JP2006128743A - Encrypted information generating apparatus, encrypted information reproducing apparatus, encrypted information generating program, and encrypted information reproducing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of a conventional electronic watermark embedding method wherein it takes much time and cost to convert an image and a voice/audio signal, coding efficiency is degraded and it leads to a possibility of causing quality deterioration in the image signal or the like when encrypted information unassociated with the original signal is embedded to the image signal or the like. <P>SOLUTION: A counter 303 counts a code length of a code word from a variable length coder 106 to designate an inserted position in the code words to which the encrypted information is to be embedded. A variable length code replacing unit 301 replaces a bit signal of the encrypted information outputted from an encryption conversion unit 302 with a corresponding bit of the code word resulting from applying variable length coding to a quantization value of an MDCT coefficient supplied from a minimum code quantity detector 107. In this case, when the code word after the replacement does not exist in a Huffman code book used by the variable length coder 106, a code word closest to the code word after the replacement is selected from the Huffman code book. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an encryption information generation device, an encryption information reproduction device, an encryption information generation program, and an encryption information reproduction program, and in particular, encryption information for generating a bitstream by adding encryption information to a digital signal such as an image or sound. The present invention relates to a generation apparatus, an encryption information reproduction apparatus for reproducing encryption information from the bit stream, an encryption information generation program, and an encryption information reproduction program.

  There is a digital watermark technique as one transmission method of encryption information. This digital watermark technology is a technology that embeds and hides some information in multimedia data such as images and sounds. Various methods for embedding some information in multimedia data have been proposed (see Non-Patent Documents 1 and 2, for example).

  Non-Patent Document 1 proposes an information embedding method based on changes in MPEG (Moving Experts Group) code, particularly DCT (Discrete Cosine Transform) coefficients, motion vectors, and quantization characteristics. Non-Patent Document 2 proposes a method of diffusing an image signal with a PN sequence and synthesizing signature information with an image according to a direct spreading method. In this non-patent document 2, when the spread image signal combined with the signature information is despread, the signature information is spread over the entire image signal, and the spread signature information does not cause a large noise to the image signal. Therefore, it is disclosed that the image signal including the signature information is almost the same as the original image, and on the other hand, in order to confirm the signature information, the image signal may be diffused with the same spreading code as that on the transmission side. .

  In addition, as an information embedding method of the above-described digital watermark technology, the applicant of the present invention is an encryption that can reliably and easily detect any region of image data in a frame image that has been tampered with. An information transmission device and an encryption information transmission program have been proposed (see, for example, Patent Document 1).

  The conventional encryption information transmission device described in Patent Document 1 includes a recording device and a playback device. The recording device takes frame image data into an image memory, and divides the frame image data into a large number of regions in a divided region setting unit. The embedded code creation unit creates a set of embedded codes so that a calculation result by a predetermined function using a plurality of embedded codes associated with each other as a variable becomes a predetermined identification code. Are embedded in each image data of the area by a predetermined position association rule. In the playback device, image data is divided under the same conditions as the recording device, each embedded code is extracted, the embedded code is grouped based on the rule, and an operation for obtaining an identification code is performed using the predetermined function. The presence / absence of falsification is determined based on whether or not identification codes are obtained for all pairs.

Hiroshi Ogawa, Takao Nakamura, Yoichi Takashima, "Copyright Information Embedding Method in Digital Video Using DCT", IEICE, SCSI'97-31G Atsuko Onishi, Kazuhiro Oka, Koko Matsui, "Watermark Signature Method for Images Using PN Sequences", IEICE, SCSI'97-26B JP 2004-228783 A

  However, in the conventional various digital watermark embedding methods as described above, when encryption information that is watermark information is embedded and transmitted in an image or audio / audio signal, the conversion processing of the image, audio / audio signal takes time and cost. Such a problem arises.

  In addition, in the conventional encryption information transmission apparatus, if encryption information that is not related to the original signal is embedded in an image or a sound / audio signal, the efficiency of the coding may be reduced, and the quality of the image or the sound / audio signal may be deteriorated.

  The present invention has been made in view of the above points. An encryption information generation apparatus, an encryption information reproduction apparatus, and an encryption information generation capable of easily embedding and reproducing encryption information in a codeword output by an encoding process. An object of the present invention is to provide a program and an encryption information reproduction program.

