KR102348633B1 - Video encryption and decryption method and apparatus - Google Patents

Abstract

The embodiment relates to a method and apparatus for encrypting and decrypting a video, and performs encryption and decryption of a video by changing a byte value used for decoding using a start code of a bitstream.

Description

VIDEO ENCRYPTION AND DECRYPTION METHOD AND APPARATUS

The embodiment relates to a method and apparatus for encrypting and decrypting a video, and more particularly, to a method and apparatus for encrypting a video to prevent unauthorized users from playing and viewing the video, and decrypting an encrypted video to play hidden video content it's about

As a method of encrypting video data, there is a method of encrypting the entire video data using a standard encryption algorithm or selectively encrypting only an important part of the video data.

The latter method is called selective encryption or partial encryption. Since selective encryption encrypts only a part of the video data, processing performance is superior compared to the case of encrypting the entire video data. In addition, the selective encryption method is mainly used because it can make the encrypted data satisfy the video standard specification.

Selective encryption encrypts residual data and motion vectors, which are important elements among video data. Such encryption may be included during the video encoding process or may target video data generated after encoding.

The conventional native encryption method encrypts the entire video bitstream. Therefore, although the security strength is high, since the entire bitstream is encrypted using an encryption algorithm such as AES, there is a problem in that the amount of computation is large and the data increase during encryption.

In addition, since the selective encryption method encrypts a part of the video bitstream by using an encryption algorithm such as AES, the amount of calculation can be reduced compared to the conventional native encryption method, but it can be decoded and the approximate contents can be grasped, so the security strength is low. There is a problem.

Video encryption and decryption method and apparatus according to the embodiment, by encrypting a part of a bitstream to reduce the complexity of calculations required to encrypt the video, prevent the encrypted video from being decoded, and can increase the security strength of encryption To provide a method and apparatus.

An embodiment is an image encryption method, encoding the input image into a compressed bitstream using an encoder, and decoding the compressed bitstream using a start code and encrypting the bitstream by changing a plurality of byte information to be used, wherein the compressed bitstream includes the plurality of start codes.

In addition, the bitstream according to the embodiment further includes a plurality of Network Abstraction Layer Units (NAL Units), wherein the NAL Units include a NAL Unit Header and a Raw Byte Sequence Payload (RBSP), and encrypting the bitstream generating a change table for the first byte value of the NAL Unit Header, retrieving the start code using the bitstream, retrieving the NAL Unit Header using the start code, and and changing first byte values of all NAL unit headers according to the change table.

In addition, the encoding according to the embodiment includes encoding the input image into the compressed bitstream using an HEVC codec.

In addition, an embodiment is a method of decrypting an encrypted video, comprising the steps of receiving an encrypted bitstream corresponding to the encrypted video - The encrypted bitstream includes a plurality of start codes and a plurality of Includes a NAL unit, wherein the NAL Unit (Network Abstraction Layer Unit) is composed of an encrypted NAL Unit Header and RBSP (Raw Byte Sequence Payload) -, searching for a start code in the encrypted bitstream, the searched start code Searching for a subsequent NAL unit, decoding the encrypted NAL unit header according to a change table to generate a decrypted bitstream, and a decoder using the decrypted bitstream to restore video data and the change table is a change table for a first byte value of the encrypted NAL Unit Header.

Also, the encrypted image according to the embodiment is generated using an HEVC codec, and the step of restoring the video data includes restoring the decoded bitstream into video data using the HEVC codec.

In addition, generating the decrypted bitstream according to the embodiment comprises comparing the encrypted NAL Unit Header and RBSP byte values with the HEVC standard to infer the change table, and according to the inferred change table , generating a decrypted bitstream by decrypting the encrypted NAL unit header.

In addition, generating the decrypted bitstream according to the embodiment comprises inferring the change table by comparing the byte size of the RBSP with the HEVC standard, and according to the inferred change table, the encrypted NAL Unit Header and decoding to generate a decoded bitstream.

In addition, generating the decrypted bitstream according to the embodiment comprises inferring the change table by comparing the RBSP value and the NAL unit order with the HEVC standard, and according to the inferred change table, the encrypted and generating a decoded bitstream by decoding the NAL unit header.

In addition, generating the decrypted bitstream includes changing the encrypted NAL unit header to an arbitrary value, determining whether video data restoration is successful according to the changed value, and changing the encrypted NAL unit header to the changed value. Storing whether the video data restoration is successful according to generating a bitstream.

In addition, the embodiment is an apparatus for encrypting an input image, an encoder that encodes the input image into a compressed bitstream, and a start code for decoding the compressed bitstream. and an encryption unit for encrypting the bitstream by changing a plurality of bytes of information used, wherein the compressed bitstream includes the plurality of start codes.

