Information signal transmission system

Abstract

The information signal transmission system of the present invention is so designed as to convert the analog information signal into digital information data and to transmit these digital data after enciphering a part of the digital data. It can therefore maintain the secrecy of the transmitted information signal and can employ a low-speed enciphering process, thereby reducing the magnitude of hardware and reducing its cost.

Claims

What is claimed is:

1. An image processing method, comprising steps of:

a) inputting predictive encoded image data and reference image data which has been used for predictive encoding the predictive encoded data;

b) encrypting the reference image data; and

c) outputting the predictive encoded image data without encrypting and the encrypted reference image data, wherein an amount of data of the reference image data per a unit of image is larger than that of the predictive encoded image data.

2. A method according to claim 1, wherein the predictive encoded data is obtained by calculating differential data between the reference image data and image data following the reference image data.

3. A method according to claim 2, wherein the predictive encoded image data are prepared for plurality of units of image while the reference image data is prepared for one unit of image.

4. A method according to claim 1, wherein the predictive encoded image data is quantized for reducing an amount of data per a unit of image.

5. An image processing device, comprising:

a) inputting means for inputting predictive encoded image data and reference image data which has been used for predictive encoding the predictive encoded data;

b) encrypting means for encrypting the reference image data; and

c) outputting the predictive encoded image data without encrypting and the encrypted reference image data, wherein an amount of data of the reference image data per a unit of image is larger than that of the predictive encoded image data.

6. A device according to claim 5, further comprising predictive encoding means for predictive encoding image data to obtain the predictive encoded image data by calculating differential data between the reference image data and image data following the reference image data.

7. A device according to claim 6, wherein said predictive encoding means generates the predictive encoded data for plurality of units of image while the reference image data is input to said predictive encoding means.

8. A device according to claim 6, wherein said predictive encoding means quantizes the differential data for reducing an amount of data per a unit of image.

9. An image processing method, comprising steps of:

a) inputting first image data and second image data, the second image data having larger amount of information per a unit of image than the first image data;

b) encrypting the second image data;

c) outputting the first image data without encrypting; and

d) outputting the encrypted second image data.

10. A method according to claim 9, wherein the second image data has larger number of bits per a pixel than the first image data.

11. An image processing device, comprising:

a) inputting means for inputting first image data and second image data, the second image data having larger amount of information per a unit of image than the first image data;

b) encrypting means for encrypting the second image data;

c) means for outputting the first image data without encrypting; and

d) means for outputting the encrypted second image data.

12. A device according to claim 11, wherein the second image data has larger number of bits per a pixel than the first image data.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for transmitting information signals.

2. Related Background Art

In recent years there have been significant progresses in the definition of images, as exemplified by the television image from the NTSC system to the high-vision system. In the recording of such high-definition image on a recording medium such as a tape or a disk, or in the transmission of such image to a distant location by a satellite, an optical fiber or a cable, digital transmission is superior to analog transmission in consideration of factors deteriorating the image quality such as the S/N ratio of signal, jitter generation etc.

Such digital transmission provides an advantage that the image quality deterioration is not generated in record/reproducing systems employing tape or disk even after repeated dubbings, but may lead to a major social issue, because it facilitates frequent illegal copyings or dubbings. Also in a charged communication in a communication or broadcasting system utilizing satellite, optical fiber or cable, there may result illegal reception of information by unauthorized persons.

For this reason, in the conventional digital signal transmission, particularly in the data transmission particularly for computers, there has been employed a method of applying predetermined ciphering to all the data to be transmitted, and deciphering the data at the receiving side with cipher key data corresponding to said predetermined ciphering.

In the following there will be explained conventional examples of such ciphering, with reference to FIGS. 1 and 2.

FIG. 1 is a flow chart of a ciphering method of the U.S. data encryption standard (hereinafter called DES) disclosed in the FIPS gazette 46 of Jan. 15, 1977, and FIG. 2 is a flow chart of a method for forming the ciphering function shown in FIG. 1.

Such conventional data ciphering algorithm shown in FIGS. 1 and 2 is already published as "Data Encryption Standard" as mentioned above.

This data encryption standard will be explained in more details, with reference to FIGS. 1 and 2.

