Method and apparatus for secure data transmission via network

A method and apparatus for secure data transmission via network. Transmission side transmits processed data (DB), second signed data (SB, 740) obtained by applying one-way function to merged data of the processed data (DB) and first signed data of an original image and ciphering the output of the one-way function with transmission side secret key, and ciphered signed data (SAE) obtained by ciphering the first signed data with reception side public key. Data reception side enciphers received ciphered signed data (SAE′) with reception side secret key to obtain third signed data (SA′), applies one-way function to merged data (DC′) of received processed data (DB′) and the third signed data (SA′), enciphers received second signed data (SB′) with transmission side public key (KDB), compares result obtained by applying the one-way function to the merged data with result obtained by enciphering the second signed data for data valification.

BACKGROUND OF THE INVENTION

The present invention relates to security in exchanging data via a network, and particularly relates to security in transmitting an original image or processed data of a partial image or the like produced by working the original image when an image obtained by scanning a form, chit, slip or the like is electronically exchanged via a network.

As technology relating to security in data transmission, for example, there has been known a digital signature disclosed, for example, in S. Tujii and M. Kasahara: Cryptography and Information Security, p. 127–139, SHOKODO (1999).

SUMMARY OF THE INVENTION

FIG. 7is a block diagram showing an example of the configuration of a data transmission apparatus for transmitting data obtained by working or processing an input image of a form or the like.

When data is transmitted between a branch office A1000and a processing center1005connected via a network1010as shown inFIG. 7, a data reception side can verify that received data was transmitted from a proper transmission side, and can verify that the received data has not been substituted. Such verification is realized by public public key cryptography using a secret key and a public public key produced by the transmission side.

FIG. 2Ashows an example of processing flow of data transmission using a digital signature in the data transmission apparatus shown inFIG. 7. Object data DA to be transmitted is obtained (Step200). A hash function is applied to the object data DA (Step205). The output of the hash function is ciphered with a secret key KEA of the data transmission side so that signed data SA is produced (Step210). The data DA and SA are transmitted to the data reception side (Step215). On the other hand,FIG. 2Bshows an example of processing flow for verifying the validity of the transmitted data. Object data DA′ and signed data SA′ are obtained (Step220). A hash function is applied to the data DA′ (Step225). The signed data SA′ is enciphered with a public key KDA distributed in advance (Step230). Then, the results of Step225and Step230are compared (Step235), and the validity of the data is verified on the basis of the result of the comparison (Step240). Here, it is concluded that there has been no illegal act if the compared data are coincident with each other, and there was some illegal act if they are not coincident with each other.

However, there is no way to verify whether the processed data was produced from the original image or not and carry out the aforementioned verification at the same time. Further, if the data has been substituted, there is no way to find the original image.

In governmental or non-governmental offices dealing with a vast volume of forms, slips, chits or the like, there are needs to convert paper media into digital media and connect deployed centers and branch offices to use the digital media to thereby speed up services. To satisfy such needs, there has appeared a configuration of service in which paper media are converted into images and the images are applied to a work flow. In such a configuration, processed data such as partial images required for services are managed on account of efficiency in data transmission or the like. Such partial images of a medical/insurance document as shown inFIG. 6, of original images, partial images required for services, for example, a reference number, a consultation month, a medical code, a room number, a birth date, etc. are cut out or picked up and transmitted from the branch office A1000to the processing center1005via the network1010inFIG. 7. If the whole of the original image is to be transmitted, the volume of data becomes large. In addition, if the original image is displayed, there is a fear that information involving privacy leaks out. Therefore, required partial images are cut out or picked up and transmitted from the branch office A to the processing center. Operators engage in data input service while viewing the displayed partial images.

However, when data is transmitted via a network, original images or processed data flowing on the network may be eavesdropped or listened in or illegally substituted partially or wholly. Further, illegal transactions may be achieved by impersonation. It is desired to prevent such problems. In order to prevent such problems, it is necessary to verify an illegal act of substitution based on impersonation.

As a method of the verification, a digital signature based on public key cryptography has been known as described above. However, if the original image or the processed data per se is listened in and a secret key used in an image input portion or a processed data processing portion is stolen, the eavesdropper or listener-in may substitute the original image or the processed data easily or transmit data to a transmission line by impersonation. Thus, there arises a problem that the data reception side cannot detect such an illegal act and may be deceived and make an inappropriate process. Therefore, it is desired to provide a method for verifying substitution of the original image or the processed data based on impersonation while verifying whether the processed data was produced from the original image or not and further for finding the original image easily if it is concluded that the original image has been substituted.