In addition, the bitstream according to the embodiment further includes a plurality of Network Abstraction Layer Units (NAL Units), wherein the NAL Unit is composed of a NAL Unit Header and a Raw Byte Sequence Payload (RBSP), and the encryption unit includes the NAL Unit A change table for the first byte value of the header is generated, the start code is retrieved using the bitstream, the NAL unit header is retrieved using the start code, and all NAL unit headers are retrieved according to the change table. Change the value of the first byte of

Also, the encoder according to the embodiment encodes the input image into the compressed bitstream by using an HEVC codec.

In addition, an embodiment is an apparatus for decrypting an encrypted image, a communication unit receiving an encrypted bitstream corresponding to the encrypted image - The encrypted bitstream includes a plurality of start codes and a plurality of includes a NAL Unit, wherein the NAL Unit (Network Abstraction Layer Unit) is composed of an encrypted NAL Unit Header and RBSP (Raw Byte Sequence Payload) -, a start code is retrieved from the encrypted bitstream, and after the retrieved start code A decoder that searches for a NAL unit of and, the change table is a change table for the value of the first byte of the encrypted NAL Unit Header.

Also, the encrypted image according to the embodiment is generated using an HEVC codec, and the decoder includes the step of reconstructing the decoded bitstream into video data using the HEVC codec.

In addition, the decryption unit according to the embodiment compares the byte values of the encrypted NAL Unit Header and RBSP with the HEVC standard, infers the change table, and decrypts the encrypted NAL Unit Header according to the inferred change table to generate a decoded bitstream.

In addition, the decryption unit according to the embodiment compares the byte size of the RBSP with the HEVC standard to infer the change table, and according to the inferred change table, decrypts the encrypted NAL Unit Header to generate a decrypted bitstream do.

In addition, the decryption unit according to the embodiment compares the RBSP value and the NAL unit order with the HEVC standard to infer the change table, and according to the inferred change table, decrypts the encrypted NAL unit header to decode the bitstream create

In addition, the decryption unit according to the embodiment changes the encrypted NAL unit header to an arbitrary value, determines whether video data restoration is successful according to the changed value, and restores video data according to the changed value of the encrypted NAL unit header Success or failure is stored, the change table is inferred according to whether video data restoration is successful according to the change value, and the encrypted NAL unit header is decrypted according to the inferred change table to generate a decrypted bitstream.

Video encryption and decryption method and apparatus according to an embodiment encrypt a part of a bitstream to reduce the complexity of calculations required to encrypt the video, prevent the encrypted video from being decoded, and increase the security strength of encryption there is

1 is a block diagram showing the configuration of a conventional video encryption and decryption apparatus.
2 is a block diagram of a video encryption and decryption apparatus according to an embodiment.
3 is a conceptual diagram for explaining the structure of a bitstream according to an embodiment.
4 is an example of a video bitstream compressed with the HEVC codec expressed by the Hex Edit application according to the embodiment.
5 is a flowchart illustrating a video encryption method according to an embodiment.
6 is an example in which an HEVC compressed bitstream is encrypted according to an embodiment.
7 is a flowchart illustrating a video decoding method according to an embodiment.
8 is a flowchart illustrating a video decoding method according to an embodiment.
9 is a diagram illustrating whether video is normally reproduced according to a change in a byte value of a NAL unit header according to an embodiment.

Hereinafter, the embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings, but identical or similar components are given the same and similar reference numerals, and overlapping descriptions thereof will be omitted. The suffixes "module" and "part" for components used in the following description are given or mixed in consideration of only the ease of writing the specification, and do not have distinct meanings or roles by themselves. In addition, in describing the embodiments disclosed in the present specification, if it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted. In addition, the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and the technical idea disclosed herein is not limited by the accompanying drawings, and all changes included in the spirit and scope of the present invention , should be understood to include equivalents or substitutes.

Terms including an ordinal number such as 1st, 2nd, etc. may be used to describe various elements, but the elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

When an element is referred to as being “connected” or “connected” to another element, it is understood that it may be directly connected or connected to the other element, but other elements may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle.

The singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present application, terms such as “comprises” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, a configuration of a conventional video encryption and decryption apparatus will be described with reference to FIG. 1 .

1 is a block diagram showing the configuration of a conventional video encryption and decryption apparatus.

Referring to FIG. 1 , a conventional video encryption and decryption apparatus includes an encoder 110 , an Encryptor 120 , a network 130 , a Decryptor 140 , and a decoder 150 .

The encoder 110 converts the input video data (I) into a compressed bitstream (B). Encryptor 120 generates an encrypted bitstream (B') using the compressed bitstream (B). At this time, the Encryptor 120 uses a naive method or a selective encryption method.

The naive method or the selective encryption method uses an encryption algorithm such as AES (Advanced Encryption Standard) for all or part of a video bitstream. Because the naive encryption method encrypts the entire video data, the security strength is high, but there is a disadvantage that the amount of calculation is large and the data increase during the encryption process is large.

The selective encryption method encrypts a part of the video data and distorts the video so that the contents of the video cannot be fully understood.

