Jarkko Holappa, Reijo Savola
VTT Technical Research Centre of Finland, Kaitoväylä 1, FIN-90570 Oulu, Finland
Keywords: Digital television, MHP, security threats, digital convergence.
Abstract: Digital convergence is introducing more diverse digital television services. The return channel, which
enables interactive television, is a key to this development and may be considered the most vulnerable
element of the terminal device in terms of information security. Accordingly, its protection from threats
brought about by Internet use, such as malicious programs, is of the essence. Multimedia Home Platform
(MHP) is one of the most important technologies enabling interactive television. The information security
threats related to it are examined from the viewpoint of the service developer. Threat analysis presented in
this paper is carried out in Finnish companies that include digital-TV broadcasters, MHP-platform
developers, service developers and telecom operators.
As a service environment, digital television places
very high requirements on the usability and
information security solutions. The user group is
highly heterogeneous, ranging from children to
senior citizens. One cannot make many assumptions
regarding the level of information technology know-
how this group possesses. Usability of state-of-the-
art terminal devices is not fully sufficient. For
example, the consumers’ trust in the new media is
not increased by inconsistent practices in software
updates of terminal devices, carried out other than
within the program stream.
The trend for digital convergence is also
present in digital television solutions – mainly as
convergence of the return channel with other
channels of digital content distribution. The services
are integrated with different kinds of systems and
networks, resulting in a situation where there are
environments that have been developed using
different types of practices and quality standards.
The goal of this study is to increase awareness
of information security threats connected with
digital television in different phases of the service
development cycle. Focus is on security solutions
with the Multimedia Home Platform (MHP) and a
return channel. The research methods employed in
this study include interviews with Finnish and
European industrial companies, literature searches
and extensive rounds of commentary among experts
of the domain area. A more complete discussion of
the interview results is presented in (Holappa et al.
Digital television in Finland and most of the Europe
is based on the DVB (Digital Video Broadcasting)
standards (DVB 2005). Terrestrial networks use the
DVB-T standard, cable networks utilize DVB-C and
satellite broadcasts are based on the DVB-S
standard. Mobile handheld devices can receive
digital television broadcasts using the DVB-H
standard, which is based on DVB-T. The above-
mentioned standards mainly differ from each other
in the modulation techniques that are optimized to
the appropriate transport path, and end-user
equipment differs correspondingly.
For the time being, data stream in the digital
television network is mainly transport of audio and
video using DVB techniques in a dedicated network
from broadcaster to receivers. In addition to audio
and video it is possible to transfer data and produce
data services. Audio and video is encoded in the
broadcast system and combined into one MPEG2-
bitstream in a multiplexer (ISO/IEC IS 13818-1,
2000).. One bit stream is known as multiplex. In
addition to audio, video and signaling information, it
is possible to transfer data using Internet Protocol
based services (Södergård 1999), (FICORA).
Holappa J. and Savola R. (2006).
In Proceedings of the Eighth International Conference on Enterprise Information Systems - ISAS, pages 508-515
DOI: 10.5220/0002493505080515
2.1 Multimedia Home Platform
At the moment, MHP (Multimedia Home Platform)
(ETSI 2002) based services are broadcast in
Germany, Italy and Spain, of which Italy is
considered the frontrunner in the introduction of
MHP services. MHP pilot projects and declarations
of supporting MHP are being made in almost every
European country.
MHP is an open standard and defines a general
purpose interface between interactive applications
and digital television receivers. The applications are
written in Java programming language and XHTML
markup-language, in which case a Java-based
browser is transported in the DVB stream. This
enables platform independency at both the hardware
and operating system level. The MHP architecture is
defined on three levels, as described in Table 1
(ETSI 2002).
Table 1: Parts of the MHP architecture.
Layer Task
Resources Demultiplexing of MPEG-formed signal,
processing of audio and video signal, I/O
devices, CPU, memory and graphics
Uses resources in order to offer a higher
level view from the platform to the
Applications MHP implementations include application
management (“navigator”), which directs
the MHP platform and applications run on
The MHP standard has three different kinds of
profiles, as presented in Table 2.
