=Paper=
{{Paper
|id=None
|storemode=property
|title=Towards Enhancing Web Application
Security Using Trusted Execution
|pdfUrl=https://ceur-ws.org/Vol-1011/4.pdf
|volume=Vol-1011
|dblpUrl=https://dblp.org/rec/conf/trust/NamilukoPS13
}}
==Towards Enhancing Web Application
Security Using Trusted Execution==
https://ceur-ws.org/Vol-1011/4.pdf
Towards Enhancing Web Application Security
Using Trusted Execution
Cornelius Namiluko, Andrew J. Paverd, and Tulio De Souza
Department of Computer Science, Oxford University
Wolfson Building, Parks Road, Oxford OX1 3QD, UK
Email: [firstname.lastname]@cs.ox.ac.uk
Abstract. The web continues to serve as a powerful medium through
which various services and resources can be exposed or consumed through
web applications. Web application platforms such as webinos facilitate
communication between the various smart devices in a personal network.
Although modern web applications use various cryptographic techniques
for authentication and encryption, the security of these techniques is di-
rectly linked to the security of the private (secret) keys. Although various
techniques exist to protect these keys, we argue that the use of secure
hardware can provide stronger security guarantees. In particular, we de-
scribe our work-in-progress experiments towards using functionality pro-
vided by a Trusted Execution Environment (TEE) in web applications.
These experiments include an implementation of the webinos platform
integrated with ARM TrustZone technology. Our preliminary results are
promising in terms of both the feasibility of implementing this architec-
ture and the performance of the system.
Keywords: ARM TrustZone, GlobalPlatform, Trusted Execution En-
vironment, webinos,
1 Introduction
Wide-spread use of smart mobile devices has opened up a range of new possibil-
ities for web applications. Feature-rich web applications can be designed to use
resources such as web cameras, GPS receivers and Near Field Communication
(NFC) transceivers to provide interactive services. As a result, personal informa-
tion such as location, messages and contacts is increasingly being exposed to the
web leading to various security concerns about the confidentiality, integrity and
availability of this sensitive information. Rather than relying on software alone
to manage access to resources on these devices, it has been proposed that protec-
tion should be included as part of the hardware platform [3]. Grawrock [3] argues
that a viable approach towards device security is through trusted execution —
a paradigm in which non-security sensitive operations cannot influence sensitive
operations even though both take place on the same platform. This provides
the capability to control access to sensitive information and resources. However,
trusted execution functionality is normally provided at a low level of abstraction
and in order for applications running at a higher level of abstraction to utilize
this functionality, there must be mechanisms to expose the functionality in a
flexible manner without compromising security.
In this paper, we propose that the security of web applications can be en-
hanced through a device-independent framework that enables web applications
to utilize the functionality provided by trusted execution. We focus on webinos 1 ,
a state-of-the-art platform for running web applications across multiple devices.
Details of the webinos architecture are presented in Section 2. We propose that
webinos can be enhanced to take advantage of trusted execution functionality
provided by ARM TrustZone technology described in Section 3. In Section 4, we
present our enhanced webinos architecture in which various cryptographic oper-
ations can be performed in the trusted environment in order to protect sensitive
information such as cryptographic keys. We describe our ongoing experimental
work in Section 5 and present a preliminary evaluation in Section 6. Our pre-
liminary results are promising both in terms of the feasibility of implementing
this architecture and the performance of the system.
2 webinos Architecture
Devices such as mobile phones, smart TVs, home appliances, energy meters
and even cars are now capable of connecting to the Internet, leading to the so-
called Internet of things. It is often the case that an individual will own multiple
Internet-connected devices, each providing specific functionality or services. In
order to take advantage of the composite set of services, there must be a mech-
anism for interconnecting these devices and facilitating resource sharing.
The webinos platform is an example of a system that achieves this objective.
Based on node.js technology, the webinos platform provides an infrastructure
for securely executing web applications across multiple devices. Through a set of
APIs [9] such as geolocation, NFC and contacts, the webinos platform facilitates
access to these services and resources by web applications. Using webinos, a
device can access services and resources provided by a different device within
the user’s personal network (called a Personal Zone). To enable this, each device
runs a webinos component called a Personal Zone Proxy (PZP) and all devices in
a particular zone are interconnected either through peer-to-peer communication
or using a central component called the Personal Zone Hub (PZH).