  Another object of the present invention is to provide an encryption information generation device, an encryption information reproduction device, an encryption information generation program, and an encryption information reproduction program that do not reduce the encoding efficiency.

  In order to achieve the above object, the encryption information generating apparatus of the present invention is obtained by encrypting desired embedded information in a codeword obtained by variable-length encoding an information signal using a variable-length codeword table. In a cryptographic information generating apparatus for generating a bit stream in which encrypted information is embedded, an encoding means for obtaining a code word by variable-length encoding an information signal using a variable-length code word table, and a code length of the code word A first counting means for counting and designating an insertion position in a code word for embedding encryption information in accordance with a predetermined counting rule; and a code word portion at an insertion position in the code word designated by the first counting means, When the code word after replacement is present in the variable length code word table, the code word after the replacement is output, and the code word after replacement is stored in the variable length code word table. When not present, the bit stream from the code replacement unit for selecting and outputting the code word closest to the replaced code word in the variable length code word table and the code word in which the encryption information output from the code replacement unit is embedded Output means for generating and outputting.

  In order to achieve the above object, the encryption information reproducing apparatus of the present invention includes an analysis unit that receives a bitstream generated by the encryption information generation apparatus of the first invention as an input and extracts a codeword from the bitstream. The code length of the code word output from the analysis means is counted, the separation position in the code word is designated according to the same predetermined counting rule as the first counting means, and the separation position in the designated code word And a second count means for extracting the codeword portion as embedded encryption information.

  In order to achieve the above object, the encryption information generation program of the present invention adds desired embedded information to a codeword obtained by variable-length encoding an information signal using a variable-length codeword table by a computer. In a cipher information recording program for generating a bit stream in which cipher information obtained by encryption is embedded, an encoding means for obtaining a code word by variable-length coding an information signal using a variable-length code word table A first count unit that counts the code length of the codeword and designates an insertion position in the codeword in which the encryption information is embedded according to a predetermined count rule, and a codeword in the codeword designated by the first count unit If the codeword part at the insertion position is replaced with encryption information, and the replaced codeword exists in the variable-length codeword table, the replaced codeword A code replacement means for selecting and outputting a code word closest to the replaced code word in the variable length code word table when the output and replaced code word does not exist in the variable length code word table; and a code replacement means The computer is caused to function as output means for generating and outputting a bit stream from a codeword in which encryption information output from is embedded.

  In order to achieve the above object, the encryption information reproduction program of the present invention is a computer that receives a bitstream generated by a computer based on the encryption information generation apparatus or encryption information generation program of the present invention as an input. An analysis unit that extracts a code word from the input bit stream, and a code length of the code word output from the analysis unit are counted, and a separation position in the code word is designated according to the same predetermined counting rule as the first counting unit. The codeword portion at the separation position in the designated codeword is made to function as second counting means for taking out as embedded encryption information.

  In the encryption information generation device and encryption information generation program of the present invention, a codeword that embeds encryption information by counting the code length of a codeword obtained by variable-length encoding an information signal using a variable-length codeword table Since the code word part at the insertion position in the designated code word is replaced with the encryption information, the encryption information as the watermark information is embedded in the image or the audio / audio signal and transmitted. Compared with the conventional digital watermark technology, it is possible to embed encryption information in a code word easily.

  Further, in the encryption information generation apparatus and encryption information generation program of the present invention, when a codeword after replacement exists in the variable length codeword table, the codeword after replacement is output, and the codeword after replacement is variable length When the code word table does not exist, the code word closest to the replaced code word is selected and output in the variable length code word table.

  According to the present invention, it is possible to easily embed and reproduce encryption information in a code word output by an encoding process. Further, according to the present invention, when the codeword after replacement does not exist in the variable-length codeword table, the codeword closest to the codeword after replacement is selected in the variable-length codeword table. Alternatively, it is possible to suppress the deterioration of the quality of the voice / audio signal, and it is possible to prevent a reduction in encoding efficiency by selecting a code word close to the code length of the original code word.

  Next, embodiments of the present invention will be described with reference to the drawings. Note that, here, as an example, the present invention is applied to an MPEG-2 / AAC (Advanced Audio Coding) audio encoding system, and an MPEG-2 / AAC audio encoding unit, an encryption information reproduction unit are included in the encryption information generating apparatus according to the present invention. It is assumed that an MPEG-2 / AAC audio decoding unit is employed in the apparatus.

