A Secured Method for Image Steganography Based On Pixel Values

Transcription

1 A Secured Method for Image Steganography Based On Pxel Values Tarun Gulat #, Sanskrt Gupta * # Assocate Professor, Electroncs and Communcaton Engneerng Department, MMEC, M.M.U., Mullana, Ambala, Haryana, Inda * Research Scholar, Electroncs and Communcaton Engneerng Department, MMEC, M.M.U., Mullana, Ambala, Haryana, Inda Abstract: Steganography s the scence of communcaton that hdes secret nformaton nsde the multmeda sgnal n such a way that the exstence of secret nformaton s concealed. In ths paper mage steganography s done. The text strng s concealed n the cover mage as a payload. The technque s based on pxel value dfferencng and pxel value sum. A secret key s used to control the message embeddng process. At the recever stego mage s manpulated to get the text out of t. PSNR and capacty are used to measure the stego mage qualty. Keywords Steganography, Pxel Value Dfferencng, Pxel Value Sum, Securty. I. INTRODUCTION Durng the last few decades, nternet s becomng a very popular medum for communcaton. But data securty durng transfer through t has become a major challenge. There are two approaches [1] to send the nformaton. One s cryptography, n whch the nformaton s transferred n form of unntellgble text. But n cryptography, ntruder can easly detect the presence of some secret nformaton by observng t. Also, ntruder can apply the cryptanalyss to obtan the nformaton. Another approach s steganography. Steganography makes communcaton unntellgble for the ntruder. In steganography, the secret message s hdden nsde the another carrer so that t looks nnocent as t s not hdng any secret message. Only the authorzed recpent can detect the presence of some ntellgble nformaton. Steganography [2] s art and scence of secret communcaton whch hdes the exstence of the secret data nsde another data to protect t from unauthorzed users. Many dfferent carrers such as audo, vdeo and dgtal mages can be used, but dgtal mages are mostly used because of ther frequency over the nternet. In mage steganography nformaton can be exclusvely stored n mage. The mage used for hdng the secret nformaton s called cover mage. Steganography hdes the nformaton n the cover mage [3] and the fnal mage so formed s called stego mage. Also, the reverse of ths.e. breakng of steganography s called steganalyss. It s mportant that the stego mage must be free from notceable change, so that the thrd party wll not be able to detect any changes and treat ths cover mage as usual mage and secret data send through ths cover mage remans safe. Steganography can be done usng dfferent methods lke Least Sgnfcant Bt Substtuton method, Pxel Value Dfferencng Method, Pxel Value Sum and Dfferencng. In the processng of LSB substtuton [4], the secret data s embedded n the LSB of the pxels n the cover mage. PVD technque [5] s a steganographc method based on dfference of the two consecutve pxels. It hdes the secret data nsde the mage n the nonoverlappng consecutve pxels by changng the dfference value. On the other hand PVS deals wth the sum of the two consecutve pxels n the cover mage. The methods are mplemented n order to obtan the hgh embeddng capacty, more securty and the vsual effects of the mage fle remans preserve. The proposed method of mage steganography s an mprovement to PVS and PVD technque [6] by nsertng a secret key nsde t to make the system more secured [7]. Ths paper s organzed as follows. In secton II prevous work done for both PVD and LSB s presented. In secton III methodology used for hdng secret data along wth securty key s descrbed. In secton IV results of all the technques descrbed n ths paper are compared and fnally conclusons are gven n secton IV. II. PREVIOUS WORK Work has been done n the feld of mage steganography and authors have proposed varous algorthms: A. Least sgnfcant bt substtuton Method The LSB s the lowest sgnfcant bt n the byte of each pxel n the mage. Ths steganography embeds the secret nformaton n the least sgnfcant bts of pxel values of the cover mage. Ths type of embeddng procedure s qute smple. It requres eght bytes of the pxels to store 1 byte of the secret data.e. LSB. Rest of the bts n the pxels remans the same. ISSN: Page 610