There are several use cases for webinos [8] but for the purpose of this paper,
we consider a specific scenario in which a user wishes to use a smart TV to watch
a video stored on his or her smartphone. Figure 1 shows the overall webinos
architecture relevant to this scenario.
Since the smart TV is webinos-enabled, a web application running on the TV
can make the appropriate API calls to request the video from the smartphone.
1
webinos is an EU-funded project and affiliate program aiming to define and de-
liver an Open Source Platform and software components for the Future Internet
http://www.webinos.org
Fig. 1. Architecture of webinos — showing only the components discussed here
As part of this process, the TV must establish a secure communication link to
the smartphone as shown in Figure 1. The key webinos components shown in
the figure are explained below.
Certificate Manager — The certificate manager component provides func-
tions for generating cryptographic keys and certificates for use in Transport
Layer Security (TLS) connections. The implementation of this component relies
on OpenSSL and runs on all webinos enabled devices. The component exposes
a genRSAKey function, which returns either a 1024 or 2048 bit RSA keypair.
Key Store — The keys generated by the certificate manager and any pass-
words used in webinos are stored in a keystore. This allows for secure storage
even across platform reset events. In the webinos architecture, the keystore func-
tionality is provided using native platform mechanisms such as gnome keyring.
TLS Server — A TLS server is instantiated as part of webinos to support
both client-server and peer-to-peer device connections. The server uses a secret
key from the keystore and the cryptographic primitives provided by the underly-
ing node.js platform which in turn uses OpenSSL to establish TLS connections.
3 Trusted Execution Environments
Various hardware-based mechanisms have been developed to provide enhanced
security guarantees by building on well-established security principles such as
defence in depth, least privilege and isolation. An architectural pattern that has
emerged from these mechanisms is the Trusted Execution Environment (TEE).
The fundamental concept of a TEE is that it allows specific software opera-
tions to be executed in isolation from the rest of the system. At present, the
most common use case for a TEE is to provide a root of trust for other as-
pects of the system by performing certain security critical operations such as
the management and storage of cryptographic keys in the TEE. Due to the
hardware-enforced isolation from the rest of the system, it is possible to trust
the software executed in the TEE without having to trust any other software on
the system. In some cases, it is also possible to prove the degree of isolation to an
external entity. Various implementations of the TEE architectural pattern have
been developed for different platforms by both industry and academia including
the Flicker research project [4] and ARM TrustZone technology [1].
ARM Trustzone is a security technology that provides a hardware-enforced
TEE on ARM platforms. Trustzone is implemented as a set of security extensions
on certain processor cores based on the ARM version 6 or version 7 architec-
ture [1]. As shown in Figure 2, Trustzone partitions the platform hardware into
two distinct worlds, namely the normal world and the secure world. With the
support of other TrustZone-enabled platform hardware elements, this ensures
that components running in the normal world do not have access to resources
belonging to the secure world. The general approach is to run a minimal secure
kernel in the secure world in parallel with a feature-rich OS in the normal world.
Fig. 2. ARM TrustZone Software Architecture [1]
By implementing TrustZone as a processor extension, it is possible for a
single core to execute both the normal world and the secure world in a time-sliced
manner thus eliminating the need for a separate security co-processor whilst still
ensuring full isolation. Transitions between the normal and the secure worlds
are managed by a secure software component running in a new processor mode
called secure monitor mode, shown as the Monitor in Figure 2. Whilst TrustZone
hardware is already available, the software required to use this functionality is
still in a state of flux. Recently, the GlobalPlatform consortium released the
GlobalPlatform TEE API Specification [2], in an effort to standardize access to
TEE functionality across different devices.
