Research Article Improved Encrypted-Signals-Based Reversible Data Hiding Using Code Division Multiplexing and Value Expansion

Transcription

1 Securty and Communcaton Networks Volume 2018, Artcle ID , 9 pages Research Artcle Improved Encrypted-Sgnals-Based Reversble Data Hdng Usng Code Dvson Multplexng and Value Expanson Xany Chen, Hadong Zhong, Lzh Xong, and Zhhua Xa Jangsu Engneerng Center of Network Montorng, Jangsu Collaboratve Innovaton Center on Atmospherc Envronment and Equpment Technology, School of Computer and Software, Nanjng Unversty of Informaton Scence and Technology, Nanjng , Chna Correspondence should be addressed to Zhhua Xa; xa zhhua@163.com Receved 28 September 2017; Revsed 1 December 2017; Accepted 21 January 2018; Publshed 15 February 2018 Academc Edtor: Rém Cogranne Copyrght 2018 Xany Chen et al. Ths s an open access artcle dstrbuted under the Creatve Commons Attrbuton Lcense, whch permts unrestrcted use, dstrbuton, and reproducton n any medum, provded the orgnal work s properly cted. Compared to the encrypted-mage-based reversble data hdng (EIRDH) method, the encrypted-sgnals-based reversble data hdng (ESRDH) technque s a novel way to acheve a greater embeddng rate and better qualty of the decrypted sgnals. Motvated by ESRDH usng sgnal energy transfer, we propose an mproved ESRDH method usng code dvson multplexng and value expanson. At the begnnng, each pxel of the orgnal mage s dvded nto several parts contanng a lttle sgnal and multple equal sgnals. Next, all sgnals are encrypted by Paller encrypton. And then a large number of secret bts are embedded nto the encrypted sgnals usng code dvson multplexng and value expanson. Snce the sum of elements n any spreadng sequence s equal to 0, lossless qualty of drectly decrypted sgnals can be acheved usng code dvson multplexng on the encrypted equal sgnals. Although the vsual qualty s reduced, hgh-capacty data hdng can be accomplshed by conductng value expanson on the encrypted lttle sgnal. The expermental results show that our method s better than other methods n terms of the embeddng rate and average PSNR. 1. Introducton Encrypton and data hdng are two common approaches for protectng aganst nformaton leakage [1 3]; the former s used to protect the content tself [4], whereas the latter s used to protect the hdden data [5]. Whle t s a problem for senstve applcatons, such as mltary mages and medcal mages, reversble data hdng (RDH) s an effectve method for these specal scenaros, whch ams to recover both embedded data and the orgnal mage. In the past two decades, many classc RDH algorthms have been proposed, such as lossless mage compresson-based methods [6], dfference expanson- (DE-) based methods [7], hstogram shftng- (HS-) based methods [8], nteger-to-nteger transform-based methods [9], and dual-mage-based methods [10]. However, wth the popularty of outsourced storage servces [11, 12], the tradtonal RDH s not sutable n these scenaros, especally wth regard to the requrement of hgh securty. Therefore, the research of prvacy protecton n cloud computng has attracted consderable attenton n recent years [13 15]. Among these studes, encrypted-magebased reversble data hdng (EIRDH) provdes the possblty that the mage owner can encrypt the mage before uploadng t to the servce provder, and then the servce provder can embed some addtonal message nto the ncomprehensble encrypted mage for steganography or authentcaton. The authorzed users or recevers can recover both the addtonal message and the orgnal mage. The exstng EIRDH methods can be grouped nto three categores: vacatng room after encrypton (VRAE) methods [16 22], reservng room before encrypton (RRBE) methods [23 25], and reversble mage transform (RIT) methods [26, 27]. The framework of VRAE was proposed by Zhang [18], n whch secret bts can be embedded after encryptng the orgnal mage. Specfcally, the data hder can dvde the encrypted mage block nto two sets and embed secret bts by flppng three LSBs of a set. To decrease the extracted-bts error rate, Hong et al. [19] and Lao and Shu [20] evaluated the complexty of mage blocks. Recently,

