The Anti-Piracy Measure Using Encryption of Embedded Products May Mitigate the Security Strength

doi:10.4236/cn.2013.53B2079

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Communications and Network, 2013, 5, 430-433

http://dx.doi.org/10.4236/cn.2013.53B2079 Published Online September 2013 (http://www.scirp.org/journal/cn)

The Anti-Piracy Measure Using Encryption of Embedded

Products May Mitigate the Security Strength

Zhilong Xiong, Rui Zhang, Xin Zhan, Zhenglin Liu

School of Optical and Electronic, Huazhong University of Science and Technology, Wuhan, China

Email: [email protected]

Received June 2013

ABSTRACT

In this paper, firstly we describe the piracy problem of embedded products. Then we formulate the security features of

anti-piracy embedded products. Finally we prove that the anti-piracy measure using encryption of embedded products

may mitigate t he security str ength.

Keywords: Embedded Products; Anti-Piracy; Encryption; Security Strength; Copyright

1. Introduction

There are a vast number of embedded devices in a wire-

less network, such as wireless routers, handheld termin-

als and access points. In the fierce competition of the

communications and consuming electronics market, there

is a real-world problem: A design house takes several

years to design an embedded product. Then they send the

design information to a manufacturer, they find that the

manufacturer produces their embedded products stealthily.

In view of this situation, many design houses have pro-

vided their anti-piracy schemes. Even so, the problem of

piracy is serious. The reason for this issue is that they

don’t realize the security features for the anti-pi rac y em-

bedded products and often misuse the encryption tech-

nology against piracy.

2. Describ e the Embedded Product Piracy

The situation is always like this: The pirate pretends to

be a consumer and buy an embedded product. After that

he can analyze the embedded product and get some de-

sign information about it. Then he produces the pirated

products on large scale based on the design information.

Finally, the manufacturer will be responsible for produc-

tion. And fro m the Figure 1, we know that the manufac-

turer can easily take the design information rather than

Figure 1. Embedded products from design to production

and to sale.

the consumer. So, by analysis, it is evident that the key

problem between the designer and the manufacturer can

be represented in Figure 2:

Figure 2. Embedded products fr om design to production.

Obfuscation, Watermarking, and Tamper proofing for

Software Protection was introduced in [1]. “Code pack-

ing transforms a program into a packed program by com-

pressing or encrypting the original code and data into

packed data and associating it with a restoration ro utine”

in [4]. Security framework for embedded systems was

discussed, and then copyright protection model has been

proposed based on specific crypto memory IC in [3]. In

[5], some software protection solutions in embedded con-

dition, including the implementation schemes in pure soft-

ware witho ut any support from hard ware, and the higher

strength schemes bonding with specified hardware have

been introduced.

Surreptitious software, proposed by C. Collberg and J.

Nagra in [1], is a promising technology which can be

used as the anti-piracy measure of embedded products.

However the main goal of the surre ptitious software is to

protect the software which is running on the embedded

product, not the embedded product itself. Code packing

in [4] is effectively used to protect embedded software

against reverse engineering. But, if embedded software

has the portability, the pirate can simply bypass this se-

curity feature by transplanting embedded software. The

limitation in [3,5] is their security strength based on a

The design information

provided by the designer

to produce

Embedded products

manufactured by the

manufacturer To sellEmbedded products

bought by the consumer

The design information

provided by the designer

to produce

Embedded products

manufactured by the

manufacturer

*Corresponding author.

Z. L. XIONG ET AL.

431

specified hardware. They assume that the information in

the specified hardware can’t be got by the pirate. But the

pirates often get the information when they pretend to be

the manufacturer.

Our aim is to prevent the manufacturer from producing

embedded products stealthily. In other words, if the de-

signer wants to produce one million products, we should

insure that the production quantity of the manufacturer

will be not more than one million. To achieve it, the an-

ti-piracy embedded products should have some special se-

curity features. Now let’s formulate these security features.

3. The Security Features of Anti-Piracy

Embedded Product

Some terms are defined as follows:

E (The abbreviation of “embedded products”) is the

collection of embedded products.

