KR101533950B1 - Broadcast encryption method and system - Google Patents

Abstract

The present invention relates to a broadcast encryption method and system, and more particularly, to a broadcast encryption method and system, and more particularly, to a broadcast encryption method and system. Transmitting the public key to the message encryption unit and transmitting the secret key to the plurality of user terminals, respectively; The message encryption unit receiving the public key and the plain text message to be encrypted, and generating a symmetric key, a header, and a ciphertext for the plain text message based on the received public key; Generating a broadcast cipher text including the number of user terminals desiring to receive the plaintext message, the header and the cipher text, and transmitting the broadcast cipher text to the server unit; Generating a public conversion key and a secret conversion key based on the secret key received by the user terminal, and transmitting the generated publicity conversion key to the server unit; Partially decrypting the broadcast cipher text using the public key received by the server, and transmitting the partially decrypted broadcast cipher text to the user terminal; And decoding the partial decrypted broadcast cipher text received by the user terminal using the secret conversion key to obtain a plaintext message; .
According to the above configuration, the broadcast encryption method and system of the present invention generate a public-key conversion key and a secret-key conversion key by selecting a random number value from a double-linear group and then use this to easily decrypt the encrypted message through a small amount of calculation There is an effect that can be done.

Description

[0001] Broadcast encryption method and system [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadcast encryption method and system, and more particularly, to a broadcast encryption method and system capable of efficiently encrypting a message by allowing a user terminal to reduce a storage amount for a public key and perform a simple calculation.

Due to the development of IT technology, large or important security data is transmitted and received between user terminals. As described above, in order to protect the data transmitted and received between the user terminals from being exposed to the outside by the attack of the hacker, an encryption method for encrypting the transmission / reception data is used. There are two types of encryption schemes: symmetric cryptography (DES) and asymmetric cryptography (RSA).

The secret key encryption scheme (DES) is a method of performing encryption and decryption using the same key. However, it is difficult to maintain security and key management. However, the algorithm has a relatively simple and fast encryption speed and a small capacity.

In addition, the public key cryptosystem (RSA) consists of a public key and a private key used only by the user. In this case, since the public key and the secret key are managed separately, And user authentication are simultaneously performed. Therefore, such a public key encryption technique is mainly used for digital signature and non-repudiation of electronic documents, but it has a disadvantage that the algorithm used is complicated and the processing speed is slow.

In the public key cryptosystem, a broadcast cryptosystem for solving the problem of the amount of transmission or key management that occurred when a set of arbitrary user terminals becomes a recipient terminal generates a cipher text after designating a set of receiver terminals, Channel, and only a legitimate user terminal belonging to a set of receiver terminals can decode the message. Only a legitimate user terminal belonging to a set of a receiver terminal can acquire a symmetric key used in encrypting a message, so that no additional key management is required, and since a recipient terminal generates one cipher text even though several recipient terminals are used, It is possible to transmit messages to multiple recipients more efficiently.

In particular, the pairing delegation protocol is a method in which a user terminal requiring a pairing operation outsources a pairing operation using a third user terminal, and has a limited resource, and thus has a limitation in performing heavy operations such as pairing Lt; / RTI > In addition, since the user terminal can verify whether the third party has performed the operation correctly and the third user terminal can not obtain any information about the value to be actually paired during the outsourcing, It is safe.

The broadcast cryptosystem includes operations such as pairing during decryption as well as Identity-Based Encryption (IBE) and Attribute-Based Encryption (ABE). Such a pairing operation requires a large amount of computation, and a decryption time of an encrypted message is prolonged, which makes it difficult to apply it to a mobile device with a small amount of resources.

In order to solve the problems of the related art as described above, the present invention provides a method and apparatus for decoding a public key by using a random number of a group of linear groups as a masking value, Cast encryption method and system.

