LICENSE TRANSFER MECHANISMS THROUGH SEAMLESS

SIM AUTHENTICATION

Rights Management based on SIM Keys

Josef Noll, György Kálmán

University Graduate Center, UniK

Instituttveien 25, 2027 Kjeller, Norway

Ulf Carlsen

Agder University College

Grooseveien 36, 4898 Grimstad, Norway

Keywords: Content, access, license, user, SIM, home, NFC, DRM, device, network, authentication.

Abstract: Critical issues in the acceptance of wireless services are the authentication and authorisation to these

services. This paper presents the SIM as device for Mobile phone/SIM card based authentication. The

mobile phone can be used for physical access (admittance) and service access using near field

communication (NFC). It has the potential becoming the identity provider in the virtual/electronic world,

enabling wireless network access, VPN and Mobile Commerce application access.

The paper extends the seamless service access into the digital rights management, suggesting methods on

how the rights keys can be managed on the SIM card, while content remains distributed on the customer

devices. Final focus is on the requirements for future SIM cards in order to support the suggested methods.

1 INTRODUCTION

Authentication is the key for a customer relation,

and the entry for value-added services. The mobile

customer is used to having her mobile phone around,

and the SIM card opens for authentication and

encryption in every wireless network (Bluetooth,

WLAN, WiMAX) in addition to GSM and UMTS.

This paper applies not only to mobile networks,

but service access in mobile, wireless and near field

networks. Broadband penetration is expected to

reach 60 % in certain European regions in 2007, and

80 % of those households will built this home

network wireless (Noll, Ribeiro, & Thorsteinsson,

2005). The same paper suggests that centralized

network storage will be a focal point in private

homes. Together with the anticipated upstream

capacity expected from future broadband access, e.g.

ADSL 2+, this will lead to content usage at home

and elsewhere. Initiatives like the EU’s FP6 project

OBAN enable access to home content, based on

seamless network access in visiting wireless

networks (OBAN, 2006). As the user will have her

mobile phone around, we suggest to base both

network access, service access and rights

management on the SIM card of the mobile phone.

This paper will first justify why the mobile

phone has the potential to serve as an identifier in

the digital world. Having addressed the potential

home services and service scenarios, the paper will

provide an overview over current developments for

network and service access. Developments

addressing RFID/NFC and Bluetooth based

authentications, and functionality in the mobile

network through WAP gateway and Traffic

Analyser. The final part of the paper will address

rights management, based on near field, touch-based

authentication.

2 SIM BASED SEAMLESS

AUTHENTICATION

Access to content is based on the possession of the

material, typically a CD, DVD or a device carrying

the content. With faster access networks, digital

333

Carlsen U., Noll J. and Kálmán G. (2006).

LICENSE TRANSFER MECHANISMS THROUGH SEAMLESS SIM AUTHENTICATION - Rights Management based on SIM Keys.

In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 333-338

 SciTePress

content does not longer need to be carried around,

only the access rights have to follow the user.

In this paper we focus on methods of using

different identification mechanisms for the variety of

services. Service access is based on unique access

keys in the SIM card, and provided through wireless

communications to the identifier.

2.1 Security Demands

Depending on the content, access might be public,

limited to a group or limited to a single user.

Examples of public content are picture galleries.

Group limited content might be address databases,

private pictures or DVDs owned by the family.

Single user content is typically confidential, being it

access codes or eCommerce services.

The identification of the user should follow the

requirements of the application. We suggest

following the mechanisms suggested by the

Initiative for open authentication (OATH, 2006), i.e.

SIM authentication (SIM), Public Key Infrastructure

(PKI), and One-Time-Password (OTP).

The mobile phone has the capabilities of

providing all of them: SIM, PKI and OTP, and thus

may provide the security requirements for various

applications in the virtual world.

2.2 Service Access

SIM authentication is already used as transaction

receipts for content download, e.g. ring tones.

Including authentication methods through Bluetooth

and Near Field Communications (NFC), SIM-based

authentication opens for all types of service access,

providing admittance (keys, access cards, and

tickets), payment (wallet) and content access

(home). Examples of such services are presented in

figure 1.

Bonus card

Wallet

Keys

Monthly pass

Content

access

Ticket

Access card

Electronic

Figure 1: Examples of service access through SIM in near

field, personal area, wireless and mobile networks.

2.3 Home Content Access

Somogyi (2006) extended the seamless

authentication to personalisation of services. The

WAP gateway (see figure 2) adds an information

string to the http header, which is forwarded to the

content server. The string contains both information

WAP gatewayWAP gateway

Figure 2: Mobile Network (WAP gateway) authentication

with user and device identification.

on the user and the device requesting the service.

The user (x-nokia-alias) is represented through a

md5 hash of the mobile ID (MSISDN), and the

device is represented through a device identifier

(mobile phone type).

