Hệ thống truy nhập có điều kiện trong truyền hình số

PHAT THANH TRUYEN H I N<br /> <br /> <br /> <br /> <br /> He thong truy nhap co<br /> dieu kien trong truyen hinh so<br /> Nguyen Quy Sy<br /> <br /> He thong truy nhap c6 dieu kien CA<br /> sd niy cd the dupc mat ma hda, riham bio ve quyen<br /> (Conditional Access) dong mot vai tro quan<br /> sd hiiu ndi dung cua nhi eung cap ndi dung (bing<br /> trong trong viec phan phoi cac djch vu truyen<br /> DRM) hoac khdng dupc mat ma hda (ndi dung khdng<br /> hinh tra tien. Muc dich chinh cua he thong<br /> dupc bio ve).<br /> nay la cung cap mot cd che kiem tra de dam - Cie ndi dung sd eua cie chuong trlrih dupc<br /> bao khach hang t r u y cap dung noi dung da ghdp vdi nhau thinh mot ludng sd chung (Su dung<br /> du'dc tra tien. Bai bao trinh bay tong quan ve MPEG-2). Cic ndi dung sd niy cd the dupe mat ma<br /> mot he thong truy cap co dieu kien siir dung hda tmdc (cho timg kerih) hoac sau kM ghdp ludng<br /> trong cac he thong t r u y e n hinh sd, d | c biet la se dupc mat ma hda de dim bio cM cac thue bao<br /> trong truyen hinh di dong. dupc phep mdi ed the xem dupc cac ndi dung niy.<br /> Day li giai doan bio ve ndi dung trayen hinh sd<br /> bing tmy cap cd dieu kien (CA).<br /> 1. G i a i THIEU<br /> - Trayen cic ludng sd da dupe ma hda qua mang<br /> Qua trlnh tmyen ndi dung ciia cic kenh chuong<br /> vidn thdng hoac quing bi:<br /> trlnh tmyen htnh sd qua mang vien thdng hay mang<br /> quing bi gdm 3 giai doan: + Cd the dupc bio ve nhu tmyen dan bing mang<br /> SG-sii dung an ninh mang 3G de bio ve tmy cap<br /> - Timg chuong trinh tmyen hinh dupe sd hda<br /> mang, hoac tmyen din qua mang xDSL ciing yeu<br /> (Men nay phd bien su dung MPEG-4). Cic ndi dung<br /> Unprotected Content<br /> <br /> <br /> <br /> <br /> DRM Protected Content<br /> <br /> Hinh 1. Tdng quan qua trinh truyen noi dung truyen hinh so<br /> <br /> <br /> <br /> <br /> 3 6 I TAP C H I CNTT&TT K Y 1 ( 2 . 2 0 1 0 )<br />  PHAT THANH TRUYEN H I N H<br /> <br /> <br /> cau xac thuc - He thdng xac thue thue bao (SAS),<br /> + Cd the khdng dugc bio ve nhu kM phit quing - Bd xio trdn,<br /> bi. - Bd giii xio trdn,<br /> - vi the thdng minh.<br /> 2. CAU TRUC CHUNG CHO HE THONG Ba thinh phan dau li a ben miy phit cdn 2 thinh<br /> CA phan sau li tren may thu (thudng li set-top-box).<br /> He thdng tmy cap ed dieu kien su dung su xao He thong quan ly thue bao (SMS - Subscriber<br /> trpn vi mat ma de ngin chin tray cap khdng dugc Management System )<br /> nhin dang, de bio ve ndi dung vi dich vu. Su xio SMS li mdt tnmg tam kirih doanh, nd "phit hinh<br /> trdn dugc sir dung de bic ve tin Meu chuong trlnh the thdng minh, gui hda don vi rihin tien tri tir<br /> vdi mdt thuat toin xic dinh, nhu li thuat toin xao thue bao". Mdt tii nguyen quan trpng cua SMS li<br /> iron Chung CSA (Common Scrambling Algorithm). CO sa dii Ueu khich hing, bao gdm thdng tin nhay<br /> Thuc te, thuat toan xio trdn dugc su dung ttong hau cim cao trong kinh doanh, nhu li thdng tin ci nhin<br /> het cic he thdng quing bi sd CA Men nay tren toin ve thue bao, nhiing sd seri cua cie set-top box vi<br /> the gidi, trong