A very important aspect in the world of software development is the security of software and it’s the most critical issues in nowadays. The software security contains protect information and information systems from unauthorized access, use, disclosure, disruption, modification, or destruction in order to provide confidentiality, integrity, and availability.
People need to hide their shared data through network communication. Because they want to maintain their privacy .
But there are some problems affect the software protection. Many software gets distributed over the Internet. Once software distributed to a client machine, the software owner actually loses all control of the (client) software. An illegal access could be obtained when software is being cracked, where illegal copying and distributing of cracked software is a form of copyright infringement.
Attacker can violate the copyrights of software by applying reverse engineering process that give attackers a chance to understand the behavior of software and extract the proprietary algorithms and key data structures from it. There are many reverse engineering tools that can provides an access control to software’s data and makes it easier for adversaries and reverse engineers to analyses software and steal the intellectual property  . Some of these tools, dis-assembler (translate binary code into readable assembly language), de-compiler (translate byte code to source code). And it is difficult to enforce copyright laws and penalties upon users. “Copyright is a form of protection grounded, it’s the certain right for an author to original work they have written”. Therefore, copyright infringement is the illegal distribution and unauthorized copying of copyrighted software. protect the copyright of software is one of the most critical issues in nowadays .
Software protection is required and we need to solve all problems of software protection. Firstly, The Software contains secret, confidential or sensitive information. To protect this data, obfuscation technique is used. Secondly, it’s necessary to protect a software implementation from reverse engineering. And third, there is the program’s execution itself, where critical code is executed and some confidential data is accessed. During execution one needs to protect the code and data from malicious intents, such as dynamic analysis and tampering. All these elements need to be sufficiently strengthened to guarantee data confidentiality and secure program execution to the user .
The obfuscation technique is an important technique aiming to protects software from the risk of reverse engineering. It transforms program into another functionally equivalent program, while hiding its internal logic to enhance the difficulty of interpretation, thus obstruct software analysis .
This research, presents a novel solution aimed to protect copyright and distributed of software, we developed Distributed obfuscation model technique that protect software from above problems. It operating at a high level of security against reverse engineering by integrating multi-levels of protections.
Even though the Distributed obfuscation model technique with multi – levels of obfuscations is robust and more security than traditional techniques,
The main contribution of this thesis, presenting a suitable solution to protect software, copyright and distributed of software over client/server against reverse engineering analysis, and these contributions is summarized as follows:
The main aim of the threat modeling is to identify the import functionalities of the software/ model and protect it.
We begin threat modeling by focusing on four key questions: ref [ book ]
“ Threat Modeling: Designing for Security Published by John Wiley & Sons, Inc. 10475 Crosspoint BoulevardIndianapolis, IN 46256 www.wiley.com Copyright © 2014 by Adam Shostack Published by John Wiley & Sons, Inc., Indianapolis, Indiana Published simultaneously in Canada “
Transmit data through network that connect server to several clients and maintain shared secret key, can be accessed by different attacker, and software can be attack by reverse engineering analysis, software protection techniques are suffer from a set of threats that our model will solve:
Threat to the client:
Danial of the service (DOS): Its any type of attack that occurs on network structure while data transmission, and it disabled a server from servicing its client. ( ref : Denial of Service Attack Techniques: Analysis, Implementation and Comparison
Khaled M. Elleithy, Computer Science Department, University of Bridgeport , Bridgeport, CT 06604, USA , Drazen Blagovic, Wang Cheng, and Paul Sideleau , Computer Science Department, Sacred Heart University
Fairfield, CT 06825, USA )
the attacker sending a lot of requests to the a server in a tempt to make it down, flooding server with large packets of invalid data
The need for robust software protection technique against tampering and reverse
engineering analysis is highly needed and recommended nowadays, and these techniques should address the lack of confidently software in an untrusted environment.
Many studies have been investigated one to one protection, where there is a clear lack of studies that are constructing the many to one protection, in which most of these approaches protect the intellectual property and seen as trade secrets.
reverse engineering analysis and modifications during distribution the software over client/server over client device.
This study is meant to address the following questions and seek answers for them:
This section summarizes briefly what each chapter explains.
Chapter One: Background.
This chapter gives the description of the thesis idea, justification for choose research, problem statement, research aims, objectives, questions, hypotheses and structure of research.
This chapter talks about my obfuscation model thesis use.
This chapter presents the testing and result.
This chapter presents the conclusion and future work.
This chapter will focus on symmetric encryption, which is the simplest type of encryption. In symmetric encryption, the key used to decrypt is the same as the key used to encrypt. You’ll start by learning about the weaker forms of symmetric encryption, the classic ciphers that are only secure against the most illiterate attacker, and then move on to the stronger forms that are secure forever.