2 Suppose the frst eght pxels of the orgnal mage have the followng gray scale values: The letter C whose bnary value s To hde ths bnary value t can replace the LSBs of these pxels to have the followng new gray scale values: In ths example, the underlned LSB s of the pxel values has been changed. The dfference between the cover (.e. orgnal) mage and the stego mage s dffcult to observe by human eye. Many algorthms have been proposed n the lterature based on LSB. Although LSB substtuton s the smplest steganography approach so far but t s not effcent n terms of securty as t s predctable. A very well-known LSB approach s presented n [8] and proposed an adaptve method based on nter pxel relatonshp. Ths approach produces very attractve results but ts retreval s very easy by applyng retreval method. There s no need of any secret nformaton or key before retreval. Ths makes t vulnerable to attacks. Another effcent approach s presented n [9] whch used neghbourhood nformaton to calculate the amount of data that can be hdden n pxels of cover mage. In ths approach, some pxels are overloaded wth data whle some pxels reman unchanged. In ths approach also, secret nformaton can be easly retreved easly. There s another effcent approach presented n [10] n whch secret key s used only to decde whether the secret nformaton bts wll be hdden n green or blue. After decdng ths, secret nformaton bts hdes n LSB of ether blue or green. Although, ths approach ntally promses securty but after that hdng secret bts n LSB s agan not secure and secret data can be extracted after puttng some effort. The major lmtaton of LSB s small sze of data whch can be embedded n such type of mages usng only LSB. The LSB s extremely vulnerable to attacks. B. Pxel Value Dfferencng Method In ths method, the secret data s embeddng n the cover mage. The cover mage pxels and secret data s gven. To hde the data by PVD, the dfference value d s calculated from the two consecutve pxel values p and p +1.e. d p p 1. Then the varous ranges s defned for value such that R [l, u ] and l <d <u. Then the wdth of the range s calculated whose logarthm wll gve the number of secret data bts(t) that wll be hde n ths range. Then a new dfference value s calculated as d' b l, where b s the decmal value of t bts of secret data. The pxel value p and p +1 can be modfed as: Where All the pxel values accordng to the dfference value are set and hence the secret data s embedded. The pxel value dfferencng method s proposed prevously by usng dfferent approaches. Wu and Tsa [11] proposed a steganographc scheme for gray level mages n 2002 to mprove the qualty of the stego-mage, whch utlzed the Human Vsual System senstvty to ntensty varatons from smoothness to hgh contrast by the selecton of the wdth of the range whch the dfference value of two neghbour pxels belongs to. Mandal and Das [12] proposed a method whch mproves the vsual qualty of the PVD method. It also estmate the fallng off problem.pvd ssued for secret data embeddng for each component(red, Green and Blue) separately. Varable number of bts are embedded n each pxel for provng the secured transmsson. Hmaksh et al. [13] provde the another steganographc method whch s based on the pxel value dfferencng scheme dscussed n [11] and [12]. The data s embedded n ths method by embeddng the secret message n odd pxel pars and the addtonal detals were stored n even pxel par. Ths method mproved the mage qualty and also the compresson rato. Han lng et al. [14] proposed a method for steganography whch uses the largest pxel value between the other three pxels close to target pxel to estmate the no of bts that can be embedded n that target pxel. The method enhances the mage qualty and ncreased embeddng capacty. C. Pxel Value sum Dfferencng Method In ths method, the sum s of the two consecutve pxel values s calculated. If, then the embeddng s done usng Pxel Value Dfferencng. For, the range of s s searched such that r [l,u ] n the same manner as n PVD, the number of t secret bts can be obtaned usng formulalog(w)+1. And then transform t bts of secret data nto decmal value b. The new sum value s calculated usng s' l b. The pxel values p and p +1 can be modfed as: ISSN: Page 611

3 III. METHODOLOGY The method s based on pxel value dfferencng and pxel value sum [6]. It s modfed to gve a hghly secured and hgh capacty data as n PVD. An mage baboon.jpg as n fg1 s a cover mage that embed the text stream. A stego mage s sent to the recever havng nformaton and fnally the text message s extracted from the stego mage as llustrated below. At Sender, Cover Image Secret Data At Recever, Embeddng Procedure Stego Image Stego Image A. Data Embeddng 1. Read the cover mage and partton t nto nonoverlappng blocks of two consecutve pxels. 2. Insert the secret key by XORng the LSB wth the 7th bt n each pxel. 3. Determne the capacty of pxels n the mage. 4. If there s a match.e. the XOR value s 0. Embed the n bts of secret message drectly usng Pxel value sum and Dfferencng. 5. Otherwse data s nverted before embeddng. 6. Repeat the procedure untl all the secret data bts s embedded. 7. Data s wrtten n the form of mage fle to obtan a Stego-mage. B. Data Extracton 1. Open the stego-mage and agan partton t nto non-overlappng blocks of two consecutve pxels. 2. Apply the secret key. 3. XOR the LSB wth 7th bt of each pxel. 4. If the XOR value s 0. Extract the n bts of the secret data drectly. 5. Otherwse the data s frst extracted and the reverse of the strng s done n order get the correct data. 6. Repeat the procedure untl all the bts of the secret data are extracted. IV. RESULTS To evaluate the performance of proposed method an mage of Taj of sze 256 X 256 s taken as cover mage as age shown n Fg. 2. The secret data stream s generated randomly. Frstly the proposed method s appled on the gray mage and then on the colored mage. The algorthm s tested for the vsual dstorton and capacty of the cover mage. Extracton Procedure Secret Data Fg. 1 Illustraton of Steganography GRAY SCALE Fg. 2 Cover Image The cover mage dstorton produced due to secret data embeddng can be measured n terms of Mean Square Error and Peak Sgnal to Nose Rato. ISSN: Page 612