According to another aspect of the present invention, there is provided a broadcast encryption method including: generating a public key and a secret key unique to a plurality of user terminals; Transmitting the public key to the message encryption unit and transmitting the secret key to the plurality of user terminals, respectively; The message encryption unit receiving the public key and the plain text message to be encrypted, and generating a symmetric key, a header, and a ciphertext for the plain text message based on the received public key; Generating a broadcast cipher text including the number of user terminals desiring to receive the plaintext message, the header and the cipher text, and transmitting the broadcast cipher text to the server unit; Generating a public conversion key and a secret conversion key based on the secret key received by the user terminal, and transmitting the generated publicity conversion key to the server unit; Partially decrypting the broadcast cipher text using the public key received by the server, and transmitting the partially decrypted broadcast cipher text to the user terminal; And obtaining a plaintext message by totally decrypting the partial decrypted broadcast cipher text received by the user terminal using the secret conversion key.

More preferably, selecting any of the first and second generation sources among the generation sources belonging to the double linear group; Selecting an arbitrary first random number belonging to the second generation source; Applying the first random number to a public key algorithm to generate a public key; And generating a secret key that is unique to each user terminal based on the first random number. The method may further include generating a public key and a secret key.

More preferably, the number of user terminals desiring to acquire a plaintext message, the public key, and a plaintext message to be encrypted are input. Selecting an arbitrary second random number belonging to a double linear group; Generating a third random number by performing a hash operation on the second random number and the plaintext message; Generating a fourth random number by performing a hash operation on the second random number; Generating a symmetric key and a header based on the third random number; Encrypting the second random number using the symmetric key; And generating a ciphertext for the plaintext message based on the encrypted second random number, plaintext message, and fourth random number, and generating a symmetric key, a header, and a cipher text.

More preferably, the method includes receiving user terminal unique information indicating a specific user terminal among a plurality of user terminals and a secret key unique to the specific user terminal; Selecting an arbitrary fifth random number belonging to the overlapped linear group and setting the selected fifth random number as a secret conversion key; Generating a public key based on the secret key and the fifth random number; And transmitting the open conversion key to the server unit. The user terminal may generate the open conversion key and the secret conversion key, and transmitting the generated open conversion key to the server unit.

Receiving a broadcast cipher text from the message encryption unit; Applying a header included in the broadcast cipher text, an encrypted second random number, and a public key to a folded linear function to generate a first partial deciphered ciphertext by decrypting a part of the broadcast cipher text; Applying the header to a folded linear function to generate a second partially decrypted cipher text by decrypting a part of the broadcast cipher text; Generating a partial decryption broadcast cipher text including the first partial decryption cipher text and the second partial decryption cipher text; And transmitting the partially decrypted broadcast cipher text to the user terminal, the method comprising partially decoding the broadcast cipher text by the server.

Receiving a partial decryption broadcast cipher text from the server unit; Calculating a symmetric key using the first partial decryption ciphertext, the second partial decryption ciphertext, and the secret conversion key among the partial decryption broadcast ciphertexts; Decrypting the third partial decryption cipher text with the symmetric key to obtain a second random number; Obtaining a plaintext message by XORing a fourth partial decryption cipher text of the partial decryption broadcast cipher text and a value obtained by performing a hash calculation on the second random number; Obtaining a third random number by performing a hash operation on the second random number and the plaintext message; Calculating a first partial decryption ciphertext and a second partial decryption ciphertext by computing the secret conversion key, the third random number, and the folded linear function; And outputting a plaintext message obtained based on the calculation result, wherein the user terminal obtains a plaintext message.

According to another aspect of the present invention, there is provided a broadcast encryption system for generating a public key and a secret key unique to a plurality of user terminals, transmitting the generated public key to a message encryption unit, To each of the plurality of user terminals; The method comprising: receiving the public key and a plaintext message to be encrypted, generating a symmetric key, a header, and a ciphertext for the plaintext message based on the received public key, calculating a number of user terminals to receive the plaintext message, A message encryption unit for generating and transmitting a broadcast cipher text including a cipher text; A server unit receiving a public key generated from a user terminal, partially decrypting the broadcast cipher text, and transmitting the partial cipher text to the user terminal; Generates a public conversion key and a secret conversion key based on the secret key, transmits the generated publicity conversion key to the server unit, totally decrypts the partially decrypted broadcast cipher text using the secret conversion key, And a user terminal.

