Method for Encryption and Decryption of Color Image Signals

Abstract: An image processing system includes an image processing apparatus having an encrypting circuit for reading an image of an original, converting the read image into an image signal, and encrypting the image signal by using data concerning encryption, a transmitting unit for transmitting the encrypted image signal to another image processing apparatus, and an image processing apparatus for receiving the encrypted, transmitted image signal and decrypting the signal by using the data concerning encryption.

Description: The present invention relates to colour image processing and the encryption and decryption of image signals. Recently, as the performance of color copying machines has been improved, crimes of forging documents, such as paper monies or securities, by using these copying machines illegally have increased in number. To prevent such crimes, a system has been studied in which data of image patterns representing documents, such as paper monies and securities, are registered in a copying machine itself beforehand, and an image identifying circuit identifies these registered data, thereby forcibly inhibiting illegal copying in accordance with the identification result. However, since the number of registrable image patterns is limited in a forgery preventing circuit of this type, it is impossible to register all available documents, such as paper monies and securities. In addition, in the case of a color copying machine separable into a reader unit and a printer unit, even when a document consistent with a registered image pattern is to be copied, the circuit of the above sort cannot function if the original reader unit is replaced with another reader unit. Also, connecting an unsuitable apparatus to the copying machine, even though it is not an illegal use as described above, lowers the signal level due to impedance mismatch between the two apparatuses, resulting in an adverse influence, such as an increase in noise of an image signal. This may interfere with the operation of the color copying machine main body and consequently introduce disadvantages to users. DE-A-4021061 discloses a black-and-white facsimile telecopier in which one or more rows of the image dots is scrambled to change the sequence and/or relative positions. Empty spaces formed during the scrambling process are occupied by dots generated by a random number generator. The coding for the scrambling is arranged with the sender prior to sending the image data. WO-A-9111884 discloses a system in which satellite television signal transmissions are encoded and descrambled. The program signal is scrambled with a key and then the key itself is twice-encrypted and multiplexed with the scrambled program signal. Decoding is performed making use of a replaceable security module in the decryption of the key. According to the invention, there is provided a colour image processing system as set out in claim 1. The invention also provides a colour image processing apparatus as set out in claim 12 and claim 16. The invention also provides a method of operating a colour image processing system as set out in claim 19. The invention further provides a method of operating a colour image processing apparatus as set out in claim 20 and claim 24. Optional features are set out in the other claims. An embodiment of the present invention provides an image processing apparatus or system capable of preventing, with an inexpensive arrangement, illegal uses which may be caused by connecting an image processing apparatus with an inadequate interface in performing transmission/reception of image signals between the image processing apparatuses, thereby eliminating adverse influences on the main image processing apparatus to introduce no disadvantages to users. An embodiment of the present invention uses an encrypting method suitable for multivalued image data. Other features and advantages of embodiments will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof, and in which: Fig. 1 is a block diagram showing a first reference image processing system; Fig. 2 is a timing chart showing control timings between signals; Fig. 3 is a flow chart for explaining the operation of a color copying apparatus 5 according to the first reference system; Fig. 4 is a block diagram showing an image processing system according to a second reference system; Fig. 5 is a timing chart showing control timings between signals according to the second reference system; Fig. 6 is a block diagram showing the circuit configuration of a main part of an image processing system according to a first embodiment of the present invention; and Fig 7 is a block diagram showing the circuit configuration of a main part of an image processing system according to a second embodiment of the present invention. 