Cryptography is derived from Greek word ‘crypto’ means secret ‘graphy’ means writing that is used to conceal the content of message from all except the sender and the receiver and is used to authenticate the correctness of message to the recipient. Cryptography is such a way that make sure of integrity, availability and identification, confidentiality, authentication of user and as well as security and privacy of data can be provided to the user .
The word cryptography may use alternatively with the words cryptology or cryptanalysis
but each of them has its own meaning that differ slightly using term ” Crypto ” which comes
from Greek ” krypto” to mean hidden and ending with “graphy” which mean writing, so the
whole word cryptography is mean to hidden writing that done as an output of encryption
process in secret system . Cryptanalysis is what the layperson calls breaking the code.
The areas of cryptography and cryptanalysis together are called cryptology .
Cryptographic systems are used to provide privacy and authentication in computer and
communication systems. As shown in figure [3.1], encryption algorithms encipher the
plaintext, or clear messages, into unintelligible cipher text or cryptograms using a key. A
deciphering algorithm is used for decryption or decipherment in order to restore the original
information. Ciphers are cryptographic algorithms .
Figure [3.1] Cryptography
Cryptography is used for many goals that can be either all achieved at the same time in one
application, or only one of them . These goals are:
one who has the decipher key.
system can prove their own identities to other parties who don’t have personal
knowledge of their identities.
from its original form.
and the message was received by the specified party, so the recipient cannot claim that
the message was not sent.
goal controls who can have access to the resources, if one can access, under which
restrictions and conditions the access can be occurred, and what is the permission level
of a given access .
Cryptosystems have two type based on the number of keys used, they are either
symmetric (private key encryption), in which case both the enciphering and deciphering keys
must be kept secret, or asymmetric (public-key encryption) in which case one of the keys can
be made public without compromising the other   .
3.2 Asymmetric encryption (public-key encryption)
Each person has a pair of keys (a public key and a private key). person’s public key is
published but the private key is kept secret. Messages are encrypted using the recipient’s
public key and can only be decrypted using his private key. In this method the sender and
the receiver eliminate the need to share keys (secret information). All communications
use only public keys, and no private key is transmitted , see figure [3.2].
Figure [3.2]: A simplified model for asymmetric encryption.
3.2.1 Rivest–Shamir–Adleman Algorithm (RSA)
3.2.1 Rivest–Shamir–Adleman Algorithm (RSA)
RSA implements a public-key cryptosystem, as well as digital signatures.
keys are not, only the person with the correct decryption key can decipher an encrypted message. Everyone has their own encryption and decryption keys.
actually originated from the sender (signature), and didn’t just come from there
(authentication). This is done using the sender’s decryption key, and the signature can
be verified by anyone, using the corresponding public encryption key .
The security of the RSA algorithm has been validated, since no known attempts to
break it have yet been successful, mostly due to the difficulty of factoring large
product of two prime numbers .
RSA operation involves four steps key generation, key distribution, encryption and
decryption. The main idea is to find large positive integers 𝒆, 𝒅 and 𝒏 such that with
modular exponentiation for all 𝒎 as equation 3.1:
(𝒎17𝒆)𝒅 𝒎𝒐𝒅 𝒏 = 𝒎
Where encryption key 𝒆 , decryption key 𝒅 and 𝒏 is a composite number which is a product of
two large prime number. Although knowing of e and 𝒏 or even 𝒎 , it is difficult to find 𝒅 . .
Key Generation: key generation can be done using the following steps :
First, we select two large prime numbers of about the same size, 𝑝 𝑎𝑛𝑑 𝑞, then compute n and
j(n) as equations 3.2, 3.3:
𝒏 = 𝒑 ∗ 𝒒
𝒋 (𝒏) = (𝒒 − 𝟏) (𝒑 − 𝟏)
After that select encryption key 𝒆, 𝟏 < 𝒆 < 𝒋(𝒏), based on relationship specified on
𝒈𝒄𝒅 (𝒆, 𝒋)) = 𝟏
(3.4) Then calculate private key using equation 3.5:
𝒅 = 𝒆18−𝟏(𝒎𝒐𝒅 𝒋(𝒏))
Finally, the public key can be computed using n and e, also private key is equal to d; RSA is
used for encryption/decryption process as following:
Encryption: message 𝑴 at senders’ side is converted into an integer 𝒎 where 𝒎 < 𝒏 and
𝒈𝒄𝒅 (𝒎 , 𝒏 ) = 𝟏 .
