Audio Steganography using Dynamic Cover Generation

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ISSN (Print) : 2319 – 2526, Volume-2, Issue-4, 2013

41

Audio Steganography using Dynamic Cover Generation

1Vivek Sampat, ²Shrita Karmokar, ³Jigar Madia, ⁴Kapil Dave & ⁵Parag Toprani

1,2 IT Department, Saraswati College of Engineering, Kharghar, Navi Mumbai – 410210, India

3IT Department, S.A.K.E.C,Chembur, Navi Mumbai – 400088, India

4IT Department, PVPP college of Engineering, Sion, Mumbai – 400022, India

5IT Department, Ramniranjan Jhunjhunwala college, Ghatkopar, Mumbai-400086

Abstract — With active research in the field of information security and steganography, it is seen that newer and better methods are being developed in order to make the information more secure and communication more reliable. Sensing the need of a fast and effective data hiding approach, we propose an advanced system of audio steganography, which generates a personalized cover dynamically for hiding data within itself. An attempt has been made to make the generated cover meaningful by keeping in mind the concept of musical scales during the generation process.

Keywords—Audio Steganography, Dynamic cover generation, Musical scale and note.

I. INTRODUCTION

One of the concern in the field of information system is the that of security and privacy. There are various methods of data hiding to overcome these problems. Some of these techniques like low bit coding, phase coding, spread spectrum and echo hiding for hiding data in audio are suggested by Bender, Walter, et al. [1].

Covert communication has been increasingly being used today as a secure means for the transmission of the data.

Audio steganography is concerned with hiding information in such a way that the users are not aware of its existence. A steganographic system embeds hidden content into a cover file in an unremarkable manner so as to not to generate suspicion. By hiding the information in the audio cover the existence of the information is sealed [2][3]. The cover that is used in most steganographic systems is only a mere carrier of information, as messages are hidden by slightly modifying the cover itself.

In our previous research [3], we suggested a new steganographic system where the cover media itself was generated by the system, and an existing cover was not used. This system, however, generated video covers, and the prerequisite for the system made it expensive. The

concept of dynamic cover generation can be used for audio steganography as well.

Zamani, Mazdak, et al. [13] have discussed how steganographic algorithms can be characterized using different properties, highlighting three of them that were most important for audio steganographic algorithms.

These properties were transparency, capacity and robustness. We will try to understand how dynamic cover generation[3] performs keeping these properties in mind in the section below:

 The transparency of property judges how well successful the system is in creating outputs in which hidden content is not perceivable. The cover generated will represent the data itself, and it is difficult to know what the cover itself means. This creates a certain level of transparency.

 The capacity of the system is the amount of data that the system can hide without distorting the cover itself. As the cover is dynamically generated, the capacity of the system improves.

This is because the cover will be generated based on the requirements. Larger amount of data may cause generation of large covers.

 The covers generated will have better robustness as the unintentional operations like lossy compression, which generally affect hidden data, are aimed at not to change the meaning of the cover itself, leaving the generated cover recognizable for decoding.

Keeping in mind the above advantages of dynamic cover generation technique, along with the current requirement of a fast, efficient steganographic process, we introduce an enhanced approach for audio steganography.

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International Journal on Advanced Computer Theory and Engineering (IJACTE)

42 II. RELATED WORK

A dynamic cover generation for steganography and the increased level of protection it provided was discussed in [3].

Steganographic systems evolved into a lot of levels.

The first level of protection is determined only by the choice of embedding algorithm. This may be the least significant bits modification algorithm, or algorithms for modifying the frequency or spatial-temporal characteristics of the container.

The second protection level of the steganographic system, as well as all levels of protection of the higher orders, is characterized by the use of Key (password) via steganographic modification. Steganographic data channels that use key schemes based distribution of a message through the container and or preprocessing of an embedded message for data hiding are more secure.

When the third protection level key scheme is used it affects the distribution of a message through the container.

The difference between the fourth protection level scheme and the third one is that in steganographic system there are two distribution functions of a message within a container are used. The first is responsible for a message samples selection according to some function G (Q, N), and the second function F (P, L) is responsible for position selection in a container for message sample hiding. Here Q – the size of message block to be inserted; N – the size (in bits) of one sample of the message file.

Problems with the existing systems:

1. In this system the cover file acts as a mere carrier of message and is a big overload in videos.

2. The system cannot encompass two algorithms at once .As all of it is hidden across the cover file using a single algorithm.

3. If this method of hiding breaks then there is no other security.

SAU-Steganographic algorithm usage KU-Key (password) usage

KIMD-Key influence on a message distribution KIMSD-Key influence on a message selection and distribution

KIC- Key influence on cover generation

The proposed system tends to overcome these problems by considering one more level of security in the system i.e level 5.

The general architecture that provides with level 5 security in a steganographic system was suggested in [3]

and is shown in fig 1.

Fig 1: General Architecture(Level 5)

The following notations are used in the architecture:

c - is a container file;

F - steganographic channel space;

SC - steganographic system;

m - message to be embedded;

E - embedding method;

ĉ - modified container file.

