Security ofSecurity of

Digital Rights Management SystemsDigital Rights Management Systems

Hugo Jonker

http://www.win.tue.nl/~hjonker/

Outline

• Introduction

• Supporting techniques

• Modelling DRM systems

• Security

• Closing remarks

Copyright in the digital era

Early content protection systems (e.g. cable tv, CSS):– Either full access or no access, no possibility to update access rights

– Content supplier also grants access rights

Current situation:– Digital versions of music/films/books (content) are being exchanged in various

(digital) manners

– Existing copy-protection measures (e.g. CSS) are not sufficient

New possibilities:– Desire to offer digitised content (e.g. over the Internet) whilst ensuring copy

protections after delivery

– Interest in offering tailor-made access to content

Legal situation Netherlands (2004): uploading bad, downloading not bad

Introduction

• copyright

• purpose

• description

• constraints

• state

Techniques

Model

Security

Closing remarks

Purpose of DRM systems

• A new content protection mechanism– As desired by those offering content

• Access control– Not just copy prevention

• Practical security– In absense of perfect security, settle for practical security (e.g. prevent “break

once, run everywhere”, updatable security measures)

Introduction

• copyright

• purpose

• description

• constraints

• state

Techniques

Model

Security

Closing remarks

General description of DRM systems

• Govern the distribution and protective measures of content– video, audio, tekst, graphics, software

• Content can only be accessed with a license– More precise: in adherence to a valid license, issued by a bona fide license

issuer

– License specifies the access rights

– License is typically bound to a device

– Unlicensed access to protected content should be impossible

• Network oriented technique– Internet, cable television, cellular phone, CD / DVD

Introduction

• copyright

• purpose

• description

• constraints

• state

Techniques

Model

Security

Closing remarks

Constraints

DRM systems (as we consider them) offer:

• No protection of analogue content– DRM protection ends when content has been rendered

• No payment mechanisms– As this can be considered a seperate problem

Introduction

• copyright

• purpose

• description

• constraints

• state

Techniques

Model

Security

Closing remarks

State of DRM development

Existing systems:– Apple: iTunes (music)

– Microsoft: MS Media DRM (music, audio/video), MS Reader (text)

– Adobe: eBooks (text)

Standards:– XrML, ODRL (right expression languages)

– <Indecs> (metadata)

– OMA (cellphones)

Developments by:– Open Mobile Alliance (cellphones)

– MPEG, OpenIPMP, SDMI, SMPTE, ISMA, OeBF, CRF, OASIS (IT industry)

Note: there is not one standard DRM system, nor a DRM system

which is market leader on all markets

Introduction

• copyright

• purpose

• description

• constraints

• state

Techniques

Model

Security

Closing remarks

Supporting techniques

Supporting techniques

General goals:– Updatability

– Interoperability

Specialised techniques– Content identification: DOI, watermarking, fingerprinting

– Stating rights: Right Expression Language, Rights Data Dictionary (REL, RDD)

– Cryptography: secure container

– Security enabling: hard/software Trusted Computing Base (TCB)

– Traitor tracing

Introduction

Techniques

• supporting techniques

• content identification

• rights expression

• cryptography

• TCB

Model

Security

Closing remarks

Content identification

Digital Object Identifier (DOI)– Lookup system using codes, similar to bar codes

– DOI number identifies content, but must be supplied with content

Watermarking– Embedding information in content without disturbing perception of content

– Embedded information can be used to identify content (e.g. a DOI)

Fingerprinting– Identifying content based on perceptual equivalence

Introduction

Techniques

• supporting techniques

• content identification

• rights expression

• cryptography

• TCB

Model

Security

Closing remarks

Rights expression

• Rights Expression Language (REL): syntax of the license

• Rights Data Dictionary (RDD): semantics of the REL

Two main contenders:

• Open Data Rights Language (ODRL)– open standard, supported by OMA

• eXtensible rights Markup Language (XrML)– proprietary standard from Contentguard, supported by MPEG, Microsoft

• Both are XML-based

Introduction

Techniques

• supporting techniques

• content identification

• rights expression

• cryptography

• TCB

Model

Security

Closing remarks

Cryptography

Various uses of cryptography

• In communications– Authentication, secure channel

• For a secure container– (possibly conceptual) container consisting of the encrypted content, metadata

describing content, and possibly access rights for the content

– Seperate encryption from key management

– Secure container can be exchanged unlimited

Introduction

Techniques

• supporting techniques

• content identification

• rights expression

• cryptography

• TCB

Model

Security

Closing remarks

Trusted Computing Base

Trusted computing base

• A component that provides a trusted platform on which

computations are performed

• Computations cannot be inspected nor disturbed

• Traditionally implemented in hardware (e.g. smartcards)