2 2 Securty and Communcaton Networks Y and Zhou [21] proposed a novel EIRDH method usng bnary-block embeddng for jont decrypton and extracton, n whch a bt-level scramblng process can prevent secret bts from loss. The methods [18 21] can embed an addtonal message from the decrypted mage. To extract secret bts n the encrypted mage, Zhang [22] proposed a novel separable EIRDH method, n whch three cases are consdered accordng to the encrypton key or data hdng key. However, t s hard to use the tradtonal RDH method for the data hder n the VRAE snce the correlaton between neghbor pxels n the encrypted mage s destroyed. The framework of RRBE was desgned by Ma et al. [23]. The data owner can reverse the room of LSBs usng the tradtonal RDH method and then encrypt the self-embedded mage. After that, the data hder embeds secret data nto the reversed LSBs of the encrypted mage. Cao et al. [24] compressed pxels n the local patch by sparse representaton and acheved a hgher reversed room than other prevous methods. To transform the orgnal mage nto an encrypted mage whch looks lke the target mage, Zhang et al. [26] proposed the EIRDH framework based on RIT, n whch an mage block s pared by smlar means and standard devaton between the orgnal and target mages. Snce the correlaton of transformed mages s not destroyed, the data hder can embed secret bts by the tradtonal RDH method. However, ths method has hgh mage dstorton snce much auxlary nformaton must be self-embedded nto the transformed mage for recoverng the orgnal mage. Recently, Hou et al. [27] mproved the vsual qualty of camouflage mages and reduced the auxlary nformaton for recordng block ndexes by adoptng k-means clusterng. Dfferent from the EIRDH, Chen et al. [28] desgned an encrypted-sgnals-based reversble data hdng (ESRDH) method, n whch the data owner dvdes each pxel of the cover mage nto two sgnals and then encrypts them by a publc key. After that, the data hder embeds secret bts nto the encrypted sgnals by the addtve homomorphsm. To reduce data expanson, Shu et al. [29] adopted a dfference expanson method to embed the message. Zhang et al. [30] proposed a lossless, a reversble, and a combned data hdng scheme for cphertext mages, respectvely, whch wereencryptedbyapublckeycryptosystemwthhomomorphc propertes. Recently, Wu et al. [31] presented an mproved ESRDH method, n whch the orgnal mage canberecoveredcompletelybydecryptngallsgnals.the method can acheve a hgher embeddng capacty and better qualty of decrypted mages than prevous ESRDH methods. In addton, compared to the tradtonal EIRDH method, the cost spent, on a relable key management system n a multparty envronment, s reduced snce the recever can share the publc key wth other denttes. Inthspaper,weproposeanmprovedESRDHmethod usng code dvson multplexng (CDM) and value expanson (VE), n whch the tradtonal CDM technology s utlzed to acheve lossless vsual qualty of decrypted sgnals, and VE technology s desgned accordng to the RDH method based on DE for further ncreasng the embeddng capacty. Compared to the current ESRDH method, the proposed method acheves a hgh embeddng capacty and good vsual qualty. Therestofthspapersarrangedasfollows.InSecton2, the related works are descrbed. In partcular, communcaton technologybasedoncdm,rdhmethodbasedonde,and ESRDH method based on sgnal energy transfer are gven. Secton 3 presents a lossless vsual qualty ESRDH method usng code dvson multplexng and hgh embeddng capacty ESRDH method usng value expanson. Secton 4 dsplays the performance of the proposed method by expermental results and Secton 5 concludes ths paper. 