wdiff draft-ietf-teep-protocol-01.txt draft-ietf-teep-protocol-02.txt

TEEP H. Tschofenig
Internet-Draft Arm Ltd.
Intended status: Standards Track M. Pei
Expires: September 10, October 16, 2020 Broadcom
D. Wheeler
Intel
D. Thaler
Microsoft
March 9,
A. Tsukamoto
AIST
April 14, 2020

Trusted Execution Environment Provisioning (TEEP) Protocol
draft-ietf-teep-protocol-01
draft-ietf-teep-protocol-02

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 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 September 10, October 16, 2020.

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
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 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Message Overview . . . . . . . . . . . . . . . . . . . . . . 3
4. Detailed Messages Specification . . . . . . . . . . . . . . . 5
4.1. QueryRequest Creating and Validating TEEP Messages . . . . . . . . . . 5
4.1.1. Creating a TEEP message . . . . . . . . . . . . . . . 5
4.1.2. Validating a TEEP Message . . . . . . . . . . . . . . 6
4.2. QueryResponse QueryRequest . . . . . . . . . . . . . . . . . . . . . . 7 6
4.3. TrustedAppInstall QueryResponse . . . . . . . . . . . . . . . . . . . . 7 . . 8
4.4. TrustedAppDelete TrustedAppInstall . . . . . . . . . . . . . . . . . . . . 8 10
4.5. TrustedAppDelete . . . . . . . . . . . . . . . . . . . . 11
4.6. Success . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.6. 11
4.7. Error . . . . . . . . . . . . . . . . . . . . . . . . . . 9 12
5. Mapping of TEEP Message Parameters to CBOR Labels . . . . . . 15
6. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . . . 11
6. 15
7. Security Consideration Considerations . . . . . . . . . . . . . . . . . . . 12
7. 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7.1. 17
8.1. Media Type Registration . . . . . . . . . . . . . . . . . 13
7.2. 17
8.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 14
7.3. 18
8.3. Ciphersuite Registry . . . . . . . . . . . . . . . . . . 15
8. 19
8.4. CBOR Tag Registry . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. 19
9.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. 20
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix 21
A. Acknowledgements Contributors . . . . . . . . . . . . . . . . . . 16
Appendix . . . . . . . 21
B. Contributors Acknowledgements . . . . . . . . . . . . . . . . . . . . 17 . . . 21
C. Complete CDDL . . . . . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 24

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 an TEE ecosystem, device vendors may use different operating
systems in the REE and may use different types of TEEs. When
application providers 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, involving a TEEP Broker.

The Trusted Execution Environment Provisioning (TEEP) architecture
document [I-D.ietf-teep-architecture] has set to provide a design
guidance for such an interoperable protocol and introduces the
necessary terminology. Note that the term Trusted Application may
include more than code; it may also include configuration data and
keys needed by the TA to operate correctly.

2. Requirements Language

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 [RFC2119].
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].

3. Message Overview

The TEEP protocol consists of a couple of messages exchanged between
a TAM and a TEEP Agent via a TEEP Broker. 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 as well be encrypted and signed
by the service provider. The TEEP protocol not only re-use CBOR but
also the respective security wrapper, namely COSE [RFC8152].
Furthermore, for attestation the Entity Attestation Token (EAT)
[I-D.ietf-rats-eat] and for software updates the SUIT manifest format
[I-D.ietf-suit-manifest] are re-used.

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 TAs, 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
subsequent message exchanges to install, update, or delete trusted
applications shall be initiated.

+------------+ +-------------+
| TAM | |TEEP Agent |
+------------+ +-------------+

QueryRequest ------->

QueryResponse

<------- or

Error

With the TrustedAppInstall message a TAM can instruct a TEEP Agent to
install a TA. The TEEP Agent will process the message, determine
whether the TAM is authorized and whether the TA has been signed by
an authorized SP. In addition to the binary, the TAM may also
provide personalization data. If the TrustedAppInstall message was
processed successfully then a Success message is returned to the TAM,
an Error message otherwise.

