A lightweight stream cipher for mobile devices using RSA and Message feedback

A lightweight stream cipher for mobile devices using RSA and Message feedback

Rahul Yadav¹, Praveen Kr. Vishnoi², Sohit Teotia³, Dhirendra Yadav⁴

^{1, 2}Dept. of IT, SITE, Nathdwara, Rajasthan

³Dept. of MCA, IET, Alwar, Rajasthan

⁴Dept. of CS, JPTC, Samirpur, Himanchal Pradesh

¹yadav.rahul@live.com, ²erpv89@gmail.com, ³sohitt@gmail.com, ⁴dhirendra.yadav.ballia@gmail.com

Abstract: An encryption method is presented to implement a symmetric stream cipher for which we have used message stream as an One Time Pad and RSA to initiate the first One Time Pad in each cryptographic step previous stream of message is used as One Time Pad for X-OR operation on next stream of message.

                Scheme presented here ensure the secure establishment of Key (First One Time Pad) with the help of well known RSA algorithm and in subsequent cryptographic steps securely transferred message stream is used as One Time Pad for next step.

Key Words & Phrases: RSA algorithm, One Time Pad, Symmetric Cryptosystem, Stream Cipher, Key Feedback, SYMBIAN Mobile Devices.

I. INTRODUCTION

Memory and processing speed of personal computing systems have increased drastically over the past few decades in the terms of processors with huge space for scalability. But for mobile devices especially SYMBIAN based devices have observed slow and steady growth. Most of the popular cryptographic systems are aimed for the computers and mobile devices often suffer in terms of memory and processing speed in order to incorporate security algorithms.

Here a model for Lightweight and symmetric stream cipher system is introduced which provide   the level of security of the higher order of most popular symmetric stream cipher, RC4.The private key is used of the form of One Time Pad with low redundancy in key and for each cryptographic step a new Key with automatic update is used through message feedback approach. Hence no Key exchange is required rather than the first step where we establish a session.^[1]

II. SYMBIAN OS BASED MOBILE DEVICES

Symbian is a mobile operating system (OS) and computing platform designed for smart phones and currently maintained by Nokia. The Symbian platform is the successor to Symbian OS and Nokia Series 60; unlike Symbian OS, which needed an additional user interface system, Symbian includes a user interface component based on S60 5th Edition. The latest version, Symbian³, was officially released in Q4 2010, first used in the Nokia N8. In May 2011 an update, Symbian Anna, was officially announced, followed by Symbian Belle in August 2011.

Symbian OS was originally developed by Symbian Ltd. It is a descendant of Psion's EPOC and runs exclusively on ARM processors, although an unreleased x86 port existed. Some estimates indicate that the cumulative number of mobile devices shipped with the Symbian OS up to the end of Q2 2010 is 385 million.

By April 5, 2011, Nokia released Symbian under a new license and converted to a proprietary shared-source model as opposed to an open source project. On February 11, 2011, Nokia announced that it would migrate away from Symbian to Windows Phone 7. In June 22, 2011 Nokia has made an agreement with Accenture as an outsourcing program. Accenture will provide Symbian based software development and support services to Nokia through 2016 and about 2,800 Nokia employees will be Accenture employees at early October 2011. ^[5]

III. COMPARISON OF PROCESSING / MEMORY CAPACITY BETWEEN COMPUTERS AND SYMBIAN MOBILES

When we compare the memory and the processing capacity between the computers and SYMBIAN based devices against the minimum hardware requirements of applications and platform used we find portable SYMBIAN devices far behind but users expectations are very high for the same. So the security systems also need to be efficient enough to overcome all the limitations of mobile devices. Here a comparison of these requirements is made. ^[5]

Windows NT	Minimum Requirement	Recommended
Secondary Storage	128 MB	2 GB with 1 GB Free
CPU	25 MHz	150 MHz
RAM	12 MB	64 MB

TABLE 1. REQUIREMENT SPECIFICATIONS OF WINDOWS NT

Windows XP	Minimum Requirement	Recommended
Secondary Storage	1.7 GB	5 GB with 2 GB Free
CPU	2.26 MHz	3.0 GHz Duel Processor
RAM	64-128 MB	512 MB

