containing the desired set of Header
Parameters. The COSE Header MUST be valid per the [RFC8152]
specification.
3. Create a COSE_Sign1 object using the TEEP message as the
COSE_Sign1 Payload; all steps specified in [RFC8152] for creating
a COSE_Sign1 object MUST be followed.
4. Prepend the COSE object with the TEEP CBOR tag to indicate that
the CBOR-encoded message is indeed a TEEP message.
4.1.2. Validating a TEEP Message
When validating a TEEP message, the following steps are performed.
If any of the listed steps fail, then the TEEP message MUST be
rejected.
1. Verify that the received message is a valid CBOR object.
2. Remove the TEEP message CBOR tag and verify that one of the COSE
CBOR tags follows it.
3. Verify that the message contains a COSE_Sign1 structure.
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4. Verify that the resulting COSE Header includes only parameters
and values whose syntax and semantics are both understood and
supported or that are specified as being ignored when not
understood.
5. Follow the steps specified in Section 4 of [RFC8152] ("Signing
Objects") for validating a COSE_Sign1 object. The COSE_Sign1
payload is the content of the TEEP message.
6. Verify that the TEEP message is a valid CBOR map and verify the
fields of the TEEP message according to this specification.
4.2. QueryRequest Message
A QueryRequest message is used by the TAM to learn information from
the TEEP Agent, such as the features supported by the TEEP Agent,
including ciphersuites, and protocol versions. Additionally, the TAM
can selectively request data items from the TEEP Agent via the
request parameter. Currently, the following features are supported:
o Request for attestation information,
o Listing supported extensions,
o Querying installed Trusted Components, and
o Listing supporting SUIT commands.
Like other TEEP messages, the QueryRequest message is signed, and the
relevant CDDL snippet is shown below. The complete CDDL structure is
shown in [CDDL].
query-request = [
type: TEEP-TYPE-query-request,
token: uint,
options: {
? supported-cipher-suites => [ + suite ],
? challenge => bstr .size (8..64),
? versions => [ + version ],
? ocsp-data => bstr,
* $$query-request-extensions
* $$teep-option-extensions
},
data-item-requested
]
The message has the following fields:
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type
The value of (1) corresponds to a QueryRequest message sent from
the TAM to the TEEP Agent.
token
The value in the token parameter is used to match responses to
requests. This is particularly useful when a TAM issues multiple
concurrent requests to a TEEP Agent.
data-item-requested
The data-item-requested parameter indicates what information the
TAM requests from the TEEP Agent in the form of a bitmap. Each
value in the bitmap corresponds to an IANA registered information
element. This specification defines the following initial set of
information elements:
attestation (1) With this value the TAM requests the TEEP Agent
to return attestation evidence (e.g., an EAT) in the response.
trusted-components (2) With this value the TAM queries the TEEP
Agent for all installed Trusted Components.
extensions (4) With this value the TAM queries the TEEP Agent for
supported capabilities and extensions, which allows a TAM to
discover the capabilities of a TEEP Agent implementation.
suit-commands (8) With this value the TAM queries the TEEP Agent
for supported commands offered by the SUIT manifest
implementation.
Further values may be added in the future via IANA registration.
supported-cipher-suites
The supported-cipher-suites parameter lists the ciphersuite(s)
supported by the TAM. Details about the ciphersuite encoding can
be found in Section 6.
challenge
The challenge field is an optional parameter used for ensuring the
refreshness of the attestation evidence returned with a
QueryResponse message. When a challenge is provided in the
QueryRequest and an EAT is returned with the QueryResponse message
then the challenge contained in this request MUST be copied into
the nonce claim found in the EAT. If any format other than EAT is
used, it is up to that format to define the use of the challenge
field.
versions
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The versions parameter enumerates the TEEP protocol version(s)
supported by the TAM A value of 0 refers to the current version of
the TEEP protocol. If this field is not present, it is to be
treated the same as if it contained only version 0.
ocsp-data
The ocsp-data parameter contains a list of OCSP stapling data
respectively for the TAM certificate and each of the CA
certificates up to the root certificate. The TAM provides OCSP
data so that the TEEP Agent can validate the status of the TAM
certificate chain without making its own external OCSP service
call. OCSP data MUST be conveyed as a DER-encoded OCSP response
(using the ASN.1 type OCSPResponse defined in [RFC2560]). The use
of OCSP is OPTIONAL to implement for both the TAM and the TEEP
Agent. A TAM can query the TEEP Agent for the support of this
functionality via the capability discovery exchange, as described
above.
