CN101710964A - Method for enciphering and deciphering MPEG2 transport stream packets - Google Patents

Abstract

The invention provides a method for enciphering and deciphering MPEG2 transport stream packets. The method comprises the following steps of: based on the length of L bits, dividing the payload of transport stream packets into n subgroups of P1, P2, P3 till Pn; enciphering the ith subgroup Pi of the payload of the transport stream packets, and outputting the cipher subgroup Ci which is the enciphered result of the bit-by-bit XOR value of Pi and IVi-1 by using a secret key K, wherein n is less than n and not less than 1; if the length of the subgroup Pn is equal to L bits, the cipher subgroup Cn output after enciphering the subgroup Pn is the enciphered result of the bit-by-bit XOR value of Pn and IVn-1 by using the secret key K; and if the length t of the subgroup Pn is less than L bits, adding L-t zeros at the right of Pn, then XORing the result with added zeros and the enciphered result of IVn-1, and finally outputting the first t bits of the XOR result as the cipher of Pn (Cn). The invention has the advantages of high safety performance and easy implementation.

Description

The encryption and decryption method of MPEG2 transport stream data packet

Technical field

The present invention relates to the digital content protection technology, relate in particular to the encipher-decipher method that adopts the transport stream data packet of MPEG2 standard compression in a kind of digital interface content protective system.

Background technology

MPEG2 transport stream in the digital television broadcasting system is transferred to user side by radio network (wired, satellite or ground) after the front end scrambling.Typical ustomer premises access equipment adopts the separation between machine and card technology to receive transport stream: the transport stream of scrambling descrambling in smart card, transport stream behind the descrambling through the digital interface between smart card and the main frame (for example, PCMCIA, USB) arrive main frame, transport stream is finished demultiplexing, source coding and output in main frame.

As shown in Figure 1, transport stream is made of continuous packet.Packet has the form of standard, and its total length is 188 bytes, and wherein preceding 4 bytes are packet packet header, next is optional elongated adaptation field, is the payload of some bytes at last.

In order to guarantee the fail safe of MPEG2 transport stream the time, need in card, the payload to transport stream encrypt again, and data packet head, adaptation field and total length of data packets remain unchanged by the digital interface between card and the main frame.Existing at present three standards define the encryption method here.

1, " CableCARD Copy Protection 2.0 Specification " adopt ECB (Electric Code Book, the electronic code book) pattern of TDES algorithm that the payload of transport stream data packet is encrypted in (2009-05-08); If the length of payload is not the integral multiple of 64 bits, need to use Cipher-Text Stealing technology (specifically seeing the U.S. Patent application of US005684876A) to keep fixing data packet length.

2, adopt CBC (Cipher Block Chaining, the link of the encrypted word group) pattern of aes algorithm that data packet payload is encrypted in " CI Plus Specification:Content Security Extensions to the Common Interface.V1.2.2009-4-16 "; If the length of payload is not the integral multiple of 128 bits, adopt the method for transparent transmission tail data to keep fixing data packet length.

3, " Digital Video Broadcasting Content Protection ﹠amp; Copy Management.Rev.1.2007-7 " in adopt the CBC pattern of aes algorithm that data packet payload is encrypted; If the length of payload is not the integral multiple of 128 bits, need to adopt another Cipher-Text Stealing technology (specifically seeing the U.S. Patent application of US20080137851A1) to keep fixing data packet length.

Said method all adopts the block cipher with fixing input length and fixing output length that the payload of packet is carried out encryption and decryption.The block length of supposing block cipher is the L bit, at first payload is divided into the grouping of some L bits when then encrypting, and then each grouping is encrypted.If the length of payload is not the integral multiple of block length L, then need special means to handle.In addition, the CBC pattern of employing block cipher has higher fail safe to the payload encryption of transport stream data packet than the employing ecb mode, adopts the Cipher-Text Stealing technology can effectively solve the problem that loaded length is not a block cipher block length integral multiple.

Summary of the invention

The present invention proposes a kind of encryption and decryption method of MPEG2 transport stream data packet, the present invention is based on block cipher, can support two kinds of conventional cryptography patterns of CBC and PCBC, also support the higher FFM pattern of a kind of fail safe to encrypt, have the security performance height, realize simple advantage.