4 TEE-enhanced webinos Architecture
The philosophy of enabling uniform and secure resource access across multiple
devices makes webinos a suitable platform for exposing secure hardware func-
tionality to web applications. The webinos platform already facilitates discovery
and access control for cross-device resource sharing. This platform uses the de-
vice OS and native applications to expose several APIs to webinos widgets (web
applications that run on devices). These APIs are an abstraction of the resources
provided by each device. We view the functionality provided by a TEE as another
type of resource that could be made accessible in a similar manner. We argue that
the security of web applications can be enhanced through the use of a TEE and
that the webinos architecture can be extended to provide this functionality to
web applications with minimal modifications. Figure 3 illustrates our proposed
webinos architecture enhanced with trusted execution in which the platform is
divided into an isolated secure domain for security-sensitive operations and a
feature-rich domain for all other operations.
Fig. 3. An architecture of webinos enhanced with TEE
4.1 Feature-rich Domain
The feature-rich domain includes the main device OS and the majority of webinos
functionality as well as any installed webinos widgets. The following components
from this domain are important in our enhanced webinos architecture:
OpenSSL with Modular Engine Functionality — Since version 0.96,
the OpenSSL library has been designed to support ENGINES [5] — modules that
can be dynamically or statically loaded to provide alternative implementations of
cryptographic functions. OpenSSL ENGINES are sometimes used for interfacing
with secure hardware such as a smartcard or Trusted Platform Module (TPM)2 .
The webinos TEE OpenSSL Engine — As shown in Figure 4, the we-
binos TEE engine is an OpenSSL ENGINE that runs in the normal world and
communicates with the secure world through the TEE client driver. This allows
2
https://github.com/ThomasHabets/openssl-tpm-engine
specific cryptographic operations to be performed in the secure world. In par-
ticular, the webinos TEE engine provides encryption, decryption and signature
operations using keys that are only accessible in the secure world. These keys
are referenced using key id fields as shown in Listing 1.1.
Listing 1.1. Sample of cryptographic operations provided by webinos TEE engine
i n t w e b i n o s p r i v a t e e n c r y p t ( char ∗ key id , ...);
i n t w e b i n o s p r i v a t e d e c r y p t ( char ∗ key id , ...);
i n t webinos sign ( char ∗ key id , . . . ) ;
4.2 Secure Domain
The enhanced architecture uses the principle of least privilege to isolate a secure
domain from the feature-rich domain. The following aspects of the secure domain
are important in our enhanced architecture:
Secure kernel — The secure kernel provides common functionality for the
secure domain and ensures that all operations in this domain are completely
transparent to the feature-rich domain. The secure kernel also enforces strict
isolation between different trusted applications in the secure domain.
Trusted webinos application — The trusted webinos application is re-
sponsible for authenticating the source of the requests from the feature-rich
domain. This could be achieved by inspecting the requests or using technology
similar to the integrity measurement architecture (IMA) as described in [6]. This
trusted application also provides key life-cycle management functionality. This
application is based on the GlobalPlatform TEE Internal Specification [2], but
can also utilize the cryptographic library included in the secure domain.
Secure domain cryptographic library — The kernel in the secure domain
is built with support for cryptographic functions. This is provided by libraries
such the OpenSSL or PolarSSL that have been installed in the secure domain.
5 Case Study: Securing TLS Sessions
It is informative to consider the scenario introduced in Section 2 because it
involves a complete life-cycle of a cryptographic operation, which is a common
scenario in most Internet-connected systems. We consider how TLS sessions
are established using the enhanced webinos architecture. This process involves
securely generating, storing and using cryptographic keys in TLS connections as
shown in Figure 4.
In order to demonstrate the feasibility of realizing this new architecture,
we have undertaken an investigation to understand how webinos makes use of
cryptographic operations and we have performed a preliminary experiment in
which an OpenSSL engine is modified to take advantage of functionality provided
by a TEE. In this experiment we do not explicitly consider secure persistent
storage of cryptographic keys. This could be achieved using functionality from
the GlobalPlatform specification (e.g. TEE CreatePersistentObject) [2] and
supported by technology such as a TPM MOBILE also running in the TEE [7].