4.3. QueryResponse Message
The QueryResponse message is the successful response by the TEEP
Agent after receiving a QueryRequest message.
Like other TEEP messages, the QueryResponse message is signed, and
the relevant CDDL snippet is shown below. The complete CDDL
structure is shown in [CDDL].
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query-response = [
type: TEEP-TYPE-query-response,
token: uint,
options: {
? selected-cipher-suite => suite,
? selected-version => version,
? evidence-format => text,
? evidence => bstr,
? tc-list => [ + tc-info ],
? requested-ta-list => [ + requested-ta-info ],
? unneeded-ta-list => [ + bstr ],
? ext-list => [ + ext-info ],
* $$query-response-extensions,
* $$teep-option-extensions
}
]
tc-info = {
component-id: bstr,
? tc-manifest-sequence-number: uint
}
requested-ta-info = {
component-id: bstr,
? tc-manifest-sequence-number: uint,
? have-binary: bool
}
The QueryResponse message has the following fields:
type
The value of (2) corresponds to a QueryResponse message sent from
the TEEP Agent to the TAM.
token
The value in the token parameter is used to match responses to
requests. The value MUST correspond to the value received with
the QueryRequest message.
selected-cipher-suite
The selected-cipher-suite parameter indicates the selected
ciphersuite. Details about the ciphersuite encoding can be found
in Section 6.
selected-version
The selected-version parameter indicates the TEEP protocol version
selected by the TEEP Agent. The absense of this parameter
indicates the same as if it was present with a value of 0.
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evidence-format
The evidence-format parameter indicates the IANA Media Type of the
attestation evidence contained in the evidence parameter. It MUST
be present if the evidence parameter is present and the format is
not an EAT.
evidence
The evidence parameter contains the attestation evidence. This
parameter MUST be present if the QueryResponse is sent in response
to a QueryRequest with the attestation bit set. If the evidence-
format parameter is absent, the attestation evidence contained in
this parameter MUST be an Entity Attestation Token following the
encoding defined in [I-D.ietf-rats-eat].
tc-list
The tc-list parameter enumerates the Trusted Components installed
on the device in the form of tc-info objects.
requested-ta-list
The requested-ta-list parameter enumerates the Trusted
Applications that are not currently installed in the TEE, but
which are requested to be installed, for example by an installer
of an Untrusted Application that has a TA as a dependency.
Requested TAs are expressed in the form of requested-ta-info
objects.
unneeded-ta-list
The unneeded-ta-list parameter enumerates the Trusted Applications
that are currently installed in the TEE, but which are no longer
needed by any other application. The TAM can use this information
in determining whether a TA can be deleted. Each unneeded TA is
expressed in the form of a component-id byte string.
ext-list
The ext-list parameter lists the supported extensions. This
document does not define any extensions.
The tc-info object has the following fields:
component-id
A unique identifier encoded as a CBOR bstr.
tc-manifest-sequence-number
The suit-manifest-sequence-number value from the SUIT manifest for
the Trusted Component, if a SUIT manifest was used.
The requested-ta-info message has the following fields:
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component-id
A unique identifier encoded as a CBOR bstr.
tc-manifest-sequence-number
The minimum suit-manifest-sequence-number value from a SUIT
manifest for the TA. If not present, indicates that any version
will do.
have-binary
If present with a value of true, indicates that the TEEP agent
already has the TA binary and only needs an Install message with a
SUIT manifest that authorizes installing it. If have-binary is
true, the tc-manifest-sequence-number field MUST be present.
4.4. Install Message
The Install message is used by the TAM to install a Trusted Component
via the TEEP Agent.