2. Related Works 2.1. Communcaton Technology Based on CDM. In communcaton systems, CDM s a knd of spectrum spreadng technology for ensurng secure nformaton transmsson and channel multplexng, n whch the sender encodes to-betransmtted bts wth a predetermned spreadng sequence, and then the recever can obtan the secret bts by the same spreadng sequences. So, the sequences that are derved by Walsh Hadamard matrx play an mportant role n CDMbased communcaton technology. Walsh Hadamard matrx conssts of 1 and 1. In addton to the frst row (column) of the matrx, other row (column) vectors are selected as the spreadng sequences, and they have two propertes. Frst, the sum of elements s equal to 0 for any sequence. Second, they are orthogonal to each other of any two dfferent sequences, so the cross-correlaton s 0. Suppose the spreadng sequences generated by Walsh Hadamard matrx are S z, z = 1,...,q} and the compound sequence C s the lnear combnaton of S z ; when the secret bt s 0, the coeffcent of S z s set as 1. Otherwse, the coeffcent s set as 1. Thus, the recever can decode the secret bts accordng to the results of dot product between S z and C. For example, three spreadng sequences from a 4-level Hadamard matrx ares 1 = (1, 1, 1, 1), S 2 = (1, 1, 1, 1), and S 3 = (1, 1, 1, 1). Obvously,S 1, S 2,andS 3 are zero means and orthogonal to each other. Suppose the secret bts are 010 ;then,thesequencesaredenotedass 1, S 2,andS 3, respectvely, and the three sequences are added to form the compound sequence C=S 1 S 2 +S 3 =(1, 3,1,1). On the recever sde, for the recever wth the spreadng sequence S 1, the decodng result s (C S 1 )/ S 1 2 = ((S 1 S 2 + S 3 ) S 1 )/ S 1 2 =(S 1 S 1 )/ S 1 2 =1, whch represents the noton that the secret bt s 1; for the recever wth S 2,theresults (C S 2 )/ S 2 2 =( S 2 S 2 )/ S 2 2 = 1, whch represents bt 0; for the recever wth S 3,theresults(C S 3 )/ S 3 2 =(S 3 S 3 )/ S 3 2 =1, whch represents bt 1. Therefore, the secret bts can be extracted. Moreover, snce a large number of secret bts are represented and transmtted by the compound sequences n dfferent ways and t s mpossble for an ntruder to guess them, the CDM-based communcaton technology s secure and can provde hgh capacty RDH Method Based on DE. The RDH method based on DEwasproposedbyTan.Assumethetwoneghborpxelsof

3 Securty and Communcaton Networks 3 O Raster scan Cover Preprocess Orgnal unt Encrypt Encrypted unt pxel p (a 0,a 1,t ) (E(a 0 ),E(a 1 ),E(t )) H Marked unt (E(a 0 ),E(a 1 ),E(t )) Embed secret bt b Encrypted unt (E(a 0 ),E(a 1 ),E(t )) If b=0, E(a0 ) =E( 1);E(a 1 ) =E(a 0) E(a 1 ) E( 1); If b=1, E(a0 ) =E(a 0) E(a 1 ) E( 1);E(a1 ) =E( 1). R Marked unt Decrypt Decrypted unt Extract (E (a 0 ),E(a 1 ),E(t )) (a 0,a 1,t ) secret bt b If a 0 <a 1,b= 0 If a 0 >a 1,b= 1 Fgure 1: The framework of ESRDH method based on sgnal energy transfer. the mage are x and y. The sender can compute the average m and the dfference h between x and y: m= x+y, 2 h=x y. Then, the secret bt b canbeembeddedastheleastsgnfcant bt (lsb) of h. And the new dfference value h can be obtaned: (1) h =2h+b. (2) Fnally, the correspondng values x and y canbecomputed and transmtted by the sender: x =m+ h +1, 2 y =m h 2. From the pxels par (x,y ), the recever can extract secret bts and recover the orgnal mage. The ntal average value m and new dfference value h canbecomputed: m= x +y, 2 h =x y. (3) (4) The secret bt b and dfference value h canbeobtanedbyh : b=lsb (h ), h= h 2. (5) And the orgnal par (x, y) can be recovered by m and h: x=m+ h+1 2, y=m h 2. (6) DE s a smple and effcent RDH method that utlzes the redundancy between two neghbor pxels to embed secret bts and acheve reversblty. In addton, we can use the data-embeddng algorthm for an mage more than once for multple-layer embeddng. When the dfference s small, a hgher embeddng capacty and better vsual qualty of thecovermagecanbeacheved.however,thetransformed values x and y should be restrcted n the range of [0, 255] ESRDH Method Based on Sgnal Energy Transfer. ESRDH method based on sgnal energy transfer was proposed by Wu et al. It conssts of three phases: mage encrypton phase, dataembeddng phase, and data extracton and mage recovery phase. There are three actve denttes n ths method. They are mage owner O, data hder H, and recever R. The framework of ths method s descrbed n Fgure 1.

