JPH044630A - Cryptographic coding device - Google Patents

Abstract

PURPOSE:To improve degree of the secrecy, to apply low speed processing to a cryptographic section, to make the hardware small and to reduce the cost by extracting only part of a digital signal to be sent and using a cryptographic key so as to cipher the part. CONSTITUTION:A signal conversion means A consists of an A/D converter (A/D) 1 converting a video signal into an 8-bit PCM signal and converts an analog picture and voice signal into a digital signal. A compressor 2 compresses the 8-bit digital signal into a 4-bit code and a distributer 3 extracts only one bit of the MSB (Most Significant Bit) from the 4-bit output of the compressor 2. A cryptographic means C consists of a cryptographic device 4 to cipher the information of only the MSB being an output of the compressor 2 by using a 64-bit key decided between a sender and a receiver in secrecy. A parallel/serial converter (P/S) 5 combines the cryptographic information and the information not ciphered being the output of the compressor 2, applies serial/parallel conversion to the result and a converted 1-bit serial data is sent to the receiver through a transmission line 6.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an encryption encoding device, and particularly to an encryption encoding device for digitally transmitting audio, image signals, and the like.

[Conventional technology]

In recent years, images have become increasingly high-definition, and for example, television images that we use on a daily basis are shifting from the NTSC system to the high-definition system. When recording such highly refined images on recording media such as tapes and disks, or transmitting them to remote locations via satellites, optical fibers, cables, etc., S
Considering image quality deterioration factors such as /N and sick, digital transmission is more advantageous than analog transmission.

On the other hand, while digital transmission has the advantage of not causing image quality deterioration no matter how many times it is tabbed in recording systems such as tapes and disks, illegal copying and duplication pose a major social problem. We also provide communication services such as satellites, optical fibers, and cables.
In the broadcasting system, there is a problem in that people who have not paid their fees or people outside the party are able to watch and listen to the video in secret.

Therefore, in conventional digital transmission, when transmitting data from a computer or the like, a method has been used in which all the data is encrypted before being sent, and the receiving side decrypts it using an encryption key.

Next, conventional examples of these encryption methods will be explained using FIGS. 5 and 6.

Figure 5 is from FIPS Publication 46 dated January 15, 1977.
The US data encryption standard disclosed in
FIG. 6 is a flowchart showing the encryption flow of the encryption 5 standard (hereinafter referred to as DES or conventional example), and FIG. 6 is a diagram showing the encryption function of FIG.

This conventional data encryption algorithm has been published as the "Data Encryption Standard" as described above.

This DBS (conventional example) will be explained below with reference to FIGS. 5 and 6.

First, this DES is a block cipher for binary data consisting of 0.1. In DES, binary data is divided into 64-bit blocks, and each block is encrypted by repeating transposition and substitution. The key has 64 hits, of which 8 are test hits for error detection, and 56 bits are valid. This key controls each substitution. FIG. 5 shows the process of DES encryption. Further, FIG. 6 shows a function fK(R>) which is the center of encryption.

In Figure 6 of the drawing, the 64-bit plaintext is first transposed. Stiffness is a fixed transposition independent of the key. Next 6
4 people are on the left side. and the right half Ro. After that, the calculation is repeated over 16 stages. Here, 10 represents the sum of m o d 2 for each bit.

Also, Ln.

Rn is the left half of 3 when the nth stage of calculation is completed.
2 bits and the right half 32 bits.

K, , is constructed from the key as shown on the right side of FIG. In FIG. 5, S I +-"・, S16 is 1 or 2. Also, contracted transposition 2a is to perform transposition by removing some of the human power. In this case, the input Eight of the 56 bits are removed, resulting in an output of 48 bits.The reduced form transposition is an irreversible transformation, and the input cannot be completely reconstructed from the output.As a result,
This makes guessing the key more difficult.

Next, the function fX(R) in FIG. 5 will be explained using FIG. 6.

In FIG. 6, in order to create the function fK(R), R is first subjected to an extended transposition 3a. Extended form transposition is transposition by duplicating some of the human power. In this case, 3
Of the 2-bit human power, 16 hits appear redundantly in the output. At the same time, K composed of keys is added bit by bit to this output, mod 2. The resulting 48 bits are divided into eight small blocks of 6 bits, and each 6 bit is divided into S, , S2 . . . . each is converted into 4 hits in S8. If you consider 6 bits as one character, you can think of it as a type of substitution. However, since the output is compressed to 4 bits, this conversion is an irreversible conversion. Therefore, fK(R) is generally an irreversible function. However, this does not mean that the transformation of equation (1) is irreversible. In fact, since equation (1) can be transformed as follows, it can be seen that Ln-1+R, , can be calculated from L, , Rn.

