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2 5 Lole Steganography for Speeh Communiation Naofumi Aoki Grauate Shool of Information Siene an Tehnology, Hokkaio Univerity Japan 1. Introution Tranmitting upplementary aty teganography, new funtion an be ae to ommuniation ytem without hanging onventional ata format. Bae on thi onept, everal appliation have been propoe for enhaning the peeh quality of telephony ommuniation. Thee appliation eretly tranmit ie information along with peeh ata itelf for enhaning the performane of ignal proeing uh a paket lo onealment an ban etenion (Aoki, 23; Aoki, 26; Aoki, 27a; Aoki, 212). The implet teganography tehnique employe in uh appliation i the LSB (Leat Signifiant Bit) replaement tehnique (Co, 28). It jut replae the LSB of peeh ata with eret meage. Sine the LSB of peeh ata i not very important in pereption, the LSB replaement tehnique i uffiient enough in many pratial ae. However, there i no way to avoi inevitable egraation of peeh aty embeing eret meage with the LSB replaement tehnique. In orer to mitigate thi problem, thi artile eribe an iea of the lole teganography tehnique for telephony ommuniation (Aoki, 27b; Aoki, 28; Aoki, 29a; Aoki, 29b; Aoki, 21a). The propoe tehnique eploit the harateriti of the fole binary oe employe in everal peeh oe, uh a G.711 an DVI-ADPCM. 2. LSB replaement tehnique The LSB replaement tehnique i known a one of the implet teganography tehnique (Co, 28). It jut embe eret meage into the LSB of over ata. The embeing proeure of the LSB replaement tehnique i programme in C language a hown in Fig. 1. In thi proeure, b repreent a 1 bit eret meage an repreent an 8bit over ata. The LSB replaement tehnique i ategorize a a loy teganography tehnique, ine it may egrae over aty embeing eret meage. if (b == ) &= FE; if (b == 1) = 1; Fig. 1. Embeing proeure of the LSB replaement tehnique programme in C language.

3 76 Reent Avane in Steganography 3. Lole teganography tehnique bae on the fole binary oe For repreenting igne integer inary ata, many peeh oe employ the fole binary oe intea of the 2' omplement, the mot ommon format of binary ata. Table 1 how how an 8 bit peeh ata i repreente by the fole binary oe a well a the 2' omplement. eimal number 2' omplement fole binary oe ~ ~ Table 1. 2' omplement an fole binary oe for repreenting 8 bit peeh ata. A hown in thi table, an 8 bit peeh ata enoe in the 2' omplement range from -128 to On the other han, an 8 bit peeh ata enoe in the fole binary oe range from -127 to Although the fole binary oe annot repreent -128, it may repreent both + an - intea. Thi reunany an be a ontainer for embeing eret meage without any egraation. The embeing proeure of the propoe tehnique i programme in C language a hown in Fig. 2. In thi proeure, b repreent a 1 bit eret meage an repreent an 8bit over ata enoe in the fole binary oe. The propoe tehnique i ategorize a a lole teganography tehnique, ine it oe not egrae over aty embeing eret meage.

4 Lole Steganography for Speeh Communiation 77 if (( & 7F) == ) { if (b == ) &= 7F; if (b == 1) = 8; } Fig. 2. Embeing proeure of the propoe tehnique programme in C language. 4. G.711 G.711 i the mot ommon oe for telephony peeh tanarize by ITU-T (International Teleommuniation Union Teleommuniation Stanarization Setor) (ITU-T, 1988). It onit of -law an A-law heme eignate a PCMU an PCMA, repetively. PCMU i mainly employe in North Ameria an Japan. It enoe 14 bit peeh ata into 8 bit ompreion ata at an 8 khz ampling rate. PCMA i mainly employe in Europe. It enoe 13 bit peeh ata into 8 bit ompreion ata at an 8 khz ampling rate. Figure 3 an 4 how the enoing an eoing proeure of PCMU. The ompreion ata of PCMU onit of 1 bit ign, 3 bit eponent, an 4 bit mantia (ITU-T, 25). The ompreion ata i enoe in the fole binary oe. Table 2 how ome of the ompreion ata an their orreponing peeh ata eoe with PCMU. A hown in thi table, the peeh ata eoe with PCMU range from - to -831, an + to Figure 5 an 6 how the enoing an eoing proeure of PCMA. The ompreion ata of PCMA onit of 1 bit ign, 3 bit eponent, an 4 bit mantia (ITU-T, 25). The ompreion ata i enoe in the fole binary oe. Table 2 how ome of the ign 14 bit peeh ata mantia 8 bit ompreion ata eponent 1 a b Fig. 3. Enoing proeure of PCMU.