The broadcast encryption method and system according to the present invention can generate a public transit key and a secret transcend key by selecting a random number from a double-linear group, and can easily decrypt the encrypted message through a small amount of computation using it The decoding time can be reduced.

In addition, the broadcast encryption method and system of the present invention have the effect of reducing the amount of data stored since the user terminal does not need to store a public key of a size proportional to the number.

1 is a schematic diagram of a broadcast encryption system in accordance with an embodiment of the present invention.
2 is a flowchart of a broadcast encryption method according to another embodiment of the present invention.
FIG. 3 is a flowchart illustrating a detailed process of generating a public key and a secret key according to the key generating unit of FIG. 2. Referring to FIG.
4 is a flowchart illustrating a detailed process of generating a symmetric key, a header, and a cipher text by the message encryption unit of FIG.
FIG. 5 is a flowchart illustrating a detailed process of generating the public key and the secret key in the user terminal of FIG.
FIG. 6 is a flowchart illustrating a detailed procedure of the partial decryption of the broadcast cipher text by the server unit of FIG. 2;
7 is a flowchart illustrating a detailed procedure of a step of acquiring a plain text message by the user terminal of FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, the present invention will be described in detail with reference to preferred embodiments and accompanying drawings, which will be easily understood by those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

1 is a schematic diagram of a broadcast encryption system in accordance with an embodiment of the present invention.

1, the broadcast encryption system 100 of the present invention includes a key generation unit 120, a message encryption unit 140, a server unit 160, and a user terminal 180.

The key generation unit 120 generates a public key and a secret key unique to a plurality of user terminals, transmits the generated public key to the message encryption unit 140, and transmits the secret key to the plurality of user terminals 180, Respectively.

The message encrypting unit 140 receives the public key and the plaintext message to be encrypted, generates a symmetric key, a header and a ciphertext for the plaintext message based on the received public key, Generates a broadcast cipher text including the number of terminals, the header and the cipher text, and transmits the generated cipher text to the server unit 160.

The server unit 160 receives the public key generated from the user terminal 180, partially decrypts the broadcast cipher text, and transmits the partial decrypted broadcast cipher text to the user terminal 180.

The user terminal 180 generates a public conversion key and a secret conversion key based on the secret key, transmits the generated publicity conversion key to the server unit 160, And decrypts the broadcast cipher text using the secret conversion key to obtain a plaintext message.

Hereinafter, a broadcast encryption method according to the present invention will be described in detail with reference to FIG.

2 is a flowchart of a broadcast encryption method according to another embodiment of the present invention.

As shown in FIG. 2, in the broadcast encryption method of the present invention, the key generation unit 120 generates a public key and a secret key unique to a plurality of user terminals (S210).

The key generation unit 120 transmits the public key to the message encryption unit 140 and transmits the secret key to the plurality of user terminals 180 in step S220.

Then, the message encryption unit 140 receives the public key and the plaintext message to be encrypted, and generates a symmetric key, a header, and a cipher text for the plaintext message based on the received public key (S230).

Thereafter, the message encryption unit 140 generates a broadcast cipher text including the number of user terminals desiring to receive the plaintext message, the header and the cipher text, and transmits the generated broadcast cipher text to the server unit 160 S240).

Subsequently, the user terminal 180 generates a public conversion key and a secret conversion key based on the secret key received, and transmits the generated publicity conversion key to the server unit 160 (S250).

The server unit 160 partially decrypts the broadcast cipher text using the public key obtained from the user terminal 180 and transmits the decrypted broadcast cipher text to the user terminal 180 ).

In operation S270, the user terminal 180 decrypts the partially decrypted broadcast cipher text received from the server unit 160 using the secret conversion key generated by the user terminal 180, thereby obtaining a plain text message.