Like other TEEP messages, the Install message is signed, and the
relevant CDDL snippet is shown below. The complete CDDL structure is
shown in [CDDL].
install = [
type: TEEP-TYPE-install,
token: uint,
option: {
? manifest-list => [ + SUIT_Envelope ],
* $$install-extensions,
* $$teep-option-extensions
}
]
The Install message has the following fields:
type
The value of (3) corresponds to an Install message sent from the
TAM to the TEEP Agent. In case of successful processing, a
Success message is returned by the TEEP Agent. In case of an
error, an Error message is returned. Note that the Install
message is used for initial Trusted Component installation as well
as for updates.
token
The value in the token field is used to match responses to
requests.
manifest-list
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The manifest-list field is used to convey one or multiple SUIT
manifests. A manifest is a bundle of metadata about a TA, such as
where to find the code, the devices to which it applies, and
cryptographic information protecting the manifest. The manifest
may also convey personalization data. TA binaries and
personalization data can be signed and encrypted by the same TA
Signer. Other combinations are, however, possible as well. For
example, it is also possible for the TAM to sign and encrypt the
personalization data and to let the TA Developer sign and/or
encrypt the TA binary.
4.5. Delete Message
The Delete message is used by the TAM to remove a Trusted Component
from the device.
Like other TEEP messages, the Delete message is signed, and the
relevant CDDL snippet is shown below. The complete CDDL structure is
shown in [CDDL].
delete = [
type: TEEP-TYPE-delete,
token: uint,
option: {
? tc-list => [ + bstr ],
* $$delete-extensions,
* $$teep-option-extensions
}
]
The Delete message has the following fields:
type
The value of (4) corresponds to a Delete message sent from the TAM
to the TEEP Agent. In case of successful processing, a Success
message is returned by the TEEP Agent. In case of an error, an
Error message is returned.
token
The value in the token parameter is used to match responses to
requests.
tc-list
The tc-list parameter enumerates the Trusted Components to be
deleted, in the form of component-id byte strings.
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4.6. Success Message
The TEEP protocol defines two implicit success messages and this
explicit Success message for the cases where the TEEP Agent cannot
return another reply, such as for the Install and the Delete
messages.
Like other TEEP messages, the Success message is signed, and the
relevant CDDL snippet is shown below. The complete CDDL structure is
shown in [CDDL].
teep-success = [
type: TEEP-TYPE-teep-success,
token: uint,
option: {
? msg => text,
? suit-reports => [ + suit-report ],
* $$teep-success-extensions,
* $$teep-option-extensions
}
]
The Success message has the following fields:
type
The value of (5) corresponds to corresponds to a Success message
sent from the TEEP Agent to the TAM.
token
The value in the token parameter is used to match responses to
requests.
msg
The msg parameter contains optional diagnostics information
encoded in UTF-8 [RFC3629] returned by the TEEP Agent.
suit-reports
If present, the suit-reports parameter contains a set of SUIT
Reports as defined in Section 4 of [I-D.moran-suit-report].
4.7. Error Message
The Error message is used by the TEEP Agent to return an error.
Like other TEEP messages, the Error message is signed, and the
relevant CDDL snippet is shown below. The complete CDDL structure is
shown in [CDDL].
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teep-error = [
type: TEEP-TYPE-teep-error,
token: uint,
err-code: uint,
options: {
? err-msg => text,
? supported-cipher-suites => [ + suite ],
? versions => [ + version ],
? suit-reports => [ + suit-report ],
* $$teep-error--extensions,
* $$teep-option-extensions
}
]
The Error message has the following fields:
type
The value of (6) corresponds to an Error message sent from the
TEEP Agent to the TAM.
token
The value in the token parameter is used to match responses to
requests.
err-code
The err-code parameter contains one of the values listed in the
registry defined in Section 8.2 (with the initial set of error
codes listed below). Only selected values are applicable to each
message.
err-msg
The err-msg parameter is human-readable diagnostic text that MUST
be encoded using UTF-8 [RFC3629] using Net-Unicode form [RFC5198].
supported-cipher-suites
The supported-cipher-suites parameter lists the ciphersuite(s)
supported by the TEEP Agent. Details about the ciphersuite
encoding can be found in Section 6. This field is optional but
MUST be returned with the ERR_UNSUPPORTED_CRYPTO_ALG error
message.
versions
The versions parameter enumerates the TEEP protocol version(s)
supported by the TEEP Agent. This otherwise optional parameter
MUST be returned with the ERR_UNSUPPORTED_MSG_VERSION error
message.
suit-reports
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If present, the suit-reports parameter contains a set of SUIT
Reports as defined in Section 4 of [I-D.moran-suit-report].