5 78 Reent Avane in Steganography ompreion ata an their orreponing peeh ata eoe with PCMA. A hown in thi table, the peeh ata eoe with PCMA range from -1 to -432, an +1 to Note that there i an overlap in the peeh ata eoe with PCMU. On the other han, there i no uh an overlap in the peeh ata eoe with PCMA. Thi iniate that a lole teganography tehnique i available for PCMU, although it i not for PCMA. ign 14 bit peeh ata mantia 8 bit ompreion ata eponent 1 a b Fig. 4. Deoing proeure of PCMU. ign 13 bit peeh ata mantia 8 bit ompreion ata eponent a b Fig. 5. Enoing proeure of PCMA.

6 Lole Steganography for Speeh Communiation 79 ign 13 bit peeh ata mantia 8 bit ompreion ata eponent a b Fig. 6. Deoing proeure of PCMA. ompreion ata +127 ~ ~ -127 eoe peeh ata (PCMU) eoe peeh ata (PCMA) Table 2. Speeh ata eoe with PCMU an PCMA.

7 8 Reent Avane in Steganography 5. Lole teganography tehnique for G.711 Taking aount of the harateriti of PCMU, eret meage an be embee into both + an - in the ompreion ata without any egraation. When i require to be embee, the ign bit of the ompreion ata i hange to be. Thi mean that the ompreion ata i hange to be +. When 1 i require to be embee, the ign bit of the ompreion ata i hange to be 1. Thi mean that the ompreion ata i hange to be -. The embeing proeure of the propoe tehnique i efine a follow. (, b ) (, b 1) (1) where b repreent a 1 bit eret meage an repreent an 8 bit ompreion ata. Thi proeure i programme in C language a hown in Fig. 7. Figure 8 how an eample of the propoe tehnique. The ompreion ata i repreente a white an blak irle aoring to the ign bit. The ign bit of the ompreion ata repreente by white irle i. On the other han, the ign bit of the ompreion ata repreente by blak irle i 1. Thi eample how 4 aniate that an ontain 4 bit eret meage in total. Aoring to their ign bit, thee ata originally ontain 4 bit eret meage repreente a (,, 1, 1). In orer to embe eret meage repreente a (, 1,, 1), the propoe tehnique hange thee ata a hown in Fig. 8. Sine all of thee are eoe to be even if their ign bit are hange, the propoe tehnique oe not egrae the peeh quality at all. if (( & 7F) == ) { if (b == ) &= 7F; if (b == 1) = 8; } Fig. 7. Embeing proeure of the propoe tehnique programme in C language. 6. DVI-ADPCM The onept of the propoe tehnique may potentially be appliable to other oe that alo employ the fole binary oe. Another eample i DVI-ADPCM. Not only G.711 but alo DVI-ADPCM i employe in telephony ommuniation a a tanar VoIP (Voie over IP) oe (RFC, 1996).

8 Lole Steganography for Speeh Communiation 81 (a) (b) amplitue amplitue time 1 1 time Fig. 8. Eample of the propoe tehnique: (a) ompreion atefore embeing, an (b) ompreion ata after embeing. DVI-ADPCM i a peeh oe bae on the ADPCM (Aaptive Differential Pule Coe Moulation) algorithm evelope by DVI (Intel' Digital Vieo Interative Group) (Mirooft, 1994). The blok iagram of the ADPCM algorithm i hown in Fig. 9. In thi iagram, (n) repreent a peeh ata an (n) repreent a ompreion ata at the time of n. DVI-ADPCM i eignate a DVI3 an DVI4 aoring to the ize of ompreion ata. DVI3 enoe 16 bit peeh ata into 3 bit ompreion ata at an 8 khz ampling rate. DVI4 enoe 16 bit peeh ata into 4 bit ompreion ata at an 8 khz ampling rate. The ompreion ata of DVI3 onit of 1 bit ign an 2 bit magnitue. The ompreion ata of DVI4 onit of 1 bit ign an 3 bit magnitue. Both of thee are enoe in the fole binary oe. Figure 1 an 11 how the eoing proeure of DVI3 an DVI4 programme in C language. In thee proeure, i a ompreion ata, i a peeh ata, i a ifferene between the previou an the urrent peeh ata, an i a tep ize (Mirooft, 1994).