Said data encryption standard is a block cipher system for binary data consisting of "0" and "1". In this system, the ciphering is achieved by dividing the binary data into paired blocks of 32 bits each, and repeating transpositions and replacements to each block. The cipher key data have 64 bits, of which 56 bits are effective while the remaining 8 bits are error detection bits, and said key controls the replacement each time. FIG. 1 shows the process of ciphering in this system, and FIG. 2 shows a function fK(R) used as the core of ciphering.

Referring to FIG. 1, the binary data of 64 bits are at first subjected to a transposition, which is a predetermined process irrespective of the cipher key data. Then the binary data of 64 bits are divided into a left half L.sub.0 and a right half R.sub.0, which are then subjected to the following operations for 16 times:

L.sub.n =R.sub.n-1

R.sub.n =L.sub.n-1.sup.fK.sub.n (R.sub.n-1) (1)

wherein "+" indicates a sum of mod2 for each bit, while L.sub.n and R.sub.n are respectively the binary data of 32 bits of the left half and those of the right half after an n-th operation.

K.sub.n is formed from the cipher key data, as shown in the right half of FIG. 1, wherein s.sub.1 . . . , s.sub.16 are "1" or "2". The contractive transposition consists of a transposition with certain input bits excluded. For example 8 bits are excluded from the input 56 bits, so that the output becomes 48 bits. Said contractive transposition is an irreversible conversion, in which the input cannot be completely restored from the output, so that the estimation of the cipher key data is rendered more difficult.

The function fK.sub.n (R.sub.n) shown in FIG. 1 will be explained further in the following, with reference to FIG. 2.

For forming the function fK.sub.n (R.sub.n), at first R.sub.n (binary data of 32 bits of the right half) are subjected to an expansive transposition, which is a transposition with certain input bits overlapped. In this case, 16 bits out of the 32 input bits appear in overlapping manner in the output. Then K.sub.n, formed from the cipher key data, is added to said output, bit by bit in mod2. The output of 48 bits thus obtained is divided into 8 small blocks of 6 bits each, and each 6 bits are converted into 4 bits by S.sub.1, S.sub.2, . . . S.sub.8. This operation can be regarded as a kind of replacement, taking 6 bits as a character, but this conversion is irreversible because the output is compressed to 4 bits. Consequently the function fK.sub.n (R.sub.n) is generally an irreversible function, but this does not mean that the conversions of equations (1) are irreversible. In fact said equations (1) can be transformed as:

R.sub.n-1 =L.sub.n

L.sub.n-1 =R.sub.n +fK.sub.n (R.sub.n-1)=R.sub.n +fK.sub.n (L.sub.n)}(2)

so that L.sub.n-1, R.sub.n-1 can be calculated from L.sub.n, R.sub.n.

L.sub.16 and R.sub.16, obtained by repeating the operation of the equations (1) 16 times, are finally subjected to a transposition to complete the ciphering.

The deciphering is conducted by a process substantially inverse to the ciphering process, namely a process proceeding from bottom to top in FIG. 1. At first there is conducted a transposition inverse to the final transposition in ciphering process. Then R.sub.n-1, L.sub.n-1 are determined according to the equations (2), and R.sub.0, L.sub.0 obtained in this manner are subjected to a transposition inverse to the initial transposition in the ciphering process to obtain the initial 64 bits.

The only way so far known for breaking the data enciphered by this system is to investigate the cipher key data one by one. If a key requires 1 microsecond for investigation, the entire key of 2.sup.56 combinations requires 2283 years, or at least several hundred years with a good luck, so that this system is practically unbreakable.

In case of digital transmission of high-definition television signal, such as the high-vision signal, with ciphering, if the analog image signal is simply A/D converted for transmission, the sampling rate has to be at least 60 MHz, according to the sampling theory, in order to secure an image signal bandwidth for example 30 MHz for preventing the deterioration in image quality. For a sampling frequency of 74.25 MHz and an A/D conversion of 8-bit digitization per sample, the signal transfer rate becomes 74.25 (MHz).times.8 (bit)=594 Mbit/s. Even if the data are compressed to 1/5 for reducing the amount of transmitted information, the transfer rate becomes as high as about 120 Mbit/s. The enciphering of such enormous amount of information requires a high-speed process in the ciphering circuit, and is extremely difficult in the magnitude of hardware and in the increased cost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an information signal transmission system capable of resolving the drawbacks mentioned above.