kM mat ma d day hudng vio viec thdng tin ve cic dieh vu, tir dd ngudi su dung (NSD)<br /> bio ve khda xio trdn thudng dugc ggi li khoi dieu dat hing. Dau tien, ea sd du Ueu dupe su dung de<br /> kMen CW (Control Word), nham cho phdp xio trpn quin ly quyen tray cap cua thue bao vi bio ve cic<br /> 0 miy phit vi giii xio trdn a miy thu. Do dd quin ndi dung vi cic dieh vu. Neu ngudi van hinh dich<br /> ly khda de dim bio CW dupe trao mdt eie an toin vu can thay doi thdng tin cua khich hing, ea sd dil<br /> cho dimg ngudi su dung da dupc nhin dang, li mdt Ueu se cap nhat bing cich them vio cic tham sd<br /> yeu td can tMet trong mdt he thdng CA. vdi y dinh thay ddi quyen tray cap cua thue bao de<br /> Hinh 2 dua ra md hinh tong the mdt he thdng CA bio ve eie dich vu vi eie ndi dung. Vi SMS se giri<br /> cho trayen Mnh sd ndi chung. Mdt he thdng CA bao mdt yeu cau cap nhat vdi thdng tin mdi tdi SAS.<br /> gdm 5 thinh phan quan trpng: He thd'ng nhan dang thue bao (SAS -<br /> - He thdng quin ly thue bao SMS, Subscriber Authorization System)<br /> <br /> <br /> Hf thong CA brit phm<br /> lUi^ cuiig cnp dtcli \-ii<br /> He tliong C'.\ trong<br /> mav thu trxi\-en hinh so<br /> BacV.Cnwinei<br /> <br /> <br /> <br /> Dftll^u<br /> co.?o<br /> klincli Iiaiig<br /> * BQ gi^i xSo trpn<br /> <br /> <br /> <br /> <br /> Qliring b^<br /> <br /> <br /> <br /> thong mml)<br /> <br /> * Btf TtAo tr$n<br /> <br /> <br /> <br /> <br /> Hinh 2. Cac thanh phan cua mot he thong CA DVB chung<br /> <br /> <br /> <br /> TAP CHI CNTT&TT KY 1 ( 2 . 2 0 1 0 ) 37<br />  PHAT THANH TRUYEN HINH<br /> <br /> He thdng nhin dang thue bao ed trach nMem tao, - CSA bao gdm hai phan: he thdng giii x.- trdn<br /> to chirc vi phin phdi ludng dir Ueu dieu kMen, vi (CDS) vi cdng nghe xio ttdn (ST), cd nhung giay<br /> du bin tin quin ly quyen han EMM (Entitlement phdp phan phdi rieng de sir dung yeu cau ky thuat<br /> Management Message) vi bin tin dieu kMen quyen cho timg phan.<br /> han ECM (EntiUement Contiol Message), dua tren - ETSI quin ly bdn cdng ty phit trien CSA. Cie<br /> SMS. Mdt EMM li mdt bin tin nhin dang mdt ngudi hang sin xuat STB se tri tien giay phdp cdng nghe<br /> dung de giii xio trdn mdt dich vu, trong khi ECM li xao trdn vi tiep tuc tti tien giay phdp con cho nhiing<br /> mdt tii Ueu mat ma eua khoi dieu kMen vi thdng ngudi mua bd xao trdn.<br /> tin ve quyen han.<br /> 2.2. He thong phan cap khoa<br /> Bg xao trpn Ndi chung, mdt he thdng CA sir dung he phan<br /> TMet bi niy sir dung mdt thuat toin manh de xio cap khoa ba ldp nhu dupc cM ra trong. CW thay<br /> trdn ndi dung (hay cdn dupe gpi li ludng trayen tii doi ngiu nMen li ldp dudi eiing trong he phin cap<br /> TS-Transport Stream). Trong he thdng DVB, bd xao khoi. Nd dugc sir dung nhu hat gidng cua bd tao ma<br /> trdn sii dung CSA de xio trdn. gii ngau nMen PRG (Pseudo Random Generator) de<br /> Bg giai xao tron tao ra mot chudi gii ngiu liMen, chudi niy dugc<br /> TMet hi niy ciing sit dung mdt thuat toin manh de diing de xio ttdn TS. CW li mot khoa bi mat, hau<br /> giii xio trdn ludng dti Ueu da dupe xio trdn. Trong het he thdng tmyen Mnh tri tien su dung mat