The cipher text 𝒄 , is calculated by using receivers public key 𝒆 , which is send to the receiver.as
𝑪 = 𝑴𝒆 𝒎𝒐𝒅 𝒏
(3.6) Decryption: At receiver’s end 𝒎 is deciphered from 𝒄 by using receiver’s private key 𝒅 by
computing equation 3.7 :
𝒄𝒅=(𝒎𝒆)𝒅= 𝒎 𝒎𝒐𝒅 𝒏
3.2.2 Diffie –Helman Algorithm (DH)
The Diffie–Hellman is a specific method of exchanging cryptographic keys. It is key
exchange method allows two parties that have no prior knowledge of each other to jointly
establish a shared secret key over an insecure communications channel. This key can then
be used to encrypt subsequent communications using a symmetric key cipher . the
following steps show how the Diffie-Hellman Algorithm Key exchanges work :
primitive root of 𝒒, such that 𝒂 < 𝒒.
𝒒, then calculate public key 𝒀
, as equation 3.8:
19 𝑨𝒀𝑨= 𝒂 ∗ 𝑿𝑨𝑨, such that 𝑿
Key generation for user B: this can be done by selecting private key 𝑿
, such that
𝑿𝑩< 𝒒, then calculate public key 𝒀
, as equation 3.2:
𝑩𝒀𝑩= 𝒂 ∗ 𝑿𝑩𝑩 𝒎𝒐𝒅 𝒒
Calculation of secret key by user A: secret key of user A can be computed as equation
𝑲 = (𝒀𝑩)𝑿𝑨 𝒎𝒐𝒅 𝒒
(3.10) Calculation of secret key by user B: secret key of user B can be computed as equation
𝑲 = (𝒀𝑨)𝑿 𝒎𝒐𝒅 𝒒
(3.11) Notice that, the result is that the two sides have exchanged a secret key value.
3.2.3 Elliptic Curve Cryptography algorithm (ECC)
ECC is an alternative mechanism for implementing public-key cryptography. ECC is
based on discrete logarithms that are much more difficult to challenge at equivalent key
lengths. The security of a public key system using elliptic curves is based on difficulty of
computing discrete algorithms in the group of points on an elliptic curve defined over a
finite field. Elliptic curve equation over a finite field 𝐹
can be described by equation
20𝑝 𝒚𝟐= 𝒙𝟑+ 𝒂𝒙 + 𝒃
Here, y, x, a and b are all within 𝐹
, and p is an integer modulo p. a and b is the
coefficients which determine what points will be on the curve. Curve coefficients have to
fulfill one condition that is:
𝑝𝟒𝒂𝟑+ 𝟐𝟕𝒃𝟐≠ 𝟎
This condition guarantees that the curve will not contain any singularities .
Each value of a and b gives a different elliptic curve. The public key is a point on the
curve and the private key is a random number. The public key is obtained by multiplying
the private key with a generator point G in the curve .
3.3 Symmetric encryption (private key encryption)
Using the same secret key in encrypt and decrypt messages. its problem is transmitting
the secret key to a legitimate person that needs it .
Figure [3.3]: A simplified model for symmetric encryption.
Advanced Encryption Standard (AES)
AES is based on substitution permutation network. It is fast in both hardware and
software. AES has affixed block size of 128, 192, 256 bits, and it can specify with block
and key sizes in any multiple of 32 bits. The block size has a maximum of 256 bits.
AES algorithm have many characteristics: resistance against all known attacks, speed and
code compactness on a wide range of platforms and design simplicity .
AES operate on 4 × 4 matrix of bytes, termed a state. The AES cipher is specified as
number of repetitions of transformation rounds that convert the plaintext into ciphertext.
Each round consists of several processing steps, including one that depend on encryption
key. A set of reverse rounds are applied to transform ciphertext back into original
plaintext using the same encryption key . The encryption algorithm is organized into
three rounds. Round 0 is simply an add key round; round 1 is a full round of four
functions; and round 2 contains only 3 functions. Each round includes the add key
function, which makes use of 16 bits of key. The initial 16-bit key is expanded to 48 bits,
so that each round uses a distinct 16-bit round key . Figure 3.4 represent AES
encryption process, and relationship between number of round and cipher key sizes,
where 10 cycles need a key length of 128 bits, 128 cycles supports a key length of 192 bit
and 14 cycles need a key length of 256 bit.
Figure 3.4: AES general encryption process 
The encryption algorithm involves the use of four different functions, or transformations:
add key, nibble substitution, shift row, and mix column, whose shown on Figure 3.5.
Figure 3.5: AES structure encryption process .
Rivest shamir adleman algorithms(RSA) / ecc /DH
Chapter Three: Models of obfuscation
Chapter 4: Proposed Model: DOSP
Chapter 5: Results and Analysis
Chapter 6: Conclusion and future work
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