TABLE 2. REQUIREMENT SPECIFICATIONS OF WINDOWS XP

Apple MAC	Minimum Requirement	Recommended
Secondary Storage	1.5 GB	5 GB with 2 GB Free
CPU	150 MHz	1.7 GHz
RAM	128 MB	512 MB

TABLE 3. REQUIREMENT SPECIFICATIONS OF APPLE MAC

SYMBIAN Mobile Devices	Low Tier SYMBIAN	Mid Tier SYMBIAN	High Tier SYMBIAN
Secondary Storage	162 MB	256 MB	1 GB
CPU	220-250 MHz	399-528 MHz	600 MHz
RAM	32-64 MB	64-128 MB	128-256 MB

TABLE 4. REQUIREMENT SPECIFICATIONS OF SYMBIAN MOBILE DEVICES

Platform	CPU & RAM	Secondary Storage
Windows NT / XP	Highly Expandable	Highly Expandable
Open Sources	Highly Expandable	Highly Expandable
Apple MAC	Less Expandable	Less Expandable
SYMBIAN	Non Expandable	Less Expandable

TABLE 5. SUPPORT TO HARDWARE EXPANSION (FOR MAC SYSTEM PARAMETERS ARE AGAINST THE STANDARD APPLE HARDWARE)

This comparison is made to calibrate the typical differences between computers and SYMBIAN mobile devices when scalability factor is excluded. Furthermore scalability offered by these platforms offers different levels of expandability and we found the SYMBIAN devices to be tightly bound with pre-installation hardware requirements, in terms of storage and processing power.

IV. LIMITATIONS ASSOCIATED WITH IMPLEMENTATION OF NORMAL CIPHER SYSTEMS IN SYMBIANS IN CONTEXT OF ALGORITHM DEVELOPMENT.

Whenever a network connection leaves a building, security to data is a must. . To obtain security objectives cryptographic techniques are used to block outside traffic from mingling with shared internal network. Crypto processing will require a lot of resources and many hosts will reap significant performance benefits if processing load is reduced. In this context different encryption algorithms will be discussed in terms of their computational overhead, confidentiality & authentication. Even though cryptography can resolve the security problem, it also creates some drawbacks. The major part of the disadvantage is computational overhead.  There is no perfect encryption algorithm so far. So people who want more secure system are trying to make the encryption algorithm more complex so that no one can break the system. But complex encryption algorithm takes more time to encrypt a message as the complexity of the crypto system increases.  In other words, if you want to use more secure system, you have to spend more time on communication.  Another problem is data overhead. During the securing procedure, depending on the algorithm that used to make it secure, it may generate some additional data. It is also an overhead in network point of view.^[2]

V. ONE TIME PAD

In cryptography, the one-time pad (OTP) is a type of encryption, which has been proven to be impossible to crack if used correctly. Each bit or character from the plaintext is encrypted by a modular addition with a bit or character from a secret random key (or pad) of the same length as the plaintext, resulting in a cipher text. If the key is truly random, as large as or greater than the plaintext, never reused in whole or part, and kept secret, the cipher text will be impossible to decrypt or break without knowing the key. It has also been proven that any cipher with the perfect secrecy property must use keys with effectively the same requirements as OTP keys.^[5] However, practical problems have prevented one-time pads from being widely used.

First described by Frank Miller in 1882, the one-time pad was re-invented in 1917 and patented a couple of years later. It is derived from the Vernam cipher, named after Gilbert Vernam, one of its inventors. Vernam's system was a cipher that combined a message with a key read from a punched tape loop. In its original form Vernam's system was not unbreakable because the key could be reused. One-time use came a little later when Joseph Mauborgne recognized that if the key tape were totally random, cryptanalytic difficulty would be increased.^[5]

VI. STREAM CIPHER

[Rue86] A stream cipher is a symmetric cipher which operates with a time-varying transformation on individual plaintext digits. By contrast, block ciphers operate with a fixed transformation on large blocks of plaintext digits. More precisely, in a stream cipher a sequence of plaintext digits, m0m1 . . ., is encrypted into a sequence of cipher text digits c0c1 . . . as follows: a pseudorandom sequence s0s1 . . ., called the running-key or the key stream, is produced by a finite state automaton whose initial state is determined by a secret key. The i-th key stream digit only depends on the secret key and on the (i−1) previous plaintext digits. Then, the i-th ciphertext digit is obtained by combining the i-th plaintext digit with the i-th keystream digit. Stream ciphers are classified into two types: synchronous stream ciphers and asynchronousstream ciphers.

