Research of Multiple Text Watermarks Technique in Electric Power System Texts

Transcription

1 Sensors & Transducers 203 by IFSA Research of Multple Text atermarks Technque n Electrc Power System Texts Xao-X XING, Qng CHEN, 2 Lan-X FU School of Optcal-Electrcal and Computer Engneerng, Unversty of Shangha for Scence and Technology, Shangha, Chna, State Grd Jbe Electrc Power Co. Ltd., Bejng, Chna, 0240 Tel: E-mal: wealthxaox@63.com Receved: 2 July /Accepted: 25 October 203 /Publshed: 3 October 203 Abstract: Amng at the relable transmsson securty problems of electrc power system texts, multple text watermarkng algorthm s frst appled nto protectng t. Take protectng the transmsson of electrcty prce n the n electrc power system text and authentcatng the content from the sender for example, and robustness watermarkng algorthm s employed to transmt the electrcty prce wth covert communcaton whch makes t possble to resst dfferent knds of attacks. The sem-fragle watermark s utlzed to confrm the dentty of the sender whch can show whether the text s stolen or msused, and fnd where the contents are tampered. The experments show that multple text watermarkng algorthm can protect the data effectvely amng at dfferent purpose whch acheves ts applcaton value. Those also show the valdty of multple text watermarkng technque used n the relable transmsson of electrc power system texts and that ths technque has a vast applcaton prospect. Copyrght 203 IFSA. Keywords: Text watermarkng technque, Multple watermarkng, Power system, Content authentcaton, Semfragle watermarkng, Robustness watermarkng.. Introducton th the popularty of modern technology n the power system and the development of multmeda technology, nformaton securty has become an urgent problem to be solved n the power system. Dgtal watermarkng technology as a powerful means to solve the securty of multmeda nformaton has been gradually appled n electrc power system. Image [, 2] and vdeo [3] watermarkng technology both can be used for covert communcaton of mportant nformaton about electrcty bargan prce and so on to mprove the securty of nformaton transmsson. Audo watermarkng technology [4] can protect the copyrght of audo fles to prevent ts theft or msuse. Mesh watermarkng technology [5, 6] can protect the copyrght of mesh model wth propretary ntellectual property rghts. Lterature [7] proposes an dea that text watermarkng technology can be appled nto relable transmsson of power system texts, but dd not practce t. Currently, text watermarkng technologes can be manly categorzed two groups: the format and content. Maxemchuk and Brassl [8] proposed an algorthm whch changes lne spacng, the character spacng and character [9] to embed watermarkng nformaton slghtly, changes of whch cannot be Artcle number P_434 33

2 dentfed by the naked eye. These three methods have hgh mperceptblty, but cannot guarantee the robustness and capacty s the best. Though the robustness of text watermarkng algorthm based on the content s very strong, t wll cause the ambguty of natural language [0], and ts mperceptblty s not hgh, and t s easy to cause the opponent s attack. These algorthms can t cater to the characterstcs of strong robustness, large capacty and hgh mperceptblty. Therefore, the method of embeddng multple watermarks s employed to meet the needs of dfferent performances. Amng at mprovng the securty of convert communcaton of mportant nformaton n electrc power system and confrmng the source of the fles by usng content authentcaton method, a multple watermarks algorthm appled nto the relable transmsson of electrc power system text s proposed. The algorthm based on changng character spacng whch has a strong robustness s used to hde electrcty bargan prce, and sem-fragle watermarkng embeddng algorthm based on changng color RGB value of characters whch has a hgh mperceptblty s also employed to confrm the dentty of the sender. The proposed multple watermarkng algorthm s tested wth embeddng, extractng watermarkng nformaton and attack experments respectvely. And the expermental results show that the system s hghly feasble, can mprove the securty of covert communcaton, and fnd precsely where the content s tampered when the text suffers from malcous attacks. It s sutable for relable transmsson of electrc power system texts and content authentcaton. 