The profiles are defined to ease implementation
of the standard. Each profile denotes the application
area and the capabilities of the receiver.
Table 2: MHP Profiles.
MHP Profile Description
The profile was made to comply with many
existing middleware systems and receivers
without a return channel.
This profile includes receivers that have return
channel capabilities. It is possible to download
applications from the DVB stream. Interactive
behaviour is also supported in the application
programming interfaces.
The most advanced profile in the MHP
standard. The profile concentrates on using
Internet content with a digital television
receiver. The Internet access profile defines a
resident browser application to the receiver, as
well as the interface for management of the
Internet use of an MHP device hardly ever
replaces a PC. Resource limitations, restrictions of
user interface and possible restrictions related to the
return channel, for example regarding used
protocols, delimit the Internet content to rather
simple email and net surfing types of applications –
e.g. network services offered by banks.
From the end user’s point of view, digital
television’s interactive features are based on the
MHP1.0.2 standard. MHP1.1 is a newer standard
that enables downloading of the applications via a
return channel, whereas MHP1.0.2 enables
downloading only via the DVB stream.
2.2 Digital Television Receivers
The most important factor in interactive service
popularization is that terminals, in other words set-
top boxes, become more general. The first set-top
boxes offered basic features for receiving digital tv
broadcasts, and models equipped with a card reader
also enabled receiving pay channels. The terminals
of the second development stage can be counted as
set-top boxes with hard drives that enable recording
programs (PVR, Personal Video Recorder) and so-
called time-shifting, in which the viewer interrupts
the tv programme for a phone call, for example, and,
after the phone call, continues viewing from where
he was interrupted. The current terminals that back
up the MHP standard do not include a hard drive.
The third development generation brings along a
genuine interactive set-top box – in other words, a
device according to the MHP1.1 standard. This
diversifies the service offering and pay content.
Convergence with the current Internet world
diminishes with the interactive channel.
2.2.1 Software Updates
New features can be updated or errors in earlier
versions of the software can be corrected through
programs on the terminal. Software updates can be
delivered with the broadcast stream. This function
enables the utilization of new features (within the
limits of the equipment functionality) of the MHP
standard as it develops. Software updates are not
being sent constantly, but they are available for a
limited period of time. Because of this, the device
manufacturers have made various solutions with
which updates can be carried out by, for example, a
maintenance company. Where information security
is concerned, the software updates are mainly a
threat to the functionality; an erroneous update can
mess up the functionality of the terminal so that only
a maintenance company or the equipment
manufacturer can restore it. Distributing erroneous
software updates on purpose can also be considered
a threat if the attacker is able to falsify the broadcast
with another transmitter.
Value-added services are applications that are used
with the remote control of the terminal and, for
example, with a keyboard. Most of the value-added
services are implemented as MHP applications. The
applications can either be installed in the device
already or they can be transmitted with the program
stream (MHP1.0) or downloaded through the return
channel (MHP1.1). This chapter briefly presents the
most common value-added services that are in use at
the moment (ArviD).
3.1 Programme Guide
EPG, Electronic Programme Guide, is the most used
and most important value-added service. With the
programme guide the viewer can browse
information about programmes and optionally
follow a tv programme at the same time. The user
interface is simple and is used with the colour and
arrow keys of the remote control. The functioning of
the guide is based on the SI (Service Information)
data sent along the broadcasted stream. The
programme guide can be implemented as built into
the receiver or as an MHP application. The
information on the programmes is updated regularly
so the receiver can tune into the right channel.
3.2 Super Teletext
Super teletext is a renewed version of the old
teletext. The user interface is super teletext browser,
page definitions are made with xhtml and CSS. In
addition to the traditional page numbers, navigation
on the pages can also be done by means of links
embedded in the text, so the browsing is very similar
to reading www pages. Super teletext requires an
MHP-compatible terminal.
3.3 Programme-Specific Services
Typically, programme-specific services can be used
only during the programme broadcast or the
availability is otherwise restricted for certain types
of transmissions, such as during the Olympics.
These kinds of services are quizzes, games and votes
related to the programmes, the results of sports
events or elections, and super teletext pages related
to the programmes.
