Securing iClouds Storage Based On Combination of RSA and AES Crypto System

Badreldin O. S. Elgabbani & Emad Abdulrahman Shafie
International Journal of Computer Science and Security (IJCSS), Volume (13) : Issue (5) : 2019 201
Securing iClouds Storage Based On Combination of RSA and
AES Crypto System
Badreldin O. S. Elgabbani boelgabbani@uqu.edu.sa
MCC/ Dep. Of Engineering/computer
Umm Al-Qura University
Makkah/ 21955/Saudi Arabia
Emad Abdulrahman Shafie eashafie@uqu.edu.sa
MCC/ Dep. Of Engineering/computer
Umm Al-Qura University
Makkah/ 21955/Saudi Arabia
Abstract
The strength and consistency of cryptographic systems in application, development is highly
significant to reduce the penetration chances of applications and files storages. Nevertheless, the
data protection systems still face challenges to protect those systems from being attacked. This
research has been designed to protect highly important documents saved in iClouds computing
storage from being exploited through illegal techniques. The research proposes a new method of
encryption that combines two of the most familiar techniques, which are based on (RSA) model
invented by Rivest, Shamir, and Adelman merged with an Advanced Encryption Standard (AES).
The new combination RSA and AES method will be used on iCloud storages to give them more
security and effectiveness as compared to standalone encryption. The main idea of the new
technique is to choose two big unpredictable prime numbers at random for public and private key
merging with trusted and widely used AES procedure. The research will be applied and evaluated
by using a case study to show the new suggested method. Moreover, the case study will be run
on iClouds technique namely drobox.
Keywords: Encryption, Decryption, iCloud, Combination.
1. INTRODUCTION
A number of ways and protocols are used to transfer files on the Internet for exchange of
significant information in different fields, like international trade, commerce and industries, and
secret military organizations.
Icloud storage is one of the most important ways of sharing and transferring files on the Internet
[1.] Shared access to Icloud storage requires that the shared files are secure and access to the
specific files is restricted to and controlled by the files owner. Encryption is a common technique
to control the use of shared files or data, and it grants privileges to known users.
Researchers dealing with crypto graphics propose a lot of papers and ideas that concern
encryption and decryption of files and data [1,2,3]. RSA (Rivest, Shamir ,and Adleman), and AES
(Advanced Encryption Standard) algorithm are the most common and widespread techniques that
are used to encrypt files. They will be discussed in detail later in this paper. This paper discusses
the effectiveness of combination of those techniques and our suggested case study shows the
extent of their success.
The paper comprises the following sections, Section 2 provides Literature review of
cryptographic, RSA and AES. Section 3 illustrate our research methodology and describe how
our proposed model will be designed. Section 4 will discuss a case study that illustrates

combination experiments of encryption RSA and AES algorithms, and in Section 5 discusses the
results and gives a conclusion and suggested future work .
2. LITERATURE PREVIEW
2.1 Cloud Computing
iCloud computing generally defined by the National Institute for Standards and Technology
(NIST) (Badger et al., 2011) “cloud computing is a model for enabling convenient, on-demand
network access to a shared pool of configurable computing resources (e.g., networks, servers,
storage, applications, and services) that can be rapidly provisioned and released with minimal
management effort or service provider interaction". This achievement represents a real genitive,
to Information security systems.
The iCloud technique is one of the greatest inventions of the new era, which makes high cost
devices, top security software, enabled for everyone, and offers the possibility to follow the
evolution of hardware and storage containers, the main idea for iCloud security is to encrypt files
before uploading.
2.2 RSA Background
The importance of encryption has been noticed since ancient times, so to maintain the privacy of
individuals, security of nations Also it is a highly important for industrial facilities, commercial
products, military and the transfer of high-confidential information. The main purpose of
encryption is to preserve country from the scourge of wars, intellectual information rumors and
Infringement of industrial inventions.
Many encryption methods have been tested and applied, but the most famous one is RSA
encryption technique it is invented in 1978 by Rivest, Shamir, and Adleman. These encryption
techniques are helped to speed encrypted of explicit texts to crypto text and vis versa[1,2,3,7,8].
2.3 The RSA Algorithm: An Overview
Depends on choosing any two primes numbers p and q, s can be deﬁned as s=p*q and choosing
L such that L and φ(s) are prime, (L, φ(s)) = 1. where p, q are prime; s and L are public.
Firstly, text should be transfer into decimal number using ASCII. If the text size larger than s, it
should be distributed into blocks in smaller parts than s. These blocks are labeled b1, b2, · · · ,br.
In theory, it could happen that some b, s is not relatively prime. [1,2,3,7,8].
2.4 RSA Algorithm
TABLE 1: RSA Algorithm [2].