2. Text atermarkng Technology Dgtal watermarkng technology s an effectve securty technology used for copyrght protecton, covert communcaton, content authentcaton, qualty detecton of multmeda nformaton. Multmeda redundant space s utlzed to embed watermarkng nformaton to acheve the purpose of securty protecton 2.. Text atermarkng Algorthm Text watermarkng technology, based on human vsual system (HVS), by fne-tunng the text format or content [, 2], embeds the watermarkng nformaton. atermarkng algorthm based on fnetunng manly the text format fne-tunngs the lne spacng, characters spacng and character propertes to embed watermarkng nformaton. Ths knd of watermarkng algorthm has good robustness, and can resst certan attack. It also has hgh mperceptblty, large capacty. atermarkng algorthm based on changng the content of a text to embed the watermarkng nformaton manly rely on the synonyms and equvalent sentence replacement to acheve the watermarkng embeddng, The robustness of ths algorthm s hgher than that based on changng format, however, due to the changes of the content, ts mperceptblty s poorer and t s less capacty Text atermarkng Framework Dgtal watermarkng system s manly composed of four parts: watermarkng generatng Gen, watermarkng embeddng Emb, watermarkng attack Att, watermarkng detecton Det. By detectng the text after the attack, the watermarkng nformaton can be extracted correctly to determne the robustness of watermarkng system. e represent the watermarkng attack model as [3] AM, AM =< { C, M,, K, C, '}, { A, C ', ata lg, atdet, atpar}, { Gen, Emb, Det, Att} > In order to facltate the understandng of ths model, some varables are descrbed as follows: C : watermarkng carrer; C : watermarked carrer; M : watermarkng message; : watermarkng; ' : extracted watermarkng; A : attack; ' : attacked watermarked carrer C C ' C + A () K : secret key; K gen, K emb, K det represent the set of secret keys used n the process of watermarkng generatng, embeddng and detecton, respectvely. atalg denotes watermarkng algorthm; atdet denotes watermarkng detector; atpar denotes watermarkng parameter. In a set, the small letter represents an element of the set of the correspondng captal letter. gen Gen : Gen([ C], M,[ K ]) (2) emb Emb : C Emb( C,, K ) (3) w Att : A Att([ atalg],[ atdet], atpar) (4) Det yes no Det C K (5) det : ([ '],[, ]) ( ',,[ ]) 3. Solutons Based on Text Dgtal atermarkng In the relable transmsson of texts n electrc power system, the mperceptblty of the algorthm s requred to be very hgh, the text cannot be changed wth perceptble changes, whch may cause the attacker s nterest, and the content of the text cannot 332

3 generate ambguty after beng changed. Therefore, algorthm based on content s not sutable and ths paper uses the algorthm based on fne-tunng text format to embed the watermarkng nformaton. In order to protect the texts n the securty of relable transmsson n the electrc power system and ncrease the trust between users, sem-fragle watermarkng and robust watermarkng are embedded at the same tme. The sem-fragle watermarkng havng hgh mperceptblty and hgh securty whch can resst some attacks can be used to authentcate contents after texts are receved, dstngush the dentty of the sender, embed the personal nformaton, send date and so on, and fnd where the contents are tampered. Robust watermarkng has a hgh ablty to resst attacks whch can be used for covert communcaton of mportant nformaton, and requres a large watermarkng capacty. It employs the method of loop embeddng watermarkng nformaton, whch ensures the text s, as long as there s at least one watermarkng nformaton avalable, stll can be extracted correctly. Therefore, the sem-fragle watermarkng embeddng algorthm based on changng character colors s used for content authentcaton, whle the robust watermarkng algorthm based on character spacng s used for hdng mportant nformaton. 4. The Text atermarkng Algorthm As descrbed n lterature [4], the RGB value combnatons varyng from (0,0,0) to (60,60,60) s very close to the ord default black, the naked eye cannot dstngush changes. Maxemchuk [5] ponts out that horzontal word dsplacements of /50 n and less readly go unnotced, vertcal lne dsplacements of /300 n and less go unnotced by readers. 