WO2012060001A1

WO2012060001A1 - Content distribution system and method for same

Info

Publication number: WO2012060001A1
Application number: PCT/JP2010/069602
Authority: WO
Inventors: 健長沼
Original assignee: 株式会社日立製作所
Priority date: 2010-11-04
Filing date: 2010-11-04
Publication date: 2012-05-10

Abstract

A mobile communication terminal uses public keys corresponding to unique information items to generate hidden queries including encrypted text in which pseudorandom numbers have been encrypted, and the mobile communication terminal transmits the hidden queries to a content server. The content server uses each of a plurality of private keys to decrypt the received hidden queries and thereby acquire a plurality of estimated pseudorandom numbers. The content server uses each of the plurality of estimated pseudorandom numbers, which correspond to each of the plurality of private keys, as common keys to encrypt a plurality of content items which correspond to each of the plurality of unique information items. The content server transmits the plurality of encrypted hidden content items to the mobile communication terminal. The mobile communication terminal uses the pseudorandom numbers as common keys to decrypt the received plurality of hidden content items. The mobile communication terminal acquires the content items that the mobile communication terminal has been able to decrypt, as content items corresponding to the unique information items.

Description

Content distribution system and method

The present invention relates to a system for distributing content based on secret information unique to a service user.

In April 2007, mobile phones were required to be equipped with a GPS function. As a result, location services such as navigation services using mobile phones expanded: the location-based services (LBS) market, and location-based services became social infrastructure. Is becoming part of

The number of mobile phones and mobile services are already saturated, and high value-added services such as navigation services and concierge services are expected.

Although LBS is expected in this way, there is a problem of privacy infringement that the location information of the service user is known to the content server and the service provider.

In the conventional LBS, the service provider obtains the location information of the service user, but the service is provided under a contract not to use it illegally.

 Not only LBS, but users (service users) do not want service providers to know information other than the minimum necessary information specific to service users when receiving services. The necessary minimum service user-specific information is, for example, the minimum information related to charging for receiving a paid service. There is a service provider that requests service-specific information such as age and gender to create an account for a paid service, but the service user is specific to the service user such as age and gender unrelated to billing I do not want to know the information. Further, the service user desires to be able to receive the service without knowing the information unique to the service user to the service provider even if the information is necessary for receiving the service.

Taking LBS as an example, the service provider provides services such as providing content corresponding to the location of the service user, so it tries to acquire location information indicating the location of the service user. On the other hand, the service user does not want the service provider to know information unique to the service user, such as location information indicating where the service user is.

On the other hand, if the location information of the service user is concealed, the content server that distributes the content corresponding to the location information cannot specify the content to be distributed, so regardless of the location information (the concealed location information Content (including content corresponding to location information different from) needs to be distributed. If the content is distributed redundantly in this way, the server that distributes the content cannot know which service user is where and which content is received.

For the service provider (content server), the number of times content is distributed according to the location of the service user is important marketing data, so it is not necessary to specify the service user who received the content, but which content is which It is necessary to know how many times it was delivered.

As described above, the service user wants to conceal unique information such as location information, but there is a request that the content server wants to know statistical information such as the number of times of content delivery corresponding to the service user's unique information. There are no prior art documents that focus on special technical issues corresponding to each other, although these are contradictory issues.

The disclosed content distribution system and method are configured as follows by a mobile communication terminal that transmits a query and a content server that distributes the content. The mobile communication terminal stores a plurality of public keys corresponding to a plurality of pieces of unique information depending on service users. The content server stores a plurality of secret keys corresponding to each of a plurality of public keys and a plurality of contents corresponding to each of a plurality of unique information. The mobile communication terminal generates a pseudo-random number and generates a concealment query including a ciphertext obtained by encrypting the pseudo-random number using one of a plurality of public keys corresponding to one of a plurality of unique information. The generated concealment query is transmitted to the content server. The content server receives the concealment query, decrypts the received concealment query using each of the plurality of secret keys, acquires each of the plurality of decryption results as a plurality of estimated pseudo-random numbers, Using each of a plurality of estimated pseudorandom numbers corresponding to each secret key as a common key, encrypting a plurality of contents corresponding to each of a plurality of unique information, and moving the plurality of encrypted contents as a plurality of concealed contents Send to communication terminal. The mobile communication terminal receives a plurality of concealed contents, decodes the plurality of concealed contents using a pseudo-random number as a common key, and acquires the decrypted contents as contents corresponding to one of the unique information .