H (The abbreviation of “hardware”) is the collection of

the embedded hardware. We use the hardware identifier

to represent it, for example we always use the serial

number of the CPU to represent hardware.

S (The abbreviation of “software code”) is the collec-

tion of the embedded software. We use the software

identifier to represent it, for example we often use the

consumer data to represent the embedded software.

e is an element of colle c tion E.

h, g is an element of collection H.

s is an element of collec tion S.

We assume that e is the design information of embed-

ded products. Because embedded products are composed

of hard ware and so ftware. We can represent e as

,hs<>

namely ,e hs

=<>

. Then the design house sends it to

manufacturer for production.

The properties of the anti-piracy embedded products

are as follows:

 Firstl y they can’t be d uplic ated by the manufac turer.

⇔

Namely e is unable to be duplicated.

⇔

,e hs=<>

, and s is able to be duplicated, so h can’t

be duplicated by the manufacturer.

⇒

Of course, h

must be unique.

 What’s more, the embedded software should have

the non-portability.

⇔

Namely, if

,,hs gs< >=<>

hg=

(,hg H∈), tha t mea ns ther e

is function relatio n bet ween h and g.

⇒

Of course s

must be unique.

By analysis above, the security features of anti-piracy

embedded product can be summarized as follows:

 h is unique and immutable. And it can’t be dupli-

cated or modified.

 s is uniq ue.

 If we represent the above function relation as f,

we can get the function equation：

()

h fs=. We call it

“the blinding function equation”. In practice, the

manufacturer is easy to get the hardware information.

It would be best to design the blinding function

as an irreversible function, so that the manufacturer

can’t conclude the information of s from h on the bas e

of the blinding function f.

Firstly, I will introduce the immutability of h. Many

desig ner s use OT P o r security chip to record the software

information. In such a way, users can’t modify the in-

formation. So, they can’t transplant the software. How-

ever, the manufacturers have the access to that informa-

tion. What’s more, the money people spend on getting

the information can be neglected, compared with the

benefit people can get from the piracy. So this method is

invalid. T he immutability means that if the manufac tures

rewrite the infor mation, it will p ay a huge price. And the

price is much higher than the value of embedded prod-

ucts.

Secondly, h should be unique, which means that dif-

ferent products can’t have the same hardware identifier.

For example, each processor has its unique identifier.

Thirdly, s should be unique, which means that differ-

ent products can’t have the same software identifier.

Though the main software code is always the same, we

can add some unique consumer data to make sure that no

two software code can be the same.

Finally, f would better be irreversible. The SHA can be

a good choice. Tho ugh this req uireme nt is not nece ssar y,

we believe that it can improve the securit y of the pro duct.

For example: if embedded product is Set Top Box, the

serial number of the CPU could be h. It is unique and

immutability. And the manufacturer can’t duplicate or

modify it. The consumer data could be s. And we can

design the SHA as the blinding function f.

4. The Anti-Piracy Measure Using

Encryption of Embedded Products May

Mitigate the Security Strength

So, by analysis, the manufacturer is unable to duplicate

or modify the hardware identifier h. Consequently, they

can’t copy embedded products simply. In order to pirate,

they have to transplant the embedded software. The key

to transplant the embedded software is to break the rela-

tion between h and s. In other worlds, their main object

of attack is bli nding functio n f and the software identifier

s. So our main protected targets are s and f. If we design

the blinding function f as the one-way hash function, the

integrality o f f will be more important than the confiden-

tiality of f. Because, e ven if the pirate knows the blinding

function f, he can’t derive s from h, the o nl y way for him

to transplant the embedded software successfully is to

modify f.

It is commonly observed that encryption techniques

are preferred and regarded as top choice. It is the best

choice for the confidentiality and the encryption tech-

nology such as digital si gnature is used to guard the inte -

Z. L. XIONG ET AL.

432

grality of a software code. Consequently, the encryption

technology is often used to defend embedded products

against piracy. But is it really works? Actually it is not

the case because of following reasons:

1) The protec tion sche mes using e ncryptio n cost so me

overhead, the more overhead we give to it, less overhead

we can give to other prote c tion schemes.