This specification defines the following initial error messages:
ERR_ILLEGAL_PARAMETER (1)
The TEEP request contained incorrect fields or fields that are
inconsistent with other fields.
ERR_UNSUPPORTED_EXTENSION (2)
The TEEP Agent does not support the request message or an
extension it indicated.
ERR_REQUEST_SIGNATURE_FAILED (3)
The TEEP Agent could not verify the signature of the request
message.
ERR_UNSUPPORTED_MSG_VERSION (4)
The TEEP Agent does not support the TEEP protocol version
indicated in the request message.
ERR_UNSUPPORTED_CRYPTO_ALG (5)
The TEEP Agent does not support the cryptographic algorithm
indicated in the request message.
ERR_BAD_CERTIFICATE (6)
Processing of a certificate failed. For diagnosis purposes it is
RECOMMMENDED to include information about the failing certificate
in the error message.
ERR_UNSUPPORTED_CERTIFICATE (7)
A certificate was of an unsupported type.
ERR_CERTIFICATE_REVOKED (8)
A certificate was revoked by its signer.
ERR_CERTIFICATE_EXPIRED (9)
A certificate has expired or is not currently valid.
ERR_INTERNAL_ERROR (10)
A miscellaneous internal error occurred while processing the
request message.
ERR_TC_NOT_FOUND (12)
The target Trusted Component does not exist. This error may
happen when the TAM has stale information and tries to delete a
Trusted Component that has already been deleted.
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ERR_MANIFEST_PROCESSING_FAILED (17)
The TEEP Agent encountered one or more manifest processing
failures. If the suit-reports parameter is present, it contains
the failure details.
Additional error codes can be registered with IANA.
5. Mapping of TEEP Message Parameters to CBOR Labels
In COSE, arrays and maps use strings, negative integers, and unsigned
integers as their keys. Integers are used for compactness of
encoding. Since the word "key" is mainly used in its other meaning,
as a cryptographic key, this specification uses the term "label" for
this usage as a map key.
This specification uses the following mapping:
+-----------------------------+-------+
| Name | Label |
+-----------------------------+-------+
| supported-cipher-suites | 1 |
| challenge | 2 |
| version | 3 |
| ocsp-data | 4 |
| selected-cipher-suite | 5 |
| selected-version | 6 |
| evidence | 7 |
| tc-list | 8 |
| ext-list | 9 |
| manifest-list | 10 |
| msg | 11 |
| err-msg | 12 |
| evidence-format | 13 |
| requested-tc-list | 14 |
| unneeded-tc-list | 15 |
| component-id | 16 |
| tc-manifest-sequence-number | 17 |
| have-binary | 18 |
| suit-reports | 19 |
+-----------------------------+-------+
6. Ciphersuites
A ciphersuite consists of an AEAD algorithm, an HMAC algorithm, and a
signature algorithm. Each ciphersuite is identified with an integer
value, which corresponds to an IANA registered ciphersuite (see
Section 8.3. This document specifies two ciphersuites.
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+-------+------------------------------------------------+
| Value | Ciphersuite |
+-------+------------------------------------------------+
| 1 | AES-CCM-16-64-128, HMAC 256/256, X25519, EdDSA |
| 2 | AES-CCM-16-64-128, HMAC 256/256, P-256, ES256 |
+-------+------------------------------------------------+
7. Security Considerations
This section summarizes the security considerations discussed in this
specification:
Cryptographic Algorithms
TEEP protocol messages exchanged between the TAM and the TEEP
Agent are protected using COSE. This specification relies on the
cryptographic algorithms provided by COSE. Public key based
authentication is used by the TEEP Agent to authenticate the TAM
and vice versa.