  First, an MPEG-2 / AAC audio encoding unit that performs audio / audio encoding will be described. FIG. 1 shows a block diagram of an example of an MPEG-2 / AAC audio encoding unit. In the figure, a block 100 indicated by stippling indicates that the processing is performed in units of scale factor bands. In the MPEG-2 / AAC audio encoding unit, the input audio signal is subjected to fast Fourier transform (FFT) by the psychoacoustic analyzer 101 to obtain a frequency spectrum, and masking is calculated based on the frequency spectrum. Then, the permissible quantization noise power based on auditory psychology is calculated for each preset frequency band.

  On the other hand, the MDCT unit 102 performs a modified discrete cosine transform (MDCT) on the input audio signal to convert it into spectrum data (hereinafter referred to as MDCT coefficient). At this time, the MDCT unit 102 switches the conversion block length based on the window selection information determined by the psychoacoustic analyzer 101, and the conversion is executed by overlapping the calculation block length by 50%.

  In the case of a long window, 2048 samples are converted into 1024 MDCT coefficients, and in the case of a short window, 256 samples are converted into 128 MDCT coefficients. The scale factor calculator 103 divides the frequency band based on human auditory characteristics into a plurality of scale factor bands in units of 1024 MDCT coefficients from the MDCT unit 102, and calculates each scale factor band. The number of quantization steps (scale factor) of each scale factor band is calculated so that the quantization noise does not become larger than the allowable quantization noise power calculated by the psychoacoustic analyzer 101.

  The quantizer 104 quantizes the MDCT coefficient output from the MDCT unit 102 in units of scale factor bands calculated by the scale factor calculator 103. The MDCT coefficient in the scale factor band is quantized from the scale factor calculated by the scale factor calculator 103 and the total number of quantization steps. At this time, quantization is executed by controlling the total number of quantization steps so that the number of bits required for quantization falls within the number of usable bits.

  The code book selector 105 selects a usable Huffman code book from the maximum absolute value of the quantized value. In MPEG-2 / AAC, a Huffman codebook as shown in Table 1 is selected based on the maximum absolute value of the quantized value.

例えば量子化値の最大絶対値が５であれば、ハフマンコードブックは７以上が使用可能となる。表１はハフマンコードブック８番の一部を示したものである。これについては後述する。

For example, if the maximum absolute value of the quantized value is 5, 7 or more Huffman codebooks can be used. Table 1 shows a part of the Huffman code book No. 8. This will be described later.

  The selected Huffman codebook is sent to the variable length encoder 106. The variable length encoder 106 uses the Huffman codebook selected by the codebook selector 105 as a variable length codeword table for the quantized value of the MDCT coefficient output from the quantizer 104, and changes the variable length codeword table. Encode. When a plurality of Huffman codebooks are selected, the variable-length encoder 106 performs variable-length encoding using each Huffman codebook and sends the encoded result to the minimum code amount detector 107. The variable length encoder 106 also performs variable length encoding on the scale factor output from the scale factor calculator 103, reduces redundancy, and sends the encoding result to the code amount determination unit 108.

  The minimum code amount detector 107 selects a Huffman code book that generates the smallest code amount as a result of encoding with each Huffman code book, and sends the Huffman code book and the encoded result to the code amount determiner 108.

  The code amount determination unit 108 determines whether or not the code amount generated by encoding is within the usable code amount. If the code amount exceeds the usable code amount, the code amount is generated again by performing quantization. Repeat until the amount falls below the available code amount. The encoded data output from the code amount determiner 108 satisfying the usable number of bits is multiplexed together with encoding parameters such as a sampling frequency and an encoding rate in the bit stream generator 109 and transmitted as an AAC bit stream. Is done.

  Next, an MPEG-2 / AAC decoding unit that performs audio / audio decoding corresponding to the MPEG-2 / AAC audio encoding device of FIG. 1 that performs audio / audio encoding will be described. FIG. 2 shows a block diagram of an example of the MPEG-2 / AAC decoding unit. In the figure, an AAC bit stream input to an MPEG-2 / AAC decoding unit is separated into coding parameters such as a sampling frequency and a coding rate and coded data by a bit stream analyzer 201.

  The variable length decoder 202 performs variable length decoding of the encoded data separated by the bit stream analyzer 201 into a scale factor and a quantized value based on the separated encoding parameters. Here, the scale factor is decoded using a scale factor Huffman codebook, and the quantized value is based on the Huffman codebook number obtained from the bitstream analyzer 201 in units of scale factors. Then, the Huffman codebook for the quantized value is selected and decoded. The decoded quantized value and scale factor are sent to the inverse quantizer 203.