+------------+ +-------------+
| TAM | |TEEP Agent |
+------------+ +-------------+

TrustedAppInstall ---->

Success

<---- or

Error

With the TrustedAppDelete message a TAM can instruct a TEEP Agent to
delete one or multiple TA(s). A Success message is returned when the
operation has been completed successfully, and an Error message
otherwise.

+------------+ +-------------+
| TAM | |TEEP Agent |
+------------+ +-------------+

TrustedAppDelete ---->

Success

<---- or

Error

4. Detailed Messages Specification

The CBOR-encoded

TEEP messages are protected by COSE, as the COSE_Sign1 structure. The TEEP
protocol messages are described in CDDL format [I-D.ietf-cbor-cddl] [RFC8610] below.

Outer_Wrapper = {
msg-authenc-wrapper => bstr .cbor
Msg_AuthEnc_Wrapper / nil,

teep-message => (QueryRequest /
QueryResponse /
TrustedAppInstall /
TrustedAppDelete /
Error /
Success ),
}

msg-authenc-wrapper = 1
teep-message = 2

Msg_AuthEnc_Wrapper = [ * (COSE_Mac_Tagged /
COSE_Sign_Tagged /
COSE_Mac0_Tagged /
COSE_Sign1_Tagged)]

4.1. QueryRequest

suite = int

version = int

data_item = int

QueryRequest = {
TYPE : int,
TOKEN : bstr,
REQUEST : [+data_item],
? CIPHER_SUITE : [+suite],
? NONCE : bstr,
? VERSION : [+version],
? OCSP_DATA : bstr,
* $$extensions
}

A QueryRequest message is signed by the TAM Creating and has the following
fields:

TYPE TYPE = 1 corresponds to Validating TEEP Messages

4.1.1. Creating a QueryRequest TEEP message sent from

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.

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

A QueryRequest message is used by the TAM to learn information from
the TEEP Agent.

TOKEN The TAM can learn 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 software (trusted apps), 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,
? nonce => bstr .size (8..64),
? version => [ + version ],
? oscp-data => bstr,
* $$query-request-extensions
* $$teep-option-extensions
},
data-item-requested
]

The message has the following fields:

type
The value of (1) corresponds to a QueryRequest message sent from
the TAM to the TEEP Agent.

token
The value in the TOKEN field token parameter is used to match responses to
requests. This is particualrly useful when a TAM issues multiple
concurrent requests to
responses.

REQUEST a TEEP Agent.

request
The REQUEST field request parameter indicates what information the TAM requests
from the TEEP Agent in form of a list of integer values. bitmap. Each integer 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 an entity attestation token (EAT) in the response.
If the TAM requests an attestation token to be returned by the
TEEP Agent then it MUST also include the nonce in the message.
The nonce is subsequently placed into the EAT token for replay
protection.

trusted_apps (2) With this value the TAM queries the TEEP Agent
for all installed TAs.

extensions (3) (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 (4) (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.

CIPHER_SUITE

cipher-suites
The CIPHER_SUITE field cipher-suites parameter lists the ciphersuite(s) supported by
the TAM. Details about the ciphersuite encoding can be found in
Section 5.

NONCE NONCE 6.

nonce
The none field is an optional field parameter used for ensuring the
refreshness of the Entity Attestation Token (EAT) returned with a
QueryResponse message. When a nonce is provided in the
QueryRequest and an EAT is returned with the QueryResponse message
then the nonce contained in this request MUST be copied into the
nonce claim found in the response.

VERSION EAT token.

version
The VERSION version field lists parameter the version(s) supported by the TAM.
For this version of the specification this field can be omitted.

OCSP_DATA

ocsp_data
The OCSP_DATA field 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 bo th 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.

4.2.

4.3. QueryResponse

ext_info = int

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].

query-response = [
type: TEEP-TYPE-query-response,
token: uint,
options: {
TYPE : int,
TOKEN : bstr,
? SELECTED_CIPHER_SUITE : selected-cipher-suite => suite,
? SELECTED_VERSION : selected-version => version,
? EAT : eat => bstr,
? TA_LIST : [+bstr], ta-list => [ + bstr ],
? EXT_LIST : [+ext_info], ext-list => [ + ext-info ],
* $$extensions $$query-response-extensions,
* $$teep-option-extensions
}
]

The QueryResponse message is signed and encrypted by the TEEP Agent
and returned to the TAM. It has the following fields:

TYPE TYPE = 2

type
The value of (2) corresponds to a QueryResponse message sent from
the TEEP Agent to the TAM.

