Short Message (Service) as Key for Steganography

INTRODUCTION

With the boom in communication and technology and with the widespread use of Internet, free flow of information is possible. And with this increase in technologies for transfer of information, there is a considerable increase in need for protection of this information too. This need gave birth to information security and techniques like cryptography, water marking and steganography (Amirtharajan et al., 2012; Cheddad et al., 2010) were developed.

Cryptography (Schneier, 2007) is the art of scrambling of data in an unintended format so that no one other than the authorized receiver can decode it. It would look gibberish to any third person viewing it. But it has a disadvantage in that a person looking at it would find out that it is some encoded secret message. And if he gets hold of the secret code then any third person can extract it.

Eventually steganography gained its importance because it keeps the very existence of the message as a secret. Steganography has gained much appreciation in the recent past because of this. It involves a cover image, a secret data and a key. It is implemented in various media (Cheddad et al., 2010; Petitcolas et al., 1999; Karzenbeisser and Perircolas, 2000) for example digital audio (Zhu et al., 2011), images (Bender et al., 1996; Amirtharajan and Balaguru, 2009; Chan and Chen, 2004; Janakiraman et al., 2012; Padmaa et al., 2011; Thanikaiselvan et al., 2011a, b), text (Xiang et al., 2011; Yang et al., 2011; Liu et al., 2008; Shirali-Shahreza and Shirali-Shahreza, 2006, 2007; 2008; Al-Azawi and Fadhil, 2010; Low et al., 1995; Kim et al., 2003; Niimi et al., 2003; Rabah, 2004; Huang and Yan, 2001; Beare, 2007; Shahreza 2005 or even videos (Al-Frajat et al., 2010).

Of these three, image steganography has got much commendation. Here the vital information is dissembled in a cover image and a stego-image is created. This embedded secret message is invisible to naked eye, thus making our secret data safe from intruder's eyes.

The three main characteristics of steganography areimperceptibility, capacity and its robustness (Amirtharajan et al., 2011; Amirtharajan and Rayappan, 2012a-d). The total amount of secret information that can be hidden in a Stego-image defines its capacity. Robustness is the limit of modifications an adversary would have to do before he can break the secret code and get the hidden message.

Methods in spatial domain and methods in frequency domain are the two main classifications of Information hiding (Amirtharajan et al., 2012; Rajagopalan et al., 2012). When the data is directly injected in image pixels it is spatial domain approach, whereas, when the image is first transformed into frequency domain and then embedded then it is frequency domain approach (Amirtharajan and Rayappan 2012d; Provos and Honeyman, 2003).

LSB based approach (Amirtharajan and Rayappan 2012d), PVDbased approach (Padmaa et al., 2011) and mod based (Chan and Chen, 2004) approach are the approaches available in order to increase the characteristics of steganography, i.e., to make the image more robust or more imperceptible. Before transformation the cover image exists in the spatial domain later it is transformed to time or frequency domain and again it is brought back to the spatial domain. Techniques like DCT (Provos and Honeyman, 2003). DWT or IWT (Thanikaiselvan et al., 2011a; Amirtharajan and Rayappan, 2012d) are used for transformation. Cryptography together with steganography could be an effective solution to improve the complexity (Karzenbeisser and Perircolas, 2000).

SMS is said to be born in 1980s for quick and discreet communication and is later developed to be exercised in accordance with globally employed technologies TDMA and GSM (Shahreza, 2005). Since it is non-voice, economical, speedy and targeting (sms are sent only to defined recipients) features makes it more eligible for use as cover for covert communication. SMS’s function and service is doable which makes overhearing outrageous. Maximum of 160 characters can be sent in a message which is decided by the individual service providers and networks. Lengthier smses are divided into many short messages and then sent to the destination.

This paper will propose a new way of hiding data using time delay between the successive SMS in real time application.

LITERATURE REVIEW

Let us see the frequently used terms. Medium used for veiling confidential message, termed payload, is nothing but cover. The outcome of a steganographic technique is known as stego object and the index used for embedding and recovery is called stego key.

