EMU P. Yang
Internet-Draft M. Chen
Intended status: Standards Track Li. Su
Expires: November 29, 2021 China Mobile
May 28, 2021
Use TEE Identification in EAP-TLS
draft-chen-rats-tee-identification-00
Abstract
In security considerations, identity of a device should be protected
and cannot be exposed in public. Based on this purpose, this
document specifies the architecture of TEE(Trust Execution
Environment) identification based on EAP-TLS. In this architecture,
TEE is in charge of protecting the certificate and generating
handshake keys which will be used for EAP-TLS authentication.
REE(Rich Execution Environment) is in charge of building
communication with EAP-TLS Server. A middle layer is introduced to
communicate with separate parts of EAP-TLS in TEE and REE to
implement its original functionality.
This architecture could be used in data link layer and also
application layer to implement identity authentication under the
protection of TEE and EAP-TLS.
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 November 29, 2021.
Yang, et al. Expires November 29, 2021 [Page 1]
Internet-Draft EAP TLS TEE identity May 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
(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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architecture Overview . . . . . . . . . . . . . . . . . . . . 4
3.1. Middle Layer Message . . . . . . . . . . . . . . . . . . 4
3.2. information pre-stored inTEE . . . . . . . . . . . . . . 5
3.3. key derivation process in TEE . . . . . . . . . . . . . . 6
3.4. Mutual Authentication Procedure . . . . . . . . . . . . . 6
3.5. Ticket Establishment . . . . . . . . . . . . . . . . . . 8
3.6. Resumption . . . . . . . . . . . . . . . . . . . . . . . 8
3.7. Termination . . . . . . . . . . . . . . . . . . . . . . . 8
3.8. Hello Retry Request . . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Identity of a device in security region is always important.
However, there is still no a unified and secure mechanism that can
attest a remote device's identity. Another issue is how to store and
protect this attest process is still undetermined. This document
tries to use TEE and EAP-TLS to create a secure procedure to attest a
device's identity.
In this document, TEE (Trusted Execution Environment) described in
draft-ietf-teep-architecture-14 will be involved. This environment
emphasizes that any code within that environment cannot be tampered
with, and that any data used by such code cannot be read or tampered
with by any code outside that environment. On the contrary, REE
Yang, et al. Expires November 29, 2021 [Page 2]
Internet-Draft EAP TLS TEE identity May 2021
(Rich Execution Environment) is an environment that code and data in
that environment may be tampered with. TEE is a scarce resource in
devices, not every step or relative processes can be included in TEE.
EAP-TLS1.3 protocol, defined in RFC 5216[RFC5216], which is
recommended by IETF because of its swift and security features is
treated as a security method that can provide client-server mutual
authentication. This method is based on the assumption that both
client and server are trusted or uncompromised by any attacker.
Usually, the server of authentication is highly protected and
surveilled by operators, which could be considered as a trust party.
But client, especially IoT device, is more likely to be vulnerable
due to the lack of sufficient security mechanisms.
The primary goal of this document provides a remote identity
attestation method which uses EAP-TLS as the essential authentication
protocol and TEE as the security shelter to store and execute the
certificate and private key derivations. The specific method is to
add a middle layer in REE to exchange data in the form of EAP-TLS
between EAP-TLS server and TEE/REE. In application scenarios, this
method could be used in transport layer authentication, application
layer authentication and other scenarios.
2. Terminology
The readers should be familiar with the terms defined in.
In addition, this document makes use of the following terms:
TEE: Trust Execution Environment.
REE: Rich Execution Environment.
IML: Inner Middle Layer.
EML: External Middle Layer.
peer: The entity that responds to the authenticator.
backend authenticator server: A backend authentication server is an
entity that provides an authentication service to an
authenticator. When used, this server typically executes EAP
methods for the authenticator.
EAP server: The entity that terminates the EAP authentication method
with the peer. In the case where no backend authentication server
is used, the EAP server is part of the authenticator. In the case
Yang, et al. Expires November 29, 2021 [Page 3]
Internet-Draft EAP TLS TEE identity May 2021
where the authenticator operates in pass-through mode, the EAP
server is located on the backend authentication server.
3. Architecture Overview
This architecture will bring in a Middle Layer which is implemented
in TEE and REE to translate information between TEE and EAP-TLS
Client. The structure of this Middle Layer is shown below.
In figure one, the middle layer is separated in two parts: inner
middle layer (IML) and external middle layer (EML). The IML is
responsible for:
+------------------------------------------------------+
| +----------------------------+ REE |
| | TEE | |
| | +---------------+ +------+ | +-------------------+ | +-------+
| | | certificates| | | | |---------+ | | | |
| | +---------------+ | inner| | || | | | | |
| | +---------------+ |middle<---->external| EAP-TLS| | |EAP-TLS|
| | | key | | layer| | ||middle | Client <-----> server|
| | | derivation | | | | ||layer | | | | |
| | +---------------+ +------+ | |---------+ | | | |
| +----------------------------+ |-------------------+ | +-------+
+------------------------------------------------------+
Figure 1: architecture of middle layer
a. Key derivation b. Response to EML when relevant to encryption
and decryption.