〈1st Reference System〉 Fig. 1 is a block diagram showing a first reference processing system. Referring to Fig. 1, this system is separated into a color copying apparatus 5 incorporating a scanner unit 12 and a printer unit 13, and an external controller 4 as an interface for performing input/output of color images with respect to an external image processing apparatus. The color copying apparatus 5 may, of course, be constituted by a scanner and a printer independent of each other. The color copying apparatus 5 and the external controller 4 are electrically connected to each other through a signal line for transmitting an image information signal 1 as color image data and a signal line for transmitting an encryption information signal 2 as information concerning encryption. The encryption information signal 2 is a signal for transmitting information concerning encryption as described below and is exchanged through a bidirectional signal line. When color image data is input from the scanner unit 12 of the color copying apparatus 5, the encryption information signal 2 is supplied from the color copying apparatus 5 to the external controller 4. The encrypted image information signal 1 is decrypted in accordance with the encryption information signal 2 by an encrypting circuit 21 and an image processing circuit 20 of the external controller 4. When color image data is output from the external controller 4 to the printer unit 13 of the color copying apparatus 5, the encryption information signal 2 is supplied from the external controller 4 to the color copying apparatus 5. The encrypted image information signal 1 is decrypted by an encrypting circuit 11 and an image processing circuit 10 of the color copying apparatus 5. Note that image clocks, image sync signals, communication lines for performing condition control of the apparatus, and the like are omitted from Fig. 1. The color copying apparatus 5 incorporates the encrypting circuit 11 for controlling the image processing circuit 10. The encrypting circuit 11 performs encryption in transmitting color image data to the external controller 4 and decryption upon receiving color image data from the external controller 4. That is, in sending color image data read by the scanner unit 12 to the external controller 4, the encrypting circuit 11 generates data related to encryption to be supplied to the external controller 4. When color image data is supplied from the external controller 4 to the printer unit 13, the encrypting circuit 11 generates data for decrypting the data from the external controller 4. In the color copying apparatus 5, encryption is performed when color image data is to be supplied to the external controller 4, and decryption, which is the inverse process of encryption, is performed when color image data is supplied from the external controller 4 to the printer unit 13; these two modes are executed by a combination of the encrypting circuit 11 and the image processing circuit 10. There is another mode, a forgery preventing mode of the color copying apparatus itself. A configuration for this mode is incorporated in the image processing circuit 10. That is, a determining circuit is incorporated as a forgery preventing function to be executed when the printer unit 13 is to copy an image read by the scanner unit 12. If this determining circuit determines that copying is for forgery, the printer unit 13 is disabled to perform a copying operation. The external controller 4 includes the encrypting circuit 21 and the image processing circuit 20, which performs decryption of the image information signal 1 directly or indirectly upon receiving the encryption information signal 2. When the external controller 4 is connected to a host computer, the image processing circuit 20 directly encrypts color image data supplied from the host computer. In this case, the image processing circuit executes the encryption by receiving an encrypting instruction from the encrypting circuit 21. The external controller 4 performs encryption in sending color image data to the color copying apparatus 5 and decryption upon receiving color image data from the color copying apparatus 5. These encryption and decryption are executed by a combination of the encrypting circuit 21 and the image processing circuit 20. It should be noted that a plurality of types of encrypting methods are used. The operation of this reference system will be described in detail below. Fig. 2 is a timing chart showing control timings for the image information signal 1, the encryption information signal 2, an image clock, and a sync signal. The image clock is a clock signal serving as a reference for other signals. Referring to Fig. 2, the scanner unit reads in data of each image information signal at the leading edge of the image clock. The sync signal is used as both a sync signal for use between lines of raster image signals and a sync signal for switching the contents of the encryption information signal 2 into a pattern (1) at a leading edge (A) and a pattern (2) at a leading edge (B). Each pattern represents the encryption signal described above and contains a number indicating the type of encryption, numerical information concerning synchronization, and the like. According to the system as described above, a cryptogram understandable only between the external controller 4 and the color copying apparatus 5, which have the same specifications, is used. The use of this cryptogram can prevent replacement with an illegal external controller incapable of decrypting the cryptogram, for example, an external controller for forgery purposes. This can effectively make it very difficult for a third person to use the system for forgery purposes. An operation related to forgery prevention will be described first. Fig. 3 is a flow chart for explaining the operation of the color copying apparatus 5. Note that the operation explained below is controlled entirely by a CPU (not shown) of the color copying apparatus 5. In steps S10, S12, and S14, any of a copy instruction from a copy start key (not shown), a print instruction from the external controller 4, and an original read instruction from the external controller 