Attestation
A TAM can rely on the attestation evidence provided by the TEEP
Agent. To sign the attestation evidence, it is necessary for the
device to possess a public key (usually in the form of a
certificate) along with the corresponding private key. Depending
on the properties of the attestation mechanism, it is possible to
uniquely identify a device based on information in the attestation
evidence or in the certificate used to sign the attestation
evidence. This uniqueness may raise privacy concerns. To lower
the privacy implications the TEEP Agent MUST present its
attestation evidence only to an authenticated and authorized TAM
and when using EATS, it SHOULD use encryption as discussed in
[I-D.ietf-rats-eat], since confidentiality is not provided by the
TEEP protocol itself and the transport protocol under the TEEP
protocol might be implemented outside of any TEE. If any
mechanism other than EATs is used, it is up to that mechanism to
specify how privacy is provided.
TA Binaries
Each TA binary is signed by a TA Signer. It is the responsibility
of the TAM to relay only verified TAs from authorized TA Signers.
Delivery of a TA to the TEEP Agent is then the responsibility of
the TAM, using the security mechanisms provided by the TEEP
protocol. To protect the TA binary, the SUIT manifest format is
used and it offers a variety of security features, including
digitial signatures and symmetric encryption.
Personalization Data
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A TA Signer or TAM can supply personalization data along with a
TA. This data is also protected by a SUIT manifest.
Personalization data signed and encrypted by a TA Signer other
than the TAM is opaque to the TAM.
TEEP Broker
As discussed in section 6 of [I-D.ietf-teep-architecture], the
TEEP protocol typically relies on a TEEP Broker to relay messages
between the TAM and the TEEP Agent. When the TEEP Broker is
compromised it can drop messages, delay the delivery of messages,
and replay messages but it cannot modify those messages. (A
replay would be, however, detected by the TEEP Agent.) A
compromised TEEP Broker could reorder messages in an attempt to
install an old version of a TA. Information in the manifest
ensures that TEEP Agents are protected against such downgrade
attacks based on features offered by the manifest itself.
TA Signer Compromise
The QueryRequest message from a TAM to the TEEP Agent can include
OCSP stapling data for the TAM's certificate and for intermediate
CA certificates up to the root certificate so that the TEEP Agent
can verify the certificate's revocation status. A certificate
revocation status check on a TA Signer certificate is OPTIONAL by
a TEEP Agent. A TAM is responsible for vetting a TA and before
distributing them to TEEP Agents, so TEEP Agents can instead
simply trust that a TA Signer certificate's status was done by the
TAM.
CA Compromise
The CA issuing certificates to a TAM or a TA Signer might get
compromised. A compromised intermediate CA certificate can be
detected by a TEEP Agent by using OCSP information, assuming the
revocation information is available. Additionally, it is
RECOMMENDED to provide a way to update the trust anchor store used
by the TEE, for example using a firmware update mechanism. If the
CA issuing certificates to devices gets compromised then these
devices might be rejected by a TAM, if revocation is available to
the TAM.
Compromised TAM
The TEEP Agent SHOULD use OCSP information to verify the validity
of the TAM's certificate (as well as the validity of intermediate
CA certificates). The integrity and the accuracy of the clock
within the TEE determines the ability to determine an expired or
revoked certificate. OCSP stapling data includes signature
generation time, allowing certificate validity dates to be
compared to the current time.
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Compromised Time Source
As discussed above, certificate validity checks rely on comparing
validity dates to the current time, which relies on having a
trusted source of time, such as [RFC8915]. A compromised time
source could thus be used to subvert such validity checks.
8. IANA Considerations
8.1. Media Type Registration
IANA is requested to assign a media type for application/teep+cbor.
Type name: application
Subtype name: teep+cbor
Required parameters: none
Optional parameters: none
Encoding considerations: Same as encoding considerations of
application/cbor.
Security considerations: See Security Considerations Section of this
document.
Interoperability considerations: Same as interoperability
considerations of application/cbor as specified in [RFC7049].
Published specification: This document.
Applications that use this media type: TEEP protocol implementations
Fragment identifier considerations: N/A
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person to contact for further information: teep@ietf.org
Intended usage: COMMON
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Restrictions on usage: none
Author: See the "Authors' Addresses" section of this document
Change controller: IETF
8.2. Error Code Registry
IANA is also requested to create a new registry for the error codes
defined in Section 4.