SMS-texting (Beare, 2007): It is a new language used throughout the world for rapid communication. SMS texting has discovered new abbreviated form of English (!) which faces callous censure. Despite this, it has gained popularity as it consumes less time, high redemption cum open rate and its ease of use is also worth mentioning. To quote an example, in place of “Good morning”, it is enough to say “Gud mrn”.

Existing text steganography in SMS (Shirali-Shahreza, 2006): This method has predefined catalog of words and their corresponding ellipsis. In a text (SMS), in lieu of bits zero and one, the steganographic algorithm replaces word and acronym respectively which are part of the predefined list. Only the people knowing the routine can recover hidden information.

Persian/Arabic text steganography (Shirali-Shahreza and Shirali-Shahreza, 2006, 2008; Al-Azawi and Fadhil, 2010): This method makes use of Arabic and Persian fonts to hide data as they have special and unique characters. Their linguistic pattern contains more dots; thus, their displacement is used to screen large volume of secret data in text. This technique is applicable only for Arabic and Persian and not for English, since the latter has only two letters having dots (i, j).

LINE shifting (Low et al., 1995): The technique best apt for the printed texts wherein there is a requirement for the vertical shift of the lines of the printed text to a few degrees (say up/down shift of 1/300 inch). The clandestine fact is then concealed within, through crafting a novel text shape. However, the scheme has a hitch of its own. In case, any out of the ordinary instruments used could observe the distance, then by the distance monitoring & essential changes, the hidden secret is destroyed. Moreover, if OCR or retyping of text takes place, buried message will be ruined.

WORD shifting (Low et al., 1995; Kim et al., 2003): Here, the shifting of the words is done horizontally or by altering the distance between them, is employed for rooting data in texts. A drawback here lies in using OCR programs or the Re-typing the text resulting in the mar of the hidden information. This method is best suited where the space between words keeps varying in texts. Filling up a line by modification of distance amidst words is pretty universal; it has comparatively less identity in terms of recognition. However, if anyone knows the distance between words, one can go for comparison of the text at hand and algorithm by using difference methodology and can extract the concealed information. Despite this routine consumes more time, high stake in knowing the hidden content is palpable.

Feature Coding (Bender et al., 1996; Rabah, 2004): In Feature Coding, a few text characteristics are tainted, like, some characters’ concluding parts (like b, d or h) are enhanced, say, either abbreviated or stretched out and therein, the information is buried. By this way, a voluminous amount of secret can be infixed with leaving no trace for the readers. If the characters are retained in their original preset shape, information gets lost and re-typing of text by OCR may annihilate the secrets.

Open spaces (Huang and Yan, 2001): In the method- open white spaces, information hiding in texts is implemented by the addition of more white spaces. They can be inserted at each paragraph’s end or between words or at the end of each line. Therefore, this mechanism gets employed in random texts without grabbing readers’ interest. Nonetheless, quantity of information hidden by open SPACES is limited and besides, covert data may be wiped out if the additional white spaces are deleted by text editing programs.

Sematic method (Niimi et al., 2003): In this methodology, text hiding is done through utilizing the words’ synonyms. This feature is more secure in spite of re-typing and OCR. However, the meaning of the text may succumb to variations by this method.

Stealth steganography in SMS (Shirali-Shahreza, 2006): In this work, steganography is done on picture SMS messages. Here, after converting the picture into black and white and apt layout for mobiles, it is segmented into 3x3 dimensioned blocks. Password is used to encode the covert data and for each block if steganography is possible and if tested positive, 1 bit of secret data is embedded by changing that particular block. Recovery is just the opposite of embedding. After morphological recovery of secret, picture message can be hoarded in the mobile of the receiver with no secret data.

PROPOSED METHOD

In this method, imperceptibility and robustness is very high, capacity is moderate and security lies in the algorithm. The proposed schematic diagram is given in Fig. 1.