In this document, the EML could be set as a part of EAP-TLS Client
function which is responsible for:
a. Communicate with EAP-TLS Server b. Request encryption and
decryption relevant messages from IML.
The communication mechanism between IML and EML should follow the
specific trust computing architecture like Intel Enclave or TCG TSS
which is out of this document's scope.
3.1. Middle Layer Message
The message transmitted between IML and EML will follow the format of
TLS1.3[RFC8446], but not all TLS1.3 message will be transmitted. The
IML only accept message related to encryption and decryption. The
structure of Middle Layer Message is shown below.
Yang, et al. Expires November 29, 2021 [Page 4]
Internet-Draft EAP TLS TEE identity May 2021
enum{
Random;
keyshareExtension;
PreSharedKeyExchange
CertificateList
CertificateVerify
Finished
NewSessionTicket
ApplicationData
Alert
}ParameterType
Struct{
bool request// true:request; false response
ParameterType type
uint24 length
select(type){
case Random randomValue
case KeyshareExtension keyshareextensionValue
case PreSharedKeyExchange value;
case CertificateList
case CertificateVerify
case Finished
case NewSessionTicket
case ApplicationData
case Alert
}
}MiddleLayerMessage
3.2. information pre-stored inTEE
(1) Certificate that complies with X509.3. In general, the ID of the
TEE enabled device is the certificate. In specific, the ID of the
device is "subject name" and "subjectUniqueID". In this
architecture, the certificate of this device is the only item that
needs to be stored in TEE before the process of EAP-TLS starts. And
regarding to how to get this certificate or update this certificate
is out of scope. The EAP-TLS will never allowed to afford outside
the TEE in plain text.
(2) Handshake Context during EAP-TLS procedure. During the EAP-TLS
procedure TEE need to store the handshake context which is generated
by REE. This is because EAP-TLS procedure needs handshake context
and certain private key to generate CertificateVerify and Finished
information.
Yang, et al. Expires November 29, 2021 [Page 5]
Internet-Draft EAP TLS TEE identity May 2021
3.3. key derivation process in TEE
Key derivation process MUST be executed in TEE.
3.4. Mutual Authentication Procedure
In figure 2, there are two steps that need the TEE to be invoked.
The first is TLS-ClientHello Parameter Response which will provide
parameters of key_share, signature_algorithm, psk_key_exchange_modes,
and pre_shared_key. These parameters will be sent to REE, and REE
will use process of TLS-ClientHello to send these messages to EAP-TLS
Server. The second step is TLS-Finished Parameter Response which
will provide parameters of TLS Certificate, TLS CertificateVerify,
and TLS Finished(not confirmed yet). The specific description of
these two steps will be discussed in section 2.2 and 2.3.
Divisions of Responsibility: TEE is in charge of the cipher security,
REE is in charge of the conversation integrity. And there may have
some tamper-like dos attacks, but there have no phony attack and leak
of keys.
EAP-TLS Peer
+--------------------+
+-----+ +-----+ +-------+
| TEE | | REE | |EAP|TLS|
+--+--+ +--+--+ |server |
| | +-------+
| | | EAP-Request/
| <-----------------------+ Identity
| EAP-Response/ |
| Identity(privacy-friendly) |
| Recommend random hex +------->
| | |
| | EAP-Request/
| <----------------+ EAP-Type=EAP-TLS
| | (TLS Start)
| Middle layer |
<----------------+ Message 1 |
| | |
Middle layer | |
Message 2 +--------------> |
| | |
| EAP-Response/ |
| EAP-Type=EAP-TLS+----------->
| (TLS ClientHello) |
| | EAP-Request/
| | EAP-Type=EAP-TLS
| | (TLS ServerHello,
Yang, et al. Expires November 29, 2021 [Page 6]
Internet-Draft EAP TLS TEE identity May 2021
| <----------------+ TLS EncryptedExtensions,
| | TLS CertificateRequest,
| | TLS Certificate,
| | TLS CertificateVerify,
| | TLS Finished)
| Middle Layer |
<---------------+Message 3 |
| | |
Middle Layer | |
Message 4 +----------------> |
| | |
| EAP-Response/ |
| EAP-Type=EAP-TLS |
| (TLS Certificate, |
| TLS CertificateVerify, |
| TLS Finished) +------------>
| | |
| | EAP-Request/
| | EAP-Type=EAP-TLS
| | (TLS Application
| <---------------+ Data 0x00)
| | |
| Middle Layer |
<--------------+ Message 5 |
| | |
Middle Layer | |
Message 6 +---------------> |
| | |
| EAP-Response/ |
| EAP-Type=EAP-TLS+------------->
| | |
| <------------------+EAP-Success
| | |
| | |
Figure 2: Mutual TEE Identification based on EAP-TLS
In order to complete ClientHello Message, the Key_Share Extension
message is needed. This message involves the key derivation function
which Must be executed in TEE. So the Middle Layer Message 1 is
KeyShareExtension requirement.