The most famous stream cipher is the Vernam cipher, also called one-time pad that leads to perfect secrecy (the ciphertext gives no information about the plaintext). Stream ciphers have several advantages which make them suitable for some applications. Most notably, they are usually faster and have a lower hardware complexity than block ciphers. They are also appropriate when buffering is limited, since the digits are individually encrypted and decrypted. Moreover, synchronous stream ciphers are not affected by error-propagation.^[3]

VII. RC4: STREAM CIPHER APPROACH

In cryptography, RC4 (also known as ARC4 or ARCFOUR meaning Alleged RC4) is the most widely used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks). While remarkable for its simplicity and speed in software, RC4 has weaknesses that argue against its use in new systems. It is especially vulnerable when the beginning of the output key stream is not discarded, or nonrandom or related keys are used; some ways of using RC4 can lead to very insecure cryptosystems such asWEP.

RC4 uses a variable length key from 1 to 256 bytes to initialize a 256-byte state table.  The state table is used for subsequent generation of pseudo-random bytes and then to generate a pseudo-random stream which is XORed with the plaintext to give the ciphertext.  Each element in the state table is swapped at least once.

  

• The RC4 key is often limited to 40 bits, because of export restrictions but it is sometimes used as a 128 bit key.  It has the capability of using keys between 1 and 2048 bits.   RC4 is used in many commercial software packages such as Lotus Notes and Oracle Secure SQL. 

• The RC4 algorithm works in two phases, key setup and ciphering.  Key setup is the first and most difficult phase of this algorithm.  During a N-bit key setup (N being your key length), the encryption key is used to generate an encrypting variable using two arrays, state and key, and N-number of mixing operations.  These mixing operations consist of swapping bytes, modulo operations, and other formulas.  A modulo operation is the process of yielding a remainder from division.  For example, 11/4 is 2 remainder 3; therefore eleven mod four would be equal to three.

• Once the encrypting variable is produced from the key setup, it enters the ciphering phase, where it is XORed with the plain text message to create an encrypted message.  XOR is the logical operation of comparing two binary bits. If the bits are different, the result is 1.  If the bits are the same, the result is 0.  Once the receiver gets the encrypted message, he decrypts it by XORing the encrypted message with the same encrypting variable.

VIII. LIMITATIONS FOUND IN RC4 FOR SPEEDUP PERFORMANCE ON SYMBIANS

Being efficiently fast for the computer systems, RC4 algorithm is based on the use of a random permutation. Analysis shows that the period of the cipher is overwhelming likely to be greater than 10¹⁰⁰. Eight to sixteen machine operations are required per output byte, and the cipher can be expected to run very quickly in software. We can fast the process and improve the operations for mobile devices by giving attention to the fallowing improvement areas.

1.        Elimination of pseudorandom number generator

2.        Elimination of Static Vector array S[256].

a.        Non initialization of S vector.

b.        Skipping of the permutation of S vector.

c.        Removal of time complex swap operations on S vector.

