Information different cover objects (signals) can be used

Information
hiding technique is a new kind of secret communication technology. The majority
of today’s information hiding systems uses multimedia objects like audio.
Embedding secret messages in digital sound is usually a more difficult process.
Varieties of techniques for embedding information in digital audio have been
established. In this paper we will attend the general principles of hiding
secret information using audio technology, and an overview of functions and
techniques.

1. Introduction

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The fast improvement of
the Internet and the digital information revolution caused major changes in the
overall culture. Flexible and simple-to-use software and decreasing prices of
digital devices (e.g. portable CD and mp3players, DVD players, CD and DVD
recorders, laptops, PDAs) have made it feasible for consumers from all over the
world to create, edit and exchange multimedia data. Broadband Internet connections
almost an errorless transmission of data helps people to distribute large
multimedia files and make identical digital copies of them. In modern
communication system Data Hiding is most essential for Network Security issue.
Sending sensitive messages and files over the Internet are transmitted in an
unsecured form but everyone has got something to keep in secret. Audio data
hiding method is one of the most effective ways to protect your privacy.

 

2. Overview

 

General principles of
data hiding technology, as well as terminology adopted at the First
International Workshop on Information Hiding, Cambridge, U.K. 1 are
illustrated in Figure 1. A data message is hidden within a cover signal
(object) in the block called embeddor using a stego key, which is a secret set
of parameters of a known hiding algorithm. The output of the embeddor is called
stego signal (object). After transmission, recording, and other signal
processing which may contaminate and bend the stego signal, the embedded
message is retrieved using the appropriate stego key in the block called
extractor 2.

A number of different
cover objects (signals) can be used to carry hidden messages. Data hiding in
audio signals exploits imperfection of human auditory system known as audio
masking. In presence of a loud signal (masker), another weaker signal may be
inaudible, depending on spectral and temporal characteristics of both masked
signal and masker 3 Masking models are extensively studied for perceptual
compression of audio signals 2 In the case of perceptual compression the
quantization noise is hidden below the masking threshold, while in a data
hiding application the embedded signal is hidden there. Data hiding in audio
signals is especially challenging, because the human auditory system operates
over a wide dynamic range. The human auditory system perceives over a range of
power greater than one billion to one and a range of frequencies greater than
one thousand to one. Sensitivity to additive random noise is also acute. The
perturbations in a sound file can be detected as low as one part in ten million
(80 dB below ambient level).However, there are some “holes” available. While
the human auditory system has a large dynamic range, it has a fairly small
differential range. As a result, loud sounds tend to mask out quiet sounds.
Additionally, the human auditory system is unable to perceive absolute phase,
only relative phase. Finally, there are some environmental distortions so
common as to be ignored by the listener in most cases 4. Now we will discuss
many of these methods of audio data hiding technology.

 

3. Previous
works

 

This section presents
some common methods used for hiding secret information in audio. Many software
implementations of these methods are available on the Web and are listed in the
relatives section. Some of the latter methods require previous knowledge of
signal processing techniques, Fourier analysis, and other areas of high level
mathematics. When developing a data-hiding method for audio, one of the first
considerations is the likely environments the sound signal will travel between
encoding and decoding. There are two main areas of modification which we will
consider. First, the storage environment, or digital representation of the
signal that will be used, and second the transmission pathway the signal might
travel 4.

 

3.1. Parity
coding

 

One of the prior works
in audio data hiding technique is parity coding technique. Instead of breaking
a signal down into individual samples, the parity coding method breaks a signal
down into separate regions of samples and encodes each bit from the secret
message in a sample region’s parity bit. If the parity bit of a selected region
does not match the secret bit to be encoded, the process flips the LSB of one
of the samples in the region. Thus, the sender has more of a choice in encoding
the secret bit, and the signal can be changed in a more unobtrusive fashion
5. Figure 2, shows the parity coding procedure.