9 82 Reent Avane in Steganography (a) tep ize (n) (n) ompreion (n) ˆ( n 1) ˆ ( n) z -1 ˆ( n ) eompreion tep ize (b) (n) eompreion ˆ( n ) ˆ ( n) ˆ ( n 1) z -1 tep ize Fig. 9. Blok iagram of ADPCM: (a) enoing proeure, an (b) eoing proeure. = >> 2; if ( & 1) += >> 1; if ( & 2) += ; if ( & 4) = -; += ; Fig. 1. Deoing Proeure of DVI3 programme in C language.

10 Lole Steganography for Speeh Communiation 83 = >> 3; if ( & 1) += >> 2; if ( & 2) += >> 1; if ( & 4) += ; if ( & 8) = -; += ; Fig. 11. Deoing Proeure of DVI4 programme in C language. 7. Lole teganography tehnique for DVI-ADPCM The tep ize of DVI-ADPCM range from 7 to a hown in Fig.12 (Mirooft, 1994). When the magnitue of the ompreion ata i an the tep ize i 7, the peeh ata eoe with DVI4 oe not epen on the ign of the ompreion ata. Thi onition allow a lole teganography tehnique that an embe eret meage without any egraation. The embeing proeure of the propoe tehnique i efine a follow. int [89] = { 7, 8, 9, 1, 11, 12, 13, 14, 16, 17, 19, 21, 23, 25, 28, 31, 34, 37, 41, 45, 5, 55, 6, 66, 73, 8, 88, 97, 17, 118, 13, 143, 157, 173, 19, 29, 23, 253, 279, 37, 337, 371, 48, 449, 494, 544, 598, 658, 724, 796, 876, 963, 16, 1166, 1282, 1411, 1552, 177, 1878, 266, 2272, 2499, 2749, 324, 3327, 366, 426, 4428, 4871, 5358, 5894, 6484, 7132, 7845, 863, 9493, 1442, 11487, 12635, 13899, 15289, 16818, 185, 235, 22385, 24623, 2786, 29794, }; Fig. 12. Step ize of DVI-ADPCM. (, 7, b ) (, 7, b 1) (2) where b repreent a 1 bit eret meage, repreent a 4 bit ompreion ata, an repreent a tep ize. Thi proeure i programme in C language a hown in Fig. 13. Note that there i no uh a onition that allow a lole teganography tehnique for DVI3. Thi mean that a lole teganography tehnique i not available for DVI3 in the ame manner of the propoe tehnique for DVI4.

11 84 Reent Avane in Steganography if (( & 7) == && == 7) { if (b == ) &= 7; if (b == 1) = 8; } Fig. 13. Embeing proeure of the propoe tehnique programme in C language. 8. Capaity of the propoe tehnique The apaity of the propoe tehnique wa evaluate by uing peeh ata obtaine from atual telephony environment, uh a a private room, an offie room, a afeteria, an a railroa tation. In thee onition, 8 male peeh ata (m1 m8) an 8 female peeh ata (f1 f8) were ollete. A hown in Table 3, the uration of the peeh ata enote a L wa more than 12. The voie ativity ratio of the peeh ata enote a R wa at aroun 5 %, ine telephony peeh generally how the half uple truture ue to the alternate onveration proe (Wright, 21). RMS (Root Mean Square) of the bakgroun noie wa alulate from voie inative interval. private room offie room afeteria railroa tation peeh m1 m2 f1 f2 m3 m4 f3 f4 m5 m6 f5 f6 m7 m8 f7 f8 L () R (%) RMS (B) Table 3. Speeh ata obtaine from atual telephony environment.

12 Lole Steganography for Speeh Communiation apaity [%] RMS [B] Fig. 14. Capaity of the propoe tehnique for PCMU: Cirle, triangle, iamon, an quare repreent the apaity of a private room, an offie room, a afeteria, an a railroa tation, repetively. Soli line repreent the average apaity obtaine from a imulation uing a peeh ialogue atabae. The apaity of the propoe tehnique for PCMU i hown in Fig.14. Thi figure alo how a oli line that repreent the average apaity obtaine from a imulation uing a peeh ialogue atabae (ATR, 1997). It i iniate that the apaity of the propoe tehnique epen on the bakgroun noie in eah telephony environment. The apaity range from 3.3 % to 6.4 % for the peeh ata obtaine from a private room in whih the bakgroun noie i almot impereptible. It i interprete that the apaity range from 264 bp to 512 bp in thi onition. On the other han, the apaity range from.24 % to.44 % for the peeh ata obtaine from a railroa tation in whih the bakgroun noie i very annoying. It i interprete that the apaity range from 19.2 bp to 35.2 bp in thi onition. The apaity of the propoe tehnique for DVI4 a well a PCMU i hown in Table 4. Compare with PCMU, the apaity for DVI4 i muh maller. Note that the apaity for DVI4 i very mall even if the bakgroun noie i almot impereptible. The apaity