Method 1: Steps to follow to encrypt:

Fig. 1:	Schematic diagram of the proposed methods

Extraction Method
Once the desired person knows in which way you have assigned the time, he or she can decrypt it (reverse of encryption).

Advantages:

Disadvantage: When delay is used in minutes, the characters sent is very less (time-depends on the message content).Time taken to send 27 characters at a stretch from(a to z and space) is 6.3 h. Example:

Method 2: Steps to be followed while embedding:

“etaon rishd lfcmu gypwb vkxjq z”

Allocate time for each character according to the above. But it makes the job easy for the hackers. So, change the time allocated to each character every time you send message or keep a particular sequence fixed but give less time allocation for the most frequently used words.

Schedule the messages using your cell phone. 4. Now send the messages to the desired person. He will receive the message in which the send time is specified. Table 1-3 provide the time allocated to symbols, characters and numbers.

Table 1:	Time delay allocated for characters and symbols

Table 2:	Time delay allocated for characters and numbers

Table 3:	Time delay allocated for alphabets, characters and symbols

Extraction method: Once the desired person knows in which way you have assigned the time, he or she can decrypt it (reverse of encryption).

Advantages:

Disadvantage: When delay is used in minutes, the time taken to deliver all the messages is high. On comparing it with the above method the time taken to send a passage or message is reduced.

Example: Feel good when somebody Miss you Feel better when somebody Loves you But feel best when somebody never forgets you Good Friday Time taken is 17.16 h.

Method 3: Steps to be followed while embedding:

Allocate time for each character according to the above. Number of ways in which time is allocated for characters, numbers and symbols are:

Take any one way from the above number of ways.
For example: Let the message to be delivered be –Acharge” In SMS language-“chrg”
Time allocated are “4, 9, 19 and 8 min” Total time = 40 min:

Extraction method: Once the desired person knows in which way you have assigned the time, he or she can decrypt it(reverse of encryption).

Advantages:

Disadvantage: When delay is used in minutes, the characters sent is very less.

Example: Feel good when somebody Miss you Feel better when somebody Loves you But feel best when somebody never forgets you Good Friday.

SMS language:

Time taken is 17.61 h

Method 4: Steps to be followed while embedding:

Decryption method: Once the desired person knows in which way you have assigned the time, he or she can decrypt it (reverse of encryption).

Advantage:

Disadvantage: When delay is used in minutes, the characters sent are very less.

Example: Feel good when somebody Miss you Feel better when somebody Loves you But feel best when somebody never forgets you Good Friday.

SMS language:

Time taken is less than the previous method

Method 5: Steps to be followed while embedding:

Extraction method: Once the desired person knows in which way you have assigned the time, he or she can decrypt it (reverse of encryption).

Advantage:

Disadvantage: When delay is used in minutes, the characters sent is very less.

Example: Feel good when somebody Miss you Feel better when somebody Loves you But feel best when somebody never forgets you Good Friday.

SMS language:

Method 6: Once java program is made in a way that messages can be scheduled in seconds, time duration is reduced considerably.

Example: Feel good when somebody Miss you Feel better when somebody Loves you But feel best when somebody never forgets you Good Friday
Total number of words is 105

SMS language:

Method 7: Way to reduce time consumption: Since, scheduling messages with respect to minutes takes more time, follow the below to reduce the time consumption:

CONCLUSION AND FUTURE IMPROVEMENTS

This method is first of its kind in using time as a cover to hide the secret. When compared to other methods, this steganography form is very simple and secure since one cannot imagine of hiding in texts traded between millions per day. The added advantage here is that it is felicitous to all languages and platforms and its ease in implementing is also a remarkable trait. Even if one senses the mystery, he or she cannot recover the data unless and until he or she knows the index and platform of embedding and especially the key. Hence SMS based steganographic technique is a remarkable path to private communication and this method copes up to the crucial panorama of a perfect, lossless and nonintrusive communication.