CN102075812B - Data receiving method and system of digital television - Google Patents

Abstract

The invention discloses a data receiving method and system of a digital television. The data receiving method of the digital television comprises the following steps: receiving and analyzing a data packet coming from a server; filtering out encrypted management information, encrypted authorization control information and key management information from the analyzed data packet; decrypting the encrypted management information and the encrypted authorization control information according to the key management information; extracting encrypted control words from the decrypted authorization control information according to the decrypted authorization management information; decrypting the encrypted control words according to the key management information; and descrambling received audio-video streams according to the control words. By adopting the technical scheme, the invention has the advantages that data is prevented from being obtained illegally, the lawful right of a user is protected, the data security is high and the cost is low.

Description

Method and system for receiving data of digital television

Technical Field

The invention relates to the technical field of digital televisions, in particular to a method and a system for receiving data of a digital television.

Background

The CAS (Conditional Access System) is a System for controlling a user to receive a broadcast service, that is, the user can only receive an authorized broadcast service, and the purpose of the CAS is to implement a paid service of the broadcast service through authorization management. And the CAS controls the broadcast service by scrambling the broadcast data, and only an authorized user can descramble and normally receive the broadcast data, thereby receiving the broadcast service. Scrambling and descrambling are a pair of symmetrical, reversible processes and transmit control words to the user terminal in synchronization with the broadcast data. Thus, control of the broadcast service is translated into protection of the scrambling control word.

The scrambling and descrambling technology is used for encrypting and decrypting digital programs, and the basic principle is that a scrambling control word encryption transmission method is adopted, and a user side decrypts the digital programs by using an intelligent card. In an MPEG transport stream, there are two data streams associated with the transmission of control words: ECM (Entitlement Control Message) and EMM (Entitlement Management Message), Control words encrypted by Service Key (SK) are transmitted in ECM. The service key, which encrypts the control word, is transmitted in EMM, and the service key is encrypted by a user personal assignment key (PDK) before being transmitted, and the EMM further includes an address, user authorization information, such as a program or a time slot that the user can watch, a viewing fee paid by the user, and the like. The user personal assignment key (PDK) is stored in the user's smart card. At the user terminal, the set-top box obtains the PI D values of the EMMs and the ECMs, then filters the ECMs and the EMMs from the TS stream, and sends the ECMs and the EMMs to the smart card through the smart card interface. The intelligent card firstly reads a user Personal Distribution Key (PDK), the PDK is used for decrypting EMM, a Service Key (SK) is taken out, then the Service Key (SK) is used for decrypting ECM, CW is extracted, the CW is sent to a descrambler through an intelligent card interface, and the descrambler can descramble scrambled transmission streams by using the CW.

Fig. 1 is a logic structure diagram of a data receiving system of a digital television in the prior art, in the data receiving system of the digital television, a network parsing module 110 receives a data packet from a server and parses the data packet, a conditional access module 120 filters authorization management information and authorization control information from the data packet, the authorization control information is embedded with a control word, a smart card 130 extracts the control word from the authorization control information according to the authorization management information and returns the control word to the conditional access module 120, and a descrambler 140 descrambles a received audio/video stream by using the control word. However, in the data receiving system of the digital television, the data packet containing the authorization control information and the authorization management information is transmitted from the server network to the user terminal in the form of plaintext, and the control word returned by the smart card is also visible plaintext, which may be obtained illegally by hackers, thereby damaging the legal benefit of the user and bringing about a safety hazard to the user.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method for receiving data of a digital television, which can prevent illegal acquisition of data and further maintain the legitimate rights and interests of users, aiming at the problem of potential safety hazards in the data reception of the digital television in the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows: a data receiving method of a digital television is provided, which comprises the following steps:

receiving a data packet from a server and analyzing the data packet, wherein the data packet comprises encrypted authorization management information, encrypted authorization control information and key management information, the authorization control information is embedded with encrypted control words, and the key management information comprises protection key information, algorithm information and protection key length information;

filtering out encrypted authorization management information, encrypted authorization control information and encrypted key management information from the analyzed data packet;

decrypting the encrypted authorization management information and the encrypted authorization control information according to the key management information;

extracting encrypted control words from the decrypted authorization control information according to the decrypted authorization management information;

decrypting the encrypted control word according to the key management information;

and descrambling the received audio and video stream according to the control word.

In the data receiving method of the digital television, the data protection unit decrypts the authorization management information and the authorization control information in the encryption protection unit.

In the data receiving method of the digital television according to the present invention, the method further includes:

and storing the filtered key management information into a memory.