In addition, if the transmitted data has been substituted, it is necessary to find the substituted original image in early stages and extract necessary information again.

It is an object of the present invention to provide a method in which in the case where an original image or processed data was listened in and a secret key used in a data input portion or in a processed data processing portion was stolen, even if the listener-in transmits substituted data of the original image or the processed data by impersonation, the data reception side judges such an illegal act and verifies whether received data was produced from the original image or not.

It is another object of the present invention to provide a method in which the data reception side verifies whether the processed data is produced from the original data or not, and if the data reception side finds that the received data is substituted image, the data reception side obtains the original image quickly.

In order to attain the foregoing objects, in a data transmission method according to an aspect of the present invention, a data transmission side merges processed data DB obtained by working or processing an original image DA with signed data SA obtained by applying a digital signature to the original image. Then, the data transmission side applies a one-way function to the merged data, and ciphers the output of the one-way function with a secret key of the data transmission side so as to obtain signed data SB. Then, the signed data SA obtained by applying a digital signature to the original image DA is ciphered with a public key of a data reception side so that ciphered signed data SAE is obtained. Then, the data transmission side transmits the processed data DB, the signed data SB and the ciphered signed data SAE to the data reception side.

On the other hand, the data reception side obtains ciphered signed data SAE′ and enciphers the ciphered signed data SAE′ with a secret key of the data reception side to thereby obtain signed data SA′. The data reception side merges obtained processed data DB′ with the signed data SA′, and applies a one-way function to the merged data. Then, the data reception side enciphers obtained signed data SB′ with a public key of the data transmission side, and compares the output of the one-way function applied to the merged data obtained by merging the processed data DB′ and the signed data SA′ with the result of enciphering the signed data SB′ with a public key of the data transmission side. Thus, data validity is verified.

In the date transmission method according to another aspect of the present invention, the data transmission side merges an original image DA with signed data SA obtained by applying a digital signature to the original image. Then, the data transmission side applies a one-way function to the merged data, and ciphers the output of the one-way function with a secret key of the data transmission side so as to obtain signed data SB. The signed data obtained by applying a digital signature to the original image DA is ciphered with a public key of a data reception side so that ciphered signed data SAE is obtained. Then, the data transmission side transmits the original image DA, the signed data SB and the ciphered signed data SAE to the data reception side.

On the other hand, the data reception side obtains ciphered signed data SAE′ and enciphers the ciphered signed data SAE′ with a secret key of the data reception side to thereby obtain signed data SA′. The data reception side merges obtained original image DA′ with the signed data SA′, and applies a one-way function to the merged data. Then, the data reception side enciphers obtained signed data SB′ with a public key of the data transmission side, and compares the output of the one-way function applied to the merged data obtained by merging the original image DA′ and the signed data SA′ with the result of enciphering the signed data SB′ with a public key of the data transmission side. Thus, data validity is verified.

According to a feature of the present invention, in place of the signed data SA obtained by applying a digital signature to the original image in the data transmission apparatus according to the present invention described in the first and in the last, signed data obtained by applying a digital signature to data associated with the original image may be used. As the data associated with the original image data, for example, the volume of data of the original image, the number of black pixels included in a binarized image obtained by processing the original image, and so on, may be used.

Another feature of the present invention is as follows. When disagreement is given as the result of comparison of the output of the one-way function applied to the merged data with the result of enciphering the signed data SB′ with the public key of the data transmission side in the data transmission apparatus according to the present invention described in the first and in the last:

the data reception side transmits the signed data SA′ obtained by enciphering the received ciphered signed data SAE′ with the secret key of the data reception side to the data transmission side; and

the data transmission side searches for an original image corresponding to signed data coinciding with the signed data SA′ sent to the data transmission side.

According to a further aspect of the present invention, a data transmission apparatus comprises:

first ciphering means for receiving an electronic image of an original image and a first secret key as inputs, and outputting a first digital signature obtained by ciphering the electronic image with the first secret key;

processing means for receiving the electronic image as input, and outputting a partial or processed image of the electronic image;

second ciphering means for receiving the partial or processed image, the first digital signature and a second secret key as inputs, merging the partial or processed image and the first digital signature, ciphering obtained merged data with the second secret key, and outputting an obtained second digital signature;

third ciphering means for receiving the first digital signature and a public key as inputs, and obtaining ciphered data of the first digital signature with the public key; and

transmitting means for transmitting the partial or processed image, the second digital signature, and the ciphered data of the first signature to an external data channel.

