CN100521772C

CN100521772C - Method for restricting number of channel watched by user at same time

Info

Publication number: CN100521772C
Application number: CNB2007101186402A
Authority: CN
Inventors: 何永忠; 韩臻; 李晓勇
Original assignee: Beijing Jiaotong University
Current assignee: Beijing Jiaotong University
Priority date: 2007-07-11
Filing date: 2007-07-11
Publication date: 2009-07-29
Anticipated expiration: 2027-07-11
Also published as: CN101094384A

Abstract

The invention is used to limit the amount of channels watched by users by adding the layers of the cipher key, adopting Hash function to generate control word, increasing the update frequencies of control word, and limiting the amount of the control words sent by user in one update cycle. By the invention the TV program provider can get the correlative charges according the amount of TV set and the amount of subscribed programs.

Description

A kind of method of restricting number of channel watched by user at same time

Technical field

The present invention relates to a kind of method of restricting number of channel watched by user at same time, to pay television broadcast, particularly the method for the key management of condition receiving system, distribution and use in the Digital Television belongs to television broadcasting reception technique field.

Background technology

In the charge digital television system, operator generally adopts condition receiving system (CAS) to make unauthorized user not watch, and validated user can come by the key that condition receiving system distributes the program decoding is normally watched.Typical C AS is made up of transmitting terminal and receiving terminal, and key structure wherein is three layers a key hierarchy structure, comprises control word CW, authorization key AK and user's master key MPK.Transmitting terminal selects a CW to import as pseudo-random generator at random, with its output program data stream is encrypted.CW must be distributed to legal users, and method is by AK CW to be encrypted (forming authorization control message ECM), and user's master key MPK encrypts (formation entitlement management message) to AK then.Program data stream, ECM and the EMM that encrypts and both digital signature of back send to receiving terminal.Receiving terminal can deciphering obtains AK to EMM by MPK, and deciphering obtains CW to ECM with AK, then the program stream deciphering to encrypting.Usually, CW needed upgrade once in per 5-20 seconds.Digital cable customers can be ordered a plurality of different television channels according to demand, and digital television program operator can be determined different expenses standards at requirements of different users.The Digital Television operation way is now, and one family is bought a digital TV set-top box, and a subscriber card can be watched program for a television set.Another kind of mode is that the function of television set integrated digital television set-top box still needs a subscriber card decipher the program of ordering equally.Deposited user's master key MPK in the subscriber card.If a user has multiple TV set, just need a plurality of digital TV set-top box and many subscriber cards, to realize pattern according to the charge of user terminal number.The problem of this method is that the expense that the user is used for hardware device increases, and causes the waste of set-top box and subscriber card resource; Because the charge of main frame and attached machine is different, attached machine is lower, and the user can be sold to another one user use to the set-top box of random and user like this; Even more serious is, can design a kind of digital TV set-top box, having only one to receive under the subscriber card situation, can decipher the program of a plurality of different channels simultaneously, for a plurality of television set terminal plays.Such set-top box product has been arranged on the market at present.Its principle is: because the program encryption key is constant in a period of time, therefore, thereby receiver can inquire repeatedly during this period of time that subscriber card obtains the decruption key of different channel, deciphers channel content, then for the user provides a plurality of channels simultaneously.

Purpose of the present invention is exactly at the problems referred to above that exist, a kind of method that can restricting number of channel watched by user at same time is proposed, be that the user can use a digital TV set-top box and a subscriber card, in the receiving terminal quantity that this user orders in advance, a plurality of terminal televisions of user are independent TV reception simultaneously.

Summary of the invention

In order to overcome the deficiencies in the prior art, the invention provides a kind of method of restricting number of channel watched by user at same time.

Basic assumption: subscriber card is the physics tamperproof, and the assailant can not steal user's master key wherein, can not revise wherein program and data; The assailant can the production figures TV set-top box or can be changed the software systems of set-top box.Be that subscriber card is believable, and set-top box is incredible.

The objective of the invention is to be achieved through the following technical solutions: have the following steps:

1, but user of restriction only has the method for a terminal program receiving bag: at the program transmitting terminal, all using independently to each channel, control word CW encrypts under the effect of pseudo-random number maker, all CW are regular update, and the time of upgrading is synchronous fully.Give all identical sequence numbers of control word CW in each update cycle, initial value is 1, and after CW upgraded, sequence number increased progressively 1.In subscriber card, a sequence number counter SNC is set, initial value is 0.At control word CW in update cycle, set-top box will need sequence number SN and the channel of the current control word CW of channel that deciphers to send to subscriber card, if SN is greater than SNC, and other authorization messages that meet this user, then subscriber card sends to set-top box with the current control word CW of channel association, and sequence number counter SNC is set to SN.In a control word CW update cycle, set-top box just can only be deciphered the TV programme of a channel like this, only can play (number of terminals that this method can not limited subscriber be watched same television channel simultaneously) for television terminal.Because a television terminal can be changed channel at any time in the process of watching, therefore in order to guarantee the normal switching TV program of television terminal, the update cycle of control word CW should be short as far as possible.If key management method does not change, just cause the transmission quantity of control word CW to increase greatly.In order to address this problem, the present invention adopts the mode of Hash password chain to carry out the distribution of control word CW.Concrete grammar is to increase by one between authorization key AK and the control word CW and add control key CK.AK encrypts CK, and the control word CW of each channel generates by hash function then: and CW=Hash (CK, SN).Other key and algorithm remain unchanged.