Hereinafter, with reference to FIG. 3 to FIG. 7, the detailed steps of each step will be described in detail.

First, prior to describing the detailed process of the present invention, the premise conditions will be briefly described.

은 소수

를 위수로 갖는 겹선형 그룹(bilinear group)을 나타내는데, 이때

는 상기 겹선형 그룹

의 생성원(generator)이라 하고,

을 겹선형 함수로 정의한다. 이러한, 상기 겹선형 함수란, 겹선형 그룹

와

에서 모두 이산대수문제(discrete logarithm problem)가 어렵다고 가정할 때, 겹선형성(bilinearity), 비소실성(non-degeneracy) 또는 계산가능성(computability)의 조건을 만족하는 함수를 나타낸다.

Is a prime number

And a bilinear group having the same number of bases,

Lt; RTI ID = 0.0 >

And a generator,

Is defined as a folded linear function. Such a folded linear function means that the folded linear group

Wow

We denote functions satisfying the conditions of bilinearity, non-degeneracy, or computability, assuming that the discrete logarithm problem is difficult.

와,

에 대하여

가 되는 조건을 나타내며, 상기 비소실성(non-degeneracy)이란,

을 만족하는

가 존재하는 조건을 나타낸다. 또한, 상기 계산가능성(computability)이란, 겹선형 그룹에 속하는 임의의

에 대해서

를 효율적으로 계산할 수 있는 알고리즘이 존재하는 조건을 나타낸다. Here, the bilinearity refers to any two elements belonging to the double linear group

Wow,

about

Quot; non-degeneracy &

Satisfy

Is present. Further, the computability means that an arbitrary value belonging to a double linear group

about

Which is an algorithm that can efficiently calculate.

FIG. 3 is a flowchart illustrating a detailed process of generating a public key and a secret key according to the key generating unit of FIG. 2. Referring to FIG.

를 입력받는다. 이후, 겹선형 그룹에 속하는 생성원 중 임의의 제1 생성원

및 제2 생성원

을 선택한다(S211). As shown in FIG. 3, when the key generation unit 120 receives the number of total user terminals to which the encrypted message is to be transmitted

. Then, any one of the generation sources belonging to the double linear group

And a second generation source

(S211).

중 특정 사용자단말을 나타내는 사용자단말 고유정보

를 설정하고, 이와 같이 설정된 사용자단말 고유정보

와, 상기 제1 생성원

및 제2 생성원

에 기초하여 특정 사용자단말에 대한

를 연산한다. Thereafter, the number of the input total user terminals

User terminal unique information indicating a specific user terminal

And sets the user terminal unique information

And a control unit

And a second generation source

Lt; RTI ID = 0.0 >

.

를 선택하고(S212), 선택한 상기 제1 난수

와 상기 제1 생성원

에 기초하여 제1 변수

를 설정한 후, 두 개의 해쉬함수

를 임의로 설정한다. Subsequently, an arbitrary first random number belonging to the double linear group

(S212), and selects the first random number

And the first generation source

Based on the first variable

, Then the two hash functions

.

, 제1 변수

및 두 개의 해쉬함수

,

를 공개키 알고리즘에 적용하여 공개키

를 생성한다(S213).Accordingly,

, The first variable

And two hash functions

,

To the public key algorithm,

(S213).

에 대하여 상기 제1 생성원

및 제1 난수

에 기초하여 각각의 사용자단말별 고유한 비밀키

를 생성한다(S214).Thereafter, each of the specific user terminals

The first generation source

And a first random number

A secret key unique to each user terminal

(S214).

를 메시지암호화부(140)로 전송하고, 상기 복수 개의 사용자단말(180)로 상기 비밀키

를 각각 전송한다. If the key generation unit 120 generates the public key

To the message encryption unit (140), and transmits the secret key

Respectively.

Accordingly, the message encryption unit 140 receives the public key and the plain text message to be encrypted, and generates a symmetric key, a header, and a ciphertext for the plain text message based on the received public key.