DESCRIPTION OF THE EMBODIMENTS

The present invention utilizes a digital signature based on public key cryptography. The principle will be described with reference toFIG. 5andFIGS. 1A and 1B. In a rough flow of data, an original image720is obtained by an image input operation at an image input portion700of a branch office780, and is worked or processed at a processing operation portion705. Then, processed data730is transmitted from a data transmission server785to a service process portion of a processing center710via networks750and715so as to be subjected to a service. In this flow, if listen-in is carried out on the networks and a secret key used in the image input operation or the processing operation is stolen, there arises a problem of data substitution by impersonation.

Next, in order to explain the principle, description will be made about data to be dealt with. Reference numeral720represents an original image of information written on a recording medium such as paper read out by scanning the recording medium with a scanner704;725, signed data obtained by a digital signature using a secret key used in the image input operation;730, processed data processed or worked in the processing operation portion;735, the signed data725;740, signed data obtained by merging the processed data730and the signed data735to thereby form one unit of merged data and applying a digital signature to the merged data with a secret key of the processing operation portion;745, data obtained by ciphering the signed data735with a public key used in the service process of the processing center710;755, a data group to be transmitted to the processing center710, constituted by the data730,745and740. Further, reference numeral760represents data including data765obtained by listening in to the data group755on the network750and substituting the data730, and signed data770obtained by merging the data765and745to thereby form a block of merged data and applying a digital signature to the merged data with the secret key stolen from the processing operation portion. Reference numeral775represents substituted data sent to and received by the processing center710by impersonation.

Conventionally, signed data obtained by a digital signature using the processed data730and the secret key in the processing operation unit is used. Therefore, a listener-in who stole the secret key in the processing operation portion can substitute the processed data easily, make up the signed data and transmit those data to the processing center while impersonating the processing portion. However, the data reception side cannot verify such an illegal act.

FIG. 1Ais a flow of processing on the data transmission side inFIG. 5. Object data DA which is an original image and processing information are obtained (Step100). Here, for example, when a partial image is dealt with, the processing information means coordinates of a partial area to be dealt with. Then, processing with the object data DA and the processing information is performed (Step105), and a digital signature is applied to the object data DA so that signed data SA is obtained (Step107). The signed data SA is ciphered with a public key KDC used in the service process of the data reception side so that ciphered signed data SAE is obtained (Step110). Next, the processed data DB and the signed data SA are merged to form a block of data DC (Step115). A hash function is applied to the merged data DC (Step120), and the output of the hash function is ciphered with a secret key used in the processing operation portion so that signed data SB is obtained (Step125). The data DB, SB and SAE are transmitted to the data reception side (Step130). Here, the data DB corresponds to the data730inFIG. 5; SB, the data740; and SAE, the data745.

On the other hand,FIG. 1Bis a flow of processing carried out on the data reception side inFIG. 5. Here, received processed data DB′, signed data SB′ and ciphered signed data SAE′ are obtained (Step135). The ciphered signed data SAE′ is enciphered with a secret key KEC of the service process portion of the data reception side so that data SA′ is obtained (Step140). The data DB′ and SA′ are merged to form a block of data (Step145), and a hash function is applied to merged data DC′ (Step150). Then, the signed data SB′ is enciphered with a public key KDB of the processing operation portion of the data transmission side (Step155). The results of Step150and155are compared (Step160). On the basis of the result of the comparison, the data reception side can verify whether an illegal act was effected or not (Step165).

The important point in this processing is the fact that one who can encipher the ciphered signed data SAE′ is the data reception side because the data reception side has a secret key thereof. Even if a listener-in substitutes data or remakes signed data with the substituted data and the ciphered signed data, the results in Step160cannot agree with each other.

As is understood from the aforementioned flow, the ciphered signed data is not always required to be signed data of the original image, but it may be information relating to the original image, or the like. Examples of the information relating to the original image include: the volume of data of the original image; the number of black pixels included in a binarized image obtained by processing the original image; and so on.