The present invention adopts following technical scheme to realize: a kind of encryption method of MPEG2 transport stream data packet, and it comprises:

Steps A: the payload of transport stream data packet is divided into n grouping: P ₁, P ₂, P ₃..., P _nThe length of wherein preceding n-1 grouping is the L bit, last P that divides into groups _nLength be less than or equal to the L bit, n is more than or equal to 1;

Step B: to i grouping P of payload in the transport stream data packet _iCarry out encryption, output ciphertext block C _i, this ciphertext block C _iFor using key K to P _iWith IV _I-1Carry out the result of enciphering transformation by bit XOR value, wherein, n＞i 〉=1;

Step C: if grouping P _nLength equal the L bit, then to the grouping P _nEncryption after the ciphertext block C that exports _nFor using key K to P _nWith IV _N-1Carry out the result of enciphering transformation by bit XOR value; If grouping P _nLength t less than the L bit, at P _nThe right mend L-t " 0 ", then with result after the zero padding and IV _N-1The encrypted result XOR, at last with XOR result's preceding t bit as P _nCiphertext C _nOutput;

Wherein, IV _iBe conversion F (Mode, P _i, C _i, IV _I-1) intermediate variable of output, and IV _iLength be L, and one of them input parameter Mode of conversion F value respectively when selecting CBC pattern, PCBC pattern and FFM pattern for use: 0,1 and 2.

Wherein, if the payload of transport stream data packet only constitutes a grouping P ₁, then adopt the CFB pattern to P ₁Encrypt, suppose P ₁Length be t, t≤L is at first at P ₁The right mend L-t " 0 ", then with result after the zero padding and IV ₀The encrypted result XOR, at last with XOR result's preceding t bit as P ₁Ciphertext C ₁Output.

Wherein, when i=1, first grouping of encryption transport stream data packet P ₁Input parameter IV ₀, and parameter Mode and key K all are shared parameters known between encryption side and the deciphering side.

In addition, the present invention discloses a kind of decryption method of MPEG2 transport stream data packet, and it comprises:

Steps A: the payload of the MPEG2 transport stream data packet of encrypting is divided into n grouping (n＞1): C ₁, C ₂, C ₃..., C _n, wherein the length of preceding n-1 grouping is the L bit, last P that divides into groups _nLength be less than or equal to the L bit, n is more than or equal to 1;

Step B: to i grouping C of payload in the transport stream data packet _iBe decrypted processing, the grouping P of i payload in the output transport stream packet _i, this P that divides into groups _iFor to ciphertext block C _iDecipher conversion earlier, again with IV _I-1Obtain by the bit XOR, wherein, n＞i 〉=1;

Step C: if last ciphertext block C _nLength equal the L bit, then to the grouping C _nDecryption processing after the payload grouping P that exports _nFor to ciphertext block C _nDecipher conversion earlier, and and IV _N-1Obtain by the bit XOR; If ciphertext block C _nLength t less than the L bit, at C _nThe right mend L-t " 0 ", then with result after the zero padding and IV _N-1The encrypted result XOR, at last with XOR result's preceding t bit as the payload P that divides into groups _nOutput;

Wherein, IV _iBe conversion F (Mode, P _i, C _i, IV _I-1) intermediate variable of output, and IV _iLength be L, and one of them input parameter Mode of conversion F value respectively when selecting CBC pattern, PCBC pattern and FFM pattern for use: 0,1 and 2.

Wherein, if the payload of the transport stream data packet of encrypting only constitutes a grouping C ₁, then adopt the CFB pattern to C ₁C is supposed in deciphering ₁Length be t, t≤L is earlier at C ₁The right mend L-t " 0 ", then with result after the zero padding and IV ₀The encrypted result XOR, at last with XOR result's preceding t bit payload P as deciphering back transport stream data packet ₁Output.

Wherein, when i=1, first grouping of decryption processing transport stream data packet C ₁Input parameter IV ₀, and parameter Mode and key K all are shared parameters known between encryption side and the deciphering side.

Compared with prior art, the present invention has following beneficial effect:

The present invention is based on grouping and encrypt or decryption processing, and support multiple encrypted work pattern, have the strong advantage of applicability.In addition, when the length of effective load is not the integral multiple of password block length, the present invention uses the method that is similar to the CFB pattern that the nubbin data are handled, and simply a lot of than the Cipher-Text Stealing technology to the nubbin data processing method, and fail safe is equivalent to the CFB pattern.