2, all terminals of same user are ordered under the situation of same program bag, can the access terminal method of number of limited subscriber: in subscriber card, a television terminal counter C is set, supposes that the television terminal number that the user orders is N.At control word CW in update cycle, subscriber card sends to N control word CW of N channel association in the program bag that set-top box and user order at most.In a control word CW update cycle, set-top box just can only be deciphered N different channel and be play for N television terminal like this.

3, all terminals of same user are ordered under the situation of different program bags, can the access terminal method of number of limited subscriber: sequence number counter array SNCS[0:n-1 is set], initial value is 0.Corresponding sequence number variable SNCS[i of each terminal i].Other method is with first kind of situation (but user of restriction only has a terminal program receiving bag).

4, support the method for the normal play of many pictures of terminal Digital Television: the program sender sends each channel program with two kinds of definition.A kind of is normal high definition program, and another kind is the low definition program.The low definition program adopts looser control measure, makes a terminal a plurality of low definition programs of can decoding simultaneously.

Effect of the present invention and advantage are: a user only needs a set-top box just can watch program for all television sets of this user, and simultaneously, limited television operator can be collected correlative charges according to user's television set number and the number of programs of ordering.This has just reduced the input of user aspect set-top box on the one hand, has guaranteed the income of operator on the other hand.Subscriber card is only depended in its fail safe, and irrelevant with set-top box or television set terminal.

Description of drawings

Fig. 1 is key hierarchy figure of the present invention;

Fig. 2 is that program of the present invention sends and the reception flow chart.

Embodiment

The present invention is further illustrated below in conjunction with the drawings and specific embodiments.

Embodiment 1:

As shown in Figure 1, the key structure of condition receiving system is four layers a key hierarchy structure, comprises control word CW, control key CK, authorization key AK and user's master key MPK.User's master key MPK is positioned at the top of key hierarchy structure, uses this key that authorization key AK is encrypted, and forms entitlement management message EMM.Use AK that control key CK is encrypted and form authorization control message ECM.Use CK and control word CW sequence number SN, by hash function generate control word CW:CW=Hash (CK, SN).For example, when SN=1, CW1=Hash (CK, 1); During SN=2, CW2=Hash (CK, 2); During SN=3, CW3=Hash (CK, 3) or the like.

Various key updating frequencies can be determined according to the operation situation.As long as user's master key MPK does not abolish, MPK is just permanently effective; Authorization key AK upgraded once in general one day; Control key CK update time can be at 10 seconds to 1 minute.Need select different values concrete update time according to demand for services, network condition etc.

Embodiment 2:

But limit the embodiment that a user only has a terminal program receiving bag: condition receiving system CAS is made up of transmitting terminal and receiving terminal, as shown in Figure 2.User's master key MPK has imported in the subscriber card when subscriber card is produced.After the user bought the program bag, transmitting terminal generated authorization key AK that should the program bag, and regular update.The program of each channel that transmits for needs, transmitting terminal is selected a control key CK at random, and the control word CW of this channel generates by hash function: CW=Hash (CK, SN), wherein SN is a control word CW sequence number, and hash algorithm can be selected SHA1-128, perhaps RC6 for use.CW encrypts program data stream with the output of PRG as pseudo-random generator PRG input.CK must be distributed to legal users, and method is by AK CK to be encrypted (forming authorization control message ECM), and user's master key MPK encrypts (forming entitlement management message EMM) to AK then.SN, the ECM of program data stream of encrypting and correspondence and EMM and both digital signature of back send to receiving terminal.Because CW can be produced at input CK and SN by hash algorithm, does not therefore need independent transmission.Transmitting terminal must be selected the suitable control word CW update cycle.Because receiving terminal can only be deciphered the program of a channel simultaneously, therefore, after subscriber card sends to the set top box decodes device with the control word CW of a program, in the update cycle, just can not send the current control word CW of another channel.On the other hand, the user may need to change channel, so the update cycle can not be oversize.Suggestion update cycle T is 0.1 second to 0.5 second.At the program transmitting terminal, transmitting terminal is set program initial sequence number SN=1 (when SN reaches maximum, reverting to 1 automatically), selects authorization key AK and control key CK; At moment nT, upgrade SN=SN+1, and to each channel calculate independently control word CW=Hash (CK, SN), CW control pseudorandom number generator to [nT, n+1T) Nei program encrypt and and SN be compounded to form ciphered program and flow ETS.With AK CK and SN are encrypted formation authorization control message ECM then, user's master key MPK encrypts AK and forms entitlement management message EMM then.Ciphered program stream ETS, ECM and EMM and both digital signature of back send to receiving terminal.At user's receiving terminal, a sequence number variable SNC is set in the subscriber card equally, initial value is 0.Subscriber card obtains AK according to current EMM with the deciphering of user's master key, and ECM obtains CK with the AK deciphering.Digital television decoder receives that being responsible for deciphering behind the program stream of encryption obtains program stream.At control word CW in update cycle, decoder will need the channel current sequence number SN that deciphers to send to subscriber card, if SN is greater than SNC, and other authorization messages that meet this user, then subscriber card is with the current control word CW=Hash (CK of channel, SN) send to set-top box, and sequence number variable SNC is set to SN, otherwise makes mistakes.In a control word CW update cycle, set-top box just can only obtain a channel decryption control words CW like this, therefore the TV programme that can only decipher a channel.