The encrypted bitstream (B') generated by the Encryptor 120 is transmitted to the Decryptor 130 using the network 130 . Decryptor 130 generates a decrypted bitstream (B) by decrypting the encrypted bitstream (B'). At this time, the Dectyptor 130 decrypts the encrypted bitstream (B') using the same Naive method or Selective encryption method as the Encryptor 120 .

The decoded bitstream B generated by the Dectyptor 130 is input to the decoder 150 , and the decoder 150 converts the decoded bitstream B into reproducible video data I.

Hereinafter, a configuration of a video encryption and decryption apparatus according to an embodiment will be described with reference to FIG. 2 .

2 is a block diagram of a video encryption and decryption apparatus according to an embodiment.

Referring to FIG. 2 , the video encryption and decryption apparatus according to the embodiment includes an encoder 110 , an encryption unit 210 , a communication unit 220 , a decoder 230 , and a decoder 150 .

The encoder 110 converts the input video data (I) into a compressed bitstream (B). In this case, the encoder 110 may convert the input video data (I) into a compressed video bitstream (B) using the HEVC codec.

The encryption unit (Scrambler, 210) generates an encrypted bitstream (B') using the compressed bitstream (B). In this case, unlike the Encryptor 120 of FIG. 1, an encryption algorithm such as AES is not used. That is, the Native method and the Selective method are not used. Instead, the encryption unit (Scrambler, 210) searches the start code (Start code) included in the video bitstream (B), and mixes and encrypts the start code with a specific important byte used for decoding among a plurality of bytes thereafter do. That is, the encryption unit (Scrambler, 210) generates an encrypted bitstream (B') by changing specific byte information used for decoding by using the start code included in the compressed video bitstream (B). More details on a method of generating the encrypted bitstream B′ will be described later with reference to FIGS. 3 to 6 .

The communication unit 220 transmits the encrypted bitstream to the decoding unit (Descrambler, 230) using a network or a wired/wireless communication network.

The decryption unit (Descrambler, 230) decrypts the received encrypted bitstream (B') using the communication unit 220 . At this time, like the encryption unit (Scrambler, 210), the start code included in the encrypted bitstream (B') is searched and the encrypted byte information is decrypted using this. That is, the decryption unit (Descrambler, 230) generates a compressed video bitstream (B) by decrypting the encrypted byte information using the start code included in the encrypted bitstream (B'). A more detailed method of decrypting the encrypted bitstream B' will be described later with reference to FIGS. 7 to 9 .

The decoder 150 converts the compressed video bitstream B generated by the decoder (Descrambler) 230 into reproducible video data.

Hereinafter, a start code and a Network Abstraction Layer Unit (NAL Unit) will be described with reference to FIG. 3 .

3 is a conceptual diagram for explaining the structure of a bitstream according to an embodiment.

Referring to FIG. 3 , a video bitstream compressed with the HEVC codec is derived based on a start code. More specifically, the compressed video bitstream B generated by the encoder 110 includes a start code and a NAL unit.

The NAL unit arranged after the start code consists of a NAL unit header and RBSP (Raw Byte Sequence Payload). The NAL Unit Header has a fixed size of 2 bytes. The NAL Unit Header includes a forgotten zero bit, a nal unit type, and a nuh layer id.

1 bit from the most significant of the NAL Unit Header means the forbidden zero bit, and the forbidden zero bit always has a value of 0. 2 bits located after the forbidden zero bit means nal unit type and has a value of 0~63. 6 bits located after nal unit type means nuh layer id and has a value of 0~63. However, the nuh layer id always has a value of 0 in the case of the base layer.

Therefore, in the case of the base layer, the forbidden zero bit and the nuh layer id have a value of 0, so the first byte of the NAL Unit Header is determined according to the nal unit type.

Hereinafter, the start code and the NAL unit of the bitstream will be described with reference to FIG. 4 .

4 is an example of a video bitstream compressed with the HEVC codec expressed by the Hex Edit application according to the embodiment.

Referring to FIG. 4 , the start code has a value of 00 00 01. Since the video bitstream compressed with the HEVC codec consists of a continuation of a start code and a NAL unit, the NAL unit can be searched by searching for the start code. That is, the first byte value of the NAL unit can be searched for by using the start code.

The first byte value of the NAL Unit Header according to the nal unit type value will be described with reference to Table 1 below.

[Table 1]

Table 1 is a table summarizing the value of the first byte of the NAL Unit Header according to the nal unit type value defined in the HEVC standard document.

As shown in Table 1, the nal unit type can have a value of 0~63, but the values of 10~15, 22~31, 41~47, and 48~63 are not used because they are not defined. Therefore, the values that are actually used are 0~9, 16~21, and 32~40.