Now, repeating the calculation of equation (1) 16 times, L,6.
After finding R, , transpose it one last time to finish the encryption.

Next, decoding will be explained.

Decryption can be performed by performing almost the opposite operation of encryption.

Simply put, all you have to do is proceed from the bottom to the top in Figure 5. First, perform the inverse transposition of the last transposition of encryption, and calculate R1-1゜Ln-1 using the following formula (2). Once Ro and Lo are obtained, the first transposition of encryption is By performing the reverse transposition, the original 64 bits can be obtained.

Until now, there is no known way to decipher DES ciphertext other than by solving the keys one by one. Suppose it takes 1 microsecond to check whether it is the correct key or not. At this time, 256
It would take 2,283 years to find all the keys. Even if you are very lucky, it will take several hundred years.

(Problems to be Solved by the Invention) As explained above, in the conventional example, in the case of high-definition video images such as high-definition, if an analog image signal is simply A/D converted and transmitted, If you try to secure a signal band of 30MHz or more,
According to the sampling theorem, sampling must be performed at a rate of at least 60 MHz, 74.25 MHz, 8
When converting bits into A/D, the transmission rate is 74.25 (
MHz) x8 (bit) = 594 (Mbit
/s). Therefore, even if the amount of information is compressed to 115 to save transmission capacity, it will be approximately 120 (Mbit
/s). Encrypting and transmitting such a huge amount of information requires high-speed processing by the encryption unit.

The problem was that it was extremely difficult in terms of hardware size and cost.

This invention was made to solve the above-mentioned problems, and by encrypting a part of the encoded data using the encoding method using an encryption key and transmitting it, the secrecy is increased, and the encryption section An object of the present invention is to provide an encryption/encoding device that processes data at low speed, uses smaller hardware, and reduces cost.

[Means to solve the problem]

Therefore, in the present invention, there is provided a signal converting means for converting an image/audio signal from analog to digital, a data transmitting means for transmitting the image/audio signal converted by the signal converting means, and a data transmitting means for transmitting the image/audio signal converted by the signal converting means. The above objective is achieved by an encryption/encoding device comprising an encryption means for encrypting a part of the information using an encryption key.

[Effect]

The encryption/encoding device of the present invention converts the image/audio signal from analog to digital using the signal conversion means, encrypts a part of the digital image/audio data using the encryption key using the encryption means, and transmits it using the data transmission means. do.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram of an encryption/encoding device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a compressor in this embodiment.
FIG. 3 is a block diagram of the sign determination type decoding circuit of FIG. 2, and FIG. 4 is a block diagram of the decoding apparatus in this embodiment.

As mentioned above, FIG. 1 shows an embodiment of the encrypted predictive coding transmission system of the present invention, in which 8-bit data is compressed into a 4-bit code, and the MSB1 of the 4-bit signal is compressed.
FIG. 2 is a configuration diagram in which only bits are extracted, encrypted, and transmitted.

In FIG. 1 of the drawings, A is a signal converting means, which is an A/D converter (
It is a means for converting image/audio signals from analog to digital. B is the data transmission means, such as a recording system such as a tape or disk, a satellite, or an optical fiber.

It is composed of a transmission line 6 which is a communication broadcasting system such as a cable,
This is means for transmitting the image/audio signals converted by the signal converting means A. C is an encryption means that uses a 64-bit key secretly decided between the sender and receiver to encode the MSB (MO5T 51gn1ficant) of the output of the compressor (described later).
It is a means for encrypting a part of the digital image/audio data using an encryption key (details will be described later). 2 is a compressor that compresses an 8-bit digital signal into a 4-bit code, 3 is a distributor that extracts one hit of only the MSB from the 4-bit output of the compressor 2, and 5 is encrypted information that encrypts only the MSB. This is a parallel-to-serial converter (P/S in the figure) which performs parallel-to-serial conversion by combining the unencrypted three-hit information excluding the MSB of the compressed amount output. The 1-bit serial data from the parallel-to-serial converter 5 is sent to the receiving side through a transmission line 6.