4 4 Securty and Communcaton Networks SupposetheszeofthecovermagesN 1 N 2 and the pxel s p [0, 255], 1 N 1 N 2.Inspredbythesgnal energy transfer, one sgnal can be represented by the sum of other sgnals. Therefore, p can be represented as a 0 +a 1 + t,wherea 0 s selected randomly from 0,1,2,...,x }, x s obtaned by x =2 p /2, a 1 s equal to a 0,andt s set to be t =p 2a 0.Andthen,themageownercanencryptthethree sgnals accordng to the publc key that was generated by the Paller encrypton algorthm. Let the encrypted pxels be represented by (E(a 0 ), E(a 1 ), E(t )). The data hder embeds the secret bt b nto E(a 0 ) and E(a 1 ) and generates the marked sgnals E(a 0 ) and E(a 1 ).Ifthesecretbts0,thenE(a 0 ) = E(a 0 a 1 1), E(a 1 )=E(a 0 +a 1 +1). If the bt s 1, then E(a 0 )=E(a 0 + a 1 +1), E(a 1 )=E(a 0 a 1 1).Sncea 0 =a 1 and Paller encrypton mantans the addtve homomorphc propertes, then the embedded formulas can be reduced to E(a 0 )= E ( 1), E(a 0 )E(a 1 )E(1), E(a 1 )= E(a 0 )E(a 1 )E(1), E ( 1), f b=0, f b=1, f b=0, f b=1. To extract the secret bt and recover the cover mage, the recevercandecryptthemarkedsgnals(e(a 0 ), E(a 1 ), E(t )) accordng to the prvate key generated by Paller encrypton and obtan the decrypted unt (a 0,a 1,t ). Then,the decrypted pxel s denoted by p =a 0 +a 1 +t.becauseofa 0 + a 1 =a 0+a 1, the decrypted mage s a cover mage. After that, the bt b can be extracted by comparng a 0 and a 1 : (7) b= 0, f a 0 <a 1, 1, f a 0 >a 1. (8) Ths method acheves a lossless vsual qualty snce the decrypted mage s the orgnal one. It also can process encoded multmeda snce each separated unt of the encoded multmeda can be recovered completely. Therefore, there s no underflow or overflow problem and there s no need to embed any auxlary nformaton. 3. The Proposed Method 3.1. Lossless Qualty ESRDH Method Based on CDM. To mantan the lossless qualty of the decrypted mage and mprove the embeddng capacty, nspred by communcaton technology based on CDM, we propose a lossless vsual qualty ESRDH method only usng CDM. Suppose that the generated spreadng sequences are S z,z = 1,...,q} and the length s denoted as l = q + 1, where l must be the power of 2 such as 2, 4, 8. Therefore, the preprocess and encrypton can be summarzed as follows. Frstly, dvde each pxel unt p as p =a 1 + +a l +t, where t s obtaned by t =p mod l and a 1,...,a l are set to be (p t )/l. Secondly, defne the vector V =[a 1,...,a l ] as an embedded vector, so each unt p canberepresentedas (V,t ). Fnally, the mage owner encrypts each unt by a publc key generated by Paller encrypton, and the encrypted unt (E(V ), E(t )) s generated, where E(V ) = [E(a 1 ),...,E(a l )]. Now, the data hder can embed secret bts b z (z = 1,...,q}) nto E(V ) usng CDM. Ths means the number of bts whch can be embedded nto the th (1 N 1 N 2 ) pxel s q. At the begnnng, the secret bts b z can be transformed to w z whch consst of 1and1: w z = 1, f b z =0 1, f b z =1. Then, we can obtan the compound sequence C by C = w 1 S w q S q ; the elements of C are [C (1),...,C (l)]. Theycanbeencryptedbythepublckeyand can generate an encrypted compound sequence EC = [E(C (1)),...,E(C (l))]. Snce Paller encrypton has addtve homomorphc propertes, EC can be embedded nto E(V ) by the followng formula: E(V ) = (E (a 1 ),...,E(a l )) =(E(a 1 +C (1)),...,E(a l +C (l))) =(E(a 1 ) E(C (1)),...,E(a l ) E(C (l))), (9) (10) where the new vector E(V ) can be denoted as E(V ) = [E(a 1 ),...,E(a l )]. Fnally, the recever can decrypt the marked sgnals (E(V ), E(t )) by a prvate key and obtan (V,t ). V can be represented by V = [a 1,...,a l ] or V =V +C.Because of a 1 = = a l and for any dfferent spreadng sequences, they are zero means and orthogonal to each other; the result of dot product between V and S z (z = 1,...,l}) can be summarzed as V S z =C S z =l 2 w z. (11) Therefore, w z canbeobtanedbythefollowngformula: w z = V S z l 2 = sgn (V S z ). (12) And b z can nversely be transformed by formula (9). Snce the sum of elements s equal to 0 for any spreadng sequences, we have a 1 + +a l =a 1 + +a l. (13) The drectly decrypted pxel s p,andwehavep =a 1 + +a l +t =p.asaresult,thedecryptedpxelstheorgnal one. In other words, based on CDM, ESRDH acheves lossless vsual qualty of mages. And the data-embeddng process does not cause an underflow/overflow problem. In addton, the embeddng rate can be mproved to be q bts per pxel (bpp) such as q = 1,3}. So, t can be determned by the number of spreadng sequences q.