Description of drawings

Fig. 1 is the composition structural representation of the transport stream of reference format;

Fig. 2 is the payload encryption method among the present invention;

Payload nubbin encryption method among Fig. 3 the present invention;

Payload decryption method among Fig. 4 the present invention;

Payload nubbin decryption method among Fig. 5 the present invention.

Embodiment

The invention provides a kind of encryption and decryption method of MPEG2 transport stream data packet payload.This method can provide 3 kinds of different encryption modes as required, be respectively: CBC (Cipher Block Chaining, cipher block chaining) pattern, PCBC (Propagating Cipher Block Chaining, the expansion cipher block chaining) pattern, than CBC and the higher a kind of encryption mode of PCBC fail safe, this case abbreviates the FFM pattern as.When the length of effective load is not the integral multiple of password block length, this method uses the method that is similar to the CFB pattern that the nubbin data are handled, and simply a lot of than the Cipher-Text Stealing technology to the nubbin data processing method, fail safe is equivalent to the CFB pattern.

For ease of describing, each parameter to this case embodiment is described below earlier:

In this case embodiment, input parameter comprises: IV ₀, mode parameter Mode, key K, P ₁, P ₂, P ₃..., P _nWherein, IV ₀, mode parameter Mode and key K be the shared parameter between encryption side and the deciphering side; P ₁, P ₂, P ₃..., P _nBe the grouping situation of payload in the transport stream data packet, the length of the n-1 of front grouping all is the block length L of block cipher, last P that divides into groups _nLength smaller or equal to L.Encryption method of the present invention is output as ciphertext block: C ₁, C ₂, C ₃..., C _nWherein, the length of preceding n-1 grouping all is the block length L of block cipher, and the length of last grouping equals corresponding clear packets P _nLength.E _KIt is the enciphering transformation that key K limits.

In addition, the conversion F that relates in this case subsequent descriptions is defined as follows: the input parameter of conversion F has 4, is respectively: IV _I-1, P _i, C _iAnd Mode, i 〉=1 here; The output of conversion F is intermediate variable IV _i(i 〉=1), IV _iLength be L.The value of mode parameter Mode has three: 0,1 and 2, represent CBC pattern, PCBC pattern and the FFM pattern of encryption method respectively.Among the figure "

" represent by the bit XOR.When the Mode value is 0, and F (0, P _i, C _i, IV _I-1)=C _i, (i 〉=1); When the Mode value is 1,

(i 〉=1); When the Mode value is 2,

Encryption method of the present invention is when encrypting a MPEG2 transport stream data packet, and at first the payload with packet is divided into n grouping (n＞1): P ₁, P ₂, P ₃..., P _nThe length of wherein preceding n-1 grouping is the L bit, last P that divides into groups _nLength smaller or equal to the L bit.

As shown in Figure 2, if last grouping P _nLength equal the L bit, then the cipher mode of n clear packets is consistent, promptly to i of payload in MPEG2 transport stream data packet grouping P _iThe ciphertext block C that exports after the encryption carries out (n 〉=i 〉=1) _iFor using key K to P _iWith IV _I-1Carry out the result of enciphering transformation by bit XOR value, can represent with following formula:

Wherein, IV _i=F (Mode, P _i, C _i, IV _I-1), n 〉=i 〉=1.

As shown in Figure 3, if last grouping P _nLength less than the L bit, then before the cipher mode of n-1 clear packets be consistent, P but last divides into groups _nAdopt the cipher mode of similar CFB pattern.Suppose grouping P _nLength be t, t＜L is at first at P _nThe right mend L-t " 0 ", then with result after the zero padding and IV _N-1The encrypted result XOR, at last with XOR result's preceding t bit C _n ^*As P _nCiphertext C _nOutput.Can represent with following formula:

Wherein, IV _i=F (Mode, P _i, C _i, IV _I-1), n-1 〉=i 〉=1;

${C_n}^{*}\left|\right|{C_n}^{**}=E_K\left({\mathrm{IV}}_{n-1}\right)\⊕P_n\left|\right|00,$ C _n＝C _n ^*。