In the data receiving method of the digital television, the decryption is carried out by an RSA method.

In the data receiving method of the digital television of the present invention, the step of decrypting includes:

A1. dividing the ciphertext into n ciphertext blocks and numbering the ciphertext blocks sequentially, wherein the n ciphertext blocks are C_jJ =1, 2, …, n, where n is a natural number greater than 1, and the length of each ciphertext block is the same as the length of the protection key;

B1. decrypting the n ciphertext blocks to generate a corresponding plaintext block P according to the following formula_j，

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=\mathrm{DECR}\left(C_1\right)\&CirclePlus;\mathrm{OD};$

$P_j=\mathrm{DECR}\left(C_j\right)\&CirclePlus;C_{j-1};$ j＝2，3，…，n;

Wherein,

for the exclusive or, DECR () is to decrypt by RSA method, OD is to protect the key;

C1. the generated plaintext block P_jAnd combining the plaintext into the plaintext in sequence.

In the data receiving method of the digital television of the present invention, the step of decrypting includes:

A2. dividing the ciphertext into m ciphertext blocks and numbering the ciphertext blocks sequentially, wherein the m ciphertext blocks are D_iI =1, 2, …, m, where m is a natural number greater than 1, and the length of each ciphertext block is one byte less than the length of the protection key;

B2. for the m ciphertext blocks D according to the following formula_iPerforms decryption to generate a corresponding plaintext block Q_i，

${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1=\mathrm{DECR}\left(D_1\right)\&CirclePlus;{\mathrm{OD}}^{\&prime;};$

$Q_i=\mathrm{DECR}\left(D_i\right)\&CirclePlus;{D_{i-1}}^{\&prime;};$ i=2，3，…，m;

Wherein,for bit exclusive OR, DECR () for decryption by RSA method, OD' for protecting the other bytes of the key except the first byte, D_i-1Is' a D_i-1Other bytes except the first byte;

C2. the generated plaintext block Q_iIn order of groupAnd synthesizing a plaintext.

The invention also provides a data receiving system of the digital television, which comprises a network analysis module, a conditional access module, an intelligent card and a descrambler, wherein the conditional access module comprises a filtering unit and a data protection unit,

the network analysis module is used for receiving a data packet from a server and analyzing the data packet, wherein the data packet comprises encrypted authorization management information, encrypted authorization control information and key management information, the authorization control information is embedded with encrypted control words, and the key management information comprises protection key information, algorithm information and protection key length information;

the filtering unit is used for filtering the encrypted authorization management information, the encrypted authorization control information and the encrypted key management information from the analyzed data packet;

the data protection unit is used for decrypting the encrypted authorization management information and the encrypted authorization control information according to the key management information;

the intelligent card is used for extracting the encrypted control word from the decrypted authorization control information according to the decrypted authorization management information;

the data protection unit is further configured to decrypt the encrypted control word according to the key management information;

and the descrambler is used for descrambling the received audio and video stream according to the control word.

In the data receiving system of the digital television according to the present invention, the system further includes:

a memory for storing the filtered key management information.

In the digital television receiving system of the invention, the data protection unit decrypts by an RSA method.

In the data receiving system of a digital television according to the present invention, the data protection unit includes:

a first splitting subunit, configured to split the ciphertext into n ciphertext blocks and number the ciphertext blocks sequentially, where the n ciphertext blocks are C_jJ =1, 2, …, n, where n is a natural number greater than 1, and the length of each ciphertext block is the same as the length of the protection key;

a first decryption subunit, configured to decrypt the n ciphertext blocks C according to the following formula_jPerforms decryption to generate a corresponding plaintext block P_j，

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=\mathrm{DECR}\left(C_1\right)\&CirclePlus;\mathrm{OD};$

$P_j=\mathrm{DECR}\left(C_j\right)\&CirclePlus;C_{j-1};$ j＝2，3，…，n;

Wherein,

for the exclusive or, DECR () is to decrypt by RSA method, OD is to protect the key;

a first combining subunit for combining the generated plaintext block P_jAnd combining the plaintext into the plaintext in sequence.