Another object of the present invention is to provide an information signal transmission system capable of maintaining the secrecy of information in the transmission of information signal.

In an aspect of the present invention, the foregoing objects can be attained by an information signal transmission system comprising:

conversion means for converting analog information signal into digital information data;

cipher means for enciphering a part of the digital information data released from said conversion means; and

transmission means for transmitting the digital information data of which a part is enciphered by said cipher means.

Still another object of the present invention is to provide an information signal transmission system capable of reducing the speed of enciphering processing, thereby compactizing the hardware and reducing the cost.

In another aspect of the present invention, the foregoing object can be attained by an information signal transmission system comprising:

conversion means for converting analog information signal into digital information data;

data compression means for applying a data compression process to the digital information data released from said conversion means, thereby forming compressed data;

cipher means for enciphering a part of the compressed data released from said data compression means; and

transmission means for transmitting the compressed data, of which a part is enciphered by said cipher means.

The foregoing and still other objects of the present invention, and the features thereof, will become fully apparent from the following detailed description of the embodiments, which is to be taken in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a conventional ciphering process;

FIG. 2 is a flow chart showing a method for forming a function to be employed in the enciphering process shown in FIG. 1;

FIG. 3 is a block diagram of an information signal transmission system constituting a first embodiment of the present invention;

FIG. 4 is a block diagram of a compressor in the information signal transmission system shown in FIG. 3;

FIG. 5 is a block diagram of a sign determining decoding circuit in the compressor shown in FIG. 4;

FIG. 6 is a block diagram of a decoder in the information signal transmission system shown in FIG. 3;

FIG. 7 is a block diagram of an information signal transmission system constituting a second embodiment of the present invention;

FIG. 8 is a view showing the format of transmitted data in the information signal transmission system shown in FIG. 7;

FIG. 9 is a block diagram, as a third embodiment of the present invention, showing a compressor in the information signal transmission system shown in FIG. 7;

FIG. 10 is a block diagram, as a second embodiment of the present invention, showing a decoder in the information signal transmission system shown in FIG. 7;

FIG. 11 is a block diagram, as a third embodiment of the present invention, showing a compressor in the information signal transmission system shown in FIG. 7;

FIG. 12 is a view of all sample data of an image frame divided into plural sample blocks, in the information signal transmission system of the third embodiment;

FIG. 13 is a view of each of the sample blocks shown in FIG. 12;

FIG. 14 is a view showing functions of the compressor and the decoder in the information signal transmission system of the third embodiment, wherein (a) shows the state of digitization in a division value converting circuit in the compressor shown in FIG. 9, while (b) indicates the state of decoding in the decoder;

FIG. 15 is a view showing the format of the transmitted data in the information signal transmission system of the third embodiment; and

FIG. 16 is a block diagram showing, in the third embodiment of the present invention, a decoder in the information signal transmission system shown in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now the present invention will be clarified in detail by preferred embodiments thereof.

FIG. 3 is a block diagram of an information signal transmission system constituting a first embodiment of the present invention.

Said system is so constructed as to compress 8-bit data, corresponding to a sample, to 4-bit data, and to transmit said compressed data after enciphering of MSB (most significant bit) only.