In another aspect of the content distribution system and method, the concealment query includes a bit string obtained by padding the ciphertext with a bit string at a first predetermined bit position of a pseudorandom number.

According to still another aspect of the content distribution system and method, the mobile communication terminal and the content server store in advance a pseudorandom number generation rule and a bit string of a first predetermined bit position of the pseudorandom number generated based on the generation rule. Keep it.

According to still another aspect of the content distribution system and the method thereof, the content server may include a plurality of decoding results when the bit string of the second predetermined bit position of each of the plurality of decoding results is the same as the bit string of the first predetermined bit position. Obtained as each estimated pseudo-random number.

In still another aspect of the content distribution system and method, the content server counts the number X of concealment queries received during a predetermined period, and sets the bit string length of the bit string at the first and second predetermined bit positions to p. And the bit string at the second predetermined bit position of each of the plurality of decoding results is different from the bit string at the first predetermined bit position and is estimated corresponding to the unique information j which is one of the plurality of unique information In response to a concealment query including ciphertext using one of the public keys corresponding to the unique information j, the number of times Yj for which the random number j has not been obtained is counted. The number of times Z at which the concealed content j corresponding to the information j is distributed is estimated as Z = X− (2 ^ p) × Yj.

A specific aspect of the content distribution system and method is a plurality of pieces of unique information depending on the service user, for example, position information where the service user is located.

According to the disclosed content distribution system and method, the service user can conceal the unique information, access the content server, and receive the desired content (corresponding to the concealed unique information). Further, according to the aspect in which the content server includes the distribution number estimation unit, the corresponding content distribution number can be estimated even if the unique information of the service user is kept secret.

It is a block diagram of a location information service system. It is a hardware block diagram of a mobile communication terminal. It is a hardware block diagram of a content server. It is a processing flow at the time of service operation. It is a processing flow of concealment query generation. It is a data format of a concealment query. It is a processing flow of concealment query reception. It is a processing flow of generation of confidential content. It is a block diagram of the descrambling key distribution system of pay broadcasting.

A content distribution system and method disclosed as an embodiment of the present invention are configured as follows by a mobile communication terminal that transmits a query and a content server that distributes the content.

The mobile communication terminal stores a plurality of public keys corresponding to each of a plurality of pieces of unique information depending on the service user such as position information where the service user is located and broadcast channel information that the service user wants to watch. is doing. The content server stores a plurality of secret keys corresponding to each of a plurality of public keys and a plurality of contents corresponding to each of a plurality of unique information. The content is, for example, guide information related to the position corresponding to the position information and release key information of the scramble key of the broadcast program corresponding to the broadcast channel information.

The mobile communication terminal generates a pseudo random number, generates a concealment query including a ciphertext obtained by encrypting the pseudo random number using a public key corresponding to unique information, and transmits the generated concealment query to the content server. To do. The content server receives the concealment query, decrypts the received concealment query using each of the plurality of secret keys, and acquires each of the plurality of decryption results as a plurality of estimated pseudorandom numbers. Furthermore, using a plurality of estimated pseudorandom numbers corresponding to each of a plurality of secret keys as a common key, a plurality of contents corresponding to each of a plurality of unique information are encrypted, and a plurality of encrypted contents are concealed. Is transmitted to the mobile communication terminal as an encrypted content. The mobile communication terminal receives a plurality of concealed contents, decrypts the received concealed contents using a pseudo-random number as a common key, and acquires the decrypted contents as contents corresponding to unique information.

The concealment query may include a bit string obtained by padding the ciphertext with a bit string at a first predetermined bit position of a pseudo-random number. The mobile communication terminal and the content server may use a pseudo-random number generation rule and the generation rule. The bit string of the first predetermined bit position of the pseudo-random number generated based on it may be stored in advance. In such a case, the content server obtains each of the plurality of estimated pseudo-random numbers when the bit string at the second predetermined bit position of each of the plurality of decoding results is the same as the bit string at the first predetermined bit position. .