5 Securty and Communcaton Networks Hgh Embeddng Capacty ESRDH Method Based on VE. In Wu et al. s method and ESRDH method based on CDM, the sgnal t s not used to embed secret bts. To further ncrease the embeddng capacty, the ESRDH method based onvesproposed.inwuetal. smethod,therangeoft s [p 4 p /2, p ], whch wll decrease the vsual qualty of the decryptedmagebecausetheabsolutevalueoft s too large. However, n the ESRDH method based on CDM, the range of t s [1, q], and t s enough small, so the ESRDH based on VE s an effcent method. In Secton 3.1, the pxel unt (V,t ) s encrypted and sent to the data hder. Instead of only embeddng secret bts nto V, t also can embed bts n ths secton. Suppose t s expanded 2 k (k=1,2)tmes and the decmal number of (b 1 b k ) 2 s D.So,k LSBs of t can be empted to embedded secret bts by t =2 k t +D.Then,p canbeconstructedbythesum of a 1,...,a l,t, and t can be reduced to p +t t.snce p [0, 255] and t t [0,Rmax], thusp [0, R max], wherer max =(2 k 1) (q+1). Therefore, data embeddng can possbly cause an overflow problem. To solve ths problem, t should be preprocessed, and the formula can be summarzed as ts = t, 0 p 255 R max, (14) t Rmax, 255 R max <p 255. The range of t s changed from [0, q] to ts [ Rmax,q R max] [0,q].So,fts < 0, ts s the changeable one. Otherwse, t s the orgnal one. Frstly, the encrypted unt (E(V ), E(ts )) can be obtaned by a publc key. Secondly, D should be encrypted to E(D ) by the same key.andthentsembeddedntoe(ts ), so a new encrypted value E(ts ) canbegenerated,whchcanbesummarzedas E(ts )=E(2k ts +D )=E(ts ) 2k E(D ). (15) Thrdly, the recever decrypts E(ts ) by the correspondng prvate key and denotes t as ts. After that, the embedded bts (b 1 b k ) 2 can be obtaned by extractng k LSBs of ts.so,ts canbecalculatedby ts = ts D 2 k, (16) where D s the decmal number of (b 1 b k ) 2. Fnally, the orgnal t should be recovered by t = ts, ts 0, (17) ts +Rmax, ts <0. And the pxel p canberecoveredbythesumofothersgnals. Based on ESRDH usng CDM, the proposed method can further mprove the embeddng rate usng VE. The embedded rate can be ncreased by k bpp such as k = 1, 2}. Furthermore, there s no need to embed any auxlary nformaton to recover the orgnal t.however,theresa possblty that an overflow problem arses, whch may cause mage dstorton Algorthm of ESRDH Method Based on CDM and VE. AccordngtoSectons3.1and3.2,theframeworkofESRDH methodbasedoncdmandvesshownnfgure2,and thealgorthmcanbedvdedntothreephases:preprocess and sgnal encrypton phase, data-embeddng phase, and data extracton and mage recovery phase. The detals are descrbed as n Algorthm Expermental Results As s shown n Fgures 3(a) 3(d), four dfferent grayscale mages wth dfferent features are selected as the test mages, whcharelena,pepper,salboat,andbaboon.theszeof these pctures s ThedevelopmenttoolsMyeclpse8.6, whch s used on an Intel Core 5 CPU (2.8 GHz) wth 8 GB of memory. The embeddng rate (ER) and vsual qualty of the decrypted mage are two mportant ndcators to measure the performance of the EIRDH method, and they can be calculated by ER = Embeddng Capacty The sze of cover mage, PSNR =10lg 2552 N 1 N 2 N 1 N 2 =1 (p p ) 2, (18) where p and p are the orgnal and modfed pxel values, respectvely. In the proposed method, f the ESRDH method based on CDM s used to embed secret bts, the ER s q bpp, and PSNR s +. InTable1,whenq = 1 and q = 3, the embeddng capacty (EC) s = and = , and the correspondng ER s 1 bpp and 3 bpp, respectvely. And lossless vsual qualty of the decrypted mage can be acheved. The decrypted mages wth the hdden data were not further processed, as shown n Fgure 4. The plan text mages recovered from the four encrypted mages were all dentcal to the orgnal one. In addton, we can utlze the VE method to further mprove ER, and up to q+kbpp can be acheved. In addton, PSNR wll be changed by settng k. For example, bts can be embedded usng CDM and VE methods when q=1, k=2. However, PSNR of Lena s decreased to db. The other results about EC, ER, and PSNR of dfferent test mages are shown n Table 1. Furthermore, although the ER of the four mages s 3 bpp when q=1, k=2,orq=3,thepsnrof these decrypted mages are dfferent. To assess the tme overheads on encrypton, embeddng, and decrypton, we assessed the statstc effcency performance of the proposed method for dfferent test mages when q=3and k=1n Table 2. In ths table, the embeddng tme s small because secret bts are embedded by multplcaton, whch also reflects the noton that sgnals encrypton and decrypton spend a long tme. However, snce the operatons of CDM and VE were all performed n a homomorphc encrypton doman, the encrypted sgnals wth the hdden data were protected by the Paller cryptosystem. Therefore, the Paller cryptosystem n our method s an mportant

6 6 Securty and Communcaton Networks O Raster scannng Cover Preprocess Orgnal Encrypt Encrypted pxel p unt U unt %5 H Compound Encrypt Encrypted sequence C value E(C ) Embed usng CDM 30 1 Secret bts 30 2 Encoded Encrypt Encrypted bts D value E(D ) Embed usng VE R Recover Extract Extract Decrypted Decrypt Marked pxel usng VE usng CDM unt U unt EU Fgure 2: The framework of the ESRDH method based on CDM and VE. (a) (b) (c) (d) Fgure 3: Four test mages. (a) Lena, (b) Pepper, (c) Salboat, and (d) Baboon. (a) (b) (c) (d) Fgure 4: Drectly decrypted mages. (a) Lena, (b) Pepper, (c) Salboat, and (d) Baboon.