4 These are defned as: Where I 1 and I 2 n the MSE equaton are the pxel values n the cover and stego mage respectvely and m, n are the dmensons of the cover mage along the horzontal and vertcal axes. The MSE value for mages s calculated for each colour plane of the mage and then the average of the MSE of all the planes gves the Mean Squared Error between Cover and stego mage. Capacty s another parameter. It s the sze of the data n a cover mage. Capacty depends on the total number of bts per pxel and the number of bts embedded n each pxel of the mage. Capacty s represented by bts per pxel (bpp) P S N R Proposed scheme Fg. 4 Varaton n PSNR PVD Gray scale Method The expermental data presented n Table1 and 2 ndcate the Capacty and PSNR respectvely of mage for proposed scheme. The aforesad table also provde comperatve data for the other methods. Table 1. CAPACITY Image Proposed PVD PVD Scheme and PVS Gray scale GRAY SCALE Fg. 5 Stego Image The stego mage s obtaned from cover mage by embeddng secret data stream to t. The secret key s also used for the secured transmsson of the message to protect t from ntruders attack. Stego mages correspondng to the cover mages s shown n Fg. 5. The mages look smlar and are mperceptble to human eye. C A P A C I T Y Table 2.PSNR Image Proposed PVD and PVD Scheme PVS Gray scale Proposed scheme PVD and PVS PVD Fg. 3 Varaton n Capacty Gray Scale Method V. CONCLUSION In ths paper, a technque for mage steganography have been studed. Ths technque utlzes the sum or dfference values for a partcular pxel along wth the secret key for better securty. By the expermental results t has been concluded that the proposed method has good capacty and good vsual fdelty. The PSNR value and capacty s compared for dfferent technques dscussed n ths paper. The secret key s requred to keep the prvacy of the data. The low PSNR value of the mage does not change the vsualty of the mage and also by seeng the mage ntruder wll not get to know the presence of some useful nformaton. A trade off between these three terms s requred whle selectng a steganographc scheme. REFERENCES [1] Shamm Ahmed Laskar and Kattamanch Hemachandran, Hgh Capacty data hdng usng LSB Steganography and Encrypton, Internatonal Journal of Database Management Systems ( IJDMS ) Vol.4, No.6, pp , December [2] Lpng J, Xaolong L, Bn Yang and Zhhong Lu, A further study on a PVD-based steganography, Proceedng of IEEE conference [3] Chn-ChenChanga,Ju-YuanHsaob and Ch-ShangChana Fndng optmal least-sgnfcant-bt substtuton n mage ISSN: Page 613

5 hdng by dynamc programmng strategy Pattern Recognton Socety, Publshed by Elsever Scence,2002. [4] Champakamala, B.S, Padmn.K and Radhka DK Least Sgnfcant Bt algorthm for mage steganography IJACT Vol 3, No. 4, pp , [5] V. S. Shrgupp, A Novel Approach for hdng data n Image Steganography by usng Three Pxel Par Dfferencng Method, Internatonal Journal of Advanced Research n Electroncs and Communcaton Engneerng, Vol. 4(12), pp , [6] A. Tyag, R. Roy, S. Changder, Hgh Capacty Image Steganography based on Pxel Value Dfferencng and Pxel Value Sum, Proceedng of IEEE, [7] Ankta Sanchet Pxel Value Dfferencng Image Steganography Usng Secret Key IJITEE, Vol. 2(1), Dec [8] Na-I Wu, "A Study on Data Hdng/or Gray-Level and Bnary Images." [9] M. Hossan, SA Haque, F. Sharmn, "Varable Rate Steganography n Gray Scale Dgtal Images Usng Neghborhood Pxel Irformaton", Proceedngs of Internatonal Conference on Computer and Informaton Technology, Bangladesh, [10] S. M. Masud Karm, Md. Safur Rahman, Md. Ismal Hossan, "A New Approach for LSB Based Image Steganography Usng Secret Key", Proceedngs of 14th Internatonal Conference on Computer and InformatonTechnology, Bangladesh, [11] Da-Chun Wu, Wen-Hsang Tsa, A steganographc method for mages by pxel-value dfferencng Pattern Recognton Socety, Publshed by Elsever Scence,pp , [12] J. K. Mandal and Debashs Das Colour Image Steganography Based On Pxel Value Dfferencng In Spatal Doman IJIST Vol.2, No.4, July [13] Hmaksh, Verma,H.K., Sngh, R.K., Sngh,C.K., B- Drectonal pxel-value dfferencng approach for Color Image.,Proceedng of IEEE, [14] Han-lng Zhang, Guang-zh Geng and Ca-qong Xong Image Steganography usng Pxel-Value Dfferencng Second Internatonal Symposum on Electronc Commerce and Securty,IEEE, ISSN: Page 614