2) The encryption protects the confidentiality of data,

but as s umi n g t ha t a se cr et ke y r e mai n s hid d e n. Thi s means

that we have to add some new protected target such as

the secret key. If we use the encryption to protect our

new protected target, we still have to add some new pro-

tected target for the same reason. At last, we have to use

other protection schemes for the new protected target.

So, by analysis, it is found that anti-piracy measure

using encryption of embedded product may mitigate the

security strength. To prove it, let’s analyze the relation

between our protected targets and the new protected tar-

gets.

We can represent the new protected targets as the en-

crypti on fu nctio n equat ion, na mely

(,)

y ekx=. And k is

the secret key, x is plaintext, e is the enc rypt io n func tio n,

and y is cip her te xt.

For a specific k, each plaintext x has only one cipher-

text y for it. This is just like our relation bet ween h and s.

In fact, if we have the ability to keep y, e, k and x safe,

we must have the ability to keep h, s, f safe. Because we

can design a secure blinding function S as

hy=

fe=

and s = x. Furthermore, the new protected target,

namely

(,)

y ekx=, has one more protected element ‘k’.

So the new protected target is more difficult to protect

than our original protected ta rget.

We assume that C is the maximum overhead of our

production schemes which embedded products can afford.

is a protection scheme we used, c is the protection

overhead, and

()Gc

represents the security strength of

the protection scheme

. For the same kind of produc-

tion scheme, we assume that the security strength is pro-

portional to the protection overhead, namely

12cc<

(c1)( 2)G Gc<. Obviously (C)G represents the maxi-

mum securi ty strength.

is the protection scheme using encryption, while

is not. Obviously 2( )

represents the maximum

security strength of the protection scheme without using

encryption. Now we add the protection scheme

. We

assume that the protection overhead of

is c. A nd we

can record the maximum security strength for the new

mix protection scheme as

{1(),2()}GcG Cc−

1) If we are unable to keep the encryption function

(,)

y ekx= safe, the protection scheme G1 will be invalid.

And the maxi mum security st rength of the ne w mix pro-

tection scheme

{1(),2()}GcG Cc−

will reduce to

{ 2()}GCc−, namely

2( )GCc−

2) If we have the ability to keep the encryption func-

tion

(,)

y ekx= safe. F rom the a na l ysi s give n a b ove , we

know that the added protected target

(,)

y ekx= is mo re

difficult to protect than our original protected target

()

h fs=. And the maximum security strength for the

added protected target is

2( )GCc−

. Even if we make

sure that our original protected target is safe so that the

maximum security strength of the new mix protection

scheme is totally depended on our added protected target,

the ma xi mum secur it y str e ngth o f t he ne w mi x p ro t ec tio n

scheme will still re duce to

2( )GCc−

In a nutshell, regardless of whether the protection scheme

is valid, the maximum security strength of the new

mix protection scheme will reduce. We can also get three

deductions below:

1) More encryption technology we add, more new

protected targets will be added, and more difficulties in

protection.

2) More encryption technology we add, the less max-

imum security strength we can have.

3) When

can’t fulfill the requirement security

strength of our protected target, adding

can’t fulfill

the require ment too.

5. Conclusions

This paper concerns the piracy problem of embedded

products and their anti-piracy schemes using encryption.

We formulate the security features of anti-piracy em-

bedded products and prove that the anti-piracy measures

using encryption of embedded products may mitigate the

secur ity st re ngth.

In this paper, the basic assumption here is that the

embedded software is in NVRAM (non-volatile memory).

Our ongoing research work is to analyze the security fea-

tures when the embedded software is loaded into RAM

(Rando m Access Memory). It is our ultimate goal to pr o-

vide the perfect theoretical guidance for design houses

against piracy.

6. Acknowledgment

This work was supported in part by National Natural

Science Foundation of China (No.60973034, Grant

No.61176026).

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Z. L. XIONG ET AL.

433

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