4.. Based on Change the Font Color RGB Values s Sem-Fragle atermarkng Algorthm The purpose of ths algorthm s to authentcate the content of the transmtted texts. Therefore, semfragle watermarkng can be employed. It s requred to have the followng features: ) Imperceptblty. After embeddng watermarkng nformaton, the text does not produce vsble changes, because capacty and mperceptblty are mutually contradctory and the ncrease n capacty wll result n the declne n mperceptblty. Therefore, ths algorthm sacrfces part of capacty to ensure mperceptblty; 2) Detectng and sgnng tampered contents. It s an mportant property of the sem-fragle watermarkng. The tampered content must be precsely postoned and dsplayed; 3) Securty. The key space should be large enough to resst exhaustve attack method. Accordng to the test of human cone s senstvty to color shows that the senstvty of the naked eye to dfferent RGB components of color s dfferent, and the human eye s most senstve to red, followed by green and blue. Therefore, the algorthm changes lower two bts of the font color of G components and lower two bts of B components to acheve the watermarkng embeddng. By usng ths algorthm, though each two characters can be embedded wth a watermarkng byte wthout calculatng error correcton codng at the expense of a certan capacty, the mperceptblty can be better protected Pretreatment In order to enhance the robustness and securty of the watermarkng nformaton, t needs encryptng and error correcton codng before beng embedded. Take transmttng the electrcty bargan prce of electrc power system for example, where the watermarkng nformaton s the sender s nformaton State Grd Tel0000. The watermarkng nformaton and the key to be embedded are converted nto bnary sequences ww 2w3 wn = { } K kk2k3 km = { } w 0,, n (6) k 0,, m (7) A one-to-one crcular modulo encrypton method s used to obtan a new watermarkng sequence: M mmm (8) = 2 3 mn m = w k n ( mod m) Take advantage of the Hammng code aaaaaaa 2 0to encode the encrypted watermarkng sequence. S, S2, S 3 represents the correcton factor n the supervsory relatonshp. Table 2 shows that when mod 4 = 0, a new bnary sequences s generated: where t 7* l /4 H = hhh 2 3 ht, (9) = { } h 0,, t Table. Error correctng codes and wrong code poston correspondng relaton table. Fault code S, S2, S3 poston 00 a0 0 4 S, S, S 2 3 Fault code poston a 00 a 0 a5 00 a2 a6 0 a3 000 none 333

4 Table 2. Informaton bts and supervson bt correspondence table. nformaton supervson bt bt aaaa 2 0 aaa nformaton supervson bt bt aaaa aaa aaaa aaa 2 0 aaaa aaa atermarkng Embedded ) In order to make the poston where the watermarkng nformaton s embedded random to prevent the attackers from gettng the watermarkng nformaton, Lnear Congruence Generator (LCG) s employed. Pre-embeddng space D of a text s calculated, and the RGB values of all the characters are changed to (0,0,0), the most common used color n ord. The Lnear Congruence Generator s used to generate the pseudo random sequence { y j }, j =, 2, 3 t The basc Lnear Congruence Generator teratve formula s: y = n ( a* y + n c)mod m ( m > + 0), (0) y [0, m ] 0 where y 0 s the seed, a s known as the multpler, c s the ncrement and m s the modulus. The currently generated random number, y n+,depends only on the prevous one, y n,when the values of a, c and m are gven. 2) Step : Traverse the word text and, for the character j ( j <N), t s embedded wth watermarkng nterval dentfer sgnsart. RGB values are modfed to (,3,3) and (,3,4) respectvely. Step 2: Select character j. If j <N, go to step 5; Otherwse, judge nterval dentfer. If the dentfer embeddng has been completed, go to step 3. Otherwse, go to step ; Step 3: If h =, set the RGB value of the current character to (,,); set the RGB value of the next character to (,,2); If h = 0, set the RGB value of the current character to (,2,2); set the RGB value of the next character to (,2,3); Step 4: Repeat step -3 to embed watermarkng nformaton. Step 5: Complete the embeddng watermarkng nformaton and save the text atermarkng Detecton Step : Input key and convert t nto bnary sequence K ; Step 2: Traverses the text and fnd where of the RGB value of font color s modfed. Accordng to the rules of embeddng, extract 0, and obtan the bnary sequence S ; Step 3: Sequence S s decoded and corrected to get the bnary sequence M ; f mod 7 = 0, calculate correcton factor. If each bt of the three-bt correcton factor s 0, the watermarkng has not been tampered. If other values are obtaned, fnd where the content s tampered, make a wrong code corrected and remove supervson bt. Step 4: Cycle modulus s operated on Key K and the bnary sequence M to get bnary sequence of watermarkng and convert t to obtan the watermarkng sgnal Robust atermarkng Algorthm Based on Changng Character Spacng to Embed atermarkng Informaton Ths algorthm s desgned for covert communcaton of fle contents whch requres hgh robustness and suffcent capacty for hdden nformaton, hgh mperceptblty and safety. Therefore, watermarkng algorthm based on changng the character spacng s chosen as a robust algorthm used n power system. Based on HVS, the changes n character