The seamless SIM based authentication was

demonstrated for various types of home content: a

photo gallery, music and community address book.

2.4 Touch Authentication Through

NFC

Adding Near Field Communications (NFC, 2006) to

the phone extends the capability of service access to

proximity/vicinity based applications (see figure 1).

Payment and admittance are two potential services

enabled through NFC (Lopez Calvet, 2005). NFC is

a specific RFID implementation, bringing the

physical world and the electronic world together by

help of radio frequency identification (RFID).

The established standard uses 13.56 MHz as an

operating frequency, and incorporates the ISO/IEC

standards 14443 for proximity card operations,

ISO/IEC 15693 for vicinity card operations. This

paper investigates in further details the split of

radiofrequency (RF) and identification (ID). We

suggest moving the ID into the SIM card, and leave

the RF in the device (see figure 3).

Moving the ID handling into the SIM card

provides various advantages for authentication and

DRM management:

• Collection of security items (keys, admittance,

identity) in one place makes the solution

convenient for the user

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• Replacement of user devices without loosing

credentials

• Device independent DRM management

• Advanced protection for misuse, as the SIM

can be disabled remotely

• Potential for backup/restore functionality

The major challenge is the standardisation of the

interface between the RF (= NFC communication

unit) and the SIM card, indicated as NFC2SIM

interface in figure 3. Standardisation of the interface

is ongoing, but does not cover DRM handling yet.

Smartcard interfaces

ISO/IEC 7816

NFC

communication

unit

SIM

NFC

reader

NFC2SIM

Figure 3: NFC communication with split functionality: RF

in the device, and ID handling in the SIM card needs a

new interface between NFC and SIM (NFC2SIM).

The following chapters suggest the functional

architecture, and state requirements both for the

interface and the SIM card.

3 NFC AND SIM BASED RIGHTS

MANAGEMENT

This chapter describes rights management based on

communication and security functionality of the

NFC equipped mobile phone. It will first suggest a

functional architecture for rights management, and

will then postulate in detail the requirements for

license transfer.

3.1 Functional Requirements

The functional requirements are based on the

following assumptions:

• Content will be available in a digital form.

• A variety of devices will access content.

• A ubiquitous network allows content access

wherever the user is.

• The SIM card is the secure place to store

identities and access rights.

• The user owns the SIM, access/content

providers will install access keys to the SIM.

• Rights Management is delegated to the SIM.

Figure 4 represents the steps for content access

fulfilling the functional requirements stated earlier.

We have selected access to home content as

example, suggested by Noll, Ribeiro &

Thorsteinsson (2005).

Internet

Home access,

.mpg, .mp3, .jpg

NFC

communication

unit

SIM with

DRM keys

NFC2SIM

4. Request DRM key

for selected content

5. Return DRM key

1. Request for home content

2. Seamless authentication and

redirect to personalised content

3. Streaming of

encrypted content

NFC

Internet

Home access,

.mpg, .mp3, .jpg

Home access,

.mpg, .mp3, .jpg

NFC

communication

unit

SIM with

DRM keys

NFC2SIM

4. Request DRM key

for selected content

5. Return DRM key

1. Request for home content

2. Seamless authentication and

redirect to personalised content

3. Streaming of

encrypted content

NFC

Figure 4: Functional scenario for SIM based DRM

handling of home content.

The access to home content contains the

following elements: The home content storage, the

media player, the personal device and the network

elements interconnecting the devices. The access is

performed in the following steps:

1. The user requests home content by

addressing his home content storage.

2. The user device is authenticated in a seamless

matter, and access to content is provided.

3. The content is adapted to the capabilities of

the media player and network capacity, and

streamed to the media player.

4. The media player asks for an authentication

from the personal device, here NFC.

5. The personal device provides authentication

for decryption of content in the media player.

Steps 1-3 are realised in prototypical

implementations (Somogyi, 2006). Steps 4 and 5 are

challenging, as they include NFC as communication

medium, NFC2SIM as protocol for exchange of

information between the NFC and the SIM card, and

handling of DRM keys on the device in general. The

following paragraph will address DRM specific

issues in this solution.

3.2 DRM Specific Issues

This paper postulates the split of licensing keys and

content in a DRM management system. Such a

LICENSE TRANSFER MECHANISMS THROUGH SEAMLESS SIM AUTHENTICATION - Rights Management based

on SIM Keys

335

solution will enable the user to carry his content

rights wherever he goes, and allows content access

both on all media players. It will be more convenient

for the user, and enhance the acceptance for

licensing. Typical application areas are:

• Usage of content on any media player able to

handling the media format

• Purchase of licenses through mobile channels

• Distribution of gift licenses

• Permanent of time-limited transfer of licenses

from one user to another

• Backup/update/restore of license keys

The following chapter will address license issues

in DRM systems.