Fig. 4. The workflow of webinos when enhanced with TEE
5.1 Development Environment
The OpenVirtualization project3 aims to create an open source software stack
from TrustZone that implements the GlobalPlatform TEE API [2]. In order
to accelerate the development of TrustZone software, Winter et al. [11] have
created a software development and emulation framework for ARM TrustZone
as part of the SEPIA research project. This framework includes a modified port
of the qemu-system-arm processor emulator that supports TrustZone extensions
for certain ARM processors and is available as an open source project called
qemu-trustzone 4 . In order to develop a proof-of-concept implementation of our
enhanced architecture, we use a combination of the OpenVirtualization software
and the qemu-trustzone emulator. The OpenVirtualization project provides a
software development kit (SDK) for building the normal world and secure world
kernels. At present, the SDK only supports Linux 2.6.38-rc7 as the normal world
kernel and so we are using a Debian “squeeze” root filesystem image for the ARM
architecture. We have successfully built the OpenVirtualization images, as well
as the normal world and secure world kernels and have run the system using
qemu-trustzone. We have used this emulated system for our initial experiments
and obtained some preliminary results as described in the following section.
6 Evaluation
In this section, we evaluate the extent to which our enhanced webinos archi-
tecture makes TEE functionality available to mobile web applications. webinos
provides an abstraction layer, in the form of APIs, that enables web applications
3
http://www.openvirtualization.org/
4
https://github.com/jowinter/qemu-trustzone
to make use of resources and services provided by other devices. Building on this
approach, there are two primary ways in which webinos can be used to bring
the security benefits of a TEE to web applications: The first is to provide direct
access to TEE functionality through dedicated APIs and the second is to en-
hance the security of current webinos APIs using TEE. An example of the first
approach would involve extending the Secure Elements API in webinos [10] to
allow access to TEE functionality. An example of the second approach would be
to redesign an existing component such as a policy manager so security-sensitive
parts of the component are executed in the secure domain. By leveraging open
standards upon which webinos is built, the enhanced architecture, therefore,
enables TEE functionality to be exposed to web applications in a platform neu-
tral manner. This allows web applications to use the same interfaces to TEE
functionality across different devices, leading towards cross-platform security.
Although the implementation of the architecture is ongoing, preliminary re-
sults are promising. We have successfully run webinos in the normal world OS
and have proxied all cryptographic functions through the engine with minor mod-
ifications. We are able to make calls to the secure world using the TEE client
library provided by the OpenVirtualization SDK and have successfully built part
of the OpenSSL library into the secure world. We are currently implementing
the communication interfaces between the engine the secure domain. One of our
objectives is to demonstrate the feasibility of implementing this proposed archi-
tecture and, as discussed in the previous sections, this appears to be feasible and
will only require minimal changes to webinos or the underlying node.js platform.
Another important consideration for this kind of architecture is system perfor-
mance. Using the current implementation, a preliminary performance analysis
has been performed to determine how this compares to other implementations
such as [6]. The overall performance of the system in [6] is limited by the perfor-
mance of a separate cryptographic co-processor, the TPM, which has not been
designed as a high-performance device. In [6], the overall time taken for the pri-
mary cryptographic operation (an RSA signature operation) was in the order of
1000 milliseconds but in our current experiment, preliminary tests have shown
that the equivalent operation can be performed in the order of 10 milliseconds
because all computations take place on the main CPU. This level of performance
latency would be essentially unnoticeable in web applications because it is lower
than average communication latencies over the Internet. Although this result
has been obtained using the TrustZone emulation framework [11] on a different
hardware architecture, we expect to demonstrate similar results on real-world
hardware in the near future.
7 Conclusion
Web applications make use of resources on mobile devices such as cameras or
navigation systems to create an interactive experience for users. As a result,
they are becoming an attractive channel for attacks against mobile devices. Web
applications can take advantage of platform features such as Trusted Execution
Environments to protect sensitive information. However, TEE features are nor-
mally provided at a low level of abstraction and so in order for these features
to be useful for web applications, a platform independent and standards-based
approach is essential. We have proposed, demonstrated and tested an enhanced
webinos architecture augmented with ARM TrustZone technology. Although this
work is ongoing, preliminary results from our experiments are promising in terms
of feasibility of implementation and system performance.
Acknowledgements
The work described here is funded by the webinos project with collaboration
from the SEPIA project. The authors thank Johannes Winter, Ronald Toegl
and Martin Pirker for their support and insights on TrustZone technology and
qemu. We also thank the OpenVirtualization community and support team for
their assistance. Andrew Paverd is funded by the Future Home Networks and
Services project sponsored by British Telecom.
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