A Fast Audio Encryption Based Random Sequences
Generated Using
Linear Feedback Shift Register Defined Over Z4
Yashaswini A S1, Deepak D2
Canara Engineering college, Benjanapadavu
1M.tech
Student [4th sem], Dept. of CS&E
1arya.kannanth3@gmail.com
2Asst.
Professor Dept. of CS&E
2deepak.d@canaraengineering.in
Abstract-Cryptography is an important building block used
authentication, and non-repudiation but reveals the fact that
in communication system to provide confidentiality and
communication is happening.
authenticity. Due to the advancement in use of audios in
Modern cryptography concerns itself with the following
computers, over the internet and other audio communication
four objectives:
channels the need to secure the audio is very much essential.
In the current internet community, secure data transfer is
limited due to its attack made on data communication. So
i.
from being read by non-legitimate persons )
more robust methods are chosen so that they ensure secured
data transfer. The Z2 based cryptographic operation is used
Confidentiality (a message should be protected
ii.
Integrity (the receiver should be able to examine
in general, presently used in all most all applications has got a
whether a message was changed during the
major drawback that it can be used by only one kind of
transmission)
algorithm that is exclusive-OR. In case of extension of
algorithm
for
arithmetic
operation,
the
iii.
minimum
requirement is Z4. In this work we use this Z4 system of
generation of pseudorandom number in audio cryptographic
Non-repudiation (the sender should not be able
to deny having sent message)
iv.
Authentication (the receiver should be able to
identify the origin of message)
application.
Cryptography itself can be divided into transposition and
Keywords- Non-binary audio cryptography, parallel
substitution.
processing, Z4 system, additive algorithm, multiplicative
algorithm, affine algorithm.
Transposition is a rearrangement of letters of a message
according to a certain algorithm. In other words
1. Introduction
In the field of Data Communication, security-issues have
Transposition is an encryption in which the letters of the
message are rearranged–(permutation of bits).
the top priority. Classical cryptography is one of the ways
Substitution is a more robust and versatile form of
to secure plain text messages. Cryptography addresses the
cryptography. As the name suggests, characters in the
necessary elements for secure communication namely
original text (known as plaintext in crypto speak), are
privacy, confidentiality, key exchange,
substituted by other characters or symbols using certain
algorithm.
Cryptographic systems are divided into two types of
II.
Binary Audio Cryptography
II.
systems:
I.
I.
Non-binary Audio Cryptography
Secret-Key(Symmetric) cryptosystems
2. Literature Review
Public-Key(Asymmetric) cryptosystems
1.1 Secret-Key Cryptosystems:
Random binary sequences are used as running key
Both the sender and receiver have previously set up secret
sequence in stream cipher system. Here message is in the
information called key in which they use this information
form of binary sequence is encrypted by adding bit by bit
for encryption and Decryption.
modulo 2 a binary random sequence called key sequence
and decrypted at the receiver using the same random key
sequence generated at the receiver.
Linear Feedback Shift Registers (LFSRs) are important
building blocks for generating key-sequences. Maximum
length sequences called m-sequences generated by an n
stage
Figure1.1: Secret key cryptosystems
Linear Feedback Shift Registers have very good
randomness properties such as long period, ( 2n-1),
balance,
1.2 Public-Key (asymmetric) Cryptosystems:
The sender uses public key of the receiver to send
a message securely. The receiver then uses private key to
recover original information.
ideal
autocorrelation
and
good
statistical
properties which are desirable characteristic [1].
Also
LFSR can be easily implemented both in hardware and
software.
However
m-sequences
have
low
linear
complexity. For an m-sequence of length 2n-1 the linear
complexity is n. In this case only 2n consecutive bits are
required to determine the feedback polynomial of the LFSR
and hence the entire sequence. In the practical stream
cipher designs, a large linear complexity of the key stream
is obtained by a nonlinear transformation of the LFSR
output sequence or nonlinear feedback shift register
The use of nonlinear feedback mechanism to produce
Figure1.2: Public key cryptosystems
1.3 Audio cryptography:
In which the cipher text and the key correspond to music in
pseudorandom sequence is discussed in [2], [3]. Some of
the methods of transformation define three general design
categories combination generators; filter generators and
clock controlled generators [2].
which the phase has been changed. Playing the cipher-text
and the key together one can obtain music which is either
However the existing encryption algorithms use bit by bit
loud or quiet depending whether the plaintext is 0 or 1.
operations. In this bit by bit the only possible operation is
XOR. To introduce other additional operations the
Classification of Audio Cryptography:
minimum requirement is a byte. This leads to the
introduction of Non-binary system i.e our proposed system
i.
Modulo Additive
[4].
ii.
Modulo Multiplicative
iii.
Affine( combination of two)
3. Proposed System
Methodology:
Transposition and Z4 System [6] for Audio Encryption
highlights use of cryptography and their use in highly
In this process of audio encryption from the source audio
Secured Audio cryptography system. The proposed audio
stream is taken. This may be of the format 2 k where k
cryptography scheme is perfectly secure and easy to
depends on the audio structure. (For example if k is 3 then
implement. In this work we discuss the property of binary
one byte 4 means 16 bit or two bytes …). After taking the
sequences generated using linear feedback shift register [5]
data from the source, this will be split in to n number of 2 2
defined over Z4 and its application in audio cryptography.
sets. These n sets are encrypted using the method
In this algorithm random number is generated based on
mentioned in this section earlier. After completion of the
feedback shift register with seed value / values. Since the
encryption all n number of 22 sets is concatenated to get the
audio cryptography has got importance of on-line
cipher text. This cipher text is sent to the destination and
processing, it should have faster encryption and decryption
decrypted accordingly.
process. For making the processes faster, we use parallel
operation for encryption and decryption.
The main objectives of this work are:
The proposed system has a block in which we have
described about encryption, this block of encryption is
divided in to three separate categories. First one is additive
second one is multiplicative and last is affine. In additive