4 is a flowchart illustrating a detailed process of generating a symmetric key, a header, and a cipher text by the message encryption unit of FIG.

, 상기 공개키

및 암호화하고자 하는 평문 메시지

를 입력받는다(S231).As shown in FIG. 4, when the message encryption unit 140 receives the number of user terminals to receive the plaintext message

, The public key

And a plaintext message to be encrypted

(S231).

에 속하는 임의의 제2 난수

를 선택한다(S232). Fold linear group

Lt; RTI ID = 0.0 >

(S232).

와 평문 메시지

를 해쉬연산

하여 제3 난수

를 생성한다(S233).Thereafter, the second random number

And plaintext messages

Hash operation

The third random number

(S233).

를 해쉬연산

하여 제4 난수

를 생성한다(S234).The second random number

Hash operation

The fourth random number

(S234).

에 기초하여 대칭키

및 헤더

를 생성한다(S235). The third random number

The symmetric key < RTI ID =

And header

(S235).

에 기초하여 대칭키

는

=

와 같이 연산되고, 이때, 상기 대칭키

는 메시지를 암호화 및 복호화하는데 사용되는 것을 나타내며, 상기 g는 공개키를 나타낸다. 또한, 헤더

는

와 같이 연산된다.That is, first, the third random number

The symmetric key < RTI ID =

The

=

And the symmetric key < RTI ID = 0.0 >

Represents a public key used for encrypting and decrypting a message, and g represents a public key. In addition,

The

.

를 이용하여 상기 제2 난수

를 암호화

한다(S236). Then,

The second random number < RTI ID = 0.0 >

Encrypt

(S236).

와, 평문 메시지

와 제4 난수

간 XOR 연산을 수행한 값을 포함하여 상기 평문 메시지

에 대한 암호문

을 생성한다(S237). Thus, the encrypted second random number

And a plaintext message

And the fourth random number

A value obtained by performing an inter-XOR operation on the plaintext message

Ciphertext for

(S237).

, 상기 헤더

및 암호문

을 포함하는 브로드캐스트 암호문

을 생성하여 서버부(160)로 전송한다. Accordingly, when the message encryption unit 140 receives the number of user terminals to receive the plaintext message

, The header

And ciphertext

≪ / RTI >

And transmits it to the server unit 160.

Then, based on the secret key received by the user terminal, the open conversion key and secret conversion key are generated.

FIG. 5 is a flowchart illustrating a detailed process of generating the public key and the secret key in the user terminal of FIG.

와, 상기 특정 사용자단말의 고유한 비밀키

를 입력받는다(S251).As shown in FIG. 5, among a plurality of user terminals,

A secret key unique to the specific user terminal

(S251).

에 속하는 임의의 제5 난수

를 선택하고, 선택한 제5 난수

를 비밀 변환키

로 설정한다(S252). 이때, 설정된 상기 비밀 변환키

는 사용자단말이 외부로 노출되지 않도록 비밀로 유지하는 값을 나타낸다.Thereafter,

Lt; RTI ID = 0.0 >

And selects the fifth random number

A secret conversion key

(S252). At this time,

Represents a value that keeps the user terminal secret so that the user terminal is not exposed to the outside.

및 제5 난수

에 기초하여

와 같이 연산하여 공개 변환키

를 생성한다(S253). 이때, 생성된 상기 공개 변환키

는 서버부(160)와 사용자단말(180)간에 사용하는 공개키를 나타낸다.Also,

And the fifth random number

On the basis of

And outputs the open conversion key

(S253). At this time,

Represents a public key used between the server unit 160 and the user terminal 180. [

를 서버부(160)로 전송한다(S254).Thereafter, the user terminal 180 generates the public-

To the server unit 160 (S254).

Accordingly, the server unit 160 partially decrypts the broadcast cipher text received using the public key.