Registration requests are evaluated after a three-week review period
on the teep-reg-review@ietf.org mailing list, on the advice of one or
more Designated Experts [RFC8126]. However, to allow for the
allocation of values prior to publication, the Designated Experts may
approve registration once they are satisfied that such a
specification will be published.
Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register an error code:
example"). Registration requests that are undetermined for a period
longer than 21 days can be brought to the IESG's attention (using the
iesg@ietf.org mailing list) for resolution.
Criteria that should be applied by the Designated Experts includes
determining whether the proposed registration duplicates existing
functionality, whether it is likely to be of general applicability or
whether it is useful only for a single extension, and whether the
registration description is clear.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.
8.3. Ciphersuite Registry
IANA is also requested to create a new registry for ciphersuites, as
defined in Section 6.
8.4. CBOR Tag Registry
IANA is requested to register a CBOR tag in the "CBOR Tags" registry
for use with TEEP messages.
The registry contents is:
o CBOR Tag: TBD1
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o Data Item: TEEP Message
o Semantics: TEEP Message, as defined in [[TBD: This RFC]]
o Reference: [[TBD: This RFC]]
o Point of Contact: TEEP working group (teep@ietf.org)
9. References
9.1. Normative References
[I-D.ietf-rats-eat]
Mandyam, G., Lundblade, L., Ballesteros, M., and J.
O'Donoghue, "The Entity Attestation Token (EAT)", draft-
ietf-rats-eat-04 (work in progress), August 2020.
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"A Concise Binary Object Representation (CBOR)-based
Serialization Format for the Software Updates for Internet
of Things (SUIT) Manifest", draft-ietf-suit-manifest-09
(work in progress), July 2020.
[I-D.moran-suit-report]
Moran, B., "Secure Reporting of Update Status", draft-
moran-suit-report-00 (work in progress), October 2020.
[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>.
[RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560,
DOI 10.17487/RFC2560, June 1999, <https://www.rfc-
editor.org/info/rfc2560>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
<https://www.rfc-editor.org/info/rfc5198>.
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[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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>.
9.2. Informative References
[I-D.ietf-sacm-coswid]
Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identification Tags", draft-
ietf-sacm-coswid-15 (work in progress), May 2020.
[I-D.ietf-teep-architecture]
Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", draft-ietf-teep-architecture-12 (work in
progress), July 2020.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005, <https://www.rfc-
editor.org/info/rfc4122>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8915] Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R.
Sundblad, "Network Time Security for the Network Time
Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020,
<https://www.rfc-editor.org/info/rfc8915>.
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A. Contributors
We would like to thank Brian Witten (Symantec), Tyler Kim (Solacia),
Nick Cook (Arm), and Minho Yoo (IoTrust) for their contributions to
the Open Trust Protocol (OTrP), which influenced the design of this
specification.
B. Acknowledgements
We would like to thank Eve Schooler for the suggestion of the
protocol name.
We would like to thank Kohei Isobe (TRASIO/SECOM), Kuniyasu Suzaki
(TRASIO/AIST), Tsukasa Oi (TRASIO), and Yuichi Takita (SECOM) for
their valuable implementation feedback.
We would also like to thank Carsten Bormann and Henk Birkholz for
their help with the CDDL.
C. Complete CDDL
Valid TEEP messages MUST adhere to the following CDDL data
definitions, except that "SUIT_Envelope" is specified in
[I-D.ietf-suit-manifest].