For example, if the nal unit type is 32 and the forbidden zero bit and nuh layer id are 0, the first byte of the NAL Unit Header has a Hex value of 0x40. Therefore, if the first byte of the NAL Unit Header located after the start code shown in FIG. 4 is 0x40, it means that the nal unit type is VPS_NUT (Video Parameter Set). In addition, if the first byte of the NAL Unit Header is 0x42, it means that the nal unit type is SPS_NUT (Sequence Parameter Set), and if the first byte of the NAL Unit Header is 0x44, it means that the nal unit type is PPS_NUT (Picture Parameter Set), If the first byte of the NAL Unit Header is 0x26, it means that the nal unit type is IDR_W_RADL (Instantaneous Decoding Refresh With RADL Pictures).

The HEVC decoder performs different decoding functions according to the first byte of the NAL Unit Header following the start code. Accordingly, the first byte information of the NAL Unit Header is important information for decoding. The video encryption method according to the embodiment encrypts the video by changing the value of the first byte of the NAL Unit Header so that the decoder cannot correctly decode it. In addition, the encrypted video is decrypted by changing the value of the first byte of the encrypted NAL Unit Header to the original value.

In addition, the above-described byte value is merely an example, and the embodiment is not limited thereto.

Hereinafter, a video encryption method according to an embodiment will be described with reference to FIG. 5 .

5 is a flowchart illustrating a video encryption method according to an embodiment.

Referring to FIG. 5 , in step S310 , an input video image is converted into a compressed video bitstream using the encoder 110 . In this case, the input image may be converted into a bitstream by using the HEVC codec.

In step S320, a NAL Unit Header change table is generated using the encryption unit (Scrambler, 210). As described above, by performing encryption by changing the first byte value of the NAL Unit Header, the first byte value of the NAL Unit Header is actually used as in the “First Byte of NAL Unit Header” column of Table 1 above. Creates a NAL Unit Header change table to change randomly within a range of 25 values.

Hereinafter, an example of a NAL Unit Header change table will be described with reference to Table 2.

[Table 2]

Table 2 is an example of a NAL Unit Header change table. The NAL Unit Header change table of Table 2 means that the value of the first byte of the NAL Unit Header of the compressed video bitstream is changed from the original value to the changed value. At this time, the changed value is changed randomly within the range of 25 values actually used as in the “First Byte of NAL Unit Header” column, but the NAL Unit Header change table is created so that the original value is not the same as the changed value. The values described in Table 2 are merely examples, and the examples are not limited thereto.

In step S330 , the encryption unit Scrambler 210 searches for a start code included in the compressed video bitstream generated in step S310 . Since the bitstream compressed with the HEVC codec is composed of the start code and the NAL unit pressure, it is to search the NAL unit by searching the start code.

In step S340, the encryption unit (Scrambler, 210) searches for the value of the first byte of the NAL Unit Header, and corresponds to the original value of the NAL Unit Header change table generated in step S320. Change the value of the first byte of The NAL Unit Header appears immediately after the end of the start code. Accordingly, the NAL unit header may be searched using the start code found in step S330 . Also, in step S340, by changing the value of the first byte of the NAL Unit Header, it is possible to encrypt the video so that decoding cannot be performed.

In step S340, it is checked whether the first byte values of all NAL unit headers included in the compressed video bitstream generated in step S310 are changed and encrypted. After that, when the values of all NAL Unit Header are not changed, step S330 is performed again. That is, the first byte value of the unaltered NAL Unit Header is changed by searching for the restart code. When the values of all NAL Unit Header are changed, encryption of the input video is completed.

Hereinafter, a video encryption result according to the embodiment will be described with reference to FIG. 6 .

6 is an example in which an HEVC compressed bitstream is encrypted according to an embodiment.

Referring to FIG. 6 , B1 indicates a compressed bitstream before the compressed video bitstream is encrypted, and B2 indicates a result of encrypting the compressed bitstream of B1.

00 00 01 indicated by a dotted line indicates a start code, and a byte value indicated by a solid line immediately after the start code indicates the first byte value of the NAL Unit Header. The first byte values of the NAL Unit Header of the compressed bitstream before encryption are 0x40, 0x42, 0x44, 0x26, 0x02, 0x04.

The value of the first byte of the NAL unit header of the compressed bitstream before encryption is changed in response to the NAL unit header change table of Table 2 above. That is, 0x40, 0x42, 0x44, 0x26, 0x02, 0x04, which are the first byte values of the NAL Unit Header of the compressed bitstream before encryption, are changed to 0x4C, 0x24, 0x0E, 0x00, 0x06, 0x48, respectively, indicating that an encrypted bitstream is generated. indicates.

Hereinafter, a video decoding method according to an embodiment will be described with reference to FIG. 7 .

7 is a flowchart illustrating a video decoding method according to an embodiment.

Referring to FIG. 7 , in step S410 , an encrypted bitstream generated using the above-described video encryption method is received using the communication unit 220 . Also, in step S420 , a NAL unit header change table used to generate an encrypted bitstream using the communication unit 220 may be received.

In step S430, the decoder (Descrambler, 230) may search for a start code in the encrypted bitstream, and search for a NAL unit existing after the start code. In step S440, the decoder (Descrambler, 230) restores the first byte value of the changed NAL unit header to the original value using the NAL unit header change table received in step S420, and decrypts it.