ma<br /> he thdng DVB, bd giii xio trdn su dung he thdng ddi ximg, tire li CW vira li khoi xio trdn viia li khoi<br /> giii xio trdn (CDS) chung de giai xio trdn. giii xio trdn. Xem xdt den tinh bio mat tM CW nen<br /> dupc lim mdi trong khoing 5 den 20 giay. Su Uen<br /> The thong minh<br /> ket cic ldp cua he thdng phan cap khoi li su dung<br /> The thdng minh dupc sir dung nhu "mdt dau Meu<br /> mdt khoi nhin dang AK (Authorization Key) de mat<br /> ciia quyen han de giii xio trdn eae tin Meu quing<br /> ma CW vi sau dd tao ra ECM. Khoi nhin dang AK<br /> bi". SMS phit hinh the thdng minh vi xic nhin<br /> li duy nhat cho timg kenh vi ddi kM dupe gpi li<br /> tinh hpp le thdng qua viec lip trlnh chiing trade vdi<br /> cMa khda dich vu cho nhi cung cap CA. Nd thudng<br /> eie khda de nhin dang tray cap tdi cac ndi dung<br /> xuyen dupe cap rihat moi chu ky nap tien, dieu dd<br /> chuong trlnh hay cic dich vu, hoac ci hai.<br /> phu thudc vio chinh sach dich vu nap tien cua nhi<br /> 2.1. Xao trpn va giai xao trpn kinh doanh, cd the li mdt Man hay mdt thing. Mdi<br /> Mdt TS dupe mat mi bdi bd xio trdn vdi mdt thuat kM CW dupe lim mdi, cM phit quing bi mdt ECM<br /> toin dii manh, nhim glim tdi tMeu khi nang tan duy nhat, do dd giup tiet kiem bang thdng Meu qui<br /> cdng cua tin tie. Bd xio ttdn ed the dupc bit dau tii vi giim tii trao ddi vdi he thdng phan cap khoa hai<br /> mdt CW nhu li mdt cMa khda mat ma, hoac dupc ldp. Ldp tren cimg su dung khoi rieng ehinh MPK<br /> tao bdi mdt CW dupc sir dung de dat cho trang thii (Master Private Key) de mat ma AK ciing vdi thdng<br /> dau cua bd tao ma gii ngau nMen de nd dua ra mdt tin quyen tmy cap khic.<br /> khoi mat ma. Dau ra ciia bd trdn dugc phan phdi<br /> Doan mat ma da dupc tao ra li EMM. MPK li duy<br /> den NSD qua mang quing bi. CW dugc lay lai tir TS<br /> nhat cho mdi thue bao. Nd dugc luu trong mdt the<br /> da bi trdn vi dugc sir dung de tri lai ndi dung gdc<br /> thdng minh, the niy dupe SMS phat hinh dim bao<br /> vdi thuat toin giii xao ttdn tuong img.<br /> an ninh.<br /> To chirc DVB chau Au da phit trien mdt chuan cho<br /> ECM, EMM va TS da xio trdn se dupc ghf vio<br /> xio trdn vi giii xio ttdn, vi du nhu CSA:<br /> <br /> <br /> 3 8 I TAP CHI CNTT&TT KY 1 (2.2010)<br />  PHAT THANH TRUYEN HINH<br /> <br /> MAy elm Mn>- tliu<br /> <br /> <br /> TU* thdng ittlnli<br /> SMS<br /> * j<br /> 1<br /> ^ *<br /> Decrypt2<br /> Quy«ii t i u y<br /> AK<br /> ^<br /> Encrypti<br /> 1<br /> Decry pt1<br /> "<br /> 1<br /> CW<br /> PRG<br /> =M M<br /> r\ PRG<br /> <br /> j V<br /> TS ••<br /> +<br /> B$ x^o trpn ECM ' / BO giai x^o tr&n<br /> TS*<br /> <br /> <br /> <br /> Hinh 3. Cau tnic ba tang khoa<br /> <br /> mdt TS mdi vi phan phdi tdi thue bao qua kenh dupe tMet ke trong SMC se dupc dit vio de giii ma<br /> quing bi. Miy thu se chdn the nhd vio STB, giii CW can tMet cho viec giii xio trdn.<br /> ma EMM rdi den ECM, vi eudi ciing nhin lai CW de Trong phuong thirc dua tten khoi, mdt he thdng<br /> giii xio trpn TS da dupe bio mat. Can chit y ring phan cap khoa se dupc sii dung li he thdng phan<br /> pMa miy thu phii su dung PRG gidng vdi chudi gii cap khoa 3 mirc da cM ra trong phan trade.