4 DIGITAL RIGHTS

MANAGEMENT

The purpose of DRM (Digital Rights Management)

systems is to ensure that digital objects and

resources can only be accessed in an authorised

manner. DRM enforces mandatory access control

(Reid & Caelli, 2005) typically on a per-content

basis, often extended with further limitations e.g. to

allow access for a limited timeframe only or to a

specific number of views or runs. RELs (Rights

Expression Languages) such as OMA REL (OMA,

2006) and (XrML, 2001) are used to state these

access conditions. The actual content is often

cryptographically protected, with decryption keys

and -attributes residing in the license. The license

therefore also needs to be protected both during

transfer and storage.

4.1 Mobile Licensing

Many DRM systems for mobile systems have been

proposed over the years, including OMA DRM

(OMA, 2006), Microsoft Windows Media DRM

(WinDRM, 2006) and Apple's FairPlay system.

OMA DRM and Windows Media DRM keep

REL-defined licenses separately from content. On

the other hand, FairPlay incorporates licensing

information into the music file itself. While self-

protecting documents can be convenient and hassle-

free from a distribution point-of-view (since the

license is always present together with the document

itself), maintaining licenses separately from the

content ultimately provides a greater flexibility with

regards to license updates, as licenses (if allowed by

the policy) may be renewed or forwarded without

also having to download the entire content once

again.

4.2 License Backup

The ability to carry out data backup is a fundamental

security requirement and principle. DRM systems

limit the backup of licenses, as they prevent

duplication of digital objects and/or their associated

licenses/rights, thereby precluding individuals and

organisations from implementing a proper backup

policy. For example, if a license is locked to a

specific device (i.e. node-locked) and this device

becomes defect, obsolete or lost, then

restoring/transferring the license to a new device

may not be feasible. A backup restore operation to a

different device (for a non node-locked license)

could equally well constitute an illegal duplication

of the license. Some licenses contain state

information which changes as the licensed object is

accessed. One such example is counter-based

licenses which allow a certain number of

views/executions of a licensed object. Since the

backup copy of this license generally does not

contain the most recent state information, a backup

restore would cause this state information to be lost

and therefore grant the user additional rights.

Ensuring compliancy between DRM solutions

and ordinary data backup principles is an important

but difficult challenge. If an object is split into a

protected content part (the licensed object) and a

license then the DRM system normally allows the

licensed object to be freely copied, duplicated and

backed up through any traditional techniques. There

is no danger of misuse since the licensed object can

only be accessed through its license. Such copying

can also be viewed as proliferation of the content,

and is supported by OMA DRM and Microsoft

Media DRM. The challenge is in the license

handling. OMA DRM allows licenses (which in

their terminology are called Rights Objects) to be

backed up and restored to the same device or to a

device in a defined device domain, and also

provided that the license does not contain dynamic

state information. Windows Media DRM includes an

option where licenses may be backed up and

restored on a different computer (WinDRMF, 2006).

Upon restore, a centralised fraud detection service

hosted either by Microsoft or the content owner

keeps track of the number of different

computers/devices onto which the license has been

restored. If a given threshold is reached the restore

operation is aborted.

The FairPlay DRM model integrates the

licensing information into the media itself. The

system opens up for a fair amount of copying,

allowing copying between any number of iPods and

onto CDs. However, direct copying from iPods onto

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other music players is prohibited. The DRM system

proposed in (Messerges & Dabbish, 2003) allows

copying of licenses within a defined family domain.

The backup/restore functionality of all these

systems have several shortcomings. The threshold

limit might through unfortunate circumstances be

reached/exceeded, or it might for good reasons be

set to zero (backup/restore is disabled) by a content

owner who does not wish to open up for any

possibility of potential illicit copying, e.g. because

the content has a high commercial value. Forming

and maintaining device domains will have an

administrative cost and might be a hassle-factor for

the user – and what will the rules be for allowing

new devices into a domain? If a domain cannot be

established and the device gets lost or becomes

obsolete, restore can not take place. If the license

contains stateful information, restore cannot take

place either. In sum, there are still quite a few

pitfalls which may hinder effective backup.

4.3 License Transfer

This section proposes a license transfer mechanism

and protocol which meets some of the challenges

pointed out above. It reconciles the apparent

conflicting requirements for maintaining license

backups while preventing license duplication.

Consider a single-user, unlimited license which

we may label L. For simplicity we ignore the past, so

the license will be valid from now and onwards, i.e.

within the timeframe [t

, unlimited〉, where t

denotes the current time.