The content server further includes an estimation unit for the number of times that the concealed content j corresponding to the unique information j is distributed, counts the number X of concealment queries received during a predetermined period, and the first and second predetermined P is the bit string length of the bit string at the bit position, and the bit string at the second predetermined bit position of each of the plurality of decoding results is different from the bit string at the first predetermined bit position and is an estimated random number corresponding to the unique information j The unique information in the plurality of concealed contents corresponding to the concealment query including the ciphertext using one of the public keys corresponding to the unique information j is counted. The number of times Z at which the concealed content j corresponding to j is distributed is estimated as Z = X− (2 ^ p) × Yj.

This embodiment is a location information service system in which location information of a user (service user) is used as unique information, and a content server distributes content corresponding to the location information to the user. Terms used in this embodiment are defined.
(1) Position information The position information includes latitude data and longitude data.

(2) Location ID
The location ID is an identifier indicating each region obtained by dividing the region where the location information service is provided by the content server into region 1, region 2,..., Region n. In this embodiment, the position ID is an integer value from 1 to n, and for example, the position ID of area 3 is 3.

(3) Public Key Cryptography with Block Length k Public key cryptography with block length k refers to a public key encryption algorithm in which the bit length of plaintext to be encrypted is k.

(4) Public key i, private key i (i = 1 to n)
The public key i and private key i indicate that the content server supports the location IDi of each region in advance when the region where the location information service is provided is divided into region 1, region 2,..., Region n. Then, using a public key cryptosystem key generation algorithm, a pair of a public key i having a block length k and a private key i is generated, and the public key i is made public to the mobile communication terminal of the service user. Is held by the content server.

(5) Position ID determination Position ID determination has a table in which a region ID is divided into region 1, region 2,..., Region n, and a position information corresponding to each region. The position ID corresponding to the position information of the longitude data is determined. Since the shape of each area is generally a polygon, the position information of the table is represented by the vertex coordinates (latitude data, longitude data) of the polygon, and the position ID is determined by comparing with the acquired position information.

(6) Determination of the public key for generating the concealment query In the determination of the public key for generating the concealment query, the public key i generated in advance corresponding to the position IDi is determined.

(7) Common key encryption method This is one of common key encryption method algorithms having a key length of k bits determined in advance between the content server and the service user (mobile communication terminal).
That is the definition of the term.

FIG. 1 is a configuration diagram of a location information service system, which is a content distribution system of the present embodiment, during service operation. As shown in FIG. 1, the location information service system provides a service user 110 who uses a service, a mobile communication terminal 100 owned by the service user, and contents in a service providing area 130 where the location information service is provided. Content server 120. The service providing area 130 is divided into area 1, area 2,..., Area n and n areas. In FIG. 1, a case where the service user 110 is divided into region 1, region 2, region 3, and region n is illustrated, and the service user 110 is located in region 3 and holds the mobile communication terminal 100. The service user 110 transmits the concealment query D100 to the content server 120, and the content server 120 distributes the concealed content D200 to the service user 110 in response to the received concealment query D100. Note that the content held by the content server 120 is one content i corresponding to the region i (position IDi). The content i may be updated with the passage of time, but the correspondence with the area i (position IDi) is maintained.

FIG. 2 is a hardware configuration diagram of the mobile communication terminal 100. The mobile communication terminal 100 includes a CPU 101, an auxiliary storage device 102, a memory 103, a tamper resistant storage device 105, a display device 106, an input / output interface 107, a communication antenna 108, and a position information acquisition device 109. Are connected by an internal signal line 104 such as a bus.

The auxiliary storage device 102 stores a program for executing processing to be described later and a public key i (i = 1 to n) for generating a concealment query corresponding to the position IDi (i = 1 to n). . The program is loaded into the memory 103 and executed by the CPU 101.

The position information acquisition device 109 includes a global positioning system (GPS), and the GPS measures latitude data and longitude data where the mobile communication terminal 100 is located.

FIG. 3 is a hardware configuration diagram of the content server 120. The content server 120 includes a CPU 121, an auxiliary storage device 122, a memory 123, a tamper resistant storage device 125, a display device 126, an input / output interface 127, and a communication device 128 via an internal signal line 124 such as a bus. Connected and configured.

The auxiliary storage device 122 stores a program for executing processing using a secret key to be described later, and the tamper resistant storage device 125 stores a secret key i (i = i = i) corresponding to the position IDi (i = 1 to n). 1 to n) are stored. The program is loaded into the memory 123 together with the secret key and executed by the CPU 121. The auxiliary storage device 122 stores content provided as a location information service.