In step S450, it is checked whether the first byte of all NAL unit headers included in the encrypted bitstream are decrypted to their original values. (S430) is performed again. That is, the first byte of the undecoded NAL Unit Header is decoded to the original value by searching for the start code again. When the first byte of all NAL Unit Header is decoded to the original value, the decoding step is completed.

Hereinafter, a method of inferring a NAL unit header change table and a video decoding method according to an embodiment will be described with reference to FIG. 8 .

8 is a flowchart illustrating a video decoding method according to an embodiment.

Referring to FIG. 8, the method of decoding video by inferring the NAL Unit Header change table does not receive the NAL Unit Header change table used for encryption, unlike the video decryption method of FIG. 7, but by estimating the NAL Unit Header change table for video to decrypt

In step S410, after receiving the encrypted bitstream, in step S460, the decoder (Descrambler, 230) uses the encrypted bitstream and HEVC standard information to change the NAL Unit Header change table used for encryption. estimate

If the NAL Unit Header change table used for encryption is unknown, the number of 25! (15,511,210,043,330,985,984,000,000) cases is to find 25 values that are changed in correspondence to the original 25 values before encryption of the first byte of the NAL Unit Header. exist. Even if there are 4 types of the minimum nal unit type value included in one compressed bitstream, there are ₂₅ P ₄ (303,600) cases, so there is a problem that a large amount of calculation is required to find the change table.

Therefore, when the NAL Unit Header change table used for encryption is unknown, the NAL Unit Header change table used for encryption can be inferred by using the characteristics of the bitstream. First, as described with reference to FIG. 3 , the NAL unit consists of a NAL unit header and an RBSP. Accordingly, the original value of the first byte of the NAL Unit Header can be estimated according to the value of the RBSP.

Hereinafter, a method of estimating the NAL unit header change table using the RBSP value will be described with reference to Tables 3 and 4.

[Table 3]

Table 3 is a part of the RBSP syntax confirmed in HEVC standard information when the nal unit type in Table 1 has a value of 32 and the First Byte of NAL Unit Header is VPS_NUT (Video Parameter Set) having a value of 0x40. The RBSP of VPS_NUT consists of the first 2 bytes: vps_video_parameter_set_id (4 bits), vps_baase_layer_internal_flag (1 bit), vps_base_layer_available_flag (1 bit), vps_max_layers_minusl (6 bits), vps_max_sub_layers_minusl (6 bits), then vps_max_sub_nesting_minusl (6 bits), vps_max_sub_layers_minusl (3 bits), 2 bytes are composed of vps_reserved_0xffff_16bits (16 bits). Therefore, in the encrypted bitstream, read 2 bytes of the NAL Unit Header following the start code and then read 4 bytes of RBSP to know that if the first 2 bytes are not 0xFFFF and the subsequent 2 bytes are 0xFFFF, the first byte of the NAL Unit Header should be VPS_NUT of 0x40. can

[Table 4]

Table 4 shows the RBSP syntax confirmed in the HEVC standard document when the nal unit type in Table 1 is 38 and the First Byte of NAL Unit Header is FD_NUT having a value of 0x4C.

Referring to Table 4, in the RBSP of FD_NUT, all bytes are composed of 0xFF. Therefore, it can be inferred that the first byte of the NAL Unit Header should be FD_NUT of 0x4C if 0xFFFFFFFF by reading 2 bytes of the NAL Unit Header next to the start code from the encrypted bitstream and reading the next 4 bytes of RBSP. Accordingly, the NAL Unit Header change table can be inferred using the RBSP value in this way.

In addition, the NAL Unit Header change table used for encryption may be estimated according to the size of the RBSP. Hereinafter, a method of estimating the NAL Unit Header change table used for encryption according to the size of the RBSP will be described with reference to Tables 5 to 7.

[Table 5]

Table 5 shows the RBSP syntax confirmed in HEVC standard information when the nal unit type is 35 in Table 1 and the First Byte of NAL Unit Header is AUD_NUT having a value of 0x46. The RBSP of AUD_NUT is composed of 3-bit pic_type and 5-bit rbsp_trailing_bits for byte alignment, and the size of the RBSP is 1 byte. Therefore, it can be seen that the first byte of the NAL Unit Header should be AUD_NUT of 0x46 after reading 2 bytes of the NAL Unit Header next to the start code from the encrypted bitstream and the start code comes after 1 byte of the RBSP.

[Table 6]

Table 6 shows the RBSP syntax confirmed in HEVC standard information when the nal unit type is 36 in Table 1 and the First Byte of NAL Unit Header is EOS_NUT having a value of 0x48. The RBSP size of EOS_NUT is 0 bytes. Therefore, after reading 2 bytes of the NAL Unit Header next to the start code from the encrypted bitstream, and the start code immediately following the start code, it can be seen that the first byte of the NAL Unit Header should be EOS_NUT of 0x48.