  The inverse quantizer 203 inversely quantizes the quantized value in units of scale factor bands, using the overall quantization step number and scale factor, which are one of the encoding parameters output from the bitstream analyzer 201, MDCT coefficients are calculated. This MDCT coefficient is input to an IMDCT (Inverse Modified Discrete Cosine Transform) 204, where it is subjected to inverse MDCT conversion to an audio signal and output.

  The present invention is applied to the above-described MPEG-2 / AAC audio encoding system, and an embodiment thereof will be described below.

  FIG. 3 is a block diagram of an embodiment of the encryption information generating apparatus according to the present invention, and FIG. 4 is a block diagram of an embodiment of the encryption information reproducing apparatus according to the present invention. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and in FIG. 4, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

  First, the encryption information generating apparatus in FIG. 3 will be described. A block 300 indicated by stippling in the encryption information generating apparatus shown in FIG. 3 indicates that the processing is performed in units of scale factor bands. Compared with the MPEG-2 / AAC audio encoding unit shown in FIG. 1 described above, the encryption information generating apparatus shown in FIG. 3 has a variable length code converter 301, an encryption converter 302, and a counter 303 added. Yes.

  In FIG. 3, a variable length encoder 106 performs variable length encoding on the quantized value of the MDCT coefficient output from the quantizer 104 using the Huffman codebook determined by the codebook selector 105. When a plurality of Huffman codebooks are selected by the codebook selector 105, variable-length encoding is performed using each Huffman codebook, and the encoded results are supplied to the minimum code amount detector 107. . Furthermore, the variable length encoder 106 also performs variable length encoding on the scale factor, and supplies the encoding result obtained by reducing the redundancy to the variable length code interchanger 301.

  The Huffman code book with the smallest generated code amount output from the minimum code amount detector 107, and the encoded result of the quantized value of the MDCT coefficient subjected to variable length coding using the Huffman code book is a counter. 303 and variable length code changer 301 respectively.

  On the other hand, the embedded information to be transmitted is encrypted by the cryptographic converter 302 and then input to the variable length code converter 301. As a simple example of encryption in the cryptographic converter 302, when ASCII characters are sent, since the characters are represented by 1 byte (8 bits), it is sufficient to send 8 bits one bit at a time. In addition, as long as consistency with the encryption inverse converter 402 of the encryption information reproducing apparatus can be obtained, the encoded data using a table such as a Huffman table may be sent bit by bit.

  The counter 303 counts the number of bits of the code word of the encoding result input from the minimum code amount detector 107, and inputs the generated signal indicating the position of the code word bit corresponding to the set interval bit number into the variable length code. Send to the converter 301. Here, the number of interval bits set as an example is an arbitrary fixed value, and a generated signal is transmitted for each interval bit number. Note that this interval bit number may be set to any value as long as it is consistent with the counter 401 of the encryption information reproducing apparatus.

  Based on the signal generated from the counter 303, the variable length code converter 301 converts the bit signal of the encrypted information output from the encryption converter 302 into the quantum of the MDCT coefficient supplied from the minimum code amount detector 107. The converted value is replaced with a corresponding bit of a codeword obtained by variable length encoding. In this case, if the bit signal of the encrypted information is “1”, the variable length code converter 301 sets the corresponding bit of the code word to “1” and the bit signal of the encrypted information to “0”. ”, The corresponding bit of the code word is replaced with“ 0 ”. However, simply replacing the code word may cause a code word that does not satisfy the syntax specified by the encoding. An example using Table 1 will be described for selection of codewords by replacing relevant bits so as to satisfy the prescribed syntax.

  Table 1 shows a part of the Huffman code book No. 8. The index in Table 1 is a value calculated from the quantized value, and when the variable length encoder 106 performs variable length encoding, the code word corresponding to the index is read. Here, it is assumed that the code word to be replaced is “0x75” (= 111 0101) which is the index 14 of the Huffman codebook No. 8 shown in Table 1.

  Considering that the upper 3 bits of the code word are replaced with the information bit signal “0”, the code word becomes “0x65” (= 110 0101) when simply replaced, but this code word is Huffman codebook 8 It doesn't meet the syntax because it doesn't exist in the numbers.