FIG. 4 is a processing flow during service operation between the mobile communication terminal 100 and the content server 120.
The mobile communication terminal 100 activates a communication application and starts wireless communication with the content server 120 (S100). The mobile communication terminal 100 acquires the current latitude data and longitude data position information from the position information acquisition device 109 (S200). The mobile communication terminal 100 generates a concealment query (D100) to be transmitted to the content server 120 based on the acquired position information (S300). The mobile communication terminal 100 transmits the generated concealment query (D100) to the content server 120.

The content server 120 receives the concealment query (D100), and selects content to be distributed to the mobile communication terminal 100 in response to the received concealment query (D100) (S400). The content server 120 generates the confidential content i (i = 1 to n) (D200) to be distributed to the mobile communication terminal 100 (may be generated in advance and stored in the auxiliary storage device 122). The concealed content i (i = 1 to n) (D200) is transmitted to the mobile communication terminal 100 (S500).

The mobile communication terminal 100 that has received the concealed content i (i = 1 to n) (D200) receives the location information of the mobile communication terminal 100 from the received concealed content i (i = 1 to n) (D200). The content corresponding to (position ID) is decrypted, and the process ends (S600).

Here, the content server 120 distributes the concealed content i (i = 1 to n) corresponding to all the region IDi (i = 1 to n) of the location information service in response to one concealment query (D100). As described above, it will be described later that the concealed content i (i = 1 to n) is not necessarily distributed.

FIG. 5 is a flowchart (S300) for generating a concealment query in the processing flow at the time of service operation of FIG. The mobile communication terminal 100 determines the position IDi from the position information obtained by the position information acquisition process (S200) as described above (position ID determination) (S310). The public key i (any one of i = 1 to n) stored corresponding to the determined position IDi (i = 1 to n) is acquired from the auxiliary storage device 102 (S320). ). A k-bit pseudorandom number is generated (S330), the generated pseudorandom number is encrypted using the public key i, a k-bit ciphertext is generated (S340), and the first bit of the bit string of the pseudorandom number is generated. Bit string padding is performed on the generated ciphertext to generate a concealment query (D100) of a bit string of k + 1 bits (S350).

FIG. 6 shows a concealment query (D100) data format generated by the concealment query generation process (S300). The concealment query (D100) is data consisting of a bit string of length k + 1 bits. The k-bit ciphertext generated in (S340) is stored from the first bit to the k-th bit of the concealment query (D100). The first bit to the kth bit are referred to as a ciphertext part of the concealment query (D100). The first bit of the pseudorandom number generated in (S330) is stored in the (k + 1) th bit of the concealment query (D100). This k + 1 bit is called a plaintext part of the concealment query (D100).

FIG. 7 is a flowchart (S400) for receiving a concealment query in the processing flow at the time of service operation of FIG. The content server 120 receives the concealment query (D100) transmitted from the mobile communication terminal 100 (S410), and uses the estimated random number i (i = 1 to n), which is an area on the memory 123, as a bit string having a value of 0, for example. (S420). In order to decrypt using the secret key i (i = 1 to n), an initial value is set to the variable i (i = 1) (S430). The ciphertext part of the received concealment query (D100) is decrypted using the secret key i (i = 1 to n) stored in the tamper resistant storage device 125 (S440). Whether the first bit of the decryption result matches the plaintext part of the received concealment query (D100) is compared (S450). If they match, the decoding result is stored in the estimated random number i (S460). If they do not match, the process proceeds to S470 (the estimated random number i remains the initial value). The variable i is incremented to i + 1 (S470). If i is less than or equal to n, the process returns to S440, and if i is greater than n, the process ends (S480). With the above processing, when the first bit of the decryption result of the ciphertext part of the concealment query (D100) matches the plaintext part, the decryption result is assumed to be an estimated random number i (i = 1 to n). An estimated random number i (i = 1 to n) is obtained that remains as a value.

