USe Cases and Problem Statement of Open Trust Protocol
draft-liu-opentrustprotocol-usecase-00.txt

Abstract

This document discusses use cases of a open trust 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 September 14, 2017.

Copyright Notice

Copyright (c) 2017 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
• 2. Terminology
• 3. Scenario and Use Cases of OtrP
• 3.1. Use Case 1 - Payment
• 3.2. Use Case 2 - IoT
• 4. Use Case and Functional Requirements related to deployment scenario
• 4.1. Use Case 1 - Resource-constrained scenario
• 4.2. Use Case 2 - TA and SD management owned by OEM and SP
• 4.3. Use Case 3 - Batch mode
• 5. IANA Considerations
• 6. Security Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

1. Introduction

Chips used on smart phones, tablets, and many consumer appliances today have built-in support for a so-called Trusted Execution Environment (TEE). The TEE is a security concept that separates normal operating systems, like Linux, from code that requires higher security protection, like security-related code. The underlying idea of this sandboxing approach is to have smaller code that is better reviewed and test and to provide it with more rights. They run on the so-called Secure World (in comparison to the Linux operating system that would run in the Normal World).

TEEs have been on the market for a while and have been successfully used for a number of applications, such as payment etc. However, the technology hasn't reached its full potential since ordinary developers who could make use of such functionality have a hard time getting access to it, and to write applications for it.

The industry has been working on an application layer security protocol that allows to configure security credentials and software running on a Trusted Execution Environment (TEE) for sometime. Today, TEEs are, for example, found home routers, set-top boxes, smart phones, tablets, wearables, etc. Unfortunately, there have been mostly proprietary protocols used in this environment.

This document discusses the use cases and features of open trust protocol.

2. Terminology

OTrP:

Open Trust Protocol

Client Application:

An application running on a rich OS, such as an Android, Windows, or iOS application, provided by a SP.

Device:

A physical piece of hardware that hosts symmetric key cryptographic modules

OTrP Agent:

An application running in the rich OS allowing communication with the TSM and the TEE.

Rich Application:

Alternative name of "Client Application". In this document we may use these two terms interchangably.

Rich Execution Environment (REE)

An environment that is provided and governed by a rich OS, potentially in conjunction with other supporting operating systems and hypervisors; it is outside of the TEE. This environment and applications running on it are considered un-trusted.

Secure Boot Module (SBM):

A firmware in a device that delivers secure boot functionality. It is also referred as Trusted Firmware (TFW) in this document.

Service Provider (SP):

An entity that wishes to supply Trusted Applications to remote devices. A Service Provider requires the help of a TSM in order to provision the Trusted Applications to the devices.

Trust Anchor:

A root certificate that a module trusts. It is usually embedded in one validating module, and used to validate the trust of a remote entity's certificate.

Trusted Application (TA):

Application that runs in TEE.

Trusted Execution Environment (TEE):

An execution environment that runs alongside but isolated from an REE. A TEE has security capabilities and meets certain security-related requirements: It protects TEE assets from general software attacks, defines rigid safeguards as to data and functions that a program can access, and resists a set of defined threats. There are multiple technologies that can be used to implement a TEE, and the level of security achieved varies accordingly.

CA:

Certificate Authority

SD:

Security Domain

TFW:

Trusted Firmware

TSM:

Trusted Service Manager

3. Scenario and Use Cases of OtrP

OTrP is an open interoperable protocol that allows TSM to manage security domains and TAs running in different Trusted Execution Environment (TEE) of various devices.

Figure 1: OTrP System Overview:

              ---OTrP Message Protocol--
              |                        |
              |                        |
 --------------------           ---------------   ----------
 |  REE   |  TEE    |           |    TSM      |   |  SP    |
 |  ---   |  ---    |           |    ---      |   |  --    |
 |        |         |           |             |   |        |
 | Client | SD (TAs)|           |   SD / TA   |   |  TA    |
 |  Apps  |         |           |     Mgmt    |   |        |
 |   |    |         |           |             |   |        |
 |   |    |         |           |             |   |        |
 | OTrP   | Trusted |           |  Trusted    |   |        |
 | Agent  |  CAs    |           | FW, TEE CAs |   |        |
 |        |         |           |             |   |        |
 |        |TEE Key/ |           |  TSM Key/   |   |SP Key/ |
 |        |  Cert   |           |    Cert     |   | Cert   |
 |        | FW Key/ |           |             |   |        |
 |        |  Cert   |           |             |   |        |
 ------------------             ---------------   ----------
              |                        |              |
              |                        |              |
              -----------------------------------------
                                |
                                |
                          --------------
                          |    CA      |
                          --------------                                                 
          