3.4 Channel-Specific Services
Channel-specific services do not relate to any
programme, but they are always available when the
receiver has been tuned to the right channel. These
kinds of services can be news and stock rate services
or giving feedback to the channel. The programme
guide and super teletext are channel-specific
3.5 Services Requiring a Return
When the receiver has a need to communicate with
the service provider, a return channel is required.
These kinds of services are the previously mentioned
voting and feedback services. In the future, services
familiar from the Internet, such as email, banking
services and electronic commerce, will be the most
attractive from the consumer point of view.
Information security requirements are emphasized
when using these kinds of services.
In this section, we present a threat analysis
concentrating on security threats to digital television
world based on previous studies and industrial
interviews. These threats can be roughly divided into
threats to the digital television transmission network
and terminal device, threats to the management of
the return channel, threats due to digital convergence
and threats to service development. Table 3 depicts
this division along with simple examples in each
category and affected technologies.
Table 3: Examples of the threats against different targets.
Threat target Example Related
Downloaded faulty
software update
(containing e.g.
software bugs or
being damaged
A program signal
contains errors that
the set-top box is
not able to handle or
malware to terminal
device and its
execution in full
access privileges
because of the lack
of certificate checks.
Inadequate testing
of software
problems between
different versions of
4.1 Threats to Transmission
Network and Terminal Devices
Security threats to DVB are rather small. This is due
to the fact that the data transfer (mainly voice and
picture) is done under operator control. There are
almost no threats during the packeting and
distribution phases because the operator can monitor
and, if needed, interfere with them. From the
operator point of view, the most likely threats are
connected to the program production phase and
consumption phase, as well as to devices. However,
the number of stakeholders is increasing in the field
and, because of this transmission management is
becoming more challenging.
In practice, interception of DVB-based traffic is
still difficult for an outsider, but not impossible. It is
possible to try to forge the transmission by another
transmitter. DVB-T transmissions are based on
COFDM (Coded Orthogonal Frequency Division
Multiplexing) modulation, characterising
elimination of multipath fading in a way that the
receiver synchronises with the clear signal. In a
cable television network this enables transmission of
an intrusion signal to the receiving point using small
powers (some Watts), but the receiving point cannot
be too far away. Another threat concerning DVB is
sending flawed data during an update of system
programs. Using device protection mitigates this
threat – for example, a flash memory of in a terminal
device is only deleted after the new program has
been verified.
General threats to smart cards and payment
services are targeted to the payment service used by
digital television,. In satellite television devices
smart cards keep piracy and unauthorised use
moderate, despite the fact that the system is not
optimal as card updates are too expensive.
There are more important security threats in the
use of MHP. MHP version 1.0.2 currently limits the
interactive use of digital television. However, digital
television environment will become closer to the
Internet environment after the deployment of MHP
version 1.1. For the time being, there are no
available terminal devices or services that conform
to MHP 1.1. An analysis of the threats connected
with this standard is needed at the same time as the
technology is deployed. It is also likely that as MHP
becomes more common, the third-party components
used in the MHP devices will also become more
common. In this case it is theoretically possible that
an intruder could infiltrate a malware program to the
MHP application without the service developer
knowing about it.
Nowadays it is possible to load MHP
applications into a device only from the transmission
stream. In this case the operator is responsible for
security. Applications loaded into the so-called
Object Carousel are typically added manually,
although there are some automatic systems. The
manual addition of applications guarantees that
control over how the services are made available to
the users. On the other hand, this can cause human
errors. Although the loaded applications are added
manually, they are often connected to a local area
network. If an intruder can access this network, there
is at least a theoretical opportunity to control the
Carousel and transmit unauthorised material.
The MHP standard itself is open to many
interpretations. The interoperability of MHP
applications in different device models is still under
development, particularly in the case of MHP
standard version 1.1. This is slowing down the
process of application development and adding
potential security threats due to false interpretations.
Digital signatures can strengthen MHP security.
The digital signature process consists of three parts:
compression files, signature files and proof files.