IX. RSA CRYPTOSYSTEM

There are three stages of RSA^[4] operations named

1.        Key Generation

2.        Encryption

3.        Decryption Process.

Key Generation

—  Select two distinct large prime numbers, says p, q

—  Calculate n= p*q

—  Calculate φ(n) = (p - 1) * (q - 1)

—  Select e : gcd(φ(n), e) == 1

—  Calculate d ≡ e-1 mod φ(n)

Your Keys are

Private Key:             (d, n)

Public Key:              (e, n)

Encryption: to encrypt a message block M using the public key (e, n) into cipher C

C= M^e mod n

Decryption: to decrypt a cipher block C using the private key (d, n) into message M

M= C^d mod n

X. PROPOSED MODEL

The proposal is consisting of two step cipher scheme. Initially we exchange the key element of the RSA scheme, where the communication initiator device A sends a communication request to device B. Device B responds with its public key element (e, n) of RSA cryptosystem. Now in the scenario where the flow of the data stream is from Device A to Device B, i.e. Device A acts as a sender and Device B acts as a receiver. Now the cryptographic operations can be sought of a two step process;

1.        RSA Mode

2.        Message feedback mode

In RSA mode a session key is established and the first stream of message having 128 bits is securely transferred. In Message feedback mode the message stream of previous cryptographic step is used as a Private Key of One Time Pad forms. Security of the model is completely dependent over the RSA session establishment mechanism. The detailed operations are as:

1)       RSA Mode:

a)        RSA Public key elements are shared between communicating devices, and after this Device B having key elements (e, n) and (d, n) both. Device A have public key element (e, n) only.

b)       Device A encrypts the very first message stream M₀ having 128 bits into cipher stream C₀ using the public key (e, n) of Device B.

c)        Device A transmits C₀ to Device B.

d)       On receiving of C₀ Device B decrypts it using his own private key (d, n) and get M_0.

2)       Message feedback mode: After RSA operations on very first message stream M₀ of 128 bit subsequent message streams M_n can be ciphered with the help of M_n-1 using it as One Time Pad for X-OR operation.

a)        Encryption at Device A

For M_n where n>0

C_n =  M_n ⊕ M_n-1                       ……(1)

b)       Decryption at Device B

For C_n where n>0

M_n =  C_n ⊕ M_n-1                       ……(2)

XI. ADVANTAGES OF PROPOSED SYSTEM AND SECURITY LEVEL OFFERED

The security of this system needs to be examined in more detail. In particular, the difficulty of factoring large numbers should be examined very closely. The reader is urged to find a way to “break" the system. Once the method has withstood all attacks for a sufficient length of time it may be used with a reasonable amount of confidence.^[4]

RSA's security management strategy brings together the ISO 27001 framework, a tightly integrated set of core security technologies, strategic professional services, and a vibrant user community to make enterprise security management more efficient and effective.

The integrated Security Management Suite at the heart of this approach will include the RSA Archer eGRC Suite, RSA enVision for security information and event management (SIEM), and RSA Data Loss Prevention (DLP). It will provide a single hub to correlate and act on information from across your enterprise, including a wide variety of third-party point products. You'll be able to access information security within its business context and respond more appropriately. You can also take advantage of purpose-built solutions to specific business challenges, such as RSA Archer Incident Management and RSA Cloud Security and Compliance Solutions.

XII. CONCLUSION

The main results drown from this work are following:

1. Higher level of security offered for normal mobile communication.

2. The security level of proposed model has the same level of security to offer as RSA cryptosystem does.

3. Advantages of Public key cryptography with simplicity of Private Key environment.

4. A hybrid model which try to have advantages of both Public Key and Private Key cryptosystems

5. The exhaustive operations of RC4 algorithms are eliminated.

6. Message feedback ensures the data integrity while communication over a communication medium in Public domain.

7. The security lies totally on RSA operations, which is approximately infeasible to break.

REFERENCES

[1] Stallings W., Cryptography and Network Security, 4e, Pearson Education - New Delhi, 2002

[2]  A.V.N.Krishna, and Dr. A.Vinaya Babu, Pipeline Data Compression and Encryption Techniques in E-Learning environment,@ http://www.jatit.org/volumes/research-papers/Pipeline_Data_Compression_3_1.pdf

[3] R.A. Rueppel. Analysis and design of stream ciphers. Springer-Verlag, 1986

[4] Rivest R.L. et.al. ‘A method for obtaining digital signatures and publickey cryptosystems’, Commun. Of the ACM, Vol 21, No 2, February 1978

[5] http://en.wikipedia.org/wiki/