FIG. 6 is a flowchart illustrating a detailed procedure of the partial decryption of the broadcast cipher text by the server unit of FIG. 2;

를 통해 선택된 평문 메시지를 획득하고자 하는 사용자단말(180)이 공개 변환키

, 암호문을 수신하고자 하는 사용자단말이

에 해당하는 브로드 캐스트 암호문

, 공개키

를 입력받는다(S261). As shown in FIG. 6, among the plurality of user terminals, user terminal unique information

The user terminal 180, which wishes to acquire the selected plaintext message through the Public Transformation Key

, A user terminal desiring to receive the ciphertext

Broadcast cipher text corresponding to

, Public key

(S261).

가 상기 암호문을 수신하고자 하는 사용자단말의 수를 나타내는 집합

에 속하지 않은 경우에는 잘못된 요청을 하는 것이므로 에러 메시지를 출력한다.At this time,

Is a set representing the number of user terminals desiring to receive the cipher text

, It outputs an error message because it makes a wrong request.

가 상기 암호문을 수신하고자 하는 사용자단말의 수를 나타내는 집합

에 속하는 경우에는 브로드 캐스트 암호문이

인 경우 즉, 상기 브로드캐스트 암호문

내 포함된 헤더

, 암호화된 제2 난수

및 공개 변환키

를 하기의 수학식 1에 적용하여 상기 브로드캐스트 암호문

중 일부를 복호화함으로써, 제1 부분 복호화 암호문

을 생성한다(S262).Alternatively, the user terminal unique information

Is a set representing the number of user terminals desiring to receive the cipher text

Quot ;, the broadcast cipher text is "

That is, the broadcast cipher text

My included header

, An encrypted second random number

And public conversion key

To the following equation (1) to calculate the broadcast cipher text

The first partial decryption ciphertext

(S262).

[Equation 1]

및 상기 브로드캐스트 암호문

내 포함된 상기 헤더

인

를 하기의 수학식 2와 같이 겹선형 함수

에 적용하여 상기 브로드캐스트 암호문 중 일부를 복호화함으로써, 제2 부분 복호화 암호문

을 생성한다(S263). Then,

And the broadcast cipher text

The header

sign

Is expressed by the following expression (2)

To decrypt a part of the broadcast cipher text, thereby generating a second partial decryption cipher text

(S263).

&Quot; (2) "

및 제2 부분 복호화 암호문

을 포함하는 부분 복호화 브로드캐스트 암호문

을 생성한다(S264). 이때, 생성된 부분 복호화 브로드캐스트 암호문

은 엘가말 형태로 생성될 수 있다.The generated first partial decryption ciphertext

And the second partial decryption ciphertext

A partial decryption broadcast cipher text

(S264). At this time, the generated partial decryption broadcast cipher text

Can be generated in the form of an elongated horse.

Thereafter, the partial decryption broadcast cipher text generated by the server is transmitted to the user terminal (S265).

Thereafter, a user terminal that wishes to receive a plaintext message decrypts the partially decrypted broadcast cipher text using the secret conversion key to obtain a plaintext message.

7 is a flowchart illustrating a detailed procedure of a step of acquiring a plain text message by the user terminal of FIG.

As shown in FIG. 7, the user terminal 180 first receives the partial decryption broadcast cipher text from the server unit 160 (S271).

이 부분 복호화 되어있는지 여부를 판단한다. Subsequently, the partial decryption broadcast cipher text

It is determined whether or not the partial decoding is performed.

이 부분적으로 복호화되어 있지 않았다면 변환 알고리즘을 수행한다. 이러한 변환 알고리즘은 앞서 수학식 1 내지 2를 통해 설명한 내용과 동일하므로, 자세한 설명은 생략하도록 한다. If the partial decryption broadcast cipher text

If it is not partially decoded, it performs the transformation algorithm. Since the conversion algorithm is the same as that described above with reference to Equations 1 and 2, detailed description will be omitted.

중 제1 부분 복호화 암호문

과, 제2 부분 복호화 암호문

및 상기 비밀 변환키

를 하기의 수학식 3에 적용하여 대칭키

를 연산한다(S272).Thereafter, when the user terminal 180 receives the partial decryption broadcast cipher text

The first partial decryption ciphertext

And a second partial decryption ciphertext

And the secret conversion key

Is applied to the following equation (3)

(S272).