spacng should not exceed the threshold Pretreatment The pretreatment method s the same as s used n the algorthm based on changng the RGB values of character. But here the hdden message s electrcty bargan prce: 0000YUAN atermarkng Embedded ) The lnear congruence method s used to make the poston where the watermarkng nformaton s embedded random, text character spacng s unfed and s set to no. In order to prevent the character spacng from beng modfed whch wll cause lne overflow n the text, bndng two adjacent characters, and ndentng and wdenng ther spacng respectvely are used. 2) Step : Traverse the word text and, for the character j (j<n), t s embedded wth watermarkng nterval dentfcaton sgnsart. Here the character spacng s ncreased by 0. pounds, the next character spacng s decreased by 0. pounds. Step 2: Select character j. If j <N, go to step 5; Otherwse, judge nterval. If the dentty embeddng 334

5 dentfcaton has been completed, go to step 3. Otherwse, go to Step ; Step 3: If h =, set the current character spacng to ncrease by 0.05 pounds; set the next character spacng to reduce by 0.05 pounds; If h = 0, set the current character spacng to ncrease by 0.5 pounds; set the next character spacng to reduce by 0.5 pounds; Step 4: Repeat step -3 to embed watermarkng nformaton. Step 5: Complete the embeddng watermarkng nformaton and save the text atermarkng Detecton The watermarkng detecton method s the same as s used n the algorthm based on changng the RGB values of character. 5. Expermental Results and Analyss For both algorthms, watermarkng embeddng and extracton experments are made to verfy whether the change of text n vsual happens after the embedded watermarkng nformaton s embedded nto t, and check whether watermarkng nformaton can be extracted correctly. Through attack experments, robustness of both algorthms s tested. 5.. atermarkng Embeddng and Extractng Experment The algorthm based on changng character RGB values of color s tested by embeddng experment, and the watermarkng nformaton s State Grd Tel0000, whle the algorthm based on changng character spacng s also tested by embeddng experment, and the watermarkng nformaton s electrcty bargan prce: 0000YUAN.Both of the keys are 223. By extractng test, all watermarkng nformaton can be extracted correctly on the texts wthout sufferng attacks. And through the vsual, t s mpossble to fnd the text has been modfed after beng embedded watermarkng nformaton. Fg. 2. Text after embeddng watermarkng nformaton Attack Experment The purpose of dgtal watermarkng attack s desgned to make t mpossble to detect and extract watermarkng nformaton correctly. The robustness of watermarkng algorthm can be determned by checkng whether the watermarkng nformaton can be detected and extracted correctly after beng attacked. The texts embedded wth watermarkng nformaton are tested by attack experments. Repeat the test to prevent from generatng a rght result by chance. ) Attack based on the format. The text format attrbutes s changed n dfferent degree. a) Based on changng the RGB values of font color. Color attack on text, wholly or randomly, shows a weak robustness. But color attack on parts of the texts and any other attack on the texts show a strong robustness. And watermarkng nformaton can be detected and extracted correctly. b) Based on changng character spacng. Character spacng attack on whole texts show a weak robustness. But character spacng attack on parts of the texts and any other attack on the texts show a strong robustness. And watermarkng nformaton can be detected and extracted correctly. 2) Attack based on the content. Delete and paste operatons on text content n varyng degrees. a) Based on changng the RGB values of font color. Senstve to the tampered text content. b) Based on changng character spacng. Have a strong robustness and be able to resst attacks. 3) The Fg. 3 shows that f ether the text content or the font color changes, watermarkng algorthm based on changng RGB values of font color can accurately determne the specfc postons where the watermarkng bts are damaged to acheve content certfcaton. Fg.. The orgnal text. Fg. 3. Postonng the tampered content. 335