7 Securty and Communcaton Networks 7 Preprocess and sgnal encrypton phase Input: An orgnal mage wth a sze of N 1 N 2, the number of spreadng sequences q (q = 1, 3}), the expanded parameter k (k = 1, 2}), and publc key pk. Output: The encrypted unt EU. Step 1: Obtan the separated sgnals from the orgnal pxel p =a 1 + +a l +t, 1 N 1 N 2, whch can be calculated n Secton 3.1. Defne the embedded vector V =[a 1,...,a l ], and each pxel unt s represented as (V,t ). Step 2: Modfy t to be ts by formula (14) for preventng overflow. Step 3: Encrypt U =(V,ts ) by pk and generate an encrypted unt EU = (E(V ), E(ts )). Data embeddng phase Input: The encrypted unt EU, the number of spreadng sequences q, the expanded parameter k,publckeypk,and secret bts. Output: Marked unt EU. Step 1: Dvde secret bts nto two parts SP 1 and SP 2,whereSP 1 contans q N 1 N 2 secret bts and SP 2 contans the remanng bts. Step 2: Transform secret bts b z, z=1,...,q}n SP 1 to w z usng formula (9), and then obtan the compound sequence C for each unt EU. Step 3: Encrypt C by pk and denote t as E(C ). Step 4: Embed E(C ) nto E(V ) usng CDM. By formula (10), obtan a new vector E(V ). Step 5: Encode secret bts (b 1 b k ) 2 n SP 2 to D. D s the decmal of (b 1 b k ) 2 for each unt EU. Step 6: Encrypt D by pk and denote t as E(D ). Step 7: Embed E(D ) nto E(ts ) usng VE. By formula (15), obtan a new sgnal E(ts ).Then, generate a marked unt EU = (E(V ), E(ts )). Data extracton and mage recovery phase Input: The marked unt EU, the number of spreadng sequences q, the expanded parameter k,andprvatekeysk. Output: Secret bts and the orgnal mage. Step 1: Decrypt EU usng sk to generate U =(V,ts ). Step 2: Extract q N 1 N 2 secret bts from V by formulas (9) and (12). Step 3: Obtan (b 1 b k ) 2 by extractng k LSBs of ts. Step 4: Calculate ts by formula (16) and recover t by formula (17). Step 5: Recover the orgnal mage by calculatng p =a 1 + +a l +t. Algorthm 1 Table 1: The performance of EC, ER, and PSNR for dfferent mages. Test mage q and k EC (bts) ER (bpp) PSNR (db) q= q=1, k= Lena q=1, k= q= q=3, k= q= q=1, k= Pepper q=1, k= q= q=3, k= q= q=1, k= Salboat q=1, k= q= q=3, k= q= q=1, k= Baboon q=1, k= q= q=3, k=

8 8 Securty and Communcaton Networks Test mages Table 2: Effcency performance of the proposed method. Encrypton (m) Embeddng (m) Decrypton (m) Lena Pepper Salboat Baboon Table3:Thesgnalexpansonbetweenourmethodandtheselected methods. Methods Input sgnal (bts) Output sgnal (bts) Our method 8 2 (q + 2) 512 Wu et al. [31] Shu et al. [29] Chen et al. [28] technology for protectng mage content securty although t s not effcent enough. Table 3 denotes sgnal expanson between our method and the selected methods, ncludng Wu et al. [31], Shu et al. [29], and Chen et al. [28]. Accordng to Paller encrypton, theszeofthecpherspacessquareoftheszeofthe message space. In the table, Paller encrypton wth 512-level securty s adopted, and the plan text and the cphertext arerepresentedby512btsand1024bts,respectvely.the output sgnal of our method s related to q and can reach 2 (q + 2) 512. To solve the problem of data expanson, three alternatve methods can be consdered. The frst s to use a lower securty level, such as a 128-bt securty level and 64-bt securty level. Thus, the length of output sgnal wll be reduced to 2 (q + 2) 128 bts and 2 (q+2) 64bts, respectvely. The second s to reduce the value of q. When q=1,ts and the same as Wu et al. s method. The thrd s to use a pxel block nstead of a sngle pxel as the nput sgnal. If a 512-bt securty level s used, an 8 8pxel block canbeadoptedsncesuchablockconsstsof8 8 8 = 512 bts. Now, the length of the output sgnal s 2 (q + 2) tmes that of the nput sgnal. The average PSNR of dfferent mages when q = 1and k = 2 areshownnfgure5.atthebegnnng,thesecret bts can be embedded usng CDM, and the embeddng rate can reach 1 bpp. Snce the decrypted mage s the same as the orgnal mage, PSNR s +. Tofurthermprovethe embeddng rate, the PSNR wll be reduced and more secret bts wll be embedded usng VE. Compared wth other related methods ncludng Wu et al. [31], Shu et al. [29], and Chen et al. [28], the proposed method has a better performance n terms of the embeddng rate and PSNR. Moreover, snce the decrypted mage s the orgnal mage, the proposed method, whch only uses CDM, can be appled to deal wth encoded meda such as H.264 vdeo and JPEG mages. Besdes, real reversblty can be acheved by the proposed method. Average PSNR (db) Inf Embeddng rate (bpp) Proposed Wu et al Shu et al Chen et al Fgure 5: The average PSNR n dfferent test mages when q=1and k=2. 