3.2.
Phase Coding

 

The phase coding method
works by substituting the phase of an initial audio segment with a reference
phase that represents the data. The phase of subsequent segments is adjusted in
order to preserve the relative phase between segments. Phase coding, when it
can be used, is one of the most effective coding methods in terms of the
signal-to perceived noise ratio. When the phase relation between each frequency
component is dramatically changed, noticeable phase dispersion will occur.
However, as long as the modification of the phase is sufficiently small (sufficiently
small depends on the observer; professionals in broadcast radio can detect
modifications that are unperceivable to an average observer), an inaudible
coding can be achieved 4. . Phase coding relies on the fact that the phase
components of sound are not as perceptible to the human ear as noise is. Rather
than introducing perturbations, the technique encodes the message bits as phase
shifts in the phase spectrum of a digital signal, achieving an inaudible
encoding in terms of signal-to-perceived noise ratio 5.

Phase coding is
explained in the following procedure:

 

a.     
The original sound signal is broken up
into smaller segments whose lengths equal the size of the message to be
encoded.

b.    
A Discrete Fourier Transform (DFT) is
applied to each segment to create a matrix of the phases and Fourier transform
magnitudes.

c.     
Phase
differences between adjacent segments are calculated.

 

d.    
Phase shifts between consecutive
segments are easily detected. In other words, the absolute phases of the
segments can be changed but the relative phase differences

Spread Spectrum

 

In a normal
communication channel, it is often desirable to concentrate the information in
as narrow a region of the frequency spectrum as possible in order to conserve
available bandwidth and to reduce power. The basic spread spectrum technique,
on the other hand, is designed to encode a stream of information by spreading
the encoded data across as much of the frequency spectrum as possible. This
allows the signal reception, even if there is interference on some frequencies.
While there are many variations on spread spectrum communication, we
concentrated on Direct Sequence Spread Spectrum encoding (DSSS). The DSSS
method spreads the signal by multiplying it by a chip, a maximal length
pseudorandom sequence modulated at a known rate. Since the host signals are in
discrete-time format, we can use the sampling rate as the chip rate for coding.
The result is that the most difficult problem in DSSS receiving, that of
establishing the correct start and end of the chip quanta for phase locking
purposes, is taken care of by the discrete nature of the signal. Consequently,

 

a much higher chip
rate, and therefore a higher associated data rate, is possible. Without this, a
variety of signal locking algorithms may be used, but these are computationally
expensive 4.

 

Procedure: In DSSS, a
key is needed to encode the information and the same key is needed to decode
it. The key is pseudorandom noise that ideally has flat frequency response over
the frequency range, i.e., white noise. The key is applied to the coded information
to modulate the sequence into a spread spectrum sequence.

 

The DSSS method: The
code is multiplied by the carrier wave and the pseudorandom noise sequence,
which has a wide frequency spectrum. As a consequence, the spectrum of the data
is spread over the available band. Then, the spread data sequence is attenuated
and added to the original file as additive random noise (see Figure 4). DSSS
employs bi-phase shift keying since the phase of the signal alternates each
time the modulated code alternates (see Figure 5). For decoding, phase values
f0 and f0 + p are interpreted as a “0” or a “1,” which is a coded binary string
4. Spread Spectrum is shown in Figure 5.

 

In the decoding stage, the
following is assumed:

 

a.     
The pseudorandom key is maximal (it has
as many combinations as possible and does not repeat for as long as possible).
Consequently it has a relatively flat frequency spectrum.

 

b.    
The key stream for the encoding is known
by the receiver. Signal synchronization is done, and the start/stop point of
the spread data is known.

 

c.     
The following parameters are known by
the receiver: chip rate, data rate, and carrier frequency.