TOKEN

token
The value in the TOKEN field token parameter is used to match requests responses to
responses.
requests. The value MUST correspond to the value received with
the QueryRequest.

SELECTED_CIPHER_SUITE QueryRequest message.

selected-cipher-suite
The SELECTED_CIPHER_SUITE field selected-cipher-suite parameter indicates the selected
ciphersuite. Details about the ciphersuite encoding can be found
in Section 5.

SELECTED_VERSION 6.

selected-version
The SELECTED_VERSION field selected-version parameter indicates the protocol version
selected by the TEEP Agent.

EAT

eat
The EAT field eat parameter contains an Entity Attestation Token following
the encoding defined in [I-D.ietf-rats-eat].

TA_LIST

ta-list
The TA_LIST field ta-list parameter enumerates the trusted applications
installed on the device in form of TA ID TA_ID byte strings.

EXT_LIST

ext-list
The EXT_LIST field ext-list parameter lists the supported extensions. This
document does not define any extensions.

4.3.

4.4. TrustedAppInstall

The TrustedAppInstall message is used by the TAM to install software
(trusted apps) via the TEEP Agent.

Like other TEEP messages, the TrustedAppInstall message is signed,
and the relevant CDDL snippet is shown below. The complete CDDL
structure is shown in [CDDL].

trusted-app-install = [
type: TEEP-TYPE-trusted-app-install,
token: uint,
option: {
TYPE : int,
TOKEN : bstr,
? MANIFEST_LIST : [+ SUIT_Outer_Wrapper], manifest-list => [ + SUIT-envelope ],
* $$extensions $$trusted-app-install-extensions,
* $$teep-option-extensions
}
]

The TrustedAppInstall message is MACed and encrypted by the TAM and has the following fields:

TYPE TYPE = 3

type
The value of (3) corresponds to a TrustedAppInstall message sent
from the TAM to the TEEP Agent. In case of successful processing,
an Success message is returned by the TEEP Agent. In case of an
error, an Error message is returned. Note that the
TrustedAppInstall message is used for initial TA installation but
also for TA updates.

TOKEN

token
The value in the TOKEN token field is used to match requests responses to
responses.

TA
requests.

manifest-list
The MANIFEST_LIST manifest-list field is used to convey one or multiple SUIT
manifests. A manifest is a bundle of metadata about the trusted
app, 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 is typically signed and encrypted by the SP.
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 SP sign and/or encrypt the TA
binary.

4.4.

4.5. TrustedAppDelete

The TrustedAppDelete message is used by the TAM to remove software
(trust apps) from the device.

Like other TEEP messages, the TrustedAppDelete message is signed, and
the relevant CDDL snippet is shown below. The complete CDDL
structure is shown in [CDDL].

trusted-app-delete = [
type: TEEP-TYPE-trusted-app-delete,
token: uint,
option: {
TYPE : int,
TOKEN : bstr,
? TA_LIST : [+bstr], ta-list => [ + bstr ],
* $$extensions $$trusted-app-delete-extensions,
* $$teep-option-extensions
}
]

The TrustedAppDelete message is MACed and encrypted by the TAM and has the following fields:

TYPE TYPE = 4

type
The value of (4) corresponds to a TrustedAppDelete message sent
from the TAM to the TEEP Agent. In case of successful processing,
an Success message is returned by the TEEP Agent. In case of an
error, an Error message is returned.

TOKEN

token
The value in the TOKEN field token parameter is used to match requests responses to
responses.

TA_LIST
requests.

ta-list
The TA_LIST field ta-list parameter enumerates the TAs to be deleted.

4.5.

4.6. Success

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 TrustedAppInstall and the
TrustedAppDelete 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: {
TYPE : int,
TOKEN : bstr,
? MSG : tstr, msg => text,
* $$extensions $$teep-success-extensions,
* $$teep-option-extensions
}
]

The Success message is MACed and encrypted by the TEEP Agent and has the following fields:

TYPE TYPE = 5

type
The value of (5) corresponds to corresponds to a Error Success message
sent from the TEEP Agent to the TAM.