5. Concluson Ths paper proposes mproved encrypted sgnals-based reversble data hdng based on code dvson multplexng and value expanson. When only usng code dvson multplexng to embed bts, lossless vsual qualty of drectly decrypted mages can be acheved, and the embeddng rate can reach q (q = 1, 3}) bpp. When usng code dvson multplexng and value expanson method, the decrypted mage wll have some dstorton, but the embeddng rate can be mproved to q+k(k=1,2})bpp. The secret bts and the orgnal mage can be recovered from the decrypted mage completely. However, the sze of the encrypted mage wll be expanded because of Paller encrypton. In further work, the expanson problem may be solved usng other encrypton ways, and the property of multplcatve homomorphsm maybeutlzedtofurthermprovetheperformanceonthe embeddng rate and PSNR. Conflcts of Interest The authors declare that they have no conflcts of nterest. Acknowledgments Ths work s supported by the Natonal Natural Scence Foundaton of Chna (NSFC) ( , U , , , , , , , andu ),jangsubascresearchprograms-natural Scence Foundaton (BK ), Startup Foundaton for Introducng Talent of Nanjng Unversty of Informaton Scence and Technology (2014r026#), Open Fund of Demonstraton Base of Internet Applcaton Innovatve Open Platform of Department of Educaton (KJRP1402), Prorty Academc Program Development of Jangsu Hgher Educaton Insttutons (PAPD) Fund, Collaboratve Innovaton Center

9 Securty and Communcaton Networks 9 of Atmospherc Envronment and Equpment Technology (CICAEET) Fund, and Natonal Mnstry of Scence and Technology Specal Project Research (GYHY , 2013DFG12860, and BC ). References [1] J. Shen, D. Lu, Q. Lu, and X. Sun, A secure cloud-asssted urban data sharng framework for ubqutous-ctes, Pervasve &MobleComputng,2017. [2] Z. Fu, F. Huang, X. Sun, A. V. Vaslakos, and C. Yang, Enablng semantc search based on conceptual graphs over encrypted outsourced data, n Proceedngs of the IEEE Transactons on Servces Computng,vol.99,1939. [3] C. Yuan, X. Sun, and R. Lv, Fngerprnt lveness detecton based on mult-scale LPQ and PCA, Chna Communcatons, vol.13, no.7,pp.60 65,2016. [4] J. Shen, S. Chang, J. Shen, Q. Lu, and X. Sun, A lghtweght mult-layer authentcaton protocol for wreless body area networks, Future Generaton Computer Systems,2016. [5] X. Chen, S. Chen, and Y. Wu, Coverless nformaton hdng method based on the Chnese character encodng, Journal of Internet Technology,vol.18,no.2,pp ,2017. [6] J. Frdrch, M. Goljan, and R. Du, Lossless data embeddngnew paradgm n dgtal watermarkng, EURASIP Journal on Appled Sgnal Processng,no.2,pp ,2002. [7] J. Tan, Reversble data embeddng usng a dfference expanson, IEEE Transactons on Crcuts and Systems for Vdeo Technology,vol.13,no.8,pp ,2003. [8] Z. N, Y. Q. Sh, N. Ansar, and W. Su, Reversble data hdng, IEEE Transactons on Crcuts Systems for Vdeo Technology,vol. 16, no. 3, pp , [9] S.Lee,C.D.Yoo,andT.Kalker, Reversblemagewatermarkng based on nteger-to-nteger wavelet transform, IEEE Transactons on Informaton Forenscs and Securty,vol.2,no.3,pp , [10] H. Yao, C. Qn, Z. Tang, and Y. Tan, Improved dual-mage reversble data hdng method usng the selecton strategy of shftable pxels coordnates wth mnmum dstorton, Sgnal Processng,vol.135,pp.26 35,2017. [11] Z. Fu, K. Ren, J. Shu, X. Sun, and F. Huang, Enablng personalzed search over encrypted outsourced data wth effcency mprovement, IEEE Transactons on Parallel and Dstrbuted Systems,vol.27,no.9,pp ,2016. [12]Z.Xa,X.Wang,L.Zhang,Z.Qn,X.Sun,andK.Ren, A prvacy-preservng