FIG. 8 is a flowchart (S500) for generating the concealment content in the processing flow at the time of service operation of FIG. The content server 120 accesses the auxiliary storage device 122 and acquires the content i (i = 1 to n) to be distributed to the mobile communication terminal 100 selected in the concealment query reception process (S400) (S510). The meaning of the selection will be clarified in the following explanation. In order to encrypt the content i (i = 1 to n) using the estimated random number i (i = 1 to n), an initial value is set to the variable i (i = 1) (S520). Whether or not the estimated random number i is stored is checked (S530), and if it is stored, the content i is encrypted using a common key encryption method using the estimated random number i as a common key, and the area provided in the memory 123 Is stored in the concealed content i (S540). If the estimated random number i is not stored (in the case of the initial value stored in S420), a bit string of value 0 is stored in the concealed content i (S550). The variable i is incremented to i + 1 (S560). If i is n or less, the process returns to S530, and if i is greater than n, the process is terminated (S570).

The content server 120 may distribute the concealed content i (i = 1 to n) to the mobile communication terminal 100 as described with reference to FIG. 4, but the first bit of the estimated random number i is the concealment query ( The amount of transmission data from the content server 120 to the mobile communication terminal 100 (the number of concealed contents to be distributed) is controlled so as not to transmit the concealed content i that matches the flat part of D100) and stores a bit string of value 0. ) Is halved. Selection is made so that the number of contents to be distributed is halved in this way. As is apparent from the above description, as shown in FIG. 6, when the bit length of the equally divided part is set to 2 bits and processing similar to that described above is executed, the number of concealed contents to be distributed can be reduced to 1/4, If the bit length is 3 bits, it can be reduced to 1/8. The explanation using FIG. 4 is a case where the bit length of the plaintext part is 0 bit.

As an extreme example, if the bit length of the plaintext part is k bits and the same processing as described above is executed, the number of concealed contents to be distributed matches the estimated random number i with the k-bit pseudo random number generated by the mobile communication terminal 100 Therefore, the number of concealed contents to be distributed can be specified as one content i corresponding to the position IDi. In this case, the concealment query (D100) is not concealed.

As is clear from the above description, the bit length of the plaintext part may be increased in order to reduce the number of concealed contents to be distributed, but in order to ensure the concealment of the concealment query (D100) It is necessary to sufficiently shorten the bit length k of the random number. At the time of system construction, the bit length of the plaintext part is determined together with the bit length k of the pseudo random number based on the confidentiality required as a system specification. Next, the processing of the mobile communication terminal 100 that has received the concealed content i from the content server 120 (the concealed content decoding processing (S600) in the processing flow at the time of service operation in FIG. 4) will be described. The mobile communication terminal 100 receives the concealed content i (selected from i = 1 to n) transmitted from the content server 120 and uses the k-bit pseudorandom number generated in S330 as a common key encryption. By using the method, the concealed content i is decrypted, and the decrypted content i is acquired as the content i corresponding to the area ID i requested by the mobile communication terminal 100. The content i that can be acquired is a decryption result of the concealed content i that has been encrypted using a k-bit pseudorandom number as the estimated random number i. Even if the other concealed content i is decrypted using the k-bit pseudo-random number generated in S330, the content before being encrypted is not reproduced.

As described above, if the location information, which is unique information of the service user, is concealed, the content server distributes the content redundantly, so the number of times of content distribution corresponding to the service user's area IDi (service The number of contents that the user could decrypt and reproduce is not known. Accordingly, a process for statistically processing the redundant distribution number of contents and obtaining the distribution number of contents corresponding to the service user's area IDi will be described.

In a predetermined service period such as one day or one week, the content server 120 counts the total number of received concealment queries (D100) and sets the total number to X. Corresponding to the total number, if the number of times the estimated random number j is not obtained (the number of mismatches in S450 in FIG. 7 and the number of times content j has not been distributed) is Yj, The number of distributions Z of content j corresponding to the user's area ID j (total number of service users in area j) is obtained as Z = X− (2 ^ p) × Yj. For example, if X = 10000, p = 1, and Yj = 4900, Z = 10000−2 × 4900 = 200. This is because the content j is always distributed corresponding to the service user's area ID j (the estimated random number j is obtained).

When the predetermined service period is lengthened and the total number X of the concealment queries (D100) is increased, the ratio between the number of service users who actually received the content j in the region j and the number of distribution times Z of the content j is Converges to 1.

The plaintext part of the concealment query (D100) may be modified as follows. For example, instead of setting the plaintext part to be 1-bit length, a rule for generating a pseudo-random number such as “the first bit of the pseudo-random number is set to 1” is defined in advance between the mobile communication terminal 100 and the content server 120. If so, by checking whether the first bit is 1 in the bit string obtained when the ciphertext part is decrypted with the secret key, the generation of the pseudo random number can be eliminated with a probability of 1/2. Further, although the first bit has been described from the beginning, even in the case of p bits, the bit position is determined in advance between the content server 120 and the mobile communication terminal 100, and the value of the bit at the determined bit position You may check.