The basic underlying idea is to consecutively

subtract sub-licenses from L: Initially a new license

is subtracted from L. L

is valid during an

appropriately short time interval

t=t

-t

, i.e. during

the timeframe [t

, t

〉. At the same time, the validity

of L is reduced accordingly, and is now valid for the

remaining timeframe [t

, unlimited〉. License L is

kept on an “online backup server”. L

on the other

hand is transferred securely via a piracy-proof

channel (i.e. a channel which does not allow

duplication or “double-spending” of the license L

)

to its destination device, for example the SIM card

of a portable phone, where it is consumed. Once L

expires, or preferably a short time before, either the

destination device requests a new license from the

backup server (license pull), or the backup server

automatically transmits a new license L

(license

push). This license L

is, and subsequent licenses L

, … are extracted from L in the same manner as

The same mechanism can be applied to other

license types, e.g. to time-restricted licenses, where

the license L now has a timeframe [t

, t

] for two

specific points in time (e.g. from 1.1. to 31.12.). A

time-restricted license could also be a duration

(e.g.

t = 30d) which is converted into a fixed

timeframe [t

, t

] upon first usage. For counter-based

licenses, the counter (e.g. 100 views or runs) is split

into multiple sub-counters (e.g. 10 x 10 views).

A cryptographic protocol which is suitable for

secure and duplication-proof transfer of license from

A to B is described in (Carlsen, Hammerstad &

Gorancic, 2003). This protocol has the properties

that the licensed is transferred no more than once to

the rightful destination token, and may never be

transferred to any other token.

The online backup server could be hosted by the

vendor / content owner. It could also be a smart card

which could then be located in the home domain

indicated in figure 4. The sub-licenses are

transferred to and stored on the mobile device SIM

card. Now, if the mobile device SIM card is lost or

corrupt the damage is reduced since only sub-

licenses are stored here. Furthermore, the time

interval

t can be made small to minimise the

consequences of a lost or corrupted SIM card.

4.4 Requirements for Future SIM

Cards

The paper has demonstrated content rights

management as a potential application for future

SIM cards. SIM functionality is not limited to DRM,

but can have a more general functionality, being the

security infrastructure of the user in the digital world

(Lopez Calvet, 2005). The basic requirement for

such functionality is that the SIM can act on behalf

of the user, supporting different roles and

functionalities. This includes 3

party security

applications, e.g. keys for admittance to buildings,

authorisation to banks and other legal entities.

We suggest using a hierarchical structure, where

the SIM has a master identity module (see figure 5),

which controls the secrets.

Such an identity module might be administrated

by a legal entity, e.g. a network operator, a bank, or

the state. It can then allow administrate secret keys

for other applications, e.g. update, backup, restore.

We see this functionality happen over a secure

channel over the air, and indicated the functionality

by over the air application (OAA).

Admittance and license management are two

items which will require clock (CLK) functionality,

LICENSE TRANSFER MECHANISMS THROUGH SEAMLESS SIM AUTHENTICATION - Rights Management based

on SIM Keys

337

as admittance or licenses might only be given for

certain time intervals.

CLK

I/O

system

CPU

Memory:

ROM

RAM

EPROM

VCC, GND, RST

Secure OAA

Identity

module

I/O

Figure 5: Requirements for future SIM cards: Secure over

the air applications (OAA) and identity handling of SIM

card, as well as clock (CLK) functionality for a.o. DRM

handling.

5 CONCLUSIONS

The mobile phone can be used for physical access

(admittance) and service access using near field

communication (NFC): It may act as the security

device in wireless network access, using EAP/SIM

and Bluetooth, or using the SIM credentials for VPN

and Mobile Commerce applications. The paper

extends the seamless access into the digital rights

management, suggestion methods on how the rights

key can be managed the SIM card, while content is

distributed on the customer devices.

This paper suggests basing both network access,

service access and rights management on the SIM

card of the mobile phone. With faster access

networks, digital content does not longer need to be

carried around, only the access rights have to follow

the user. The scenario used in this paper is the access

to home content, which contains the following

elements: The home content storage, the media

player, the personal device and the network elements

interconnecting the devices.

NFC is introduced to exchange information

including NFC as communication medium, and

NFC2SIM as protocol for exchange of information

between the NFC and the SIM card. Application

keys like access or licensing keys are stored on the

SIM, and are accessed through the NFC radio. While

current DRM systems implement and enforce

mandatory access control for a limited number of

devices, our solution suggests letting license keys to

be handled from a central user device, allowing

every media player to play the content. This solution

provides a greater flexibility with regards to license

updates, as licenses (if allowed by the policy) may

be renewed or forwarded without also having to

download the entire content once again.

This paper argues that current DRM licensing

techniques are less suitable especially for higher-

value assets where the demand for proper backup

technology and mechanisms will be required. A

license transfer mechanism and protocol which

meets the requirement for backup is proposed. The

technique reconciles the apparent conflicting

requirements for maintaining license backups while

still preventing license duplication.

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