In the digital television receiving system of the present invention, the data protection unit includes:

a second splitting subunit, configured to split the ciphertext into m ciphertext blocks and number the ciphertext blocks sequentially, where the m ciphertext blocks are D_iI =1, 2, …, m, where m is a natural number greater than 1, and the length of each ciphertext block is one byte less than the length of the protection key;

a second decryption subunit, configured to decrypt the m ciphertext blocks D according to the following formula_iPerforms decryption to generate a corresponding plaintext block Q_i，

${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1=\mathrm{DECR}\left(D_1\right)\&CirclePlus;{\mathrm{OD}}^{\&prime;};$

$Q_i=\mathrm{DECR}\left(D_i\right)\&CirclePlus;{D_{i-1}}^{\&prime;};$ i=2，3，…，m;

Wherein,

is exclusive OR, DECR () is OD 'decrypted by RSA method'To protect the other bytes of the key than the first byte, D_i-1Is' a D_i-1Other bytes except the first byte;

and the second combining subunit is used for sequentially combining the generated plaintext blocks Qi into a plaintext.

In the conditional access system, the method can not only protect the data transmission from the server to the user terminal, but also protect the data transmission from the intelligent card in the user terminal to the conditional access module, thereby preventing hackers from illegally acquiring data and further protecting the legal rights and interests of users. In addition, the method has no requirement on equipment such as a CPU of the set-top box, so that the data security is high and the cost is low.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1 is a logical block diagram of a digital television receiving system of the prior art;

fig. 2 is a flowchart of a first embodiment of a data receiving method of a digital television according to the present invention;

fig. 3 is a flowchart of a second embodiment of an encryption and decryption method in a data receiving method of a digital tv of the present invention;

fig. 4 is a flowchart of an embodiment three of encryption and decryption in a data receiving method of a digital tv of the present invention;

fig. 5 is a logical structure diagram of a first embodiment of the data receiving system of the digital television of the present invention;

fig. 6 is a logical structure diagram of a second embodiment of a data protection unit in the data receiving system of the digital tv of the present invention;

fig. 7 is a logical structure diagram of a third embodiment of a data protection unit in the data receiving system of the digital tv of the present invention.

Detailed Description

As shown in fig. 2, in a flowchart of a first embodiment of a data receiving method of a digital television according to the present invention, the method includes the following steps:

in step S201, a data packet from the server is received and parsed, where the data packet includes encrypted entitlement management information, encrypted entitlement control information, and key management information, the entitlement control information is embedded with an encrypted control word, the key management information includes protection key information, algorithm information, and protection key length information, and it should be noted that the encryption of the entitlement management information, the entitlement control information, and the control word is performed at the server. In addition, the operation of the control word at the server side is as follows: firstly, encrypting the authorization control information according to a specific encryption method (the encryption method will be specifically described in the following embodiments), then embedding the authorization control information into authorization control information according to a certain method (specifically referring to the related description of the background art, and the method can be understood by those skilled in the art), and then encrypting the authorization control information embedded with the encryption control word according to the encryption method;

in step S202, the encrypted entitlement management information, the encrypted entitlement control information, and the key management information are filtered out from the parsed data packet;

in step S203, decrypting the encrypted entitlement management information and the encrypted entitlement control information according to the key management information;

in step S204, extracting an encrypted control word from the decrypted entitlement control message according to the decrypted entitlement management message;

in step S205, the encrypted control word is decrypted according to the key management information;

in step S206, the received audio/video stream is descrambled according to the control word.

Preferably, between step S202 and step S203 of the method, the method further comprises: and storing the filtered key management information into a memory.

In the first embodiment of the encryption and decryption method in the data receiving method of the digital tv according to the present invention, the encryption is performed by the RSA algorithm, and accordingly, the decryption is performed by the RSA algorithm. It should be noted that in this embodiment and the following embodiments of the encryption and decryption method, the encryption and decryption are performed on the authorization control information, the authorization management information and the control word respectively, for example, the control word is encrypted by RSA algorithm at the server, the control word is decrypted by RSA algorithm at the terminal, the authorization control information is encrypted by RSA algorithm at the server, and the authorization management information is decrypted by RSA algorithm at the terminal.

Preferably, the protection key is a JPK, which is randomly generated according to the algorithm RSA, and the RSA key pattern is 512 bits, 768 bits, or 1024 bits for security.

Preferably, the process _ play is first obtained from the ECM packet of entitlement control message to check the hash value, when the encryption _ ind of the DATA is analyzed to be 1, it is stated that the DATA is JPK as a protection key, then the relevant DATA is sent to the smart card, and the process _ play is temporarily retained until the smart card returns to process _ DATA.

The data format of the program _ play is as follows:

preferably, when the smart card returns PROTECT _ DATA, the key _ id is used to invoke the corresponding JPK from the keystore.