teep-message = $teep-message-type .within teep-message-framework
SUIT_Envelope = any
teep-message-framework = [
type: 0..23 / $teep-type-extension,
token: uint,
options: { * teep-option },
* int; further integers, e.g. for data-item-requested
]
teep-option = (uint => any)
; messages defined below:
$teep-message-type /= query-request
$teep-message-type /= query-response
$teep-message-type /= install
$teep-message-type /= delete
$teep-message-type /= teep-success
$teep-message-type /= teep-error
; message type numbers
TEEP-TYPE-query-request = 1
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TEEP-TYPE-query-response = 2
TEEP-TYPE-install = 3
TEEP-TYPE-delete = 4
TEEP-TYPE-teep-success = 5
TEEP-TYPE-teep-error = 6
version = uint .size 4
ext-info = uint
; data items as bitmaps
data-item-requested = $data-item-requested .within uint .size 8
attestation = 1
$data-item-requested /= attestation
trusted-components = 2
$data-item-requested /= trusted-components
extensions = 4
$data-item-requested /= extensions
suit-commands = 8
$data-item-requested /= suit-commands
query-request = [
type: TEEP-TYPE-query-request,
token: uint,
options: {
? supported-cipher-suites => [ + suite ],
? challenge => bstr .size (8..64),
? versions => [ + version ],
? ocsp-data => bstr,
* $$query-request-extensions
* $$teep-option-extensions
},
data-item-requested
]
; ciphersuites as bitmaps
suite = $TEEP-suite .within uint .size 8
TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA = 1
TEEP-AES-CCM-16-64-128-HMAC256--256-P-256-ES256 = 2
$TEEP-suite /= TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA
$TEEP-suite /= TEEP-AES-CCM-16-64-128-HMAC256--256-P-256-ES256
query-response = [
type: TEEP-TYPE-query-response,
token: uint,
options: {
? selected-cipher-suite => suite,
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? selected-version => version,
? evidence-format => text,
? evidence => bstr,
? tc-list => [ + tc-info ],
? requested-tc-list => [ + requested-tc-info ],
? unneeded-tc-list => [ + bstr ],
? ext-list => [ + ext-info ],
* $$query-response-extensions,
* $$teep-option-extensions
}
]
tc-info = {
component-id: bstr,
? tc-manifest-sequence-number: uint
}
requested-ta-info = {
component-id: bstr,
? tc-manifest-sequence-number: uint,
? have-binary: bool
}
install = [
type: TEEP-TYPE-install,
token: uint,
option: {
? manifest-list => [ + SUIT_Envelope ],
* $$install-extensions,
* $$teep-option-extensions
}
]
delete = [
type: TEEP-TYPE-delete,
token: uint,
option: {
? tc-list => [ + bstr ],
* $$delete-extensions,
* $$teep-option-extensions
}
]
teep-success = [
type: TEEP-TYPE-teep-success,
token: uint,
option: {
? msg => text,
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? suit-reports => [ + suit-report ],
* $$teep-success-extensions,
* $$teep-option-extensions
}
]
teep-error = [
type: TEEP-TYPE-teep-error,
token: uint,
err-code: uint,
options: {
? err-msg => text,
? supported-cipher-suites => [ + suite ],
? versions => [ + version ],
? suit-reports => [ + suit-report ],
* $$teep-error--extensions,
* $$teep-option-extensions
}
]
supported-cipher-suites = 1
challenge = 2
versions = 3
ocsp-data = 4
selected-cipher-suite = 5
selected-version = 6
evidence = 7
tc-list = 8
ext-list = 9
manifest-list = 10
msg = 11
err-msg = 12
evidence-format = 13
requested-tc-list = 14
unneeded-tc-list = 15
component-id = 16
tc-manifest-sequence-number = 17
have-binary = 18
suit-reports = 19
D. Examples of Diagnostic Notation and Binary Representation
D.1. Some assumptions in examples
o OCSP stapling data = h'010203'
o TEEP Device will have 2 TAs
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* TA-ID: 0x0102030405060708090a0b0c0d0e0f,
0x1102030405060708090a0b0c0d0e0f
o SUIT manifest-list is set empty only for example purposes
o Not including Entity Attestation Token (EAT) parameters for