  Therefore, a code word that is close to the length of the original code word in the Huffman code book No. 8, whose index value is close, and whose upper third bit is “0” is searched. Here, since the code word “0x6a” at the index 13 satisfies the condition, “0x6a” is selected and replaced from “0x75”.

  In addition, as an example of replacing the information bit signal “1”, the upper 7th bit of “0xf4” (= 1111 0100) whose original code word is the index 58 of the Huffman codebook No. 8 is the corresponding bit. If there is, the code word becomes “0xf6” (= 1111 0110) after replacement. “0xf6” exists in the Huffman codebook No. 8 (index 53), but is far from the original index value.

  Therefore, a code word that is close to the length of the original code word in the Huffman code book No. 8, whose index value is close, and whose upper 7th bit is “1” is searched. Therefore, in this case, either the index 57 (code word “0xf3”) or the index 59 (code word “0xf7”) close to the original index 58 is selected.

  In this way, when there are a plurality of codewords that can be selected by exchanging the corresponding bits, it is only necessary to determine a selection rule in advance, and here, the smaller one than the original index value is given priority, and the code Select the word “0xf3” and replace it with “0xf4”.

  The encoding result including the replaced code word and the Huffman codebook are sent to the code amount determination unit 108, and it is determined whether the code amount generated by the encoding is within the usable code amount. When the code amount is exceeded, the quantization is performed again, and the process is repeated until the generated code amount falls below the usable code amount.

  The encoded data output satisfying the usable number of bits is multiplexed together with encoding parameters such as sampling frequency and encoding rate in the bit stream generator 109 and output as an AAC bit stream.

  Note that the bit string related to the encoding parameters such as the sampling frequency and the encoding rate violates the encoding syntax when the bits are exchanged, so that the bit substitution is not performed and only the data portion is targeted. .

  In general, the most significant bit of a code word used for a variable-length code is often “1”. Therefore, when the bit replacement position is the position of the most significant bit of the code word, the replacement is not performed. It is also possible to perform bit replacement for the upper second bit of the code word, or to perform replacement for the code word corresponding to the next interval bit number.

  Next, the encryption information reproducing apparatus in FIG. 4 will be described. Compared with the MPEG-2 / AAC decoding unit shown in FIG. 2, the encryption information reproducing apparatus shown in FIG. 4 has a counter 401 to which encoded data separated by the bitstream analyzer 201 is input, and an output of the counter Is added to the encryption inverse converter 402.

  The operation of the encryption information reproducing apparatus in FIG. 4 will be described. The encoded data separated by the bit stream analyzer 201 is output to the variable length decoder 202 and the counter 401, respectively. The counter 401 counts the number of codeword bits of the input encoded data and sends the codeword bits corresponding to the number of interval bits consistent with the counter 303 of the encryption information generation apparatus to the encryption inverse converter 402. .

  The cryptographic inverse converter 402 receives the bit string of the cryptographic information output from the counter 401 as an input, and performs reverse conversion on the bit string of the input cryptographic information to obtain the original embedded information. As for the encryption method in the encryption converter 302, any method may be used as long as consistency with the encryption inverse converter 402 is obtained.

  As described above, according to the present embodiment, it is possible to easily embed and reproduce the encryption information in the codeword output by the encoding process. In addition, when embedding encryption information in a code word, a code word that is close to the length of the original code word and conforms to a predetermined encoding rule (a code word close to the original code word) is selected. It is possible to suppress the quality degradation of the image or the audio / audio signal as much as possible, and it is possible to prevent the encoding efficiency from being reduced by selecting a code word close to the code length of the original code word.

  The counter 303 of the encryption information generation device and the counter 401 of the encryption information reproduction device set a fixed value for the number of interval bits. However, if consistency can be obtained, both counters have pseudo-random number generators. May be used as the interval bit number.

  Next, the present invention is applicable not only as hardware but also as software (program), and an embodiment of the general program will be described. 5 and 6 are flowcharts showing an embodiment of the encryption information generating program of the present invention, and FIG. 7 is a flowchart showing an embodiment of the encryption information reproducing program of the present invention.

  The flowcharts of FIGS. 5 and 6 correspond to the block diagram of the encryption information generating apparatus according to the present invention shown in FIG. 3, and the flowchart of FIG. 7 is the encryption information reproducing apparatus according to the present invention shown in FIG. Corresponds to the block diagram. FIG. 6 is a flowchart showing the process branched to the auditory psychological analysis step in FIG.