[Table 7]

Table 7 shows the RBSP syntax confirmed in the HEVC standard document when the nal unit type is 37 in Table 1 and the First Byte of NAL Unit Header is EOB_NUT having a value of 0x4A.

The RBSP size of EOB_NUT is 0 bytes and exists at the end of the bitstream. Therefore, it can be seen that the first byte of the NAL Unit Header should be EOB_NUT of 0x4A when 2 bytes of the NAL Unit Header next to the start code are read from the encrypted bitstream and the bitstream is finished. Therefore, in this way, it is possible to estimate the NAL Unit Header change table used for encryption according to the size of the RBSP.

In addition, the change table of the NAL Unit Header may be estimated according to the RBSP value and the NAL Unit order. Among the NAL Units in Table 1, the NAL Unit of VPS_NUT is followed by the NAL Unit of SPS_NUT or PPS_NUT. And the NAL unit of SPS_NUT is followed by the NAL unit of PPS_NUT.

Since the NAL unit of SPS_NUT or PS_NUT can come after the NAL unit of VPS_NUT, it is difficult to know only the order, and the value of RBSP must also be checked. Hereinafter, a method of estimating the change table of the NAL Unit Header according to the RBSP value and the NAL Unit order will be described in more detail with reference to Tables 8 and 9 below.

[Table 8]

Table 8 is a part of the RBSP syntax confirmed in the HEVC standard document when the nal unit type is 33 in Table 1 and the First Byte of NAL Unit Header is SPS_NUT having a value of 0x42.

[Table 9]

Table 9 is a part of the RBSP syntax confirmed in the HEVC standard document when the nal unit type is 34 in Table 1 and the First Byte of NAL Unit Header is PPS_NUT having a value of 0x44.

Since the NAL unit of VPS_NUT can be estimated according to the value of RBSP, in Table 3, when VPS_NUT is VPS_NUT, vps_video_parameter_set_id, which is the first 4 bits of RBSP, is read and stored using RBSP syntax, and the RBSP of the NAL unit following VPS_NUT is stored. Read the first 4 bits of , and do two values. If the two values are the same, it can be seen that the NAL unit following VPS_NUT must be SPS_NUT. This is because sps_video_parameter_set_id means the same value as vps_video_parameter_set_id in the RBSP syntax for VPS_NUT of Table 3 as in the RBSP syntax for SPS_NUT of Table 8.

Also, when VPS_NUT, the first 4 bits of RBSP, vps_video_parameter_set_id, are stored, and the first 4 bits of the RBSP of the NAL unit following VPS_NUT are read and the two values are compared. have. In the case of PPS_NUT that can come after VPS_NUT, as in the RBSP syntax of Table 9, pps_pic_parameter_set_id comes first of the RBSP.

In this way, if it is known that the NAL unit following VPS_NUT is SPS_NUT, since the NAL unit following SPS_NUT is PPS_NUT, the value of the first byte of the NAL Unit Header for PPS_NUT can be known. Therefore, using the above method, the change table of the NAL Unit Header can be estimated according to the RBSP value and the NAL Unit order.

In addition, by finding out the first byte of the NAL unit header using the NAL unit order and the RBSP value, the change table of the NAL unit header can be estimated. Hereinafter, with reference to Tables 10 and 11, a method of estimating the change table of the NAL unit header using the NAL unit order and the RBSP value will be described in detail.

[Table 10]

[Table 11]

In Table 10 and Table 1, since the nal unit type is 39, when the First Byte of NAL Unit Header is PREFIX_SEI_NUT having a value of 0x4E, it is the RBSP syntax confirmed in the HEVC standard document, and the size of the RBSP can be known according to the payloadSize.

Table 11 is the RBSP syntax confirmed in the HEVC standard document when the nal unit type is 40 in Table 1 and the First Byte of NAL Unit Header is SUFFIX_SEI_NUT having a value of 0x50, and the size of the RBSP can be known according to the payloadSize.

Among the NAL Units in Table 1, PREFIX_SEI_NUT comes before VCL NAL Unit whose nal_unit_type has values of 0~9, 16~21, and SUFFIX_SEI_NUT comes after VCL NAL Unit. Therefore, PREFIX_SEI_NUT follows PPS_NUT in the bitstream, and VCL NAL Unit comes after PREFIX_SEI_NUT.

According to Table 10 and Table 11, since the size of the RBSP can be known according to the payloadSize, the value corresponding to the payloadSize is read and stored in the NAL Unit following PPS_NUT. You can see that it should be PREFIX_SEI_NUT of 0x4E.

In addition, the value corresponding to payloadSize is read from the NAL Unit following the VCL NAL Unit and stored. If the start code comes after the payloadSize size, the first byte of the NAL Unit Header should be SUFFIX_SEI_NUT of 0x50. Accordingly, by finding out the first byte of the NAL unit header using the NAL unit order and the RBSP value in this way, the change table of the NAL unit header can be estimated.