In FIG. 3, there are shown an A/D converter 1 for converting an analog video signal into a digital video signal of 8 bits per sample; a transmission channel 6 such as an optical fiber or a cable, or a recording system such as a tape or a disk; an enciphering unit 4 for enciphering only the 1-bit data of the MSB of 4-bit data released from a compressor 2 to be explained later, according to 64-bit cipher key data confidentially determined in advance between the transmitter and the receiver; a compressor 2 for compressing 8-bit digital video signal into 4-bit data; a distributor 3 for separating the 4-bit data released from the compressor 2 into the 1-bit data of the MSB and the remaining 3-bit data; a parallel-serial converter 5 for receiving the 1-bit MSB data enciphered by said enciphering unit 4 and the other unciphered 3-bit data in parallel manner and serially releasing these data to the receiving side through the transmission channel 6; a serial-parallel converter 7 for separating the data, transmitted through said transmission channel 6, into the 1-bit data of the MSB and the other 3-bit data; a deciphering unit 8 for deciphering said enciphered MSB data according to the 64-bit cipher key data determined, as explained above, in advance between the transmitter and the receiver; a coupler 9 for coupling the 1-bit MSB data deciphered by said deciphering unit 8 and the other 3-bit data released from the serial-parallel converter 7 to release 4-bit data; a decoder 10 for expanding the 4-bit data, released from said coupler 9, to 8-bit data; and a D/A converter 11 for converting the 8-bit data, released from said decoder 10, into an analog video signal.

In the following there will be explained the function of the present first embodiment.

At first explained is the data compressing operation. For compressed transmission of data obtained by digitizing a signal with a large amount of information, such as an image signal, there is already known a DPCM (differential pulse code modulation) method. This method achieves data compression by predicting the value of a sample point currently subjected to encoding, from the value of already encoded sample point, and encoding the difference (prediction error) between said predicted value and the true value, and is capable of a highly efficient encoding in a signal having a high correlation between the values of mutually close sample points, such as an image signal, by effecting a non-linear digitization in consideration for example of the deviation in the distribution of predicted errors.

FIG. 4 is a block diagram showing the structure of the compressor 2 shown in FIG. 1, for compressing 8-bit data into 4-bit data, and FIG. 5 is a block diagram showing the structure of a sign determining decoding circuit in said compressor 2. FIG. 6 is a block diagram showing the structure of the decoder 10 shown in FIG. 1.

Referring to FIG. 4, the digital video signal is supplied, in a unit of 8 bits, to an input terminal 101, then is limited within a certain range, for example within a range of digital levels of "16" to "235", by a limiter 108, and is subjected, in a subtraction circuit 102, to the calculation of difference (prediction error) from the predicted value released from a prediction coefficient multiplying circuit 103. Said predicted error data are supplied to a sign multiplexing digitizing circuit 104, which digitizes the predicted error data of 9 bits including a plus/minus sign into 4-bit data, based on digitizing characteristics in which a same value is assigned to positive and negative data as shown in Table 1. The obtained 4-bit digital data are released from an output terminal 105 and also supplied to the sign determining decoding circuit 106.

                  TABLE 1
    ______________________________________
    + side              - side
    Digitized        representa-        representa-
    value            tive value         tive value
    ______________________________________
    0       0        0
    1       1.about.4
                     1          -219    -219
    2        5.about.10
                     5          -218.about.-215
                                        -215
    3       11.about.20
                     11         -214.about.-209
                                        -209
    4       21.about.35
                     21         -208.about.-199
                                        -199
    5       36.about.55
                     36         -198.about.-184
                                        -184
    6       56.about.79
                     56         -183.about.-164
                                        -164
    7        80.about.109
                     80         -163.about.-140
                                        -140
    8       110.about.139
                     110        -139.about.-110
                                        -110
    9       140.about.163
                     140        -109.about.-80
                                        -80
    10      164.about.183
                     164        -79.about.-56
                                        -56
    11      184.about.198
                     184        -55.about.-36
                                        -36
    12      199.about.208
                     199        -35.about.-21
                                        -21
    13      209.about.214
                     209        -20.about.-11
                                        -11
    14      215.about.218
                     215        -10.about.-5
                                        -5
    15      219      219        -4.about.-1
                                        -1
    ______________________________________

• Inventors
  Enari, Masahiko;
• Assignee
  Canon Kabushiki Kaisha (Tokyo, JP)
• Published
  Dec-22-1998
• Current US Classes:
  380/217
  380/29
  380/37
  382/238
• Application #
  870461
• International Classes
  H04N 007/167; H04N 001/44; H04L 009/00
• Field of Search
  380/10 380/18 380/20 380/21 380/29 380/37
• Examiner
  Buczinski; Stephen C
• Agent
  Robin, Blecker & Daley
• US Patent References:
  3956615
  4694491
  4739510
  4752953
  4817146
  4916736
  5062136
  5398283