and copy-deterrence content-based mage retreval scheme n cloud computng, IEEE Transactons on Informaton Forenscs and Securty, vol. 11, no. 11, pp , [13] Y. Kong, M. Zhang, and D. Ye, A belef propagaton-based method for task allocaton n open and dynamc cloud envronments, Knowledge-Based Systems, vol. 115, pp , [14] J. Shen, J. Shen, X. Chen, X. Huang, and W. Suslo, An effcent publc audtng protocol wth novel dynamc structure for cloud data, IEEE Transactons on Informaton Forenscs and Securty, vol.12,no.10,pp ,2017. [15] Z. Fu, F. Huang, K. Ren, J. Weng, and C. Wang, Prvacypreservng Smart Semantc Search based on Conceptual Graphs over Encrypted Outsourced Data, IEEE Transactons on Informaton Forenscs Securty,no.99,p.1,2017. [16] X. Zhang, Z. Qan, G. Feng, and Y. Ren, Effcent reversble data hdng n encrypted mages, Journal of Vsual Communcaton and Image Representaton,vol.25,no.2,pp ,2014. [17] L. Xong, Z. Xu, and Y.-Q. Sh, An nteger wavelet transform based scheme for reversble data hdng n encrypted mages, Multdmensonal Systems and Sgnal Processng,pp.1 12,2017. [18] X. P. Zhang, Reversble data hdng n encrypted mage, IEEE Sgnal Processng Letters,vol.18,no.4,pp ,2011. [19] W. Hong, T.-S. Chen, and H.-Y. Wu, An mproved reversble data hdng n encrypted mages usng sde match, IEEE Sgnal Processng Letters,vol.19,no.4,pp ,2012. [20] X. Lao and C. Shu, Reversble data hdng n encrypted mages based on absolute mean dfference of multple neghborng pxels, JournalofVsualCommuncatonandImageRepresentaton, vol. 28, pp , [21] S. Y and Y. Zhou, Bnary-block embeddng for reversble data hdng n encrypted mages, Sgnal Processng,vol.133,pp.40 51, [22] X. P. Zhang, Separable reversble data hdng n encrypted mage, IEEE Transactons on Informaton Forenscs and Securty,vol.7,no.2,pp ,2012. [23] K. Ma, W. Zhang, X. Zhao, N. Yu, and F. L, Reversble data hdng n encrypted mages by reservng room before encrypton, IEEE Transactons on Informaton Forenscs and Securty,vol.8,no.3,pp ,2013. [24] X. Cao, L. Du, X. We, D. Meng, and X. Guo, Hgh Capacty Reversble Data Hdng n Encrypted Images by Patch-Level Sparse Representaton, IEEE Transactons on Cybernetcs, vol. 46, no. 5, pp , [25] W. M. Zhang, K. D. Ma, and N. H. Yu, Reversblty mproved data hdng n encrypted mages, Sgnal Processng,vol.94,no. 1,pp ,2014. [26] W. Zhang, H. Wang, D. Hou, and N. Yu, Reversble data hdng n encrypted mages by reversble mage transformaton, IEEE Transactons on Multmeda,vol.18,no.8,pp ,2016. [27] D. Hou, W. Zhang, and N. Yu, Image camouflage by reversble mage transformaton, Journal of Vsual Communcaton and Image Representaton, vol. 40, pp , [28] Y.-C. Chen, C.-W. Shu, and G. Horng, Encrypted sgnal-based reversble data hdng wth publc key cryptosystem, Journal of Vsual Communcaton and Image Representaton,vol.25,no.5, pp , [29] C.-W. Shu, Y.-C. Chen, and W. Hong, Encrypted magebased reversble data hdng wth publc key cryptography from dfference expanson, Sgnal Processng: Image Communcaton, vol. 39, pp , [30] X. Zhang, J. Long, Z. Wang, and H. Cheng, Lossless and Reversble Data Hdng n Encrypted Images wth Publc-Key Cryptography, IEEE Transactons on Crcuts and Systems for Vdeo Technology,vol.26,no.9,pp ,2016. [31] X. Wu, B. Chen, and J. Weng, Reversble data hdng for encrypted sgnals by homomorphc encrypton and sgnal energy transfer, Journal of Vsual Communcaton and Image Representaton,vol.41,pp.58 64,2016.

10 Publshng Corporaton Internatonal Journal of Rotatng Machnery Advances n Multmeda Journal of Engneerng Volume 2018 The Scentfc World Journal Journal of Sensors Journal of Control Scence and Engneerng Advances n Cvl Engneerng Submt your manuscrpts at Journal of Robotcs Journal of Electrcal and Computer Engneerng Advances n OptoElectroncs Volume 2018 VLSI Desgn Internatonal Journal of Navgaton and Observaton Modellng & Smulaton n Engneerng Internatonal Journal of Aerospace Engneerng Internatonal Journal of Internatonal Journal of Antennas and Chemcal Engneerng Propagaton Actve and Passve Electronc Components Shock and Vbraton Advances n Acoustcs and Vbraton