7 is a serial-to-parallel converter (S/P in the figure) that distributes the received data into the MSB 1 bit and 3 bits other than the soft one, and 8 is a serial-to-parallel converter (S/P in the figure) that distributes the encrypted MSB 1 bit information in advance as a secret between the sender and receiver as described above. A decryptor 9 decrypts the compressed information using a predetermined 64-bit key, and 9 receives the MSB 1 hit of the compressed information decrypted by the decryptor 8 and the received data other than the MSB converted from serial to parallel by the serial parallel converter 7. A combiner which combines 3 bits into 4 bits of regular compressed data; 10 a decoder which expands the 4 bits of compressed data into an 8-bit PCM signal; and 11 a D which converts the 8-bit PCM data into an analog signal. /A converter (D/A in the figure).

Next, the operation of this embodiment will be explained with reference to FIGS. 1 to 4, focusing on the data compression and encryption means C.

In the following explanation, the reason why it is effective to encrypt only the MSB 1 bit of compressed data will also be described.

First, data compression will be explained. For example, differential P CM (P
The U1SE Code Modulation (hereinafter referred to as DPCM) method is generally well known.

The DPCM has a method of predicting the value of a sample point that is currently being encoded from the value of a sample point that has already been encoded, and encoding the difference (prediction error) between the predicted value and the original value. For signals such as image signals where the correlation between values at adjacent sample points is large, highly efficient encoding is achieved by performing non-linear quantization in consideration of the bias in the generation distribution of prediction error signals. can be done.

As mentioned above, FIG. 2 shows the configuration of the compressor 2 (FIG. 1) that compresses 8-bit data into a 4-bit code, and FIG. 3 shows the code determination type of this encoding device. FIG. 3 is a diagram showing the configuration of a decoding circuit. Further, FIG. 4 shows the configuration of the decoder 10 (FIG. 1).

In FIG. 2 of the drawing, eight pieces of image data are input to an input terminal 101, and are limited by a limiter 108 to within a predetermined range, for example, 16 to 235, and are input to a subtraction circuit 102.
In this step, a difference value (prediction error) from the predicted value output from the prediction coefficient multiplication circuit 103 is calculated. This prediction error is supplied to the code multiplexing type quantization circuit 104. The quantization circuit 104 converts the 9-bit prediction error data, which includes signs indicating positive and negative, into 4-bit data based on the quantization characteristic in which the positive and negative values are superimposed and assigned the same sign, as illustrated in Table 1 below. The signal is quantized and outputted from an output terminal 105, and also supplied to a sign judgment type decoding circuit 106.

Table 1 The quantization characteristics shown in Table 1 are an example of a table that uses past decoded values to determine whether the prediction error is positive or negative and selects one representative value for prediction errors that take values between -219 and 219. By assigning one 4-bit sign to each of the positive and negative quantization steps, 5 is obtained.
This enables encoding with a number of quantization steps equivalent to bits.

This table is set so that the two divided regions, positive and negative, assigned to the same code have a level difference corresponding to the limited dynamic range of decoded values (for example, 220), and the lower end of the region is set as the quantization representative. Since it is an undershoot type, the decoding results based on the positive and negative representative values have a level difference of 220, and only one of them always falls within the dynamic range ("0 to 219"). This makes it possible to determine whether the difference value is positive or negative, as will be described later.

In addition, in the case of image signals, a difference value near 0 is important, and in order to realize superposition of nonlinear characteristics, both positive and negative signals have a symmetrical structure folded back at the center.

The code determination type decoding circuit 106 (FIG. 2) decodes the code output from the quantization circuit 104 using the predicted value that is the output of the prediction coefficient multiplication circuit 103, and supplies the decoded value to the delay circuit 107. do. After the decoded value is delayed by a predetermined period (for example, one sample period) in a delay circuit 107, it is multiplied by a prediction coefficient in a prediction coefficient circuit 103 and is supplied as a prediction value to the subtraction circuit 102 and the sign judgment type decoding circuit 106. .

Here, the operation of the sign determination type decoding circuit 106 shown in FIG. 2 will be explained using FIG. 3. In Figure 3 of the drawing, terminal 20
The 4-bit code output from the code-multiplexed quantization circuit 104 is input to 1, and the + side representative value setting circuit 20
2 and the − side representative value setting circuit 203. The typical positive and negative output values of the circuits 202 and 203 are as follows:
In each of the adder circuits 205 and 206, the terminal 20
4 are respectively added to the predicted values supplied from 4, and are supplied to the selection circuit 207 as positive and negative decoded values.

The outputs of the representative value setting circuits 202 and 203 are always “
Since the level difference of 220" is maintained, the selection circuit 207
The positive and negative decoded values supplied to the
Limited dynamic range of ~255”)
16 to 235". Therefore, if you select the positive or negative decoded value that is within the range, the correct decoded value can be obtained from code multiplexed manually. Therefore, the + side addition circuit 205 The level of the output decoded value data is compared with a threshold value "236" by the comparator 209, and the output signal controls the selection circuit 207 to select a positive or negative decoded value and output it from the terminal 208.