The DATA format of the program _ DATA is as follows:

the data format of the PROCESS _ KEY is as follows:

preferably, the protection key JPK uses the key management information JMM as a transmission channel, and the data format of the key management information JMM is encrypt _ mesgae.

The data format of this ENCRYPTED _ mesgae is as follows:

as shown in fig. 3, in the flowchart of the second embodiment of the encryption and decryption method in the data receiving method of the digital television according to the present invention, it should be noted that the encryption is performed in the server and the decryption is performed in the condition application module of the terminal. The encryption and decryption are performed on the authorization control information, the authorization management information, and the control word, respectively, for example, the control word is encrypted at the server side through step a0 to step C0, the control word is decrypted at the user terminal through step a1 to step C1, and when the control word is encrypted and decrypted through step a0 to step C0 and step a1 to step C1, the plaintext is the unencrypted control word and the ciphertext is the encrypted control word.

The step of encrypting comprises:

A0. the plaintext is divided into n plaintext blocks and the n plaintext blocks are numbered sequentially, wherein the n plaintext blocks are P_jJ =1, 2, …, n, where n is a natural number greater than 1, and the length of each plaintext block is the same as the length of the protection key;

B0. a plurality of plaintext blocks are encrypted according to the following formula to generate corresponding ciphertext blocks C_j，

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\mathrm{ENCR}({\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">P</figure-callout>}}_1\&CirclePlus;\mathrm{OD});$

$C_j=\mathrm{ENCR}(P_j\&CirclePlus;C_{j-1});$ j＝2，3，…，n;

Wherein,

is bit XOR, ENCR () is passEncrypting by an RSA method, wherein OD is a protection key;

C0. generating n cipher text blocks C_jAnd combining the ciphertext blocks in sequence.

The step of decrypting includes:

A1. dividing the ciphertext into n ciphertext blocks and numbering the ciphertext blocks sequentially, wherein the n ciphertext blocks are C_jJ =1, 2, …, n, where n is a natural number greater than 1, and the length of each ciphertext block is the same as the length of the protection key;

B1. decrypting the plurality of ciphertext blocks to generate corresponding plaintext blocks P according to the following formula_j，

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=\mathrm{DECR}\left(C_1\right)\&CirclePlus;\mathrm{OD};$

$P_j=\mathrm{DECR}\left(C_j\right)\&CirclePlus;C_{j-1};$ j＝2，3，…，n;

Wherein,

for the exclusive or, DECR () is to decrypt by RSA method, OD is to protect the key;

C1. will be generatedPlaintext block P of_jAnd combining the plaintext into the plaintext in sequence.

As shown in fig. 4, in the flowchart of the third embodiment of the encryption and decryption method in the data receiving method of the digital television of the present invention, preferably, the encryption step includes:

A2. the plaintext is split into m plaintext blocks and the m plaintext blocks are numbered sequentially, wherein the m plaintext blocks are Q_iI =1, 2, …, m, where m is a natural number greater than 1, the length of each plaintext block being one byte less than the length of the protection key;

B2. for m plaintext blocks Q according to the following formula_iPerforms encryption to generate a corresponding ciphertext block D_i，

${\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">D</figure-callout>}}_1=\mathrm{ENCR}({\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1\&CirclePlus;{\mathrm{OD}}^{\&prime;});$

$D_i=\mathrm{ENCR}(Q_i\&CirclePlus;{D_{i-1}}^{\&prime;});$ i=2，3，…，m;

Wherein,for bit exclusive OR, ENCR () for decryption by RSA method, OD' for protecting the other bytes of the key except the first byte, D_i-1Is' a D_i-1Other bytes except the first byte;

C2. and combining the generated m ciphertext blocks Di into ciphertexts in sequence.

The decryption step includes:

A3. dividing the ciphertext into m ciphertext blocks and numbering the ciphertext blocks sequentially, wherein the m ciphertext blocks are D_iI =1, 2, …, m, where m is a natural number greater than 1, and the length of each ciphertext block is one byte less than the length of the protection key;

B3. for m ciphertext blocks D according to the following formula_iPerforms decryption to generate a corresponding plaintext block Q_i，

${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1=\mathrm{DECR}\left(D_1\right)\&CirclePlus;{\mathrm{OD}}^{\&prime;};$

$Q_i=\mathrm{DECR}\left(D_i\right)\&CirclePlus;{D_{i-1}}^{\&prime;};$ i=2，3，…，m;

Wherein,for bit exclusive OR, DECR () for decryption by RSA method, OD' for protecting the other bytes of the key except the first byte, D_i-1Is' a D_i-1Other bytes except the first byte;

in addition, in FIG. 4, D_i=D_i″||D_i′；

Wherein, | | is a connector; d_i"is D_i"is used to determine the first byte of the byte.