More generally, by defining a pseudo-random number generation rule between the content server 120 and the mobile communication terminal 100 in advance, the ciphertext part is used as a secret key in the process (S450) within the concealment query reception process (S400). It is determined whether the bit string obtained upon decoding satisfies the pseudo-random number generation rule described above. If not, generation of pseudo-random numbers may be excluded.

Further, in general, the service user 110 determines a service user function using a k-bit pseudo-random number as a command argument, publishes the service user function to the content server 120, and as a plaintext part of the concealment query (D100), By adopting the generated pseudo-random service user function value, the content server compares the plaintext part with the service user function value of the bit string obtained by decrypting the ciphertext part with the secret key, and eliminates the generation of pseudo-random numbers. May be. In this case, in the bit string of length k, the number of bit strings having a given service user function value is S, R = S / (2 ^ k), and the number of distribution times Z of content j is Z = 1−Yj -(R × X) / (1-R).

Further, in the generation of pseudorandom numbers in the concealment query generation process (S300) (FIG. 5: S330) (S350), in the above-described embodiment, a pseudorandom number is generated each time the concealment query generation process (S300) is performed. However, the pair of the location ID and pseudorandom number of the concealment query generated when using the previous service may be cached, and the cached pseudorandom number may be used for the same location ID.

This embodiment is an example of a system in which a service user searches a content database while concealing unique information. The content server is a server that distributes a pay TV broadcast descrambling key, and the service user selects one channel from a plurality of pay broadcasting channels and wants to receive the descrambling key from the server. The descrambling key distribution server wants to keep the descrambling key distribution server secret.

FIG. 9 shows that the service user 110 having the communication terminal 130 selects channel 3 (140) from the pay broadcast channel list and receives the descrambling key from the descrambling key distribution server 120. It is a block diagram of a key distribution system. At this time, the service user 110 can receive the descrambling key of channel 3 from the descrambling key distribution server 120 in a state of concealing channel 3 by the same processing as in the first embodiment.

Specifically, the service user 110 sets the unique information as channel 3 150 instead of the position ID of the first embodiment, generates a concealment query (E100) corresponding to channel 3 and generates the concealment query. (E100) is transmitted to the descrambling key distribution server 140. In response to the concealment query (E100), the descrambling key distribution server 140 returns the concealed content i (i = 1 to n) (E120) having the descrambling key 160 as the content to the service user. The service user 110 that has received the concealed content i (i = 1 to n) (E120) obtains the descrambling key 160 corresponding to channel 3 150 through the concealed content decryption process.

With the above processing, the descrambling key distribution server 140 scrambles the descrambling key distribution server 140 in a state in which the service user 110 has concealed which channel the descrambling key has been received. Distribution becomes possible.

According to the embodiment described above, the service user can conceal the unique information, access the content server, and receive the desired content (corresponding to the concealed unique information). In addition, the content server can estimate the corresponding content distribution count even if the service user's unique information is kept secret.

100: mobile communication terminal, 110: service user, 120: content server, 130 service area, 140: descrambling key distribution server, 150: pay broadcast channel list, 160: descrambling key, D100, E100: concealment query , D200, E200: Confidential content.