6 The expermental results show that the watermarkng algorthm based on changng the RGB value of font color show a poor robustness when the content s tampered, and can accurately poston the changed contents and characters whose color are changed so that the recever can dentfy whether the text has been tampered whch can effectvely acheve the content authentcaton. The algorthm based on changng character spacng has a strong robustness and can resst varous formats and contend attacks except attacks wth changng character spacng. It won t lower text qualty and s an effectve algorthm wth strong robustness whch can be used to hde electrc power nformaton. Through dgtal watermarkng system composed of two above mentoned algorthms, when the text s edted or suffers from other damages, the electrcty bargan prce can be stll extracted, and the dentty of the sender can also be confrmed whch helps to confrm the authentcty of texts. The combnaton of multple watermarkng algorthm may be, to some extents, complementary when texts suffer from attacks, and can acheve varous purposes, whch makes up for the weakness of a sngle watermarkng algorthm Algorthm Performance Analyss The most mportant performance features of dgtal watermarkng technology are capacty, robustness, mperceptblty, securty and so on whch determne whether the watermarkng algorthm has a practcal value. ) Robustness analyss. a) Algorthm based on changng RGB values of font color to embed watermarkng nformaton can resst basc format attacks, but shows a poor robustness when the content s tampered. It can be used for effectve content authentcaton of texts. Once the text content s malcously modfed, t wll be hard to extract watermarkng correctly. b) Algorthm based on changng character spacng to embed algorthm watermarkng nformaton has a very strong robustness, and t can resst format and content attacks. As for the credble transmsson of electronc text n power system, t provdes an effectve protecton to resst the malcously tamperng. 2) Capacty analyss. Both watermarkng algorthms are usng (7,4) Hammng code. Each of the 7 code words contans 4-bt nformaton and 3-bt supervson. It can detect two fault codes and correct an error code. atermarkng algorthm based on font color to code modfed lower two bts of G and B component respectvely to embed watermarkng nformaton, therefore, a character can be embedded wth four-bt nformaton. Though the use of error correcton codng affects the capacty, the algorthm stll has a large capacty. atermarkng algorthm based on the character spacng to code. Through the theoretcal analyss, P=N (P s the total capacty provded for loadng watermarkng nformaton nto the text, N s the number of characters of the text), so the number of bts of watermarkng nformaton s consstent wth that of characters. Although, n order to mprove the robustness and securty, error correcton codng s ntroduced at the expense of certan data capacty, the requrement of embeddng capacty of watermarkng nformaton s enough. 3) Imperceptblty analyss. Both algorthms are desgned based on human vsual system. The changed values are wthn the thresholds where the changes are ndscernble by naked eye. In prncple, the algorthms have very hgh mperceptblty. Through embeddng watermarkng nformaton experments, t can be seen that the text doesn t be changed or be degraded vsually. 4) Securty analyss. The two algorthm uses encrypton algorthm to encrypt the watermarkng nformaton. Even f the attacker knows the watermarkng embeddng algorthm, watermarkng nformaton would not be completely obtaned wthout the key. And t embeds the nformaton n the random place whch makes t much harder for rvals to attack t. Through the above performance analyss, the proposed multple text watermarkng algorthm can acheve convert communcaton of mportant nformaton and content authentcaton n power system by takng advantage of the combnaton of two dfferent text watermarkng algorthms. 6. Conclusons Dgtal watermarkng technology can effectvely acheve covert communcaton and content authentcaton. The robust watermarkng and the sem-fragle watermarkng algorthm are used for text transmsson of electrc power system and can hde electrcty bargan prce effectvely n the transmsson to resst all knds of attacks n the transmsson. The sem-fragle watermarkng algorthm s used to authentcate the sender, whch can ncrease the trust between the sender and recever. Expermental results show that the use of multple watermarks technology can effectvely resst attacks for dfferent purposes, protect the data n many ways and mprove the securty of the data. Electrc power ndustry s the natonal pllar ndustry and, wth the mprovement of normalzaton level n the electrc power system, nformaton securty has emerges gradually. th the development of dgtal watermarkng, dgtal watermarkng technology wll have a broad applcaton space n the power system securty feld as an effectve technque to solve the problem of nformaton securty. 336

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