C3. The generated plaintext block Q_iAnd combining the plaintext into the plaintext in sequence.

As shown in fig. 5, in the logical structure diagram of the first embodiment of the data receiving system of the digital tv of the present invention, the system includes a network parsing module 310, a conditional access module 320, a smart card 330, a descrambler 340, and a memory 350. Wherein, the conditional access module 320 includes a filtering unit 321 and a data protection unit 322. The logical structure of each part is explained below:

a network parsing module 310, configured to receive a data packet from a server and parse the data packet, where the data packet includes encrypted authorization management information, encrypted authorization control information, and key management information, the authorization control information is embedded with encrypted control words, and the key management information includes protection key information, algorithm information, and protection key length information;

a filtering unit 321, configured to filter out encrypted authorization management information, encrypted authorization control information, and key management information from the parsed data packet;

a memory 350 for storing the filtered key management information;

a data protection unit 322 for decrypting the encrypted entitlement management information, the encrypted entitlement control information according to the key management information;

the smart card 330, configured to extract the encrypted control word from the decrypted authorization control information according to the decrypted authorization management information;

a data protection unit 322, further configured to decrypt the encrypted control word according to the key management information;

and the descrambler 340 is used for descrambling the received audio and video stream according to the control word.

Preferably, the data protection unit 322 decrypts by the RSA method.

Preferably, the data protection unit 322 also upgrades and/or changes the key management information at any time.

As shown in fig. 6, in the logic structure diagram of the first embodiment of the data protection unit in the data receiving system of the digital television of the present invention, preferably, the data protection unit 322 includes:

the first splitting subunit 3221 is configured to split the ciphertext into n ciphertext blocks and sequentially number the ciphertext blocks, where n ciphertext blocks are C_jWherein j =1, 2, …, n, n is a natural number greater than 1, and the length of each ciphertext block is the same as the length of the protection key;

the first decryption subunit 3222 is configured to decrypt the n ciphertext blocks Cj according to the following formula to generate corresponding plaintext blocks P_j，

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=\mathrm{DECR}\left(C_1\right)\&CirclePlus;\mathrm{OD};$

$P_j=\mathrm{DECR}\left(C_j\right)\&CirclePlus;C_{j-1};$ j＝2，3，…，n;

Wherein,

for the exclusive or, DECR () is to decrypt by RSA method, OD is to protect the key;

the first combining subunit 3223 is used for combining the generated plaintext block P_jAnd combining the plaintext into the plaintext in sequence.

As shown in fig. 7, in the logical structure diagram of the second embodiment of the data protection unit in the data receiving system of the digital television of the present invention, preferably, the data protection unit 322 includes:

the second splitting subunit 3224 is configured to split the ciphertext into m ciphertext blocks and sequentially number the ciphertext blocks, where m ciphertext blocks are D_iWherein i =1, 2, …, m, m being a natural number greater than 1, the length of each ciphertext block being one byte less than the length of the protection key;

the second decryption subunit 3225 is configured to decrypt the m ciphertext blocks D according to the following formula_iPerforms decryption to generate a corresponding plaintext block Q_i，

${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="HDA0000024302340000041.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1=\mathrm{DECR}\left(D_1\right)\&CirclePlus;{\mathrm{OD}}^{\&prime;};$

$Q_i=\mathrm{DECR}\left(D_i\right)\&CirclePlus;{D_{i-1}}^{\&prime;};$ i=2，3，…，m;

Wherein,

for bit exclusive OR, DECR () for decryption by RSA method, OD' for protecting the other bytes of the key except the first byte, D_i-1Is' a D_i-1Other bytes except the first byte;

the second combining sub-unit 3226 is configured to combine the generated plaintext block Q_iAnd combining the plaintext into the plaintext in sequence.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims (4)

1. A data receiving method of a digital television, comprising:

receiving a data packet from a server and analyzing the data packet, wherein the data packet comprises encrypted authorization management information, encrypted authorization control information and key management information, the authorization control information is embedded with encrypted control words, and the key management information comprises protection key information, algorithm information and protection key length information;

filtering out encrypted authorization management information, encrypted authorization control information and encrypted key management information from the analyzed data packet;

decrypting the encrypted authorization management information and the encrypted authorization control information according to the key management information;

extracting encrypted control words from the decrypted authorization control information according to the decrypted authorization management information;

decrypting the encrypted control word according to the key management information;

descrambling the received audio and video stream according to the control word;

the step of decrypting comprises:

A1. dividing the ciphertext into n ciphertext blocks and numbering the ciphertext blocks sequentially, wherein the n ciphertext blocks are C_jJ =1, 2, …, n, where n is a natural number greater than 1, and the length of each ciphertext block is the same as the length of the protection key;

B1. decrypting the n ciphertext blocks to generate a corresponding plaintext block P according to the following formula_j，

P₁=DECR(C₁)⊕OD;

P_j=DECR(C_j)⊕C_j-1；j＝2，3，…，n;

The ^ ^ is bit exclusive or, DECR () is to decrypt through an RSA method, and OD is a protection key;

C1. n generated plaintext blocks P_jCombining the plaintext into plaintext in sequence;

or the step of decrypting comprises:

A2. dividing the ciphertext into m ciphertext blocks and numbering the ciphertext blocks sequentially, wherein the m ciphertext blocks are D_iI =1, 2, …, m, where m is a natural number greater than 1, and each ciphertext block is one byte less in length than the protection key;

B2. for the m ciphertext blocks D according to the following formula_iPerforms decryption to generate a corresponding plaintext block Q_i，

Q₁=DECR（D₁）⊕OD′；

Q_i=DECR（D_i）⊕D_i-1′;i=2，3，…，m;

Wherein,|, XOR, DECR () decryption by RSA method, OD' other bytes than the first byte of the protection key, D_i-1Is' a D_i-1Other bytes except the first byte;

C2. the generated m plaintext blocks Q_iAnd combining the plaintext into the plaintext in sequence.

2. The data receiving method of the digital tv as claimed in claim 1, further comprising:

and storing the filtered key management information into a memory.

3. A data receiving system of digital TV comprises a network analysis module, a condition receiving module, a smart card and a descrambler, wherein the condition receiving module comprises a filter unit, characterized in that the condition receiving module also comprises a data protection unit,

the network analysis module is used for receiving a data packet from a server and analyzing the data packet, wherein the data packet comprises encrypted authorization management information, encrypted authorization control information and key management information, the authorization control information is embedded with encrypted control words, and the key management information comprises protection key information, algorithm information and protection key length information;

the filtering unit is used for filtering the encrypted authorization management information, the encrypted authorization control information and the encrypted key management information from the analyzed data packet;

the data protection unit is used for decrypting the encrypted authorization management information and the encrypted authorization control information according to the key management information;

the intelligent card is used for extracting the encrypted control word from the decrypted authorization control information according to the decrypted authorization management information;

the data protection unit is further configured to decrypt the encrypted control word according to the key management information;

the descrambler is used for descrambling the received audio and video stream according to the control words;

the data protection unit includes:

a first splitting subunit, configured to split the ciphertext into n ciphertext blocks and number the ciphertext blocks sequentially, where the n ciphertext blocks are C_jJ =1, 2, …, n, where n is a natural number greater than 1, and the length of each ciphertext block is the same as the length of the protection key;

a first decryption subunit, configured to decrypt the n ciphertext blocks according to the following formula to generate a corresponding plaintext block P_j，

P₁=DECR(C₁)⊕OD;

P_j=DECR(C_j)⊕C_j-1;j=2，3，…，n;

The ^ ^ is bit exclusive or, DECR () is to decrypt through an RSA method, and OD is a protection key;

a first combining subunit, configured to combine the generated n plaintext blocks Pj into a plaintext in sequence;

or the data protection unit includes:

a second splitting subunit, configured to split the ciphertext into m ciphertext blocks and number the ciphertext blocks sequentially, where the m ciphertext blocks are D_iI =1, 2, …, m, where m is a natural number greater than 1, and each ciphertext block is one byte less in length than the protection key;

a second decryption subunit, configured to decrypt the m ciphertext blocks D according to the following formula_iPerforms decryption to generate a corresponding plaintext block Q_i，

Q₁=DECR（D₁）⊕OD′；

Q_i=DECR（D_i）⊕D_i-1′;i=2，3，…，m;

Wherein ^ is bit XOR, DECR () is deciphered by RSA method, OD' is other bytes of protection key except first byte, D_i-1Is' a D_i-1Other bytes except the first byte;

a second combining subunit for combining the generated plaintext block Q_iAnd combining the plaintext into the plaintext in sequence.

4. The data receiving system of digital television according to claim 3, wherein said system further comprises:

a memory for storing the filtered key management information.

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