In addition, when the first byte of the NAL Unit Header is changed, the change table of the NAL Unit Header can be estimated by finding out the first byte of the NAL Unit Header according to whether or not it is reproduced normally. Hereinafter, a method of estimating the change table of the NAL unit header by changing the first byte of the NAL unit header will be described in detail with reference to FIG. 9 to be described later.

In step S430, a start code included in the encrypted bitstream may be searched, and a NAL unit existing after the start code may be searched for. In step S440, the decrypter (Descrambler, 230) restores the first byte value of the encrypted NAL unit header to the original value using the NAL unit header change table inferred in step S460 to decrypt it.

In step S450, it is checked whether the first byte of all NAL unit headers included in the encrypted bitstream are decrypted to their original values. (S430) is performed again. That is, the first byte of the undecoded NAL Unit Header is decoded to the original value by searching for the start code again. When the first byte of all NAL Unit Header is decoded to the original value, the decoding step is completed.

Hereinafter, a method of inferring a change table of the NAL Unit Header by changing the first byte of the NAL Unit Header according to an embodiment will be described with reference to FIG. 9 .

9 is a diagram illustrating whether video is normally reproduced according to a change in a byte value of a NAL unit header according to an embodiment.

Referring to FIG. 9 , the vertical direction indicated by the HEX value is the value before the first byte of the NAL Unit Header is changed, and the horizontal direction is the value after the first byte of the NAL Unit Header is changed.

When the first byte of the NAL Unit Header in the vertical direction expressed by the HEX value is changed to the values in the horizontal direction, whether 146 bitstreams among the conformance bitstreams disclosed to certify whether it is suitable for the international standard HEVC decoder are normally played will be investigated The vertical and horizontal HEX values are the same as the values in the ‘First Byte of NAL Unit Header’ column of Table 1, and the left value of the vertical Hex values is the same as the ‘Name of nal_unit_type’ in Table 1.

○, □, △, and × in Table 12 indicate whether the first byte of the NAL Unit Header is played normally. An example of the case indicated by ○ is when the first byte of NAL Unit Header in the bitstream is changed from 0x00 in the vertical direction to 0x02 in the horizontal direction. When the bitstream changed in this way is reproduced through the HEVC decoder, it is reproduced normally and marked with ○.

An example of the case indicated by □ is when the first byte of NAL Unit Header in the bitstream is changed from 0x02 in the vertical direction to 0x04 in the horizontal direction. When the changed bitstream is reproduced through the HEVC decoder, most of the 146 bitstreams are normally reproduced, but some bitstreams are reproduced abnormally and are indicated by □.

An example of the case indicated by △ is when the first byte of NAL Unit Header in the bitstream is changed from 0x02 in the vertical direction to 0x20 in the horizontal direction. When the changed bitstream is reproduced through the HEVC decoder, it is reproduced abnormally and is indicated by △.

An example of the case marked with × is when the first byte of NAL Unit Header in the bitstream is changed to 0x08 in the horizontal direction from 0x26 in the vertical direction. If the bitstream thus changed is reproduced through the HEVC decoder, it cannot be reproduced and is displayed as ×.

When the first byte of the NAL Unit Header is originally 0x40 to 0x50, the S5 region can be found by using the above-described methods for estimating the change table of the NAL Unit Header. As shown in Table 1, out of 25 values that can be the first byte of the NAL Unit Header, 9 of 0x40~0x50 can be found, so the remaining 16 values need to be found out. S1, S2, S3 and By using the characteristic of whether the S4 region is normally reproduced, the number of cases in which five values are found can be reduced.

If the first byte of the NAL Unit Header of the S1 area is originally 0x00~0x12, but it is changed, return it to one of 0x02, 0x06, and 0x0A to enable normal playback as indicated by ○. However, as indicated by □, there are some abnormal reproductions, so it returns one of 0x02, 0x06, and 0x0A.

If the first byte of the NAL Unit Header of the S2 area is originally 0x20~0x24, but it is changed, return it to one of 0x20~0x24 to enable normal playback as indicated by ○.

If the first byte of the NAL Unit Header of the S3 area is originally 0x26~0x28, but if it is changed, return it to one of 0x26~0x28 to enable normal playback as indicated by ○.

The first bytes of the 16 kinds of mixed NAL Unit Header that could not be found by using the above method of estimating the change table of the NAL Unit Header using the characteristics of the reproduction or not can be reproduced normally through the following five processes. can

First, as a first step, the first bytes of the 16 kinds of mixed NAL Unit Header are all changed to one of 0x26 ~ 0x28 of the S3 area to check whether or not to be reproduced.

to the second step. After the first step, the first bytes of the NAL Unit Header, which are abnormally reproduced, are all changed to one of 0x02, 0x06, and 0x0A in the S1 area to check whether or not to be reproduced.

In the third step, the first bytes of the NAL Unit Header, which are abnormally reproduced after the second step, are all changed to 0x2A of the S4 area to check whether the reproduction is performed.