13 86 Reent Avane in Steganography range from.29 % to.16 % for the peeh ata obtaine from a private room. It i interprete that the apaity range from 2.32 bp to 12.8 bp in thi onition. On the other han, there i no apaity for the peeh ata obtaine from a afeteria an a railroa tation. private room peeh m1 m2 f1 f2 m3 PCMU (%) DVI4 (%) offie room afeteria m4 f3 f4 m5 m6 f5 f6 m railroa tation m8 f7 f Table 4. Capaity of the propoe tehnique for PCMU an DVI4. 9. Semi-lole teganography Semi-lole teganography tehnique i an iea for inreaing the apaity of the propoe tehnique (Aoki, 21b). Thi artile eribe how the apaity of the lole teganography tehnique for PCMU an be inreae by the emi-lole teganography tehnique. Figure 15 how how the emi-lole teganography tehnique embe eret meage. In the embeing proeure, thi tehnique moifie an 8 bit ompreion ata a follow. j ( 127 j) j ( 127 j ) (3) where j ( ) repreent the amplitue moifiation level.

14 Lole Steganography for Speeh Communiation 87 The amplitue moifiation may aue uneirable lipping in the 8 bit ompreion ata, if it magnitue eee 127-j. Conequently, thi tehnique an reover the original peeh ata only when the amplitue of the 8 bit ompreion ata range from -127+j to +127-j. (a) (b) () amplitue amplitue amplitue time time 1 3 time Fig. 15. Embeing proeure of the emi-lole teganography tehnique: (a) ompreion atefore embeing, (b) amplitue moifiation, an () ompreion ata after embeing. Mot of the pratial ae meet thi onition when the amplitue moifiation level i mall enough. Thi i bae on the fat that the amplitue of peeh ata tatitially how the eponential itribution (Rabiner, 1978). In general, the maimum magnitue of the 8 bit ompreion ata i le than 127-j. In thi ene, thi tehnique an be ategorize a a reverible teganography tehnique, if thi onition i atifie. However, if thi onition i not atifie, thi tehnique annot reover the original peeh ata any more. Therefore, thi tehnique i name emi-lole teganography tehnique in thi tuy. The embeing proeure of the emi-lole teganography tehnique i efine a follow.

15 88 Reent Avane in Steganography j j ( j, b 2 ) 1 ( j, b 2) ( j, b ) ( j, b 1) 1 ( j, b 3) j j ( j, b 2 1) (4) The apaity of the lole teganography tehnique i efine a N bit, where N repreent the number of the ompreion ata in whih the eret meage an be embee. On the other han, the apaity of the emi-lole teganography tehnique i efine a N(log 2( j 1) 1) bit. The apaity of the emi-lole teganography tehnique inreae aoring to the amplitue moifiation level. However, uneirable lipping may our more frequently in uh a ituation. After the etrating proeure of the eret meage, the emi-lole teganography tehnique reover the 8 bit ompreion ata a follow. j ( j 127) ( j j) j ( 127 j) (5) Of oure, the reovery proeure i neeary for eoing the original peeh ata. However, thi proeure i omitte in the onventional telephony ytem that o not implement the emi-lole teganography tehnique. In uh a ituation, there i no way to remove the egraation from the peeh ata. In orer to evaluate uh egraation, thi tuy invetigate the quality of the moifie peeh aty uing PESQ (Pereptual Evaluation of Speeh Quality) (ITU-T, 21). PESQ i wiely employe a an objetive evaluation meaure of the peeh quality in telephony ommuniation. Taking aount of the harateriti of human auitory pereption, PESQ poitively orrelate with a ubjetive evaluation meaure uh a MOS (Mean Opinion Sore). PESQ ore range from 4.5 to -.5. The higher the PESQ ore, the better the peeh quality. Figure 16 how the average PESQ ore with 95 % onfiene interval. Thee were alulate from the 16 peeh ata employe in the evaluation for the apaity of the propoe tehnique. A hown in thi figure, it i iniate that the amplitue moifiation aue ome egraation. However, it i almot impereptible when the amplitue moifiation level i mall enough. Thi reult may potentially aure the ompatibility of the emi-lole teganography tehnique with the onventional telephony ytem. Thi mean that normal playbak of the peeh ata moifie with the propoe tehnique i till aeptable in the onventional telephony ytem that o not implement the emi-lole teganography tehnique.