Certainly, if the payload of transport stream data packet only constitutes a grouping, promptly n=1 then adopts the CFB pattern to P ₁Encrypt.Suppose P ₁Length be t, t≤L is at first at P ₁The right mend L-t " 0 ", then with result after the zero padding and IV ₀The encrypted result XOR, at last with XOR result's preceding t bit C ₁ ^*As P ₁Ciphertext C ₁Output.Can represent with following formula:

${{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="H200910109747XE0000011.png,H200910109747XE0000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}^{*}\left|\right|{{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="H200910109747XE0000011.png,H200910109747XE0000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}^{**}=E_K\left({\mathrm{IV}}_0\right)\&CirclePlus;{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H200910109747XE0000011.png,H200910109747XE0000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_1\left|\right|0,$ C ₁＝C ₁ ^*。

As shown in Figure 4, decryption method of the present invention has following input parameter: IV ₀, mode parameter Mode, key K, C ₁, C ₂, C ₃..., C _nWherein, IV ₀, Mode and K be the parameter that share encryption side and deciphering side; C ₁, C ₂, C ₃..., C _nBe the grouping of payload in the transport stream data packet of an encryption, the length of the n-1 of front grouping all is the block length L of block cipher, last C that divides into groups _nLength smaller or equal to L.Encryption method of the present invention is output as clear packets: P ₁, P ₂, P ₃..., P _nWherein, the length of preceding n-1 grouping all is the block length L of block cipher, and the length of last grouping equals corresponding ciphertext block C _nLength.D _KIt is the deciphering conversion that key K limits.The input parameter of conversion F has 4, is respectively: IV _I-1, P _i, C _iAnd Mode, i 〉=1 here; The output of conversion F is intermediate variable IV _i(i 〉=1), IV _iLength be L.The value of parameter Mode has three: 0,1 and 2, represent CBC pattern, PCBC pattern and the FFM pattern of encryption method respectively.

Be by the bit XOR.

Decryption method of the present invention is when the MPEG2 transport stream data packet of an encryption of deciphering, and at first the payload with packet is divided into n grouping (n＞1): C ₁, C ₂, C ₃..., C _nThe length of wherein preceding n-1 grouping is the L bit, last P that divides into groups _nLength smaller or equal to the L bit.

The C if last divides into groups _nLength equal the L bit, then the manner of decryption of n ciphertext block is consistent, promptly to ciphertext block C _iDecipher conversion earlier, and and IV _I-1Grouping Pi by i payload in the bit XOR acquisition MPEG2 transport stream data packet, can represent with following formula:

Wherein, IV _i=F (Mode, P _i, C _i, IV _I-1), n 〉=i 〉=1.

As shown in Figure 5, if last ciphertext block C _nLength less than the L bit, then before the manner of decryption of n-1 ciphertext block be consistent, C but last divides into groups _nAdopt the manner of decryption of similar CFB pattern.Suppose grouping C _nLength be t, t＜L is at first at C _nThe right mend L-t " 0 ", then with result after the zero padding and IV _N-1The encrypted result XOR, at last with XOR result's preceding t bit P _n ^*As C _nPlaintext P _nOutput.Can represent with following formula:

Wherein, IV _i=F (Mode, P _i, C _i, IV _I-1), n-1 〉=i 〉=1;

${P_n}^{*}\left|\right|{P_n}^{**}=E_K\left({\mathrm{IV}}_{n-1}\right)\&CirclePlus;C_n\left|\right|00,$ P _n＝P _n ^*。

Certainly, if the payload of the transport stream data packet of encrypting only constitutes a grouping, promptly n=1 then adopts the CFB pattern to C ₁Deciphering.Suppose C ₁Length be t, t≤L is at first at C ₁The right mend L-t " 0 ", then with result after the zero padding and IV ₀The encrypted result XOR, at last with XOR result's preceding t bit P ₁ ^*As C ₁Plaintext P ₁Output.Can represent with following formula:

${{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H200910109747XE0000011.png,H200910109747XE0000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_1}^{*}\left|\right|{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H200910109747XE0000011.png,H200910109747XE0000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_1}^{**}=E_K\left({\mathrm{IV}}_0\right)\&CirclePlus;{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="H200910109747XE0000011.png,H200910109747XE0000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1\left|\right|00,$ P ₁＝P ₁ ^*。

Claims (6)

1. the encryption method of a MPEG2 transport stream data packet is characterized in that, comprising:

Steps A: the payload of transport stream data packet is divided into n grouping: P ₁, P ₂, P ₃..., P _nThe length of wherein preceding n-1 grouping is the L bit, last P that divides into groups _nLength be less than or equal to the L bit, n is more than or equal to 1;

Step B: to i grouping P of payload in the transport stream data packet _iCarry out encryption, output ciphertext block C _i, this ciphertext block C _iFor using key K to P _iWith IV _I-1Carry out the result of enciphering transformation by bit XOR value, wherein, n＞i 〉=1;

Step C: if grouping P _nLength equal the L bit, then to the grouping P _nThe ciphertext block C that exports after the encryption _nFor using key K to P _nWith IV _N-1Carry out the result of enciphering transformation by bit XOR value; If grouping P _nLength t less than the L bit, at P _nThe right mend L-t " 0 ", then with result after the zero padding and IV _N-1The encrypted result XOR, at last with XOR result's preceding t bit as P _nCiphertext C _nOutput;

Wherein, IV _iBe conversion F (Mode, P _i, C _i, IV _I-1) intermediate variable of output, and IV _iLength be L, and one of them input parameter Mode of conversion F value respectively when selecting " CBC pattern ", " PCBC pattern " and " FFM pattern " for use: 0,1 and 2.

2. according to the encryption method of the described MPEG2 transport stream data packet of claim 1, it is characterized in that, if the payload of transport stream data packet only constitutes a grouping P ₁, then adopt the CFB pattern to P ₁Encrypt, suppose P ₁Length be t, t≤L is at first at P ₁The right mend L-t " 0 ", then with result after the zero padding and IV ₀The encrypted result XOR, at last with XOR result's preceding t bit as P ₁Ciphertext C ₁Output.

3. according to the encryption method of claim 1 or 2 described MPEG2 transport stream data packet, it is characterized in that, when i=1, first grouping of encryption transport stream data packet P ₁Input parameter IV ₀, and parameter Mode and key K all are shared parameters known between encryption side and the deciphering side.

4. the decryption method of a MPEG2 transport stream data packet is characterized in that, comprising:

Steps A: the payload of the MPEG2 transport stream data packet of encrypting is divided into n grouping (n＞1): C ₁, C ₂, C ₃..., C _n, wherein the length of preceding n-1 grouping is the L bit, last P that divides into groups _nLength be less than or equal to the L bit, n is more than or equal to 1;

Step B: to i grouping C of payload in the transport stream data packet _iBe decrypted processing, i of payload grouping P in the output transport stream packet _i, this P that divides into groups _iFor to ciphertext block C _iDecipher conversion earlier, again with IV _I-1Obtain by the bit XOR, wherein, n＞i 〉=1;

Step C: if last ciphertext block C _nLength equal the L bit, then to the grouping C _nDecryption processing after the payload grouping P that exports _nFor to ciphertext block C _nDecipher conversion earlier, again with IV _N-1Obtain by the bit XOR; If ciphertext block C _nLength t less than the L bit, at C _nThe right mend L-t " 0 ", then with result after the zero padding and IV _N-1The encrypted result XOR, at last with XOR result's preceding t bit as the payload P that divides into groups _nOutput;

Wherein, IV _iBe conversion F (Mode, P _i, C _i, IV _I-1) intermediate variable of output, and IV _iLength be L, and one of them input parameter Mode of conversion F value respectively when selecting " CBC pattern ", " PCBC pattern " and " FFM pattern " for use: 0,1 and 2.

5. according to the decryption method of the described MPEG2 transport stream data packet of claim 4, it is characterized in that, if the payload of the transport stream data packet of encrypting only constitutes a grouping C ₁, then adopt the CFB pattern to C ₁C is supposed in deciphering ₁Length be t, t≤L is earlier at C ₁The right mend L-t " 0 ", then with result after the zero padding and IV ₀The encrypted result XOR, at last with XOR result's preceding t bit payload P as deciphering back transport stream data packet ₁Output.

6. according to the decryption method of claim 4 or 5 described MPEG2 transport stream data packet, it is characterized in that, when i=1, first grouping of decryption processing transport stream data packet C ₁Input parameter IV ₀, and parameter Mode and key K all are shared parameters known between encryption side and the deciphering side.

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