TOKEN

token
The value in the TOKEN field token parameter is used to match requests responses to
responses.

MSG
requests.

msg
The MSG field msg parameter contains optional diagnostics information
encoded in UTF-8 [RFC3629] returned by the TEEP Agent.

4.6.

4.7. Error

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].

teep-error = [
type: TEEP-TYPE-teep-error,
token: uint,
err-code: uint,
options: {
TYPE : int,
TOKEN : bstr,
ERR_CODE : int,
? ERR_MSG : tstr, err-msg => text,
? CIPHER_SUITE : [+suite], cipher-suites => [ + suite ],
? VERSION : [+version], versions => [ + version ],
* $$teep-error--extensions,
* $$extensions $$teep-option-extensions
}

If possible, the
]

The Error message is MACed and encrypted by the TEEP
Agent. Unprotected Error messages MUST be handled with care by the
TAM due to possible downgrading attacks. It has the following fields:

TYPE TYPE = 6

type
The value of (6) corresponds to a an Error message sent from the
TEEP Agent to the TAM.

TOKEN

token
The value in the TOKEN field token parameter is used to match requests responses to
responses.

ERR_CODE
requests.

err-code
The ERR_CODE field err-code parameter is populated with values listed in a
registry (with the initial set of error codes listed below). Only
selected messages are applicable to each message.

ERR_MSG

err-msg
The ERR_MSG message err-msg parameter is a human-readable diagnostic message text that
MUST be encoded using UTF-8 [RFC3629] using Net-Unicode form
[RFC5198].

VERSION

cipher-suites
The VERSION field enumerates cipher-suites parameter lists the protocol version(s) ciphersuite(s) supported by
the TEEP Agent. This field is optional but MUST be returned with
the ERR_UNSUPPORTED_MSG_VERSION ERR_UNSUPPORTED_CRYPTO_ALG error message.

CIPHER_SUITE

versions
The CIPHER_SUITE field lists version parameter enumerates the ciphersuite(s) protocol version(s) supported
by the TEEP Agent. This field is otherwise optional but parameter MUST be
returned with the ERR_UNSUPPORTED_CRYPTO_ALG ERR_UNSUPPORTED_MSG_VERSION error message.

This specification defines the following initial error messages.
Additional error code can be registered with IANA. messages:

ERR_ILLEGAL_PARAMETER (1)
The TEEP Agent sends this error message when a request contains
incorrect fields or fields that are inconsistent with other
fields.

ERR_UNSUPPORTED_EXTENSION (2)
The TEEP Agent sends this error message when it recognizes an
unsupported extension or unsupported message.

ERR_REQUEST_SIGNATURE_FAILED (3)
The TEEP Agent sends this error message when it fails to verify
the signature of the message.

ERR_UNSUPPORTED_MSG_VERSION (4)
The TEEP Agent receives a message but does not support the
indicated version.

ERR_UNSUPPORTED_CRYPTO_ALG (5)
The TEEP Agent receives a request message encoded with an
unsupported cryptographic algorithm.

ERR_BAD_CERTIFICATE (6)
The TEEP Agent returns this error when 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)
The TEEP Agent returns this error when a certificate was of an
unsupported type.

ERR_CERTIFICATE_REVOKED (8)
The TEEP Agent returns this error when a certificate was revoked
by its signer.

ERR_CERTIFICATE_EXPIRED (9)
The TEEP Agent returns this error when a certificate has expired
or is not currently valid.

ERR_INTERNAL_ERROR (10)
The TEEP Agent returns this error when a miscellaneous internal
error occurred while processing the request.

ERR_RESOURCE_FULL (11)
This error is reported when a device resource isn't available
anymore, such as storage space is full.

ERR_TA_NOT_FOUND (12)
This error will occur when the target TA does not exist. This
error may happen when the TAM has stale information and tries to
delete a TA that has already been deleted.

ERR_TA_ALREADY_INSTALLED (13)
While installing a TA, a TEE will return this error if the TA has
already been installed.