In the fourth step, the first bytes of the NAL Unit Header, which are abnormally reproduced after the third step, are all changed to one of 0x20 to 0x24 in the S2 area to check whether or not to be reproduced.

In the fifth step, the first bytes of the NAL Unit Header, which are abnormally reproduced after the fourth step, are all changed to one of 0x10 and 0x12 in the S1 area to check whether or not to be reproduced. Therefore, the change table of the NAL Unit Header can be inferred by changing the first byte of the NAL Unit Header in this way.

Therefore, when the change table of the NAL unit header is not known, the decoder (Descrambler, 230) performs video decoding by inferring the change table of the NAL unit header by individually or in combination using the above-described change table inference methods of the NAL unit header. can do.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. is within the scope of the right. Accordingly, the foregoing detailed description should not be construed as restrictive in all respects but as illustrative. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present invention are included in the scope of the present invention.

110: Encoder 200: Encryptor
130: Network 140: Decryptor
150: decoder 210: encryption unit
220: communication unit 230: decoding unit

Claims (18)

delete delete delete As a method of decrypting an encrypted image,
Receiving an encrypted bitstream corresponding to the encrypted image - The encrypted bitstream includes a plurality of start codes and a plurality of NAL units, and the NAL Unit (Network Abstraction Layer Unit) ) is composed of encrypted NAL Unit Header and RBSP (Raw Byte Sequence Payload) -,
retrieving a start code from the encrypted bitstream;
searching for a NAL unit after the searched start code;
Decrypting the encrypted NAL Unit Header according to the change table to generate a decrypted bitstream, and
reconstructing video data using the decoded bitstream by a decoder
includes
The change table is a change table for the first byte value of the encrypted NAL Unit Header,
The encrypted image is generated using the HEVC codec,
Restoring the video data includes:
Restoring the decoded bitstream to video data using the HEVC codec,
The step of generating the decoded bitstream comprises:
Inferring the change table by comparing the encrypted NAL Unit Header and the byte value of the RBSP with the HEVC standard, and
and generating a decrypted bitstream by decrypting the encrypted NAL unit header according to the inferred change table. delete delete 5. The method of claim 4,
The step of generating the decoded bitstream comprises:
Inferring the change table by comparing the byte size of the RBSP with the HEVC standard, and
Decrypting the encrypted NAL Unit Header according to the inferred change table to generate a decrypted bitstream
Including, video decoding method. 5. The method of claim 4,
The step of generating the decoded bitstream comprises:
Inferring the change table by comparing the value of the RBSP and the NAL Unit order with the HEVC standard, and
Decrypting the encrypted NAL Unit Header according to the inferred change table to generate a decrypted bitstream
Including, video decoding method. 5. The method of claim 4,
The step of generating the decoded bitstream comprises:
Changing the encrypted NAL Unit Header to an arbitrary value and determining whether video data restoration is successful according to the changed value;
Storing the success or failure of video data restoration according to the change value of the encrypted NAL Unit Header;
inferring the change table according to whether video data restoration is successful according to the change value; and
Decrypting the encrypted NAL Unit Header according to the inferred change table to generate a decrypted bitstream
Including, video decoding method. delete delete delete As a device for decrypting encrypted images,
Communication unit for receiving an encrypted bitstream corresponding to the encrypted image - The encrypted bitstream includes a plurality of start codes and a plurality of NAL units, and the NAL Unit (Network Abstraction Layer Unit) ) is composed of encrypted NAL Unit Header and RBSP (Raw Byte Sequence Payload) -,
A decryption unit that searches for a start code in the encrypted bitstream, searches for a NAL unit after the searched start code, and decrypts the encrypted NAL unit header according to a change table to generate a decrypted bitstream, and
A decoder for reconstructing video data using the decoded bitstream
includes
The change table is a change table for the first byte value of the encrypted NAL Unit Header,
The encrypted image is generated using the HEVC codec,
The decoder is
Restoring the decoded bitstream to video data using the HEVC codec,
The decryption unit,
Infer the change table by comparing the encrypted NAL Unit Header and the byte value of the RBSP with the HEVC standard,
Decrypting the encrypted NAL unit header according to the inferred change table to generate a decrypted bitstream. delete delete 14. The method of claim 13,
The decryption unit,
Infer the change table by comparing the byte size of the RBSP with the HEVC standard,
Decrypting the encrypted NAL unit header according to the inferred change table to generate a decrypted bitstream. 14. The method of claim 13,
The decryption unit,
Infer the change table by comparing the RBSP value and the NAL unit order with the HEVC standard,
Decrypting the encrypted NAL unit header according to the inferred change table to generate a decrypted bitstream. 14. The method of claim 13,
The decryption unit,
Change the encrypted NAL Unit Header to an arbitrary value, determine whether video data restoration is successful according to the changed value,
Storing the success or failure of video data restoration according to the change value of the encrypted NAL Unit Header,
Inferring the change table according to the success or failure of video data restoration according to the change value;
Decrypting the encrypted NAL unit header according to the inferred change table to generate a decrypted bitstream.

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