4 is detected. If the copy instruction is detected, the scanner unit 12 reads an original (step S16), and a determining circuit (not shown) executes forgery determination based on the color image data read from the original (step S18). If the determining circuit determines that the read image is an image the copying of which is prohibited, the use of the printer unit 13 is inhibited (step S22). If the determining circuit determines that the image is not an object of copy prohibition, the read color image data of the original is transferred to the printer unit 13 and recorded on recording paper (step S24). If the print instruction from the external controller 4 is detected in step S12, as shown in the timing chart of Fig. 2, the encryption information signal and the color image data are supplied and at the same time decryption is performed (steps S26 and S28). In the processing operations in steps S26 and S28, if the cryptogram input processing and the decryption cannot be performed normally, as when an encryption information signal of another specification is input to disable decryption, for example, when the number of digits of data concerning encryption is detected to be different from a predetermined number, the printer unit 13 prints out an abnormal image (step S34). On the other hand, when the encryption information signal input and the decrypting are performed normally, the color image data is acquired from the external controller 4 and recorded on a recording paper by the printer unit 13 (step S32). Note that whether the cryptogram input processing and the decryption are performed normally may be detected by another method. If the original read instruction from the external controller 4 is detected in step S14, the scanner unit 12 reads an original image (step S36), and an encryption information signal is formed. The encryption information signal and the color image data are output to the external controller 4, as shown in the timing chart of Fig. 2 (step S38). When the external controller 4 performs decryption normally, the external controller 4 is allowed to send the color image data decryption normally to an external device, such as a host computer connected to the external controller 4; if not normally, the external device, such as a host computer, will receive unreproducible data. This eventually results in an inability to perform normal printing and hence in failing of forgery. In the above operation, even if a user does not have a strict security as to the management of the color copying apparatus and the external controller so that no other third person is allowed to operate the apparatuses, forgery prevention can be realized satisfactorily without using the internal determining circuit of the color copying apparatus. In particular, since the color copying apparatus 5 or the external controller 4 arbitrarily determines the type of encryption, the printer unit can be controlled to be inoperable even if the image processing circuit of the color copying apparatus 5 or the external controller 4 is replaced with another. 〈2nd Reference System〉 The above first reference system employs a method using an encryption information signal and an image information signal independent of each other. In the second reference system, a method using a composite signal of an encryption information signal and an image information signal is used. Fig. 4 is a block diagram showing an image processing system according to the second reference system. This system brings about an effect of making illegal uses more difficult by reducing the number of signal lines by combining them and by consolidating information concerning encryption and color image data together. In this system, an external controller 34 as one apparatus comprises an encrypting circuit 51 and an image processing circuit 50, as in the first reference system while a color copying apparatus 35 as the other apparatus comprises an encrypting circuit 45, an image processing circuit 40, a scanner unit 42, and a printer unit 43. A composite image information signal 31 which is a combination of the encryption information signal 2 and the image information signal 1 described above with reference to Fig. 1 is exchanged between the image processing circuits 50 and 40. Since the signals are combined in the external controller 34 and the color copying apparatus 35, the interconnection between the image processing circuit 10, the encrypting circuit 11, the image processing circuit 20, and the decrypting circuit (not shown) shown in Fig. 1 is altered to an interconnection between the image processing circuit 40, the encrypting circuit 45, the image processing circuit 50, and a decrypting circuit (not shown). Fig. 5 is a timing chart showing control timings among an image clock, a composite image information signal, and a sync signal. Referring to Fig. 5, in contrast to the timing chart of Fig. 2 explained above, a pattern (1) or (2), i.e., information such as a number indicating the type of encryption and numerical information associated with synchronization are output during an effective period (period of level HIGH) of the sync signal, and an image information signal is output during an ineffective period (period of level LOW) of the sync signal, thereby performing decryption. In this manner, the image information signal and the encryption information signal can be transmitted together through a single signal line, so the number of signal lines is reduced. In using the color copying apparatus 35 as an