Signatures are the best that state-of-the-art solutions
can offer for ensuring that the contents have not
been modified. An application signed by the Root
Certificate Authority is attached to the so-called
Permission Request File with information on which
resources can be used by the application. The Root
Certificate Authority for MHP is currently WiseKey
SA. In Finland, the practice of using signatures is
only just about to start. It is likely that the signature
certificate will be given to a big stakeholder. In this
event, smaller stakeholders will not need a
certificate of their and will be able to operate under a
network operator’s certificate. However, all
certificate holders will be responsible for their own
Currently, the main challenge to the use of
certificates is the underdevelopment of the terminal
devices – most of the digital television transceivers
do not have root certificates. This has resulted in a
situation where the signature checking and access
control of applications have been disabled by the
device manufacturers. Contrary to the MHP
standard, it is possible for an unsigned application to
open a return channel to implement modem
hijacking or change the channel.
Special care and attention is needed and the user
must check the functions based on the certificate
information. The device should have a mechanism
for these kinds of checks – e.g. if a certificate is
jeopardized, the equipment should be updated to
cope with the changed situation. In another case the
whole chain of programs could be jeopardized. It
can be assumed that most of the users are not
capable of carrying out the task of checking
functions. They will carry out a random act that
mostly grants permissions. The whole mechanism
requiring user intervention is a threat from the user’s
perspective and the implementation of it should be
carefully analysed by the service provider and
device manufacturer. Other important security
features of MHPs are resource use permissions and
channel-oriented security features. If these features
are used in the right way, the current technology is
relatively secure.
4.2 Management of Return Channel
and Threats due to Digital
The most of the security threats to the return channel
are due to the use of Internet Protocols. Because of
the trend for digital convergence, the digital
television transceivers are becoming more versatile.
To a certain extent, this becomes similar to a PC –
the models with hard disks offer storage space, the
return channel types are becoming more versatile
and the processing power will be increased in the
future. However, because of different usage, there
will be always differences to PCs. From the point of
view of resources, a digital television transceiver
will not be similar and will only follow the evolution
of PCs.
Most of the information security risks for digital
television are connected with the return channel. The
TLS (Transport Layer Security) protocol is normally
used to protect the return channel, resulting in
encrypted traffic. Unlike a www browser, the MHP
application opening the TLS connection does not
verify the server certificate (e.g. time of validity)
because the current terminal devices do not normally
have a root certificate, which is needed for the
verification; the root certificate can be transmitted
along with the application. However, this is not
compulsory and there is a chance that the certificate
chains are generated by malware.
The simplicity of set-top boxes makes them
more secure. For example, it is not reasonable to
carry out port scans in simple devices, as the devices
do not have applications worth connecting.
In practice, the most important technical
solutions for the digital television return channel at
this moment are the HTTP and HTTPS protocols,
and XHTML – which is an enhancement of the html
language based on XML. The appearance of
XHTML is more strictly defined than HTML. HTTP
is a relatively simple protocol and its
implementations in the Internet world are rather
robust. Typically, most of the problems are due to
extensions of HTML and the management of
protocols and file formats transferred over HTTP.
Implementations of these modified versions of http
introduce threats to the development of digital
television too. Cookies are a privacy threat for the
users if they are used to build up user profiles and
habits. The return channel of digital television
includes a lot of content transferred over HTTP, like
XHTML, picture formats (GIF, JPEG, PNG), MPEG
and font format PFR (MHP).
At least the picture formats are rather complex.
There have been vulnerabilities in the management
of picture formats, where the application can be
seized with a malicious input.
The threats to HTML are connected to the
reliability of their parsing implementations. Lately,
this has been taken into focus. Vulnerabilities have
been found in some parsing implementations of web
browsers; similar vulnerabilities have not been
found in XHTML and XML implementations.
The level of information security solutions in
html extensions varies a lot. In addition to the
HTML protocol, there are different vulnerabilities in
browsers that are complex programs. The threats are
due to different active content-producing extensions,
such as Java, Javascript, ActiveX and Macromedia
Reliability and easy manageability of HTTP
extension implementations are critical. The
functionality of HTTP extensions should be able to
be clearly restricted. Currently, there are no
extensions like this in the MHP standard.