&Quot; (3) "

중 상기 제3 부분 복호화 암호문

을 상기 대칭키

로 복호화하여 제2 난수

를 획득한다(S273).The partial decryption broadcast cipher text

The third partial decryption ciphertext

To the symmetric key

And outputs the second random number

(S273).

중 제4 부분 복호화 암호문

과, 상기 제2 난수

를 해쉬연산한 값

을 XOR 연산하여 평문 메시지

를 획득한다(S274).The partial decryption broadcast cipher text

4th partial decryption ciphertext

And the second random number

A value obtained by performing a hash operation

Lt; RTI ID = 0.0 > XOR &

(S274).

와 상기 평문 메시지

를 해쉬연산

하여 제3 난수

를 획득한다(S275).The second random number

And the plaintext message

Hash operation

The third random number

(S275).

, 제3 난수

를 하기의 수학식 4에 적용하여 겹선형 함수를 연산함으로써, 제1 부분 복호화 암호문

을 생성한다.The secret conversion key

, The third random number

Is applied to the following equation (4) to calculate a folded linear function, whereby the first partial decryption ciphertext

.

&Quot; (4) "

및 상기 제3 난수

를 하기의 수학식 5에 적용하여 겹선형 함수를 연산함으로써, 제2 부분 복호화 암호문

을 연산한다(S276). Also,

And the third random number

Is applied to the following equation (5) to calculate a folded linear function, whereby the second partial decryption ciphertext

(S276).

&Quot; (5) "

를 출력한다(S277).If the computation results of Equations (4) and (5) are satisfied, the plaintext message

(S277).

As described above, by generating the open conversion key and the secret conversion key using the random number selected in the grouped linear group as the masking value and calculating the operation using the conventional secret key by using the public conversion key, The public key of the terminal can be substituted for the necessary operation and the pairing operation.

The message encryption can not acquire any information about the message or secret key while performing the delegation operation and the user terminal can acquire the plaintext message using only a relatively simple operation using the partial decrypted broadcast cipher text, In terms of storage amount, efficient decoding is possible.

Further, such a broadcast encryption method and system may be stored in a computer-readable recording medium on which a program for executing by a computer is recorded. At this time, the computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer readable recording medium include ROM, RAM, CD-ROM, DVD 占 ROM, DVD-RAM, magnetic tape, floppy disk, hard disk, optical data storage, and the like. In addition, the computer-readable recording medium may be distributed to network-connected computer devices so that computer-readable codes can be stored and executed in a distributed manner.

The broadcast encryption method and system according to the present invention can generate a public transit key and a secret transcend key by selecting a random number from a double-linear group, and can easily decrypt the encrypted message through a small amount of computation using it The decoding time can be reduced.

In addition, the broadcast encryption method and system of the present invention have the effect of reducing the amount of data stored since the user terminal does not need to store a public key of a size proportional to the number.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Do.

120: Key generation unit 140: Message encryption unit
160: server 180: user terminal

Claims (8)