Here, the code determination operation in this embodiment will be explained using a specific example. Now, consider the case where the predicted value is "100" and the current human power value is "150". Prediction error is -+5
0'', the code multiplexing type quantization circuit 104 outputs 5'' as 4-bit quantized value data as shown in Table 1. In the sign judgment type decoding circuit 106, the + side decoded value data is "136" and the - side decoded value data is "-84", so "136" within the appropriate dynamic range is selected as the decoded value. Similarly, when the current human power value is "50" and the prediction error is "-50", the output of the quantization circuit 104 is "11". In this case, since the + side decoded value data is "284" and the - side decoded value data is "64", "64", which is within the appropriate dynamic range, is selected.

Next, the decoder 10 that decodes the code encoded and transmitted by the compressor 2 shown in FIG. 1 will be explained using FIG. 4.

In FIG. 4 of the drawing, a 4-bit code encoded by the encoding device (compressor) is input to an input terminal 301 and is supplied to a + side representative value setting circuit 302 and a − side representative value setting circuit 303. be done. The positive and negative representative values that are the outputs of the circuits 302 and 303, respectively, are added to the adder circuits 304 and 3.
05, respectively, are added to the predicted values supplied from the prediction coefficient multiplication circuit 309, and are supplied to the selection circuit 306 as positive and negative decoded values. Representative value setting circuit 302
．． Since the respective outputs of 303 always maintain a level difference of "256" due to the characteristics of the codes, the selection circuit 30
One of the positive and negative decoded values supplied to 6 is always outside the limited dynamic range "16-235".

Therefore, by selecting the positive or negative decoded value within the range, the correct decoded value of the code can be obtained. Therefore, the decoded value outputted from the + side adder circuit 304 is compared with the threshold value "236" by the comparator 310, and the selection circuit 306 is controlled by the output to select one of the positive and negative decoded values. The decoded value of the bit is output from the output terminal 307. Further, this decoded value is supplied to a delay circuit 308, delayed by one sample period, and sent to a prediction coefficient multiplication circuit 309. The prediction coefficient multiplication circuit 309 calculates a predicted value by multiplying the delayed decoded value by the prediction coefficient, and supplies the predicted value to each of the addition circuits 304 and 305 for decoding the later input code. A decoder can be realized with the above configuration.

Here, as can be seen from Table 1, the 4-bit compressed data to be transmitted is a code that gives the representative value of the difference value of the image data, so if even one bit of this is unknown, the image Decryption becomes completely impossible.

Therefore, for example, DES
By encrypting with a key such as (conventional example), the confidentiality of image transmission can be maintained.

In the above embodiment, the differential PCM (DPCM) method was taken as an example, and it was explained that only the MSB 1 bit of the compressed data is encrypted.
Bits other than the SB1 bit may be encrypted. Also,
It is not necessary to encrypt all pixels, but only one bit or several bits of compressed data for every few pixels may be encrypted. Furthermore, the present invention can be applied to compression methods other than the differential PCM method or to the MSB 1 bit of uncompressed PCM transmission, and the present invention can be applied to not only image data but also audio data in exactly the same way.

〔Effect of the invention〕

As explained above, by extracting only a certain part of the digital signal to be transmitted and encrypting that part with an encryption key, secrecy is increased, the encryption part is processed at a lower speed,
It has become possible to provide an encryption/encoding device that has downsized hardware and reduced costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an encryption encoding device according to an embodiment of the present invention, FIG. 2 is a block diagram of a compressor in this embodiment, and FIG.
The figure is a block diagram of the code determination type decoding circuit shown in Figure 2, Figure 4 is a block diagram of the decoding device in this embodiment, Figure 5 is a flowchart showing the flow of encryption in the conventional example, and Figure 6 is a diagram showing the encryption function of FIG. 5; A...Signal conversion means B-----Data transmission means C-----Encryption means 1...-A/D 2...Compressor 4. ...Encryptor 5...-P/S 6...Transmission line 7...S/P 8--Decoder 10-- . . . Decoder 11 . . . D/A Note that the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] Signal conversion means for converting image/audio signals from analog to digital; data transmission means for transmitting the image/audio signals converted by the signal conversion means; and a portion of the digital image/audio data. An encryption/encoding device characterized by comprising: an encryption means for encrypting with an encryption key;