example purposes
D.2. QueryRequest Message
D.2.1. CBOR Diagnostic Notation
/ query-request = /
[
1, / type : TEEP-TYPE-query-request = 1 (fixed int) /
2004318071, / token : 0x77777777 (uint), generated by TAM /
/ options : /
{
1 : [ 1 ] / supported-cipher-suites = 1 (mapkey) : /
/ TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA =
[ 1 ] (array of uint .size 8) /
3 : [ 0 ] / version = 3 (mapkey) :
[ 0 ] (array of uint .size 4) /
4 : h'010203' / ocsp-data = 4 (mapkey) : 0x010203 (bstr) /
},
2 / data-item-requested : trusted-components = 2 (uint) /
]
D.2.2. CBOR Binary Representation
84 # array(4),
01 # unsigned(1)
1A 77777777 # unsigned(2004318071, 0x77777777)
A3 # map(3)
01 # unsigned(1)
81 # array(1)
01 # unsigned(1) within .size 8
03 # unsigned(3)
81 # array(1)
00 # unsigned(0) within .size 4
04 # unsigned(4)
43 # bytes(3)
010203 # "\x01\x02\x03"
02 # unsigned(2)
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D.3. QueryResponse Message
D.3.1. CBOR Diagnostic Notation
/ query-response = /
[
2, / type : TEEP-TYPE-query-response = 2 (fixed int) /
2004318071, / token : 0x77777777 (uint), from TAM's QueryRequest
message /
/ options : /
{
5 : 1, / selected-cipher-suite = 5(mapkey) :/
/ TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA =
1 (uint .size 8) /
6 : 0, / selected-version = 6 (mapkey) : 0 (uint .size 4) /
8 : [ h'0102030405060708090a0b0c0d0e0f',
h'1102030405060708090a0b0c0d0e0f' ]
/ ta-list = 8 (mapkey) :
[ 0x0102030405060708090a0b0c0d0e0f,
0x1102030405060708090a0b0c0d0e0f ]
(array of bstr) /
}
]
D.3.2. CBOR Binary Representation
83 # array(3)
02 # unsigned(2)
1A 77777777 # unsigned(2004318071, 0x77777777)
A3 # map(3)
05 # unsigned(5)
01 # unsigned(1) within .size 8
06 # unsigned(6)
00 # unsigned(0) within .size 4
08 # unsigned(8)
82 # array(2)
4F # bytes(16)
0102030405060708090A0B0C0D0D0F
4F # bytes(16)
1102030405060708090A0B0C0D0D0F
D.4. Install Message
D.4.1. CBOR Diagnostic Notation
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/ install = /
[
3, / type : TEEP-TYPE-install = 3 (fixed int) /
2004318072, / token : 0x777777778 (uint), generated by TAM /
/ options : /
{
10 : [ ] / manifest-list = 10 (mapkey) :
[ ] (array of SUIT_Envelope(any)) /
/ empty, example purpose only /
}
]
D.4.2. CBOR Binary Representation
83 # array(3)
03 # unsigned(3)
1A 77777778 # unsigned(2004318072, 0x77777778)
A1 # map(1)
0A # unsigned(10)
80 # array(0)
D.5. Success Message (for Install)
D.5.1. CBOR Diagnostic Notation
/ teep-success = /
[
5, / type : TEEP-TYPE-teep-success = 5 (fixed int) /
2004318072, / token : 0x777777778 (uint), from Install message /
]
D.5.2. CBOR Binary Representation
83 # array(3)
05 # unsigned(5)
1A 77777778 # unsigned(2004318072, 0x77777778)
D.6. Error Message (for Install)
D.6.1. CBOR Diagnostic Notation
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/ teep-error = /
[
6, / type : TEEP-TYPE-teep-error = 6 (fixed int) /
2004318072, / token : 0x777777778 (uint), from Install message /
ERR_MANIFEST_PROCESSING_FAILED,
/ err-code : ERR_MANIFEST_PROCESSING_FAILED = 17 (uint) /
/ options : /
{
12 : "disk-full" / err-msg = 12 (mapkey) :
"disk-full" (UTF-8 string) /
}
]
D.6.2. CBOR binary Representation
83 # array(3)
06 # unsigned(6)
1A 77777778 # unsigned(2004318072, 0x77777778)
11 # unsigned(17)
A1 # map(1)
0B # unsigned(12)
69 # text(9)
6469736b2d66756c6c # "disk-full"
Authors' Addresses
Hannes Tschofenig
Arm Ltd.
Absam, Tirol 6067
Austria
Email: hannes.tschofenig@arm.com
Mingliang Pei
Broadcom
350 Ellis St
Mountain View, CA 94043
USA
Email: mingliang.pei@broadcom.com
David Wheeler
Intel
US
Email: david.m.wheeler@intel.com
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Dave Thaler
Microsoft
US
Email: dthaler@microsoft.com
Akira Tsukamoto
AIST
JP
Email: akira.tsukamoto@aist.go.jp
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