  First, the encryption information generation program will be described with reference to FIGS. The computer captures 1024 samples of PCM data obtained by PCM of the audio signal (step S01 in FIG. 5), and converts the captured PCM data into frequency spectrum data (MDCT coefficients) by MDCT (step S02 in FIG. 5). Auditory psychological analysis is performed (step S21 in FIG. 6). In this psychoacoustic analysis, as described above, the PCM data is subjected to FFT, a frequency spectrum is obtained, masking is calculated based on the frequency spectrum, and permissible quantization noise based on auditory psychology for each preset frequency band. Calculate power. After the auditory psychological analysis, the computer calculates the scale factor (step S22 in FIG. 6) and stores the calculated scale factor in the memory (step S23 in FIG. 6).

  Here, the scale factor is divided into a plurality of scale factor bands, for example, in units of 1024 MDCT coefficients for each frequency band based on human auditory characteristics as described above. This is the number of quantization steps of each scale factor band calculated so that the calculated quantization noise does not become larger than the allowable quantization noise power calculated by the psychoacoustic analysis of step S21.

  Subsequently, the computer quantizes the MDCT coefficient obtained in step S02 in the above-described quantization step of the scale factor band stored in the memory (step S03 in FIG. 5). At this time, quantization is executed by controlling the total number of quantization steps so that the number of bits required for quantization falls within the number of usable bits.

  Subsequently, the computer performs variable length coding on the quantized value of the MDCT coefficient using the Huffman codebook selected from the maximum absolute value of the quantized value, and performs the scale factor input from the memory. Is also subjected to variable length coding, redundancy is reduced, and the encoding result is obtained (step S04 in FIG. 5), and then the Huffman codebook that minimizes the amount of code generated as a result of encoding with each Huffman codebook. Is detected (step S05 in FIG. 5).

  Also, the computer encrypts the embedded information to be transmitted (step S10 in FIG. 5), counts the number of bits of the codeword of the encoding result, and calculates the number of bits of the codeword corresponding to the set interval bit number. A position, that is, a position where a bit is embedded is designated (step S11 in FIG. 5). Subsequently, based on the designation of the position where the bit is embedded in step S11, the computer converts the bit signal of the encrypted information obtained in step S10 into the corresponding bit of the codeword obtained by variable-length encoding the quantized value of the MDCT coefficient. Are switched so as to satisfy the syntax defined by encoding (step S06 in FIG. 5).

  Subsequently, the computer determines whether the code amount generated by the encoding is within the usable code amount based on the encoding result including the replaced codeword and the Huffman codebook (step of FIG. 5). S07) When the usable code amount is exceeded, the process returns to step S01 to perform quantization again, and the above processing is repeated until the generated code amount falls below the usable code amount.

  When it is determined in step S07 that the usable number of bits is satisfied, the encoded data is multiplexed together with encoding parameters such as a sampling frequency and an encoding rate, and is generated as an AAC bit stream (step S08 in FIG. 5). Then, it is determined whether or not all the PCM data has been processed (step S09 in FIG. 5), and when the processing for all the PCM data is completed, the processing is terminated.

  Next, the encryption information reproduction program will be described with reference to FIG. The computer analyzes the transmitted and input bit stream (step S31), separates it into encoded data and encoding parameters, and converts the encoded data into a scale factor and a quantized value based on the separated encoding parameters. Then, variable length decoding is performed (step S32).

  On the other hand, the computer counts the number of bits of the code word of the separated encoded data, takes out the bit string (encryption information) corresponding to the number of bit bits on the encryption recording side (step S36), and stores it in the bit string of the code word. On the other hand, reverse transformation is performed (decryption is performed) to obtain the original embedded information (step S37).

  Further, the computer inversely quantizes the quantized value in units of scale factor bands based on the quantized value and the scale factor obtained by variable length decoding in step S32, and calculates MDCT coefficients (step S33). This MDCT coefficient is subjected to inverse MDCT conversion and converted to PCM data (step S34), and then it is determined whether all MDCT coefficients have been subjected to inverse MDCT conversion (step S35), and all MDCT coefficients are subjected to inverse MDCT conversion. The processes in steps S31 to S37 are repeated until the process is completed.

  Each program described above may be read from a recording medium and loaded into a computer, or may be transmitted via a communication network and loaded into a computer.