2.5 Fundamentals of AES
In 1997, NIST announced a challenge for the successor to DES. To allay the suspicions that the
NSA had placed "back doors" in DES [9], the competition was to be open and public, and the
encryption algorithm was available for use royalty-free worldwide.
Due to that challenge AES was classified for use with high information via the world, it is defined
as a symmetric block cipher, operating on fixed-size of data. AES supports 128-, 192-, and 256-
bit keys. The length of these keys gives an advantage for resisting attempts to decrypt
encryptions keys [4].
2.6 High-level Description of The Algorithm
TABLE 2: AES algorithm [5,6,10].
2.7 Sub Bytes According To Look Up Transfer Table
Sub Bytes transform is a simple transform, which encipher 8 bit data to other 8 bit data
determining the multiplicative inverse for a given number in GF(28).
FIGURE 1: AES Sub Bytes' Technique.

2.8 Shift Rows
Shift rows is used to shift rows by certain offset technique shows below.
FIGURE 2: Shift Rows Technique.
2.9 Mix Columns
In the Mix Columns, combined each column by using an invertible linear transformation
FIGURE 3: Mix Column Technique.
2.10 Add Round Key
The sub key added by using bitwise XOR that combined each byte of the state with the
corresponding byte of the sub key
FIGURE 4: Add Round Key Technique.

3. METHODOLOGY
It's observed that the data protection methodologies faced a big challenge to protect the
information system, nevertheless the strength and consistency of cryptographic systems gives
penetration opportunities almost non-existent.
Here is a combination RSA and AES method that used in iCloud technique; it is more powerful
than RSA or AES standalone.
The method based on RSA encryption system, merged with an advanced encryption standard
AES.
It's main objectives to provide high secure for important messages by choosing randomly and
unpredictable two big prime numbers for public and private key merging with trusted and widely
used AES procedure.
3.1 Combination of RSA and AES Crypto System Model
1. Receiver generate public and private key using RSA algorithm
2. Receiver send public key to sender
3. Sender encrypt his message using AES algorithm
4. Sender encrypt the round key using Public key
5. Receiver decrypt the round key using private key
6. Receiver decrypted the whole massage using AES technique
FIGURE 5: AES and RSA Combination Encryption System.
4. PROPOSED MODEL
Overview of network architecture for cloud storage service architecture is illustrated in Two
different network entities can be identified as follows:
Receiver: an entity, which is used to retrieve the data from cloud server.
Sender: an entity, which is used to upload data to the cloud Server (CS): the cloud server is an
entity, which is managed by cloud service provider (CSP) to provide data storage service and has

significant storage space and computation resources Receiver generate public key and private
key using RSA model then make the public key available to senders.
A] Sender encrypt his plain text using AES system.
B] Sender encrypts his AES symmetric key using the public key.
C] Receiver decrypts the AES key using his private key then decrypt the cipher text.
4.1 Case Study
Makkah community college MCC keeps all it's important documents including self-study report
concerning academic accreditation, so as to submit it to the (USA council of occupation
education) in the drop box through iCloud technique.
MCC folder in the drobox being used as a cases study for this research concerning the
combination of RSA and AES for encryption system techniques through the following steps.
1- The receiver generates public key (n, e) and private key (n, d) it sends the public key
and receives encrypted message contains round key need to be decrypt so as to
decrypt the whole message.
Satisfying e*d mod (p-1) *(q-1)=1
Declare keyname;
Call RSACryptoServiceProvider;
Generate Public, private keys;
2- The Sender use the public key to encrypt the first round key, used in AES encryption
procedure by the public key
Use RSACryptoServiceProvider to
enrypt the Rijndael key.
RSA is previously instantiated:
byte[] keyEncrypted = rsa.Encrypt(rjndl.Key, false);
3- The Receiver decrypt the round key then decrypt the whole encrypted passage
The receiver gets the message and then should have to decrypt the key so as to get the
original round key after that he can encrypt the whole file the following c# interface reflect
that steps.
The AES Algrithm start by adding the round key and the procees will be due to 9 rounds five
stages
The AES algorithm applies to both encryption and decryption. The process for encryption starts
by adding the round key followed by 9 or 10 rounds of four or three stages respectively. The
same process applies for decryption in inverse stages.
The sender use AES technique to encrypt his massage
3.1 Create instance of Rijndael for symmetric decryption of the data.
3.2Generate byte arrays to create the round encrypted key.
3.3Construct the file name for the decrypted file by using File Stream to read the encrypted
input file (inFs) and save the decrypted text into output file (outFs).
Convert the lengths to integer values Create the byte arrays for the encrypted Rijndael key, and
the cipher text.
Extract the key and IV
3.4 Use RSACryptoServiceProvider to decrypt the Rijndael key.
3.5 Decrypt the key will be followed by decrypting the whole cypher text into the file stream.