ERR_TA_UNKNOWN_FORMAT (14)
The TEEP Agent returns this error when it does not recognize the
format of the TA binary.

ERR_TA_DECRYPTION_FAILED (15)
The TEEP Agent returns this error when it fails to decrypt the TA
binary.

ERR_TA_DECOMPRESSION_FAILED (16)
The TEEP Agent returns this error when it fails to decompress the
TA binary.

ERR_MANIFEST_PROCESSING_FAILED (17)
The TEEP Agent returns this error when manifest processing
failures occur that are less specific than ERR_TA_UNKNOWN_FORMAT,
ERR_TA_UNKNOWN_FORMAT, and ERR_TA_DECOMPRESSION_FAILED.

ERR_PD_PROCESSING_FAILED (18)
The TEEP Agent returns this error when it fails to process the
provided personalization data.

Additional error code 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 |
+-----------------------+-------+
| cipher-suites | 1 |
| nonce | 2 |
| version | 3 |
| ocsp-data | 4 |
| selected-cipher-suite | 5 |
| selected-version | 6 |
| eat | 7 |
| ta-list | 8 |
| ext-list | 9 |
| manifest-list | 10 |
| msg | 11 |
| err-msg | 12 |
+-----------------------+-------+

6. Ciphersuites

A ciphersuite consists of an AEAD algorithm, a HMAC algorithm, and a
signature algorithm. Each ciphersuite is identified with an integer
value, which corresponds to an IANA registered ciphersuite. This
document specifies two ciphersuites.

+-------+------------------------------------------------+
| Value | Ciphersuite
------+------------------------------------------------
0 |
+-------+------------------------------------------------+
| 1 | AES-CCM-16-64-128, HMAC 256/256, X25519, EdDSA
1 |
| 2 | AES-CCM-16-64-128, HMAC 256/256, P-256, ES256

6. |
+-------+------------------------------------------------+

7. Security Consideration 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 to by the TEEP Agent to authenticate the
TAM and vice versa.

Attestation
A TAM may rely on the attestation information provided by the TEEP
Agent and the Entity Attestation Token is re-used to convey this
information. To sign the Entity Attestation Token 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
information or in the certificate used to sign the attestation
token. This uniqueness may raise privacy concerns. To lower the
privacy implications the TEEP Agent MUST present its attestation
information only to an authenticated and authorized TAM.

TA Binaries
TA binaries are provided by the SP.It SP. It is the responsibility of
the TAM to relay only verified TAs from authorized SPs. Delivery
of that TA to the TEEP Agent is then the responsibility of the TAM
and the TEEP Broker, using the security mechanisms provided by the
TEEP protocol. To protect the TA binary the SUIT manifest is re-used re-
used and it offers a varity of security features, including
digitial signatures and symmetric encryption.

Personalization Data
An SP or a TAM can supply personalization data along with a TA.
This data is also protected by a SUIT manifest. The
personalization data may be opaque to the TAM.

TEEP Broker
The TEEP protocol relies on the 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 the TEEP Agents are protected against such
downgrading attacks based on features offered by the manifest
itself.

CA Compromise
The QueryRequest message from a TAM to the TEEP Agent may include
OCSP stapling data for the TAM's signer 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. TEEP Agents will
trust a TA signer certificate's validation status done by a TAM.

CA Compromise
The CA issuing certificates to a TAM or an SP may get compromised.
A compromised intermediate CA certificates 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 device,
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-provided 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 since OCSP stapling includes
signature generation time, certificate validity dates are compared
to the current time.

8. IANA Considerations

7.1.

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

Restrictions on usage: none

Author: See the "Authors' Addresses" section of this document

Change controller: IETF

7.2.

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.

7.3.

8.3. Ciphersuite Registry

IANA is also requested to create a new registry for ciphersuites, as
defined in Section 5.

8. 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

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

8.1.
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-03 (work in progress), February 2020.

[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., and 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-03 draft-ietf-suit-manifest-04
(work in progress), February March 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>.

[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.

[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>.

[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>.

8.2.