independent scanner or printer, the image processing circuit 40 and the encrypting circuit 45 operate in association with each other to mix the encryption information signal with the image information signal or to put the encryption pattern into the image, thereby outputting the composite image information signal to the external controller 34. When the image information signal (color image data) as a portion of the composite image information signal 31 is to be supplied from the scanner unit 42 to the external controller 34, the signal is sent from the color copying apparatus 35 to the external controller 34; when this portion is to be supplied to the printer unit 43, the signal is sent from the external controller 34 to the color copying apparatus 35. That is, bidirectional data transmission is performed. In the external controller 34, regardless of whether the color copying apparatus 35 is used as an independent scanner or printer, the image processing circuit 50 and the encrypting circuit 51 operate in association with each other to separate the encryption information signal, which is mixed in the composite image information signal 31 supplied from the color copying apparatus 35, from the composite image signal 31, thereby performing encryption and decryption. The overall operation of this system is the same as that of the first reference system described above with reference to Fig. 3 and a detailed description thereof will be omitted. According to the second reference system as described above, a composite information signal which is not easy to be separated or decrypted can be obtained by combining signals. This further enhances the effect of preventing illegal uses such as forgery. Embodiments of the present invention will now be described. 〈1st Embodiment〉 Encryption for changing the input timing of an image information signal in real will be described below in accordance with a first embodiment of the present invention. The first embodiment is an example of encryption in which a timing at which effective image data is transmitted is changed for each line after the sync signal shown in Fig. 2 becomes effective. In this embodiment, therefore, the description will be made in accordance with an arrangement for transmitting an image from a controller unit to a printer unit. Fig. 6 is a block diagram showing the circuit configuration of a main part of an image processing system according to the first embodiment. Referring to Fig. 6, a printer unit comprises a sync signal generating circuit 130, a random number generating circuit 131, a synchronous counter 132, and a first-in first-out memory (to be referred to as a "FIFO" hereinafter) 133. A controller unit comprises a synchronous counter 140 and a FIFO 141. Parts with no reference numerals are the controller unit and the printer unit, each for use in the processing described above in the previous reference systems, an image processing unit for actually performing image processing in an image processing circuit, and a recording unit for actually performing recording in the printer unit. Signals are a sync signal 150, an image information signal 151, and an encryption information signal 152. The operation of the above arrangement will be described below. The sync signal generating circuit 130 generates the sync signal 150 corresponding to the sync signal shown in Fig. 2. The random number generating circuit 131 randomly generates, in synchronism with the sync signal 150, a clock number by which an effective image information signal is sent after the sync signal becomes effective. For example, the random number generating circuit 131 generates an integer, such as a numeric value "10" or "15", in synchronism with the sync signal 150. This numeric value is information to be sent as the encryption information signal 152. The synchronous counter 140 temporarily stores color image data supplied from the image processing unit of the image processing circuit into the FIFO 141 and changes, in accordance with the encryption information signal 152, a timing at which this color image data is read out from the FIFO 141. That is, the synchronous counter 140 receives the encryption information signal 152 at its initial value set input terminal, counts a timing at which data is to be read out from the FIFO 141, and changes the read timing in accordance with data generated by the random number generating circuit 131, i.e., the image information signal 151. In this manner, the image information signal 151 shown in Fig. 6 is output to the recording unit as a signal having sync timings different between lines. In the printer unit, on the other hand, in storing the image information signal 151 in the FIFO 133, the signal is stored from color image data corresponding to the leading end of an image in accordance with the timing signal generated by the synchronous counter 132. Therefore, the signal read out from the FIFO 133 and sent to the recording unit is a synchronized signal. According to the first embodiment as described above, forgery prevention can be realized with a relatively simple circuit configuration. 