The verification as to whether the processed data was produced from the original image or not is effected by comparing the values obtained by Steps150and155inFIG. 1B. If both the values are equal to each other, it is proved that the processed data was produced from the original image without any illegal act based on listen-in. Conversely, if the values are different from each other, there is a possibility that the data has been substituted. In such a case, it may be considered that the identification (ID) of the original image cannot be found from the substituted data. In such a case, the ciphered signed data transmitted to the data reception side is enciphered on the data reception side, and the enciphered signed data is sent to the data transmission side. The data transmission side searches for data-transmission-side signed data of the original image coinciding with the enciphered signed data. Thus, the original image can be found out.

Another embodiment will be described with reference toFIG. 3about the processing operation in which a plurality of partial images are produced.

In this case, Steps300to310are the same as Steps100to110inFIG. 1A. Data processing from Step320to Step335branching from Step315, which are executed for each of the partial images, are the same as that from Step115to Step130inFIG. 1A. The processing flow ofFIG. 3is different fromFIG. 1Ain that Step315executes the data processing repeatedly several times.

FIG. 4is a flow of processing for verification about transmitted data, which flow corresponds to the processing inFIG. 3. In the same manner as on the data transmission side, Steps400to405inFIG. 4are the same as Steps135to140inFIG. 1B. Data processing from Step415to Step435branching from Step410, which are executed for each of the partial images, are the same as that from Step145to Step165inFIG. 1B. The processing flow ofFIG. 4is different fromFIG. 1Bin that Step410executes the data processing repeatedly several times.

Thus, the partial images can be transmitted to the data reception side without being extracted and subjected to any illegal act based on listen-in. In addition, such an illegal act based on listen-in can be verified.

Although description was made above about security against listen-in on the transmission of processed data, it is possible to prevent an attack on the original image from a listener-in in the same manner as the processed data.

Description will be made below about a data transmission method according to another embodiment of the present invention which can verify an illegal act of a listener-in to the original image.

FIGS. 8A and 8Bshow processing flows when object data DA which is an original image is exchanged between a data transmission side and a data reception side. Steps similar to those inFIGS. 1A and 1Bare referenced correspondingly.

FIG. 8Ais a flow of processing carried out on the data transmission side. A digital signature is applied to the object data DA which is an original image, so that signed data SA is obtained (Step107). The signed data SA is ciphered with a public key KDC of a service process portion of the data reception side, so that ciphered signed data SAE is obtained (Step110). Next, the object data DA and the signed data SA are merged to form a block of data (Step115′). A hash function is applied to merged data DC with a secret key of the data transmission side so that signed data SB is obtained (Step125). The data DA, SB and SAE are transmitted to the data reception side (Step130).

On the other hand,FIG. 8Bis a flow of processing carried out on the data reception side. Here, object data DA′, signed data SB′ and ciphered signed data SAE′ are received (Step135′). The ciphered signed data SAE′ is enciphered with a secret key KEC of the service process portion of the data reception side so that data SA′ is obtained (Step140). The data DB′ and SA′ are merged to form a block of data (Step145′), and a hash function is applied to merged data DC′ (Step150). Then, the signed data SB′ is enciphered with a public key KDB of the data transmission side (Step155). The results of Steps150and155are compared (Step160). On the basis of the result of the comparison, it is possible to verify whether an illegal act was effected or not (Step165).

Similarly to the embodiment ofFIGS. 1A and 1B, the important point in this processing is that one who can encipher the ciphered signed data SAE′ is the data reception side because the data reception side has a secret key thereof. Even if a listener-in substitutes data or remakes signed data with the substituted data and the ciphered signed data, the results in Step160cannot agree with each other. Also in this embodiment, the ciphered signed data is not always necessary to be signed data of the original image, but it may be information relating to the original image, or the like. Thus, also in this embodiment, advantageous effects similar to those in the embodiment ofFIGS. 1A and 1Bcan be obtained.

Conventionally, when data produced by a digital signature is listened in on a network and a secret key used therefor is stolen, there has arisen a problem that the listener-in may substitute the data and transmit the substituted data by impersonation so that wrongful processing is carried out on the data reception side. However, according to the aforementioned embodiments, such a data substitution or such an illegal act based on impersonation can be verified on the data reception side.

While the invention has been particularly described and shown with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail and omissions may be made therein without departing from the scope of the invention. For example, although the above description is aimed at the case where images obtained by scanning paper and thereafter processing are exchanged via networks, the present invention is not limited to such a case. For example, it is also applicable to the case where forms or the like are stored in recording media such as magnetic disks, optical disks, semiconductor memories, or the like, and images obtained by reading out original images from such recording media and thereafter processing the original images are exchanged via networks.