[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-cbor-cddl]
Birkholz, H., Vigano, C., and C. Bormann, "Concise data
definition language (CDDL): a notational convention to
express CBOR and JSON data structures", draft-ietf-cbor-
cddl-08 (work in progress), March 2019.

[I-D.ietf-teep-architecture]
Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", draft-ietf-teep-architecture-07 draft-ietf-teep-architecture-08 (work in
progress), March April 2020.

[I-D.ietf-teep-opentrustprotocol]
Pei, M., Atyeo, A., Cook, N., Yoo, M., and H. Tschofenig,
"The Open Trust Protocol (OTrP)", draft-ietf-teep-
opentrustprotocol-03 (work in progress), May 2019.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, 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/RFC8126, 10.17487/RFC8610,
June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

Appendix 2019, <https://www.rfc-editor.org/info/rfc8610>.

A. Acknowledgements

This work is based on the initial version of OTrP
[I-D.ietf-teep-opentrustprotocol] and hence credits go Contributors

We would like to those who
have contributed thank Brian Witten (Symantec), Tyler Kim (Solacia),
Nick Cook (Arm), and Minho Yoo (IoTrust) for their contributions to it.
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 Akira Tsukamoto, Isobe Kohei, Kohei Isobe, Isobe (TRASIO/SECOM), Kuniyasu Suzaki
(TRASIO/AIST), Tsukasa Ooi, Oi (TRASIO), and Yuichi Takita (SECOM) for
their valuable implementation feedback.

Appendix B. Contributors

We would also like to thank the following individuals Carsten Bormann and Henk Birkholz for
their
contributions to an initial help with the CDDL.

C. Complete CDDL

teep-message = $teep-message-type .within teep-message-framework

SUIT-envelope = bstr ; placeholder

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 /= trusted-app-install
$teep-message-type /= trusted-app-delete
$teep-message-type /= teep-error
$teep-message-type /= teep-success

; message type numbers
TEEP-TYPE-query-request = 1
TEEP-TYPE-query-response = 2
TEEP-TYPE-trusted-app-install = 3
TEEP-TYPE-trusted-app-delete = 4
TEEP-TYPE-teep-error = 5
TEEP-TYPE-teep-success = 6

version of this specification.

- Brian Witten
Symantec
brian_witten@symantec.com

- Tyler Kim
Solacia
tylerkim@iotrust.kr

- Nick Cook
Arm Ltd.
nicholas.cook@arm.com

- Minho Yoo
IoTrust
minho.yoo@iotrust.kr = 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-apps = 2
$data-item-requested /= trusted-apps
extensions = 4
$data-item-requested /= extensions
suit-commands = 8
$data-item-requested /= suit-commands

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,
? selected-version => version,
? eat => bstr,
? ta-list => [ + bstr ],
? ext-list => [ + ext-info ],
* $$query-response-extensions,
* $$teep-option-extensions
}
]

trusted-app-install = [
type: TEEP-TYPE-trusted-app-install,
token: uint,
option: {
? manifest-list => [ + SUIT-envelope ],
* $$trusted-app-install-extensions,
* $$teep-option-extensions
}
]

trusted-app-delete = [
type: TEEP-TYPE-trusted-app-delete,
token: uint,
option: {
? ta-list => [ + bstr ],
* $$trusted-app-delete-extensions,
* $$teep-option-extensions
}
]

teep-success = [
type: TEEP-TYPE-teep-success,
token: uint,
option: {
? msg => text,
* $$teep-success-extensions,
* $$teep-option-extensions
}
]

teep-error = [
type: TEEP-TYPE-teep-error,
token: uint,
options: {
? err-msg => text,
? cipher-suites => [ + suite ],
? versions => [ + version ],
* $$teep-error--extensions,
* $$teep-option-extensions
}
err-code: uint,
]

cipher-suites = 1
nonce = 2
versions = 3
oscp-data = 4
selected-cipher-suite = 5
selected-version = 6
eat = 7
ta-list = 8
ext-list = 9
manifest-list = 10
msg = 11
err-msg = 12

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

Dave Thaler
Microsoft
US

Email: dthaler@microsoft.com

Akira Tsukamoto
AIST
JP

Email: akira.tsukamoto@aist.go.jp