Generating a public key and a secret key unique to a plurality of user terminals;
Transmitting the public key to the message encryption unit and transmitting the secret key to the plurality of user terminals, respectively;
The message encryption unit receiving the public key and the plain text message to be encrypted, and generating a symmetric key, a header, and a ciphertext for the plain text message based on the received public key;
Generating a broadcast cipher text including the number of user terminals desiring to receive the plaintext message, the header and the cipher text, and transmitting the broadcast cipher text to the server unit;
Generating a public conversion key and a secret conversion key based on the secret key received by the user terminal, and transmitting the generated publicity conversion key to the server unit;
Partially decrypting the broadcast cipher text using the public key received by the server, and transmitting the partially decrypted broadcast cipher text to the user terminal; And
Decrypting the partial decrypted broadcast cipher text received by the user terminal using the secret conversion key to obtain a plaintext message;
/ RTI >
The method according to claim 1,
The step of generating the public key and the secret key by the key generating unit
Selecting any of the first generation source and the second generation source among the generation sources belonging to the double linear group;
Selecting an arbitrary first random number belonging to the double linear group;
Generating a public key by applying the first source to a public key algorithm; And
Generating a secret key unique to each user terminal based on the first source and the first random number;
The method comprising the steps of:
The method according to claim 1,
The step of generating the symmetric key, the header and the cipher text by the message encryption unit
Receiving a plain-text message to be encrypted, a number of user terminals to acquire a plaintext message, the public key, and a plaintext message to be encrypted;
Selecting an arbitrary second random number belonging to a double linear group;
Generating a third random number by performing a hash operation on the second random number and the plaintext message;
Generating a fourth random number by performing a hash operation on the second random number;
Generating a symmetric key and a header based on the third random number;
Encrypting the second random number using the symmetric key; And
Generating a ciphertext for the plaintext message based on the encrypted second random number, plaintext message, and fourth random number;
The method comprising the steps of:
The method according to claim 1,
The step of the user terminal generating the public conversion key and the secret conversion key and transmitting the generated publicity conversion key to the server unit
Receiving user terminal unique information indicating a specific user terminal among a plurality of user terminals and a private key unique to the specific user terminal;
Selecting an arbitrary fifth random number belonging to the overlapped linear group and setting the selected fifth random number as a secret conversion key;
Generating a public key based on the secret key and the fifth random number; And
Transmitting the open conversion key to the server unit;
The method comprising the steps of:
The method according to claim 1,
The step of partially decrypting the server-added broadcast cipher text
Receiving a broadcast cipher text from the message encryption unit;
Applying a header included in the broadcast cipher text, an encrypted second random number, and a public key to a folded linear function to generate a first partial deciphered ciphertext by decrypting a part of the broadcast cipher text;
Applying the header to a folded linear function to generate a second partially decrypted cipher text by decrypting a part of the broadcast cipher text;
Generating a partial decryption broadcast cipher text including the first partial decryption cipher text and the second partial decryption cipher text; And
Transmitting the partial decryption broadcast cipher text to the user terminal;
The method comprising the steps of:
6. The method of claim 5,
The step of the user terminal obtaining the plaintext message
Receiving a partial decryption broadcast cipher text from the server unit;
Calculating a symmetric key using the first partial decryption ciphertext, the second partial decryption ciphertext, and the secret conversion key among the partial decryption broadcast ciphertexts;
Decoding a third partial decryption cipher text of the partial decryption broadcast cipher text with the symmetric key to obtain a second random number;
Obtaining a plaintext message by XORing a fourth partial decryption cipher text of the partial decryption broadcast cipher text and a value obtained by performing a hash calculation on the second random number;
Obtaining a third random number by performing a hash operation on the second random number and the plaintext message;
Calculating a first partial decryption ciphertext and a second partial decryption ciphertext by computing the secret conversion key, the third random number, and the folded linear function; And
Outputting a plaintext message obtained based on the calculation result;
The method comprising the steps of:
A computer-readable recording medium on which a program for executing the method according to any one of claims 1 to 6 is recorded.
A key generation unit for generating a public key and a secret key unique to a plurality of user terminals, transmitting the generated public key to the message encryption unit, and transmitting the secret key to each of the plurality of user terminals;
The method comprising: receiving the public key and a plaintext message to be encrypted, generating a symmetric key, a header, and a ciphertext for the plaintext message based on the received public key, calculating a number of user terminals to receive the plaintext message, A message encryption unit for generating and transmitting a broadcast cipher text including a cipher text;
A server unit receiving a public key generated from a user terminal, partially decrypting the broadcast cipher text, and transmitting the partial cipher text to the user terminal;
Generates a public conversion key and a secret conversion key based on the secret key, transmits the generated publicity conversion key to the server unit, totally decrypts the partially decrypted broadcast cipher text using the secret conversion key, A user terminal;
Gt; a < / RTI > broadcast encryption system.

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