  Next, a procedure for exchanging codewords and encryption information according to an embodiment of the present invention will be described in more detail with specific examples. Here, the code word output from the minimum code amount detector 107 shown in FIG. 3 is the number of bits of the size corresponding to the length in Table 1, and the counter 303 is a bit of the code word for simplicity of explanation. The number is counted, and the corresponding bit of the code word in which the last digit of the count number is “3” is replaced with the bit of the encryption information. In addition, if the bit of the cryptographic information output from the cryptographic converter 302 is “1”, it is replaced with “1”, and if it is “0”, it is replaced with “0”.

  Assuming that the code word is output in the order of “75”, “1f6”, and “f4” from the minimum code amount detector 107 as shown in FIG. (B), and the count number of the counter 303 for counting the number of bits of this code word is as shown in FIG. (C) (however, the count number is only the last digit). Notation.)

  Here, if the bit string of the cryptographic information output from the cryptographic converter 302 in FIG. 3 is “001” as shown in FIG. 8D, the upper third bit of the input codeword “75”. As shown in FIG. 8C, the count number becomes “3”, and the upper third bit of the input codeword “75” at that time is replaced with the bit “0” of the encryption information. Similarly, in the upper 6 bits of the input codeword “1f6”, the count number is “3” as shown in FIG. 8C, and the upper 6 bits of the input codeword “1f6” at that time are the bits of the encryption information. As shown in FIG. 8C, the count number is “3” in the upper 7 bits of the subsequent input codeword “f4”, and the upper 7 bits of the input codeword “f4” at that time are replaced with “0”. It is replaced with bit “1” of the encryption information.

  Accordingly, the code word is changed in the order of “65”, “1f6”, “f6” as shown in FIG. 8E by the above replacement, but “65” as shown in FIG. 8F. Does not exist in Table 1, "1f6" is the same as the original codeword, and "f6" exists in Table 1 but is far from the original index. Therefore, as described above, the variable length interchanger 301 is such that “65” is close to the length of the original codeword “75” in Table 1, the index value is close, and the upper 3 bits are “ The code word “6a” is “0”, and the subsequent “1f6” is the same as the original codeword “1f6”.

  The following “f6” exists in Table 1 but is far from the original index, so as described above, it is close to the length of the original codeword in the Huffman codebook No. 8 of Table 1, and the index value is close. When a code word whose upper 7th bit is “1” is searched, an index 57 (code word “0xf3”) or an index 59 (code word “0xf7”) close to the original index 58 is searched. Then, if the smaller index is selected, it is replaced with “f3” corresponding to the index 57 by preconditioning from the beginning.

  In this way, the code amount determination unit 301 actually outputs code words to the code amount determination unit 108 in the order of “6a”, “1f6”, and “f3” as shown in FIG.

  Next, a specific example of the restoration operation in the encryption information reproducing apparatus for the encryption information replaced with the code word as shown in FIG. 8 will be described with reference to FIG. The counter 401 shown in FIG. 4 counts the number of bits of the input codeword shown in FIG. 9A under the condition that it is consistent with the encryption information generating apparatus side. When the input code word shown in FIG. 9A is represented by a bit display, it is as shown in FIG. 9B, and the last digit of the count number of the counter 401 is as shown in FIG.

  Based on the same counting rule as that of the counter 303 of the encryption information generating apparatus, the counter 401 designates and outputs as the replaced bit position when the last digit value is “3”. In the case of “6a”, the value “0” is output when the upper third bit in which the value of the last digit of the count number is “3”. Similarly, for the subsequent input codeword “1f6”, the value “0” is output when the upper six bits in which the last digit of the count number is “3”. Further, for the subsequent input codeword “f3”, the value “1” is output when the upper 7th bit, where the value of the last digit of the count is “3”.

  Therefore, as shown in FIG. 9D, “001” is extracted from the counter 401, which matches the encryption information (FIG. 8D) output from the encryption converter 302 of the encryption information generating apparatus. . In this way, the encryption information is restored. Here, in order to simplify the explanation, the exchange and extraction positions of the encryption information of the counters 303 and 401 are described as the last digit of the sum of the number of bits of the code word. As long as the rules are consistent, the rules are not limited to the above example.