Service developers and terminal device
manufacturers have an interest in increasing the
functions that use the return channel in digital
television devices, especially different payment
services like shopping and movie subscription
services. The security threats to these kinds of
services are similar to the threats to Internet banking
and shopping services, and similar guidelines should
be followed in their development.
It can be noted that the security threats for end
users will be more emphasized in connection with
the trend for terminal devices becoming more
developed and more common. If the devices become
more and more like conventional PCs, it is likely
that the normal PC threats will also appear in the
digital television world.
Along with the deployment of MHP 1.1, the risk
of introducing viruses into set-top boxes is
increasing. As digital television transceivers become
more common, virus writers will be more interested
in them. The typical goals of malware developers
are, e.g., converting devices to act as vehicles of
denial of service attacks or as an automatic
transmission point for set-top box spam. State-of-
the-art set-top boxes and their applications are based
on Java. Consequently, the security issues in Java
concern them too. For the present, the Java programs
used in MHP operate in their own protected
environment, the so-called sandbox. The goal of this
arrangement is that malware is not able to use the
admissible applications. For example, it is possible
to shut down the MHP part (Java virtual machine) of
a set-top box using a simple loop structure.
Independently propagating worms are not a
relevant threat today because there is no
functionality currently in use allowing the MHP
applications to be propagated among set-top boxes.
If email functionality is integrated into set-top
boxes, this threat will become concrete in the digital
television world as well.
The program memory of a set-top box is erased
during a channel change, preventing malware from
gaining a hold. However, MHP standard version 1.0
defines a so-called persistent storage interface that
enables a signed application to write files to the
long-term memory of the user device, even though it
is loaded into the device every time the application
is started. In addition, the inter-application
communication interface of MHP enables method
calls over the network using the Remote Method
Invocation (RMI) of Java. This makes the work of
an application developer easier because Java
methods running in another virtual machine and
computer can be called just like local ones, and there
is no need to think about application-dependent
protocols. An obvious security threat exists if the
transmission of method calls over the network is not
protected. However, the Java application of the
server end must create and employ the Java Security
Manager – otherwise the RMI classes cannot be
The state of the art of digital television services and
the service developer’s perspective were analysed in
the study by interviewing actors in the field in
Finland and elsewhere. In addition, the goals of
interviews were to investigate the value net of the
field of digital television, and the threats to its
different parts seen from the perspective of different
actors, and identify the special characteristics of the
service development process of digital television
services. Digital television programme production
can be divided into five main phases: programme
production, service production, packaging,
distribution and consumption. The questionnaire
presented in (Holappa et al. 2005) was used as the
basis for the interviews. This section summarizes the
perspectives brought out in the interviews.
During the interviews it was noticed that it is
essential to analyse the information security issues
connected with each phase, their potential problems,
threats and solutions.
Currently, the main security concern in the
digital television field is the security of the terminal
devices, the digital transceivers. The terminal
devices are quite vulnerable to erroneous data
stream. An example of this vulnerability was seen in
the spring of 2004 when an erroneous program
stream was damaging terminal devices in Finland
(Tietoviikko 2004). As MHP applications become
more common, the security of the terminal devices is
becoming more important. The issues to be solved
include authentication of the application, protection
of the terminal device (anti-virus software, firewalls)
and viewer privacy issues. A general view is that
with regard to information security, the buyer of a
terminal device is dependent on the device
manufacturer because the technical solutions are,
almost without exception, device-oriented, despite
the fact that there are standardised specifications for
the technical solutions. These specifications are
rather loose, enabling the same functionality to be
developed in various different ways. The
manufacturers end up with more exotic solutions,
especially when there is a need to make trade-offs
due to the restrictions of memory consumption and
computational power.
In general, the threats can be targeted at program
content, terminal devices and consumers’ privacy.
Especially harmful for the trustworthiness of
television broadcasting are malpractices connected
with the content – e.g. a situation in which the actual
content is replaced by forged content or the terminal
device is damaged by a program.
In many cases the attacks targeted at terminal
devices should be able to deal with implementation
details in order to succeed in all terminal devices.