• The use of open environments: In general, some new kind device will be equipped with open environment to provide the operating system. This has the advantage that users can add applications at any time, and there is little need to worry about their impact on the stability and security of the device. However, the open environment makes the device face more and more foreign attacks. Device manufacturers want to take advantage of this operating system, but need to effectively control the behavior of the software running on the device.
• Verification: The traditional user authentication method requires a username and password. At present, this approach is increasingly considered safe, after all, consumers will use a less confidential password or re-use the existing password, and hackers are increasingly able to invade the consumer's account. Because an application or service provider typically stores personal verification and sensitive information on its own server, such hacking is the headline of the news, causing consumers to fear and shaken business confidence. Therefore, there is a need for a more sophisticated validation mechanism to ensure that the openers of the application enjoy the necessary flexibility while protecting the consumer.
• Privacy: The device stores more and more personal information (such as contact information, photos, photos and video clips), and even sensitive data (including credentials, passwords, medical data, etc.). In order to prevent this information from being exposed to loss, theft, malware or other negative events, we need adequate security to store, process and distribute such personal data.
• Content protection: Today, more and more devices with high-definition (HD) video playback and video streaming, mobile TV playback and host 3D games and other functions. They can even become content gateway devices, and to replace the traditional set-top boxes or game consoles. In this case, the playback function of the device becomes less important, and the security requirements are more and more prominent. Therefore, not only to protect the mobile device on the full HD or ultra-high-definition content, but also to protect the device to send the content to the TV through the channel.
• Enterprise Data Access: Enterprise IT professionals often exercise caution when opening access to their internal network, fearing that the device will carry malware, the device will be stolen, or when used outside the company, there will be attacks from the internal network The As a result, IT departments often establish green lists and red lists of equipment based on the security performance of the device. They are also concerned about the characteristics of these devices always open and the implementation of password protection and device lockout functions in shutdown mode.
• Financial risk: Financial transactions through networking devices, especially mobile devices, are becoming increasingly common. These transactions include booking, remote payments, near-field payments and financial electronic transactions. Moreover, the use of mobile devices in the retail outlets shopping has become increasingly common. Moreover, mobile devices become a point-of-sale terminal, especially mobile point of sale, and this use case is now growing.

3.1. Use Case 1 - Payment

Payment technology (Especially mobile payments) is growing rapidly.

The TEE-based identity authentication application has a strong need for using OTrP. The types of TA involved mainly include the following two kinds:

• Identification: Personal identification password and biometric. Because TEE can provides larger amount of memory and data transfer, TEE can store a trusted application that is used to complete a personal password acquisition or biological identification. For the development of the relevant TA of SP, the use of OTrP can easily send the latest trusted application to the device. At the same time, because TA and REE applications are independent of each other, REE side of the corresponding application only need to make little changes because of the OTrP.
• Security interface: Mobile payment is inseparable from the security interaction between end users and consumer devices. For example, the user needs to confirm the sensitive information displayed on the screen and enter the sensitive information (such as a password) through the keyboard. A TA such as keyboard in tee is needed. When designing a keyboard in tee, you should consider how to make a timely update when an application has a vulnerability to ensure that user sensitive data is not compromised.In this case, it is necessary to use OTrP

3.2. Use Case 2 - IoT

In the field of Internet of Things, the purpose of TA is to use TEE to perform the functions of storing and managing sensitive data (eg, encryption keys) and performing sensitive operations (eg, authentication or encryption) in a secure environment in devices

In the smart home industry, a lot of security equipment are used TEE program to protect users of sensitive data, such as smart door locks. Some smart door locks even use biometrics, which makes this application in smart home very similar to the payment industry. Similarly, security products also need a secure and trusted remote update protocol to update the TA program in the device.

In the automotive (and bike) sharing industry, smart door locks use TEE technology to protect users' identity information. Operators who share automotive products need to remotely update trusted applications in smart locks.

Some high-value consumer electronics devices also have the need to use TEE and complete TA remote updates. For example, UAV (Unmanned Aerial Vehicle) devices use TEE to store sensitive operational instructions to prevent hackers from controlling the UAV's takeoff or landing by tampering with GPS location information. The manufacturer of the UAV needs to consider the easy management of the safety instructions in the UAV. For example, when the geographical location information of the prohibited flight area is changed, the equipment manufacturer should be able to update all the corresponding information stored in the device .

4. Use Case and Functional Requirements related to deployment scenario

4.1. Use Case 1 - Resource-constrained scenario

As mentioned earlier, in the shared automotive industry, smart door locks have the requirement to use OTrP. In this scenario, the update of TA in the smart door locks is facing with the problem of communication bandwidth limitation. Software and firmware updates often comprise quite a large amount of data. Therefore, it may overload the LPWAN which is typically used to transfer only small amounts of data. Binary encoding solution will be a better choice in the scenario of Low-power and Lossy Networks (LLNs), Low Power Personal Area Network (LPPAN)and Low Power Wide Area Network (LPWAN).

4.2. Use Case 2 - TA and SD management owned by OEM and SP

There are three configurations to manage TA and SD in TEE:

• The OEM wants to ensure that no service provider can talk to the TEE without the OEM’s prior approval. Once approved, the Service Provider is allowed to create security domains and install trusted apps. The OEM doesn’t require to be involved in that process.
• The OEM wants to ensure that no service provider can talk to the TEE without the OEM’s prior approval. Once approved, the Service Provider is allowed to perform lifecycle management of trusted apps within a particular security domain but cannot create any new security domains without the OEM's involvement.
• The OEM and Service provider both want to be involved in every transaction with TEE and only when they both agree the TEE can accept the OTrP message and perform actions.

The first kind of configuration can give OEM greater management authority. It could be very convenient for the management of SD and TA.

The second configuration can give OEM a certain degree of control, TA can be easily issued to SD by SP. But at the same time, how to protect the security of TAM platform and TEE terminal should be considered.

The third configuration can reduce the security risk caused by the insecure TA program but it will also increase the complexity of deployment and maintenance.

4.3. Use Case 3 - Batch mode

Batch mode operation could be more efficient in some deployment scenario. For example, some OEM may want to provision TA into many devices they know with the same device key (for privacy and batch validation purpose). A TAM may issue one OTrP message to create SD and install the TA and send to many devices without requiring each device to submit their own device attestation. The batch support will reduce the load on the service side (TAM).

5. IANA Considerations

This memo includes no request to IANA.

6. Security Considerations

TBD.

7. References

7.1. Normative References

7.2. Informative References

Authors' Addresses