This new system uses a distribution function of a message within a container F(P,L). It also uses another distribution function to select the message samples G(Q,N). These functions relate to the digital steganography used, the details of which can be found in [3].

III. PROPOSED SYSTEM

The proposed system aims at generating audio files containing a particular set of frequencies. 41 frequencies are selected of which two octaves and one additional note of 13 scales can be considered. The scale selected, amplitude used for the audio and the sample rate can be pre-determined by both sender and receiver to an acceptable value. When the receiver gets an audio with the selected values, the message can be authenticated in a way.

The detailed processes suggested for communication establishment and cover generation are explained below:

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43 Step 1: Establish Communication Rules

In this step we perform the task of establishing communication with the receiver of the message. This step is specially emphasized as it sets the basic rules of communication and steganography between the sender and receiver. During this step the scale to be used is established by the sender along with the sample rate and amplitude. Multiple scales and amplitudes can be used in a particular sequence while cover generation. The decision of whether to use multiple scales and amplitude values, and if used, the sequence of values considered for these scales and amplitudes, can be taken in this step. The rules that are set in this step will decide the level of security that can be achieved in the communication that will take place.

Step 2: Cover Generation

This process is done by taking blocks of the message to be sent. The cover generation itself will require 8 bits of the message block referred to as 'A' Block in fig 2; which are used as follows:

4 bits for note selection 2 bits for note duration

2 bits for duration of silence (after the note)

The selection of these 8 bits can be done by the use of a key, or the first 8 bits of the message block can be selected straight away.

The remaining bits of the message block will be hidden in the audio generated by the previously selected 8 bits of the same block(explained in step 3). The algorithm used for hiding these remaining bits can vary, and hence the amount of hidden data too will vary. We consider 8 bits to be hidden (referred to as D Block in fig 2) in the generated audio, hence, making the size taken for the message block 16 bits.

The step wise procedure for cover generation is given below:

(a) divide message into blocks of size 16 bits (b) Consider first 4 bits (1 to 4) of the block for

selection of note from current scale.

 The current scale is the scale that was decided upon at step 1. If multiple scales were selected in step 1, then the current scale will be the one in use for the current message block. In the case of multiple scales, the current scale may change every 'x' message blocks, where x>=1, and is per-determined in step 1.

 Selection of note for each value will depend on the current musical scale used. Considering the current scale to be the E scale, starting from E2

- 82.41Hz and 2nd octave ending at F#4 – 329.6Hz (total 2 octaves and one additional note), if the 4 bits are 0000, E2 will be selected, F#2 will be selected for 0001 and so on till E4 for 1111. It must be noted that the only ionian major scales are considered here.

(c) The next 2 bits(5 & 6) will determine the duration for which the note will be plated.

(d) The next two bits(7 & 8) will determine the duration of silence after each note.

(e) The remaining bits (9 to 16) are hidden in the generated audio.

(f) Repeat (b)-(e) for each block of message.

(g) Generate the audio

Fig 2: Cover Generation and Data Hiding Step 3: Hide data in Audio File

In this step, the D Blocks mentioned in fig 2 will be hidden in the generated audio. As explained earlier, in step 2, the system considers blocks of size 16 bits, by considering 8 bits to be added per clip generated by the particular block. However, the amount of data that can be hidden in a particular block of data can depend on the algorithm used for hiding.

The possible algorithms that can be used in order to hide the data can be echo hiding, LSB hiding, etc.

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44 IV. EXPERIMENTAL RESULTS

The system was implemented in MATLAB R2011a, using the frequency range of 82.41Hz to 659.3 Hz which are all the nodes that are found on a guitar.

The frequency selection was done keeping in mind that the audio generated did not have too high or too low frequency. Selection of notes based on scales made the generated audio meaningful, rather than just random noise. The length of the message blocks considered was 16 bits, and the algorithm used for hiding data was Echo Hiding for hexadecimal data.

The output audio file was transferred over to other systems using a variety of communication mediums and was checked after decryption to see the actual file is getting retrieved back. In almost all cases the input message was deciphered correctly without introducing noise or giving errors. The effect of noise on hidden data varied depending on the use of steganography algorithm to hide the 8 bit data in a generated audio chunk. Thus the experiment results were overall successful proving the efficiency and reliability of the steganography system.

V. CONCLUSION

With the success of our experiment results we are quite certain that the developed system is a really good technique of steganography based on a totally undiscovered domain which greatly enhances the future possibilities of this method. Also this system can tackle many difficulties of steganography like adjusting cover according to message, reducing the size of resultant file to be sent etc.

VI. FUTURE SCOPE

This technique provides an immense possible number of future work due to its novelty of cover generation based on the message to be hidden. In future a few of the areas which can be worked on can be to make the audio file available with 2 tracks of different notes of high and low frequencies playing simultaneously providing the actual feeling of a musical audio. Also the use of musical chords can be done to be able to hide more amount of data.

VII. REFERENCES

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