 

 3.4. Echo
Hiding

 

In echo hiding,
information is embedded in a sound file by introducing an echo into the
discrete signal. Like the spread spectrum method, it too provides advantages in
that it allows for a high data transmission rate and provides superior
robustness when compared to the noise inducing methods. If only one echo was
produced from the original signal, only one bit of information could be
encoded. Therefore, the original signal is broken down into blocks,

 

 

before the encoding
process begins. Once the encoding process is completed, the blocks are
concatenated back together to create the final signal 5. Echo Hiding is shown
in Figure 6.

 

Also, a message can be
encoded using musical tones with a substitution scheme. For example, a Fistone
will represent a 0 and a C tone represents a 1. A normal musical piece can now
be composed around the secret message or an existing piece can be selected
together with an encoding scheme that will represent a message 7, 8.

 

 

 

4. Proposed work

 

Here we will discuss
the disadvantages of the previous procedure and how those are different with
present method. There are two main disadvantages associated with the use of
methods like parity coding. The human ear is very sensitive and can often
detect even the slightest bit of noise introduced into a sound file, although
the parity coding method does

 

come
much closer to making the introduced noise inaudible. Another problem is
robustness. One disadvantage associated with phase coding is a low data
transmission rate due to the fact that the secret message is encoded in the
first signal segment only. Phase coding method is used when only a small amount
of data needs to be considered.

 

Least significant bit
(LSB) coding is the simplest way to embed information in a digital audio file.
By substituting the least significant bit of each sampling point with a binary
message, LSB coding allows for a large amount of data to be encoded. Among many
different data hiding techniques proposed to embed secret message within audio
file, the LSB data hiding technique is one of the simplest methods for
inserting data into digital signals in noise free environments, which merely
embeds secret message-bits in a subset of the LSB planes of the audio stream.

 

The following steps are:

 

a.     
Receives
the audio file in the form of bytes and converted in to bit pattern.

 

b.    
Each
character in the message is converted in bit pattern.

 

c.     
Replaces
the LSB bit from audio with LSB bit from character in the message.

 

This proposed system is
to provide a good, efficient method for hiding the data from hackers and sent
to the destination in a safe manner. This proposed system will not change the
size of the file even after encoding and also suitable for any type of audio
file format. Encryption and Decryption techniques have been used to make the
security system robust.

 

Low-bit encoding embeds
secret data into the least significant bit (LSB) of the audio file. The channel
capacity is 1KB per second per kilohertz (44 kbps for a 44 KHz sampled
sequence). This method is easy to incorporate.

 

5. Applications

 

Audio data hiding can
be used anytime you want to hide data. There are many reasons to hide data but
most important is to prevent unauthorized persons from becoming aware of the
existence of a message. In the business world Audio data hiding can be used to
hide a secret chemical formula or plans for a new invention. Audio data hiding
can also be used in corporate world.

 

Audio data hiding can
also be used in the noncommercial sector to hide information that someone wants
to keep private. Terrorists can also use Audio data hiding to keep their
communications secret and to coordinate attacks. In the project ARTUS1 which
aims to embed animation parameters into audio and video contents 10. Data
hiding in video and audio, is of interest for the protection of copyrighted
digital media, and to the government for information systems security and for covert
communications. It can also be used in forensic applications for inserting
hidden data into audio files for the authentication of spoken words and other
sounds, and in the music business for the monitoring of the songs over
broadcast radio.

 

6. Conclusion

In this paper we have
introduced a robust method of imperceptible audio data hiding. This system is
to provide a good, efficient method for hiding the data from hackers and sent
to the destination in a safe manner. This proposed system will not change the
size of the file even after encoding and also suitable for any type of audio
file format. Thus we conclude that audio data hiding techniques can be used for
a number of purposes other than covert communication or deniable data storage ,
information tracing and finger printing, tamper detection. As the sky is not
limit so is not for the development. Man is now pushing away its own boundaries
to make every thought possible. So similarly these operations described above
can be further modified as it is in the world of Information Technology. After designing any operation every developer has a
thought in his mind that he could develop it by adding more features to it.    

 

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