Software TCB

• conceptually impossible, but practically feasible

• Requirements:– code tamper resistance

– data tamper resistance (secure storage)

– key hiding

Introduction

Techniques

• supporting techniques

• content identification

• rights expression

• cryptography

• TCB

Model

Security

Closing remarks

Modelling DRM systems

Possible components

• Content packaging

• Media server

• License server

• Content registration server

• Authentication server

• Payment gateway

• DRM tools server

• User interface

Introduction

Techniques

Model

• possible components

• MOSES / OpenSDRM

• derived model

• process model

Security

Closing remarks

MOSES / OpenSDRM

ContentPackaging

server

Registrationserver

Authenticationserver

Licenseserver

e-Commerceserver

Media deliveryserver

DRM Toolsserver

Paymentgateway

connection

storage

player

video driver

audio driver

video card

display hardware

analogue out

sound card

audio hardware

analogue out

Server side User side

Introduction

Techniques

Model

• possible components

• MOSES / OpenSDRM

• derived model

• process model

Security

Closing remarks

Derived model (old)

packagerlicense

secure container

networkinterface

storage

playervideo driver

audio driver

video card

videooutput device

sound card

audiooutput device

network

trustedcomputing

base

distributor’s side

contentprovider

analogueoutput

user’s side

Introduction

Techniques

Model

• possible components

• MOSES / OpenSDRM

• derived model

• process model

Security

Closing remarks

Process modelIntroduction

Techniques

Model

• possible components

• MOSES / OpenSDRM

• derived model

• process model

Security

Closing remarks

Security

Security

• Intruder model– Typical intruder threat for entire DRM systems stronger than Dolev / Yao

– Dolev / Yao seems adequate for protocols

• Security goals– Theory focuses on complete(?) security

– Practice: not per se so strict• E.g. iTunes allows creating CD’s which could then be “ripped”

• Security requirements

Method

1. Stakeholder analysis• Establish core roles and incentives

2. Establish (high level) properties• Use concepts of DRM systems (see process model) to translate the incentives

into properties

3. Derive (low level) security requirements• Use process model

Introduction

Techniques

Model

Security

• method

• stakeholder analysis

• high-level properties

• security requirements

Closing remarks

Stakeholder analysis

• Parties: media company, developer, user, reseller,...

• A party can play more than one role

• Three core roles: user, license creator, content creator

• Incentives of the content creator– support new business models (e.g. bundling of content)

– Offer revenue-generating alternative to downloading (opens new market)

• Incentives of the license creator– Offering tailor-made access (new market)

– Low overhead compared to physical devices (CD / DVD)

• Incentives of the user– Legitimate and known-quality content (compared to downloading)

– Ease of use

– Pricing can be more fine-grained

Introduction

Techniques

Model

Security

• method

• stakeholder analysis

• high-level properties

• security requirements

Closing remarks

High-level properties

• Content creator1. Content is only accessible under the conditions of a valid license issued by a

bona fide license creator (includes binding of license to device)

• License creator1. The above

2. The impact of breaking the system must be constrained

• User1. Ordering licenses / content requires user participation

2. Content nor licenses can be linked to the user

Introduction

Techniques

Model

Security

• method

• stakeholder analysis

• high-level properties

• security requirements

Closing remarks

Security requirements

• Content cannot be eavesdropped

• Secure communications

• Content will only be rendered– if a valid license for the content and the renderer is available

– if all conditions of such a license have been met

• The manager / renderer ‘s inner workings cannot be influenced

• Secrets stay secrets– E.g. cryptographic keys used by manager / renderer

• Prevent “break once, run everywhere”

• Updatability

• ...

Introduction

Techniques

Model

Security

• method

• stakeholder analysis

• high-level properties

• security requirements

Closing remarks

Closing remarks

Further research

• Application of security requirements

• Formal verification of the correctness of used protocols– Secrecy, authentication

• Formal verification of other security properties of protocols– E.g. privacy

• Formal specifications pertaining to TCB

• Questions?