〈2nd Embodiment〉 The second embodiment of the present invention uses a method of changing an image information signal itself in real time in performing encryption. More specifically, in the second embodiment, a plurality of data conversion patterns are prepared beforehand by using a look-up table (to be referred to as an "LUT" hereinafter) and selected in a random manner to perform encryption of an image information signal. Fig. 7 is a block diagram showing the circuit configuration of a main part of an image processing system according to the second embodiment. Referring to Fig. 7, a printer unit comprises a sync signal generating circuit 260, a random number generating circuit 261, and an LUT 262 for storing a plurality of data conversion patterns as described above. A control unit comprises an LUT 270 which also stores a plurality of data conversion patterns as described above. Parts with no reference numerals are the controller unit and the printer unit, each for use in the processing described above, an image processing unit for actually performing image processing in an image processing circuit, and a recording unit for actually performing recording in the printer unit. Signals are a sync signal 280, an image information signal 281, and an encryption information signal 282. The operation of the above arrangement will be described below. Referring to Fig. 7, the sync signal generating circuit 260 generates the sync signal 280 corresponding to the sync signal shown in Fig. 2. The random number generating circuit 261 randomly generates, in synchronism with the sync signal 280, a pattern number to be selected from the image conversion table. The random number generating circuit 261 generates an integer, such as a numeric value "9" or "14", in synchronism with the sync signal 280. This numeric value is information to be sent as the encryption information signal 282. The LUT 270 executes image conversion for color image data supplied from the image processing unit in accordance with the data conversion pattern corresponding to the encryption information signal 282. That is, the LUT 270 connects the encryption information signal 282 to bits pattern select input terminal to execute conversion of the image data. The image information signal 281 is transmitted to the LUT 262 as data image-converted by the LUT 270. In the printer unit, on the other hand, upon receiving the image information signal 281, the LUT 262 selects a data conversion pattern which is for a reverse process of the data conversion pattern used by the LUT 270 in accordance with the random number generated by the random number generating circuit 261, thereby executing processing for restoring the original color image data. In this manner, as in the first embodiment, illegal use prevention can be realized with a relatively simple circuit configuration. Note that each of the above embodiments makes use of a relatively simple encrypting method. However, the use of a more complicated encrypting method further enhances the effect of the embodiments. In addition, a combination of an arrangement in which encryption information is transmitted by using a communication line through which commands or statuses concerning operations are exchanged, and the arrangement of performing encryption according to any of the above embodiments, makes it possible to construct a sophisticated encrypting environment where apparatuses cannot be easily used by a third person. The present invention is not limited to a system in which an external controller is connected to a colour copying apparatus through a bus. For example, an external controller may be detachably provided, like a cassette, to a color copying apparatus. Note that the present invention may be applied to either a system constituted by a plurality of devices or an apparatus comprising a single device. Note also that embodiments of the present invention can be achieved by supplying programs to a system or an apparatus. The present invention is not limited to a color copying machine but can be applied to any system where signals are transmitted/received between image processing apparatuses, for example, between an image reading apparatus, such as a scanner or a camera, and an image storage apparatus, and between an image storage apparatus and an image forming apparatus, such as a printer or a CRT. Many widely different embodiments of the present invention can be made, and the invention is not limited to the specific embodiments thereof.

Claims: A color image processing system, comprising: a color image data encryption apparatus having encrypting means (141; 270) for encrypting a color image signal on the basis of encryption data (152; 282); and a color image data decryption apparatus having decrypting means (133; 262) for decrypting the encrypted color image signal (151; 281) received from the encryption apparatus on the basis of the encryption data, and signal processing means for performing predetermined image processing on the decrypted color image signal; wherein: the encryption apparatus and the decryption apparatus are controlled such that the encrypted color image signal (151; 281) is transmitted from the encryption apparatus to the decryption apparatus, and characterised in that: the encryption data (152; 282) is generated in the decryption apparatus and is transmitted from the decryption apparatus to the encryption apparatus so as to change the encryption of the color image signal. A system according to claim 1, wherein said encryption data is transmitted at a predetermined timing relative to the transmission of the encrypted color image signal. A system according to claim 1 or claim 2, wherein said encryption data is transmitted so as to change the encryption for each scan line of the color image signal. A system according to any preceding claim, wherein said encryption apparatus or said decryption apparatus comprises an image storing