16 Lole Steganography for Speeh Communiation PESQ amplitue moifiation level Fig. 16. Degraation of peeh aty amplitue moifiation. 1. Conluion Thi artile eribe an iea for the lole teganography tehnique bae on the harateriti of the fole binary oe employe in everal peeh oe, uh a G.711 an DVI-ADPCM. In aition, an iea for the emi-lole teganography tehnique i alo eribe. The propoe tehnique take avantage of the reunany of the peeh oe. It i a ort of the loophole of the peeh oe that an be employe a a ontainer of eret meage. Suh a loophole play an important role for embeing eret meage without any egraation. The onept of the propoe tehnique may potentially be appliable to other oe that alo employ the fole binary oe. Beie G.711 an DVI-ADPCM, it i of interet to fin out the oe in whih the propoe tehnique i available. In aition, it i alo of interet to evelop ome pratial appliation that employ the propoe tehnique for tranmitting eret meage. Both of thee topi are the future work of thi tuy. 11. Aknowlegment The author woul like to epre the gratitue to the Minitry of Euation, Culture, Sport, Siene an Tehnology of Japan for proviing a grant (no ) towar thi tuy.

17 9 Reent Avane in Steganography 12. Referene Aoki, N. (23). A paket lo onealment tehnique for VoIP uing teganography bae on pith waveform repliation, IEICE Tranation on Communiation, vol.j86-b, no.12, pp Aoki, N. (26). A ban etenion tehnique for G.711 peeh uing teganography, IEICE Tranation on Communiation, vol.e89-b, no.6, pp Aoki, N. (27). A ban etenion tehnique for G.711 peeh uing teganography bae on full wave retifiation, IEICE Tranation on Communiation, vol.j9-b, no.7, pp Aoki, N. (27). A tehnique of lole teganography for G.711, IEICE Tranation on Communiation, vol.e9-b, no.11, pp Aoki, N. (28). A tehnique of lole teganography for G.711 telephony peeh, 28 Fourth International Conferene on Intelligent Information Hiing an Multimeia Signal Proeing (IIHMSP28), Harbin, China, pp Aoki, N. (29). Lole teganography tehnique for IP telephony peeh taking aount of the reunany of fole binary oe, AICIT 29 Fifth International Joint Conferene on INC, IMS an IDC (NCM29), Seoul, Korea, pp Aoki, N. (29). A lole teganography tehnique for G.711 telephony peeh, 29 APSIPA Annual Summit an Conferene (APSIPA ASC 29), Sapporo, Japan, pp Aoki, N. (21). A lole teganography tehnique for DVI-ADPCM Tranation on Funamental of Eletroni, Communiation an Computer Siene, vol.j93-a, no.2, pp Aoki, N. (21). A emi-lole teganography tehnique for G.711 telephony peeh, 21 Sith International Conferene on Intelligent Information Hiing an Multimeia Signal Proeing (IIHMSP21), Darmtat, Germany, pp Aoki, N. (212). Enhanement of peeh quality in telephony ommuniation by teganography, Multimeia Information Hiing Tehnologie an Methoologie for Controlling Data, IGI Global (To be publihe) ATR (1997). Speeh Dialogue Databae for Spontaneou Speeh Reognition Co, I., Miller, M., Bloom, J., Fririh, J., an Kalker, T. (28). Digital Watermarking an Steganography, Seon Eition, Morgan Kaufmann Publiher ITU-T (1988). G.711, Pule oe moulation (PCM) of voie frequenie ITU-T (21). P.862, Pereptual evaluation of peeh quality (PESQ), an objetive metho for en-to-en peeh quality aement of narrow-ban telephone network an peeh oe ITU-T (25). G.191, Software tool for peeh an auio oing tanarization Mirooft (1994). Multimeia Data Stanar Upate Rabiner, L.R. an Shafer, R.W. (1978). Digital Proeing of Speeh Signal, Prentie-Hall. RFC (1996). RFC189, RTP profile for auio an vieo onferene with minimal ontrol Wright, D.J. (21). Voie over Paket Network, John Wiley & Son

18 212 The Author(). Lienee IntehOpen. Thi i an open ae artile itribute uner the term of the Creative Common Attribution 3. Liene, whih permit unretrite ue, itribution, an reproution in any meium, provie the original work i properly ite.