On the other hand, different manufacturers’ devices
often use the same software components. For
example, the Java platform of MHP and the
operating system of the digital transceiver are such
large software entities that a terminal device
manufacturer often licenses them from third parties
or orders production licensing for the whole device
or software architecture from outside. Historically,
Java implementations have included many
vulnerabilities that enable the Java program to gain
broader access privileges in the target system than is
authorised, potentially offering access to the
underlying operating system and device.
Attacks that aim at breaking a certain
manufacturer’s Java implementation can be
considered more probable than attacks that target all
or many devices. For the manufacturer, the
possibility of these kinds of attacks contributes to a
remarkable financial risk. Breaking certain terminal
devices is a marginal problem and an attack targeted
at all devices is not so probable due to the diversity
of devices. From the end user’s perspective, the
attacks aimed at certain manufacturer’s devices do
not cause a remarkable financial or political risk.
Threats targeted at consumer security, such as spam
and privacy violations are more critical for the
Nowadays the threats to the system do not
address large groups of consumers since the number
of true interactive services is still relatively small.
However, as interactivity in digital television
increases, the information security issues focus
especially on the terminal device and return channel.
In particular, the end users’ position regarding
information security should be given more attention
as interactivity becomes more common. For the
purposes of the security analysis, the most essential
standard in the field is MHP
According to the interviews, digital television
broadcasting was considered close co-operation
between some central actors, but the need for co-
operation co-ordination was seen during the process
of the actor net getting larger and larger. In the near
future the group of actors is probably going to
change due to the number of services getting bigger
and the trend for increasing interactivity in the
digital television broadcasting field. So far the
markets have been rather limited, and, because of
that, the R&D effort on information security issues
has been minor.
Risk management is a central activity in service
development. A thorough analysis of risks is needed
in connection with an analysis of which of them
needs actions. It is not possible to protect against all
risks, neither it is financially reasonable. Reasonable
risk management is to involve an information
security specialist in the service development at the
design phase.
It was discovered in the interviews that at
present there are no remarkable deficiencies in the
Finnish or European legislation concerning
information security in the world of digital
television. However, we can note that in connection
with digital television reception the Privacy
Directive of Electronic Communications prohibits
the listening to and transfer of information about
such telecommunications information as channel
selection, time information, information about
commercials viewed or games played. In addition,
the developers of electronic services should take
particular account of the privacy legislation and the
regulations concerning electronic commerce.
From the privacy point of view, it has to be
remembered that, as a service platform, digital tv is
legally just like any other platform offering digital
services and the same regulations concern it. The
service developer is obligated to design features
concerning privacy and information security that are
so easy to use that the user can understand the
meaning of his actions and any possible related
responsibility issues. As a use environment, digital
tv is rather restricted, so the service developer has
great influence on how the end user can manage
information related to his privacy.
Information security means different kinds of issues
for different stakeholders – the emphasis on threats
varies in severity and solutions across different parts
of the value net. For the content producer, the most
important threats include unauthorised use and
distribution of programs or other content, and for the
network operator, erroneous program content
causing trouble in viewers’ devices. For the viewer,
threat scenarios include privacy problems and risks
of electronic commerce like theft of credit card
information. End user privacy threats in a service
provider’s products decrease the trust in this party
and actually become a threat to the continuity of the
service provider’s business.
Some of the current Internet world threats are
brought to the digital television environment
because of interactivity enabled by the MHP
standard profiles 2 (Interactive Services) and 3
(Internet Access). For the time being, the application
environment has been restricted and strictly under
the control of the digital television network
operators and broadcasting channels because the
applications come within the program signal. This is
going to change due to the emergence of MHP
version 1.1, enabling applications to be loaded via
the return channel.
Information security is a multifaceted issue,
including legal issues and human behaviour in
addition to the technical solutions – all dimensions
of information security should be taken into account
in the service development process.
The authors acknowledge a debt of gratitude to the
LUOTI programme (Development Programme on
Trust and Information Security in Electronic
Services) of Finnish Ministry of Transport and
Communications (MINTC) for funding. Ms. Päivi
Antikainen of MINTC and Mr. Kimmo Lehtosalo of
Eera Finland are acknowledged for helpful
comments and fruitful discussions, as well as all the
co-authors and interviewees of the study behind this
article – Their contribution to this work has been
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