Embodiment 3: all terminals of same user are ordered under the situation of same program bag, can the access terminal implementation method of number of limited subscriber.The step of this implementation method is identical with embodiment 2, except that following content.In subscriber card, a terminal counter C is set, the television terminal number that the user orders is N.When decoder sent a new SN (SN is greater than SNC) to subscriber card, C was set to 0.After this, before subscriber card sends to control word CW of set-top box at every turn, terminal counter C is increased by 1.If terminal counter C greater than N, then no longer sends control word CW.In a control word CW update cycle, set-top box just can only be deciphered N different channel and be play for N television terminal like this.

Embodiment 4: all terminals of same user are ordered under the situation of different program bags, can the access terminal implementation method of number of limited subscriber.The step of this implementation method is identical with embodiment 2, except that following content.Sequence number counter array SNCS[0:n-1 is set], initial value is 0.Corresponding sequence number variable SNCS[i of each terminal i].

Embodiment 5: the implementation method of supporting the normal play of many pictures of terminal Digital Television.The step of this implementation method is identical with embodiment 2, except that following content.The program sender sends each channel program with two kinds of definition.A kind of is normal high definition program, and another kind is the low definition program.The low definition program adopts looser control measure, makes a terminal a plurality of low definition programs of can decoding simultaneously.

Claims

One kind can restricting number of channel watched by user at same time method, it is characterized in that having the following steps:

A. at the program transmitting terminal, use all independently to each channel that control word CW encrypts under the effect of pseudo-random number maker, all CW are regular update, and the time of upgrading is synchronous fully;

B. give all identical sequence numbers of control word CW in each update cycle, initial value is 1, and after CW upgraded, sequence number increased progressively 1;

C. in subscriber card, a sequence number counter SNC is set, initial value is 0;

D. at control word CW in update cycle, set-top box will need sequence number SN and the channel of the current control word CW of channel that deciphers to send to subscriber card, if SN is greater than SNC, and the authorization message that meets this user, then subscriber card sends to set-top box with the current control word CW of channel association, and sequence number counter SNC is set to SN;

E. adopt the mode of Hash password chain to carry out the distribution of control word CW; Concrete grammar is to increase a control key CK between authorization key AK and the control word CW; AK encrypts CK, and the control word CW of each channel generates by hash function then: and CW=Hash (CK, SN).
2. a kind of method that can restricting number of channel watched by user at same time according to claim 1 is characterized in that having the following steps:

All terminals for same user are ordered the same program bag, and the limited subscriber number that can access terminal has the following steps:

F. in subscriber card, a television terminal counter C is set, supposes that the television terminal number that the user orders is N;

G. at control word CW in update cycle, subscriber card sends to N control word CW of N channel association in the program bag that set-top box and user order at most;

Perhaps order different program bags for all terminals of same user, the limited subscriber number that can access terminal has the following steps:

H., sequence number counter array SNCS[0:n-1 is set], initial value is 0; Corresponding sequence number variable SNCS[i of each terminal i].
3. a kind of method that can restricting number of channel watched by user at same time according to claim 1 and 2, it is characterized in that transmitting terminal selects the appropriate keys update cycle: as long as user's master key MPK does not abolish, MPK is just permanently effective; Authorization key AK upgraded once in one day; Control key CK update time was at 10 seconds to 1 minute; The control word CW update cycle is 0.1 second to 0.5 second.
4. a kind of method that can restricting number of channel watched by user at same time according to claim 1 and 2 is characterized in that subscriber card is only depended in the fail safe of this method, and irrelevant with set-top box or television set terminal.