device. A system according to any preceding claim, wherein the decryption apparatus includes means (131, 261) for generating said encryption data as a random number. A system according to any preceding claim, comprising first and second communiction lines connecting the encryption apparatus and the decryption apparatus, and wherein the system is controlled such that said encryption data and the encrypted color image signal are communicated via different communication lines. A system according to any preceding claim, wherein said encryption and decryption means include complementary data conversion look-up tables (270, 262) selectable in response to said encryption data. A system according to any preceding claim, wherein said encryption apparatus further comprises generating means for generating the color image signal. A system according to claim 8, wherein said encryption apparatus comprises an image reading apparatus for reading the image of an original document to generate the color image signal. A system according to any preceding claim, wherein said decryption apparatus comprises an image forming apparatus for printing an image in accordance with the decrypted color image signal. A system according to claim 10 when dependent on claim 9, comprising a digital color copier. A color image data encryption apparatus, comprising: encrypting means (141; 270) for encrypting a color image signal using encryption data; and communication means for communicating the encrypted color image signal (151; 281) to a color image data decryption apparatus; characterised by: reception means (140; 270) for receiving said encryption data (152; 282) from said decryption apparatus so as to change the encryption. An apparatus according to claim 12, wherein the apparatus comprises a controller. An apparatus according to claim 12, further comprising generating means for generating the color image signal. An apparatus according to claim 14, wherein the apparatus comprises a scanner or a color copying machine. A color image data decryption apparatus, comprising: means for receiving from a color image data encryption apparatus an encrypted color image signal (151; 281) encrypted using encryption data; decrypting means (133; 262) for decrypting the encrypted color image signal using the encryption data; and signal processing means for performing predetermined image processing on the decrypted color image signal; characterised by: means (131; 261) for generating said encryption data (152; 282); and communication means for communicating the encryption data to the encryption apparatus so as to change the encryption. An apparatus according to claim 16, wherein the apparatus comprises an image forming apparatus. An apparatus according to claim 17, wherein the apparatus comprises a printer or a color copying machine. A method of operating a color image processing system comprising a color image data encryption apparatus having encrypting means (141; 270) for encrypting a color image signal on the basis of encryption data (152; 282), and a color image data decryption apparatus having decrypting means (133; 262) for decrypting the encrypted color image signal (151; 281) received from the encryption apparatus on the basis of the encryption data, and signal processing means for performing predetermined image processing on the decrypted color image signal, said method comprising controlling the encryption apparatus and the decryption apparatus such that the encrypted color image signal (151; 281) is transmitted from the encryption apparatus to the decryption apparatus and characterised in that the encryption data (152; 282) is generated in the decryption apparatus and is transmitted from the decryption apparatus to the encryption apparatus so as to change the encryption of the color image signal. A method of operating a color image data encryption apparatus, comprising the steps of: encrypting a color image signal using encryption data; and communicating the encrypted color image signal (151; 281) to a color image data decryption apparatus; characterised by: receiving said encryption data (152; 282) from said decryption apparatus so as to change the encryption. A method according to claim 20, wherein the encryption apparatus comprises a controller. A method according to claim 20, further comprising the step of generating the color image signal. A method according to claim 22, wherein the encryption apparatus comprises a scanner or a color copying machine. A method of operating a color image data decryption apparatus, comprising the steps of: receiving from a color image data encryption apparatus an encrypted color image signal (151; 281) encrypted using encryption data; decrypting the encrypted color image signal using the encryption data; and performing predetermined image processing on the decrypted color image signal; characterised by: generating said encryption data (152; 282); and communicating the encryption data to the encryption apparatus so as to change the encryption. A method according to claim 24, wherein the decryption apparatus comprises an image forming apparatus. A method according to claim 25, wherein the decryption apparatus comprises a printer or a color copying machine.

Inventors: KURITA MITSURU, NAGASHIMA NAO, SUZUKI YASUMICHI, KURITA, MITSURU, NAGASHIMA, NAO, SUZUKI, YASUMICHI, KURITA, MITSURU, C/O CANON KABUSHIKI KAISHA, Nagashima, Nao, c/o Canon Kabushiki Kaisha, SUZUKI, YASUMICHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: H04N1
IPC codes: H04N1