process encryption and decryption using basic
the plain text is added modularly with the key to generate
arithmetic operations rather than using ex-OR
cipher text. In multiplicative cipher we use the concept of
parallel operations in encryption and decryption for
multiplication and multiplicative inverse for the encryption
faster processing
and decryption. In multiplicative inverse only XOR is

higher immunity to many types of attacks
possible, that means it follows binary system. The last one

study and analysis of the properties of the cipher
in
system with respect to Z4
multiplicative algorithms are used. In which the cipher text
In this work we discuss the property of binary
which we get from additive is used as plaintext for the
sequences generated using linear feedback shift
multiplicative.

register defined over Z4 and its application in audio
cryptography. In this algorithm random number is
generated based on feedback shift register with seed
value / values. Since the audio cryptography has got
importance of on-line processing, it should have faster
encryption and decryption process. For making the
processes faster, we use parallel operation for
encryption and decryption.
In this proposed Z4 system we are using 3-algoritms
for encryption and decryption process. They are
which
the
combination
of
both
additive
and
3.1 Encryption
Figure 3.1: Detailed activity diagram for encryption process
3.2 Decryption:
Figure3.2 Decryption part of Z4 system for audio encryption
model
Steps:
Steps:
1.
N-bit plain text is split into k 2-bits.
2.
Each 2-bit plain text is encrypted using the
1.
N-bit cipher text is split into k 2-bits.
random number generated by the help of mod 4
2.
Each 2-bit cipher text is decrypted using the same
3.
operation.
random number generated used in encryption
While encryption additive, multiplicative and
process by the help of mod 4 operation.
affine operations are used.
4.
3.
affine operations are used.
The encrypted k bit message is converted from
parallel to serial.
While decryption additive, multiplicative and
4.
The decrypted k bit message is converted from
parallel to serial.
3.3 Example:
Encryption Part
Audio information (Plain text) =123 i.e. 01111011
Additive Cipher (mod 4):
0 1
1
1
1
1
0
1 1
due to the XOR operations. The earlier disadvantage is
overcome in this process of Z4. This project adapts the
modular arithmetic related algorithms; hence algebraic
attack may not be possible. This arithmetic can be
implemented if and only if the number of bits used for the
operations are greater than or equal to two. This work has
got inherent immunity to side channel and known plain text
attack, since both encryption and decryption process works
in parallel.
Cipher text= 202 i.e. 11001010
6. References
4. Result
In this work secure audio encryption like, additive,
[1] S. Golomb, “Shift Register Sequences”, Aegean Park
Multiplicative and affine Non-Binary Systems are used
Press (1982) reprint, Laguna Hills,California,1967
with algorithm other than binary, which is more secure than
[2] A. Menezes, P, Van Oorschot, and S. Vanstone,
binary cipher systems. The processes of affine cipher
Handbook of Applied Cryptography. CRC Press,1997
system use two keys, which is for additive and
[3] Bruce Schneier, Applied Cryptography, Second
multiplicative, which can be considered as double secured.
Edition, John Wiley and Sons, 1996.
The parallel operation of Z4 systems gives an inherent
[4] M.J.B. Robshaw. “Stream Ciphers” , RSA Laboratories
nature of side channel attack. The nonlinearity of the key
Technical Report TR-701,Version 2.0,July 25, 1995
generation which yields in algebraic attack. Encryption and
[5] Andrew Rukhin et.al, “A Statistical Test Suite for
decryption process using with more complex algorithm on
Random and Pseudorandom Number Generators for
the basis of arithmetic operations rather than using ex-OR,
Cryptographic Applications ” , NIST Special Publication
which is used in the present existing system. Analyzing the
800-22 Revision 1, May2010
properties of cipher system with respect to Z4, by which
[6] Raghunandan K R et.al, “
proving that this is faster and more immured way of
Efficient
transferring audio. It can be used in mobile audio system
Applications Using Transposition And MultiplicativeNon-
since it is faster in process. This process can also be used
Binary System”, JERT Vol. 2 Issue 6, June - 2013
for the encryption of audio storage. Still processing is
going on, increase in performance of certain parameter is
shown later.
5. Conclusion
Basically in almost all existing audio transmission system
the security is based on binary encryption and decryption
methods. In which algorithm used for the encryption is of
only exclusive OR (XOR). Even if the system goes for
parallel process, in case of encryption algorithm used is
XOR, this leads to less immunity for cryptographic process
Audio
Encryption
Algorithm For
Online