<br /> ngiu nMen o miy phit de giii xio trdn.<br /> Trong phuong phip dua tren thuat toan, eae thuat<br /> 2.3 So sanh mat ma hoa di/a tren thuit toin dupe luu trong the thdng mitih li bi mat ehinh.<br /> toan va di/a tren khoa KM thuat toan tao WC bi xim hai, he thdng bi ran<br /> Phan niy se thio luan nhiing die tinh co bin nirt. Ddi vdi phuang phip dua tren khoi, tinh bio<br /> chinh khic biet cic he thdng CA. Nhu da de cap a mat phu thudc vio dp tui cay cua khoa, vl vay viee<br /> tien, ECM vi EMM dupc sir dung de trayen tii thdng lim mdi cac khoa (CW, AK, MPK) trong mdt thdi gian<br /> tin ve CW vi quyen mi cic thue bao dupe phep ed nhat dinh li van de cot yeu.<br /> the nhan CW vi nhiing chuong trinh dupe bio ve.<br /> Tieu de eua EMC vi EMM se nhay ddi vdi he thdng<br /> Cd hai phuong thirc mat ma hoi de tao CW cho thue<br /> Idn ed sd lupng thue bao Idn. Phuong thirc dua tren<br /> bao li:<br /> thuat toan cd tieu de Idn hon phuong thirc dua tren<br /> - Cie phuong thire mat ma hoi dua tten thuat toin khoa. Vdi he thdng phin cap ba tang, AK ehira trong<br /> - Vi mat ma khoi dua tren khoa. EMM se dupe phan phdi true tiep thdng qua MPK<br /> Trong phuong thire dua tren thuat toin, EMM ehira cho mdi thue bao mdi lan nd dupc lim mdi. Gii su<br /> tham sd dieh vu, nd li ky Meu duy nhat, thay cho ci cd S thue bao vi T kenh trayen, se cd xap xi SxT gdi<br /> khoi dich vu hay cdn dugc gpi li AK trong he thdng dupe mat ma vi trayen di. Dieu niy tdn liMeu thdi<br /> CA mat ma hoi dua tren khoi. Mdi the thdng minh gian vi die biet ric rdi ddi vdi he thdng Idn. Cd mdt<br /> chira cic thuat toin khic nhau. Mdt dimg de giii ma vii phuong thirc mat ma hoi quing bi de giim bdt<br /> CW, nhiing thuat toin khac se dupe su dung de du tii trpng cho mpi lan lim mdi vi tmyen lai cua AK.<br /> phdng trong tradng hpp bi an trdm. ECM chira mdt<br /> chuong trlnh md t i cho viec kiem tra quyen tray 3. KHA NANG LIEN KET CA<br /> cip. The thdng minh se so sinh thdng tin quyen<br /> An ninh cua he thdng CA phu thudc chu yeu vio<br /> tray cap ben trong nd vdi thdng tin ehira ttong ECM<br /> bi mat cua ea ehe sd hiiu cua ngudi bin hing de<br /> vi EMM. Neu tham tra thinh cdng, thuat toan da<br /> <br /> <br /> TAP CHI CNTT&TT KY 1 (2.2010) 39<br />  PHAT THANH TRUYEN H I N H<br /> <br /> <br /> phan phdi CW, Uen quan den quyen sd huu tri Me vi dua ra cic ECM tii nMeu he thdng CA. Nc ra,<br /> eua ngudi ban hing, do dd Uen ket cac he thdng CA vdi SimulCrypt tM tinh bio mat cua he thdng ..a yeu<br /> nhu the nio. nhat. Tuy iiMen,uu diem ehinh ciia phuong thire mat<br /> 3.1 Mat mi dong thdI-SimulCrypt ma niy li khdng tao them cM pM nio cho NSD.