Claims

A mobile communication terminal storing a plurality of public keys corresponding to each of a plurality of unique information depending on a service user, a plurality of secret keys corresponding to each of the plurality of public keys, and a plurality of the unique information A content distribution system having a content server for storing a plurality of contents corresponding to each,
The mobile communication terminal includes a pseudo-random number generator, a concealment unit including ciphertext obtained by encrypting the pseudo-random number using one of the plurality of public keys corresponding to one of the plurality of unique information A concealment query generation unit that generates a query, a first communication unit that transmits the generated concealment query to the content server, and receives a plurality of concealment content transmitted from the content server, and the pseudorandom number in common As a key, including a decryption unit that decrypts the plurality of the concealed content received, and a content acquisition unit that obtains the decrypted content as content corresponding to one of the unique information,
The content server receives the concealment query, and uses each of the plurality of secret keys, a second communication unit that transmits the plurality of encrypted contents to the mobile communication terminal as a plurality of concealed contents. An estimated pseudorandom number obtaining unit that decrypts the received concealment query and obtains each of a plurality of decryption results as a plurality of estimated pseudorandom numbers, and a plurality of the estimations corresponding to each of the plurality of secret keys A content distribution system comprising: an encryption unit that encrypts a plurality of the contents corresponding to each of the plurality of pieces of unique information using each pseudo-random number as a common key.
The content distribution system according to claim 1, wherein the concealment query includes a bit string obtained by padding the ciphertext with a bit string at a first predetermined bit position of the pseudo-random number.
The mobile communication terminal and the content server store in advance a generation rule of the pseudo random number and a bit string of a first predetermined bit position of the pseudo random number generated based on the generation rule. Item 2. The content distribution system according to Item 1.
The estimated pseudo-random number acquisition unit, when a bit string at a second predetermined bit position of each of the plurality of decoding results is the same as a bit string at the first predetermined bit position, 4. The content distribution system according to claim 2, wherein the content distribution system is acquired.
The content server further counts the number X of the concealment queries received during a predetermined period, sets the bit string length of the bit string at the first and second predetermined bit positions to p, and a plurality of the decoding results A bit string at each second predetermined bit position is different from the bit string at the first predetermined bit position, and the estimated random number j corresponding to the unique information j which is one of the plurality of unique information is not obtained. Corresponding to the concealment query including the ciphertext using one of the public keys corresponding to the unique information j, and the unique content among a plurality of the concealed contents 5. The content distribution system according to claim 4, further comprising a distribution frequency estimation unit that estimates the frequency Z of distribution of the concealed content j corresponding to the information j as Z = X− (2 ^ p) × Yj.
6. The content distribution system according to claim 5, wherein the plurality of pieces of unique information depending on the service user are position information where the service user is located.
A mobile communication terminal storing a plurality of public keys corresponding to each of a plurality of unique information depending on a service user, a plurality of secret keys corresponding to each of the plurality of public keys, and a plurality of the unique information A content distribution method by a content server that stores a plurality of contents corresponding to each of the methods,
The mobile communication terminal generates a pseudo-random number, and conceals including ciphertext obtained by encrypting the pseudo-random number using one of the plurality of public keys corresponding to one of the plurality of unique information Generate a query, send the generated concealment query to the content server,
The content server receives the concealment query, decrypts the concealment query received using each of the plurality of secret keys, and obtains a plurality of decryption results as a plurality of estimated pseudo-random numbers. Then, using each of the plurality of estimated pseudorandom numbers corresponding to each of the plurality of secret keys as a common key, encrypting the plurality of contents corresponding to each of the plurality of unique information, Transmitting content to the mobile communication terminal as a plurality of concealed content;
The mobile communication terminal receives the plurality of concealed contents, decrypts the plurality of concealed contents received using the pseudo random number as a common key, and corresponds the decrypted contents to one of the unique information A content distribution method characterized in that the content is acquired as a processed content.
The content distribution method according to claim 7, wherein the concealment query includes a bit string obtained by padding the ciphertext with a bit string at a first predetermined bit position of the pseudo-random number.
The mobile communication terminal and the content server store in advance a generation rule of the pseudo random number and a bit string of a first predetermined bit position of the pseudo random number generated based on the generation rule. Item 8. The content distribution method according to Item 7.
The content server obtains each of the plurality of estimated pseudo-random numbers when the bit string at the second predetermined bit position of each of the plurality of decoding results is the same as the bit string at the first predetermined bit position. The content distribution method according to claim 8 or 9, wherein:
The content server counts the number X of the concealment queries received during a predetermined period, sets the bit string length of the bit string at the first and second predetermined bit positions to p, and each of the plurality of decoding results The number of times that the estimated random number j corresponding to the unique information j, which is one of the plurality of unique information, is not obtained because the bit string of the second predetermined bit position is different from the bit string of the first predetermined bit position Yj is counted, and the unique information in a plurality of the concealed contents corresponding to the concealment query including the ciphertext using one of the public keys corresponding to the unique information j 11. The content distribution method according to claim 10, wherein the number of times Z at which the concealed content j corresponding to j is distributed is estimated as Z = X− (2 ^ p) × Yj.
12. The content distribution method according to claim 11, wherein the plurality of pieces of unique information depending on the service user are position information where the service user is located.