  Note that the present invention is not limited to the above-described embodiments. For example, the present invention is not limited to the MPEG-2 / AAC audio encoding system, and digital signals such as images and sounds can be converted into variable-length codes. The present invention can be widely applied to encoding / decoding methods that use compression / decompression. In addition, a transmission path for transmitting a bit stream in which encryption information is embedded in a codeword includes a communication path for wireless communication and wired communication, a recording medium, and the like, and the transmission path itself is not particularly limited.

1 is a block diagram of an example of a general encoding device of an MPEG-2 / AAC audio encoding system. FIG. FIG. 2 is a block diagram of an example of a general decoding device of the MPEG-2 / AAC audio encoding method. It is a block diagram of one Embodiment of the encryption information generation apparatus of this invention. It is a block diagram of one Embodiment of the encryption information reproducing | regenerating apparatus of this invention. It is a flowchart which shows one Embodiment of the encryption information generation program of this invention. It is a flowchart which shows the process branched to the psychoacoustic analysis of the encryption information generation program of this invention. It is a flowchart which shows one Embodiment of the encryption information reproduction | regeneration program of this invention. It is explanatory drawing of a specific example of replacement | exchange of the codeword and encryption information in an encryption information generation apparatus. It is explanatory drawing of a specific example of the encryption information decoding operation | movement in an encryption information reproducing | regenerating apparatus.

Explanation of symbols

101, 301 Auditory psychological analyzer 102, 302 MDCT unit 103, 303 Scale factor calculator 104, 304 Quantizer 105, 305 Codebook selector 106, 306 Variable length encoder 107, 307 Minimum code amount detector 108, 308 Code amount determination unit 109, 309 Bit stream generator 201, 401 Bit stream analyzer 202, 402 Variable length decoder 203, 403 Inverse quantizer 204, 404 IMDCT device 310 Cryptographic converter 311, 405 Counter 312 Variable length Code converter 406 Cryptographic reverse converter

Claims (4)

In a cryptographic information generation device that generates a bitstream in which encryption information obtained by encrypting desired embedded information is embedded in a codeword obtained by variable-length encoding an information signal using a variable-length codeword table ,
Encoding means for variable-length encoding the information signal using the variable-length codeword table to obtain the codeword;
First counting means for counting a code length of the codeword and designating an insertion position in the codeword in which the encryption information is embedded according to a predetermined counting rule;
When the codeword part at the insertion position in the codeword designated by the first counting means is replaced with the encryption information, and the replaced codeword exists in the variable-length codeword table, A code word is output, and when the replaced code word does not exist in the variable-length code word table, a code word that selects and outputs the code word closest to the replaced code word in the variable-length code word table Replacement means,
An encryption information generation apparatus comprising: output means for generating and outputting the bitstream from a codeword in which encryption information output from the code replacement means is embedded. Receiving means for receiving a bitstream generated by the encryption information generating apparatus according to claim 1 and extracting the codeword from the bitstream;
The code length of the codeword output from the analyzing means is counted, the separation position in the codeword is designated according to the predetermined counting rule same as the first counting means, and the designated code A cipher information reproducing apparatus comprising: a second count unit that extracts a codeword portion at a separation position in a word as the embedded cipher information. Encryption information for generating a bitstream by embedding encryption information obtained by encrypting desired embedding information in a codeword obtained by variable-length encoding an information signal using a variable-length codeword table by a computer In the generator program:
The computer,
Encoding means for variable-length encoding the information signal using the variable-length codeword table to obtain the codeword;
First counting means for counting a code length of the codeword and designating an insertion position in the codeword in which the encryption information is embedded according to a predetermined counting rule;
When the codeword part at the insertion position in the codeword designated by the first counting means is replaced with the encryption information, and the replaced codeword exists in the variable-length codeword table, A code word is output, and when the replaced code word does not exist in the variable-length code word table, a code word that selects and outputs the code word closest to the replaced code word in the variable-length code word table Replacement means,
An encryption information generation program that functions as output means for generating and outputting the bitstream from a codeword in which encryption information output from the code replacement means is embedded. A computer that receives a bitstream generated by a computer based on the encryption information generation device according to claim 1 or the encryption information generation program according to claim 3,
Analyzing means for extracting the codeword from the input bitstream;
The code length of the codeword output from the analyzing means is counted, the separation position in the codeword is designated according to the predetermined counting rule same as the first counting means, and the designated code A code information reproduction program which causes a code word portion at a separation position in a word to function as second counting means for extracting the code word portion as embedded code information.

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