Middle Layer Message 2 responses to message1 and returns the
KeyShareExtension to REE.
Middle Layer Message 3 includes plaintext ServerHello message and
encrypted Server Params and Auth. Since REE does not carry the
Yang, et al. Expires November 29, 2021 [Page 7]
Internet-Draft EAP TLS TEE identity May 2021
relevant private key, it will transfer this message to TEE to decode.
Message 3 also include all the context handshake in this session, in
which will be used to create CertificateVerify and Finished context.
In Message 4, TEE retains the key_share extension, and other message
context will be transferred to REE as plaintext. Message 4 also
contains context the HMAC of (finished_key, Transcript-Hash(Handshake
Context, Certificate, CertificateVerify)), which can only be
generated in TEE.
Message 5 is the encrypted application data 0x00, which will be sent
to TEE to indicate the authentication procedure is finished.
After decrypted the message 5, the plaintext will be packed in
message 6 and sent to REE. Then REE will make the determination if
the authentication procedure is finished
3.5. Ticket Establishment
If the ticket establishment context is sent by EAP-TLS Server, it
will be packed in the middle of Server's TLS Finished message and TLS
Application Data 0x00 message. This context will be included in
message 5 by REE and conveyed to TEE. After received message 5, TEE
will decrypt and retain this ticket establishment context for
resumption.
3.6. Resumption
After the Client has received a NewSessionTicket message from the
EAP-TLS Server, the Client can use PSK mode to connect with EAP-TLS
Server. This action happens in TLS ClientHello message, in which the
Pre-shared-key extension will be used. Need to notice that the
action of resumption is deployed by REE. REE determines if it will
use NewSessionTicket to rebuild connection with EAP-TLS Server. If
do so, the message 1 will include the type of NewSeesionTIcket to
TEE. After received this message, TEE will generate the Pre-shared
key extension in Message2 for REE to generate ClientHello Message.
3.7. Termination
TLS Error Alert could be sent both by EAP-TLS Server and Client. If
sent by Server, the message will be transferred to TEE to decrypt.
And the TEE will notify REE in message 4 or 6. If the TLS Error
Alert message is sent by TEE, it will be generate in message4, which
will be directly transferred to REE.
Yang, et al. Expires November 29, 2021 [Page 8]
Internet-Draft EAP TLS TEE identity May 2021
3.8. Hello Retry Request
This message happens after the EAP-TLS Server received ClientHello.
Since the negotiation is not successful, the Hello Retry Request
message will be sent in plaintext.
4. Security Considerations
This document used the concept of TEE, which can be considered as a
trusted anchor in device that cannot be tampered. But the REE of a
device cannot be fully trusted or it may be tampered by attackers.
The middle layer has two parts: the inner middle layer and the
external middle layer. Even though the message from inner middle
layer and external middle layer is already encrypted, TEE cannot
guarantee the integrity of these messages and the behavior of EAP-TLS
Client. So this architecture can make sure that crucial information
like certificate or identity cannot be obtained by illegal party, but
cannot deny DOS attack. In fact unless there is trust channel that
directly connect between TEE and EAP-TLS Server, otherwise the DOS
attack cannot be prevented. For example, in the SUCI-SUPI
architecture in 5G system the ME is in charge of establishing
communications between USIM and NG RAN. If an attacker invaded into
the ME and tampered the SUCI message, a DOS attack will be
implemented.
The other aspects of the security considerations will follow TLS1.3,
EAP-TLS, and RATs draft--ietf-rats-architecture.
5. IANA Considerations
TBD
6. Acknowledgement
TBD
7. Normative References
[RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
March 2008, <https://www.rfc-editor.org/info/rfc5216>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
Yang, et al. Expires November 29, 2021 [Page 9]
Internet-Draft EAP TLS TEE identity May 2021
Authors' Addresses
Penglin Yang
China Mobile
32, Xuanwumen West
BeiJing, BeiJing 100053
China
Email:
yangpenglin@chinamobile.com
Meiling Chen
China Mobile
32, Xuanwumen West
BeiJing, BeiJing 100053
China
Email:
chenmeiling@chinamobile.com
Li Su
China Mobile
32, Xuanwumen West
BeiJing
100053
China
Email:
suli@chinamobile.com
Yang, et al. Expires November 29, 2021 [Page 10]