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, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . 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]