<br /> <br /> SimulCrypt lim cho nd cd the mang nMeu bin tin Nhupc diem chinh eua MultiCrypt nim trong phan<br /> mdt luc, cie bin tin dupc tao ra bdi eae he thdng CA tti them tien ciia NSD. Trong nam 2001 mdt tMet<br /> khic nhau, nhung tat ci cimg cho phep dieu kMen bi a STB dupc tao ra cd gii 65USD, dit hon so vdi<br /> ndi dung MPEG da dugc xio trdn. De ma hda ddng mdt tMet bi STB vdi mdt he thdng CA dupc tich hop,<br /> thdi cd the thuc Men dugc tM ndi dung MPEG dugc tinh ci gii cho mdt modul CA (60 USD) cdng vdi gia<br /> xao trdn bing thuat toan xio trdn chung vdi khoi eua mdt giao dien CI STB tich hpp (5 USD). De xem<br /> chung. Mdi he thdng CA tao ra nhirng bin tin dieu chuong trlnh dupc xao trdn bdi mdt he thdng CA<br /> kMen cua rieng nd (ECM vi EMM) dua theo dinh khic khdng dupc cii dat trong STB can phii them<br /> dang bin tin dugc dinh ngMa bdi DVB. Ndi dung vio mdt md dun CA cho he thdng CA, vdi gii trong<br /> xio trdn vi bin tin CA cua mdi he thdng dupc ghep nim 2001 xap xi 60 USD. Mdt nhupc diem khac li<br /> kenh vio mdt ludng MPEG-TS vi quing bi tdi STB. giao dien li ed dinh vi khdng linh hoat, dieu dd din<br /> STB Ipc ra cic bin tin rieng, de tii tao khoi ma hda den gidi han hd trg cua cic chirc nang he thdng CA.<br /> Chung rdi giii xio trdn ndi dung. Ve pMa nhi cung cap dich vu, khdng can them thoi<br /> thuan thuong mai hay tang them cM pM.<br /> 3 . 2 Da m a t m a - M u l t i C r y p t<br /> <br /> Ma hda nMeu mi cho phep hoat ddng cua mdt STB<br /> vdi cie he thdng CA khic nhau qua giao dien chung 4 . KET L U A N<br /> <br /> CI (Common hiteriace). Giao dien chung niy li mot Bii bao trlnh biy tong quan eGng nhu die diem<br /> giao dien chuan de ket ndi mdt STB vdi mdt modul cua he thdng tmy cap cd dieu kien-he thdng an<br /> cd the tich rdi ra dupc (mdt modul PCMCIA chung). ninh tmyen dan cho tmyen hirih sd. Tuy nMen viec<br /> Modul PCMCIA thuc Men cac chirc ning rieng ddi su dung cic he thdng CA Men nay se gay ra khd<br /> vdi he thdng CA Uen quan. De xem chuong trlnh khan cho muc tieu Uen ket vi roaming, lim cho thi<br /> dupc ma hda bdi cic he thdng CA khic mi khdng tmdng tmyen Mnh sd dl bi phan doan, khd Uen ket<br /> dupc cii dat tren STB, ngudi dimg ed the chuyen toin cau. Ngoii ra he thdng tmy cap ed dieu kien<br /> kenh eie modul bing tay. mdi cM thda man dupe an nirih cho cie nhi khai<br /> 3.3 So sanh<br /> thac mang, nhung chua dip img dupc nhu cau an<br /> ninh cua cic rihi cung cap ndi dung. VI vay Men<br /> Sir dung SimulCrypt ddi hdi can phii cd nhung<br /> nay cimg vdi sii dung he thdng CA, trong an ninh<br /> thda thuan ve lpi ich giira cic nhi cung cap dich<br /> ndi dung tmyen Mnh sd ngudi ta cdn su dung cic<br /> vu de Uen ket cie he thdng CA lai vdi nhau, nhu li<br /> cdng nghe quan ly bin quyen sd (DRM).<br /> trao ddi cic ban tin CA. Mdt nhupc diem khic cua<br /> phuong phip niy li ting mirc sir dung bing thdng,<br /> do ban tin CA dupe sao chdp cho mpi he thdng CA Tai lieu t h a m khao ->i<br /> vi trao ddi giiia cic he thdng. Dieu dd ciing lim niy [1]. NGUYEN QUY SY.detSi "NghlSncuucSc cong nghe an ninh<br /> sinh them nMeu van de khic. Vi du lihu can them noi dung tmyen hinh so va kha nang ap dung tai Vm Nam", ma s6<br /> <br /> mdt bd ddng bd SimulCrypt de giam tdi tMeu xung 84-09-KHKT-RD, Bg TT&TT.<br /> <br /> dot tren bat ky thinh phan nio cua mdt he thdng [2]. AMfTABH KUMAR, Mobile TV: DVB-H, DMB, .3G -ems<br /> and Rich Media Applications, Elsevier Inc., 2007<br /> CA vi dupe sir dung de dieu kMen viec tao, tip hpp<br /> <br /> <br /> 40 TAP CHI CNTT&TT KY 1 ( 2 . 2 0 1 0 )<br />