FIGURE 6: AES and RSA Combination Interface Design.
The receiver uses this interface to generate two keys, Public and private keys, he sends the
public key to senders and keep private key so as to encrypt sender's message.
The sender encrypts the AES round key by RSA system using his public key. after that he
encrypt the whole message using AES system.
The receiver decrypts the round key using the private key after that he decrypts the whole file
using AES system here we observed that the key size has been chosen to be 128 bit and the
block size is 256 bit so as to use Rijndael special case of AES technique, which is quiet enough
for our case study.
rjndl.KeySize = 128;
rjndl.BlockSize = 256;
rjndl.Mode = CipherMode.CBC;

Encrypted File
FIGURE 7: Encrypted File.
FIGURE 8: Decrypted File.
5. RESULT DISCUSSION
The case study concerns 10 academic standards chairmen, distributed in different places and
different devices on the Internet, there by the public key should be available via Internet and the
private key held by the academic coordinator the one who can turn the crypto texts to the
plaintext.
We used RSA encryption asymmetric keys that are used to different public and private variables
of sizes, making it difficult to penetrate the text blinded and is less vulnerable to attacks from the
secret key to replicate easy guessing and penetration.

We used non-symmetric encryption algorithm to encrypt a symmetric secret key, and by this
procedure the following steps are achieved.
1-Hierarchical system used to protect data
2-Powerful combination system including RSA and AES are being used to protect the information
3-Avoiding RSA disadvantage, by applying RSA encryption system only on the shortage amount
of data, representing the round key, on the other hand benefit of the powerful of AES encryption
system
4-Avoiding the weakness of AES symmetric key, and on the other hand benefit from the powerful
of the rotating of blocks of AES system.
It is observed that the secret AES symmetric encryption method, used one similar key held by the
two members and this key may send via web sites protocols, so this key is easily accessible via
cryptographic analysis methods, and faced brute attack method, that used to apply each
expected key on a piece of crypto text, even up to the explicit text.
The study dealt with the use of the RSA system, to generate the public key and the private key,
and then send the public key to encrypt the round key of the system and then used to encrypt the
whole of the content, then the receiver decrypts the round key using his private key, and thus
decrypts all the content, It is a great and powerful work, but like other models, which focus on the
means of symmetric key, often exposed to the middle man attacks, used to stay between devices
and servers, and hunts the public key, and change it, followed by decrypting the round key and
the rest of the data.
This problem leaved to be deal with by professional web sites security applications.
5.1 Future Study
We suggest indepth mathematical studies using existing protocols like Certificate Authorities CA
[11]. And Transport Layer Security/ Secure Sockets Layer (TLS/SSL) in securing the data traffic
between clients and servers[12].Transoport Layer Security (TLS) protocol is used primarily to
provide privacy and data integrity between two or more computer communicating applications
when secured by TLS.
6. REFERENCES
[1] Cutler, Matthew, and David Greenstein. "System and method for social interaction, sharing
and collaboration." U.S. Patent Application No. 13/465,572.
[2] Rivest, R.; Shamir, A.; Adleman, L. "A Method for Obtaining Digital Signatures and
PublicKey Cryptosystems". MIT. 1977.
[3] Robinson, Sara. “Still Guarding Secrets after Years of Attacks, RSA Earns Accolades for its
Founders.” SIAM News, Volume 36. June 2003.
[4] Rijndael "Advanced Encryption Standard (AES)" FIPS. November 23, 2001.
[5] Morris J. Dworkin, Elaine B. Barker, James R. Nechvatal, James Foti, Lawrence E.
Bassham, E. Roback, James F. Dray Jr." Announcing the Advanced Encryption Standard
(AES) " NIST (2001).
[6] Nicolas Courtois, Josef Pieprzyk, "Cryptanalysis of Block Ciphers with Overdefined Systems
of Equations". pp267–287, ASIACRYPT 2002 Web sites references.
[7] Joan Daemen, Vincent Rijmen, "The Design of Rijndael: AES – The Advanced Encryption
Standard." Springer, 2002. ISBN 3-540-42580-2.

[8] R.L. Rivest, A. Shamir, and L. Adleman . "A Method for Obtaining Digital Signatures and
Public-Key Cryptosystems"(accessed December, 5, 2019)
http://people.csail.mit.edu/rivest/Rsapaper.pdf.
[9] Federal Information Processing Standards Publication 197 November 26, 2001.
"Announcing the ADVANCED ENCRYPTION STANDARD (AES) "
https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf.
[10] Online Domain Tools is a project of AITIS s.r.o., a privately held Czech Republic company
"AES – Symmetric Ciphers Online" http://aes.online-domain-tools.com/ (accessed
January, 21, 2019).
[11] Zakir Durumeric; James Kasten; Michael Bailey; J. Alex Halderman (12 September 2013).
"Analysis of the HTTPS Certificate Ecosystem" (PDF). The Internet Measurement
Conference. SIGCOMM. Archived (PDF) from the original on 22 December 2013. Retrieved
20 December 2013.
[12] T. Dierks; E. Rescorla (August 2008). "The Transport Layer Security (TLS) Protocol, Version
1.2". Archived from the original on 2017-12-24.

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