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Information generation apparatus, method, program, and recording medium for … — Nippon Telegraph And Telephone Corporation (US8619980B2)

Nippon Telegraph And Telephone Corporation · Google Patents

Google Patents · Patents · License: Open Access

patent, google patents, intellectual property, US8619980B2, Nippon Telegraph And Telephone Corporation, Koutarou Suzuki, en, 2013

ABSTRACT

Abstract

Hierarchical cryptography expressed in a general semiordered structure other than a tree structure is implemented. In information generation, random numbers Ï v and (Ï vj ) jÎµw(v) ÎµZ q are generated; main information k v =Ï v Î£ iÎµ{1, . . . , N-1}\w(v) v i b i *+b N * is calculated; and derivation information k vj =Ï vj Î£ iÎµ{1, . . . , N-1}\w(v) v i b i *+b j * is calculated for each jÎµw(v). In information derivation, random numbers Ï u and (Ï uj ) jÎµw(u) ÎµZ q are generated; main information k u =Ï u Î£ iÎµw(v)\w(u) u i k vi +k v is calculated; and derivation information k uj =Ï uj Î£ iÎµw(v)\w(u) u i k vi +k vj is calculated for each jÎµw(v).

Description

TECHNICAL FIELD

The present invention relates to an application of information security technology. For example, the present invention relates to hierarchical cryptography in which a decryption key having a limited decryption ability can be derived from another decryption key.

BACKGROUND ART

The technology described in Non-patent literature 1 is a known conventional technology for hierarchical cryptography.

PRIOR ART LITERATURE

Non-Patent Literature

Non-patent literature 1: Craig Gentry, Alice Siverberg, âHierarchical ID-Based Cryptography,â ASIACRYPT 2002, pp. 548-566

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In the technology described in Non-patent literature 1, a key corresponding to a child node in a tree structure can be derived from a key corresponding to a parent node, but key derivation cannot be implemented in a general semiordered structure s other than a tree structure. For example, in a structure having a parent node A, a parent node B, and a common child node C, it is not possible to derive a key of the common child node C from a key of the parent node A or to derive a key of the common child node C from a key of the parent node B.

Means to Solve the Problems

To solve the foregoing problem, an information generation apparatus according to Claim 1 includes a random number generator adapted to generate a random number Ï Y ÎµZ q and a random number Ï Yj ÎµZ q corresponding to each element jÎµw(Y) of a set w(Y); a main information generator adapted to use the generated random number Ï Y to calculate main information k Y that satisfies k Y =Ï Y Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b N *; and a derivation information generator adapted to use the generated random number Ï Yj to calculate derivation information k Yj that satisfies k Yj =Ï Yj Î£ eÎµ{1, . . . , N-1}\w(Y) Y i b i *+b j * for each element jÎµw(Y) of the set w(Y); where e is a non-degenerate, bilinear function that outputs one element of a cyclic group G T in response to inputs of N elements Î³ L (L=1, . . . , N) (Nâ§2) of a cyclic group G 1 and N elements Î³ L *(L=1, . . . , N) of a cyclic group G 2 ; b i ÎµG 1 N (i=1, . . . , N) is an N-dimensional basis vector having N elements of the cyclic group G 1 as elements; b j *ÎµG 2 N (j=1, . . . , N) is an N-dimensional basis vector having N elements of the cyclic group G 2 as elements; a function value obtained when each element of the basis vector b i ÎµG 1 N (i=1, . . . , N) and each element of the basis vector b j *ÎµG 2 N (j=1, . . . , N) are put into the bilinear function e is represented by g T ÏÂ·Î´(i,j) ÎµG T , using a Kronecker's delta function in which Î´(i,j)=1 F when i=j and Î´(i,j)=0 F when iâ j; 0 F is an additive unit element of a finite field F q ; 1 F is a multiplicative unit element of the finite field F q ; Ï is an element of the finite field F q , other than 0 F ; and g T is a generator of the cyclic group G T ; * indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; and the set w(Y) corresponds to the index Y, and w(Y)={i|Y 1 =*}.

An information generation apparatus according to Claim 4 includes a storage unit adapted to store main information k v serving as main information k Y or corresponding to an index v, derived from the main information k Y and derivation information k Yj , and derivation information k vj serving as the derivation information k Yj or corresponding to the index v, derived from the derivation information k Yj ; a child random number generator adapted to generate a random number Ï u ÎµZ q ; and a main information deriving unit adapted to use the main information k v and derivation information k vi , both of which are read from the storage unit, and the generated random number Ï u to calculate main information k u corresponding to an index u, which satisfies k u =Ï u Î£ iÎµw(v)\w(u) u i k vi +k v ; where e is a non-degenerate, bilinear function that outputs one element of a cyclic group G T in response to inputs of N elements Î³ L (L=1, . . . , N) (Nâ§2) of a cyclic group G 1 and N elements Î³ L * (L=1, . . . , N) of a cyclic group G 2 ; b i ÎµG 1 N (i=1, . . . , N) is an N-dimensional basis vector having N elements of the cyclic group G 1 as elements; b j *ÎµG 2 N (j=1, . . . , N) is an N-dimensional basis vector having N elements of the cyclic group G 2 as elements; a function value obtained when each element of the basis vector b i ÎµG 1 N (i=1, . . . , N) and each element of the basis vector b j *ÎµG 2 N (j=1, . . . , N) are put into the bilinear function e is represented by g T ÏÂ·Î´(i,j) ÎµG T , using a Kronecker's delta function in which Î´(i, j)=1 F when i=j and Î´(i, j)=0 F when iâ j; 0 F is an additive unit element of a finite field F q ; 1 F is a multiplicative unit element of the finite field F q ; Ï is an element of the finite field F q , other than 0 F ; and g T is a generator of the cyclic group G T ; * indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; a set w(Y) corresponding to the index Y is w(Y)={i|Y i =*}; Ï Y ÎµZ q is a random number; Ï Yi ÎµZ q is a random number corresponding to each element jÎµw(Y) of the set w(Y); the main information k Y corresponds to the index Y and satisfies k Y =Ï Y Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b N *; the derivation information k Yj corresponds to the index Y and satisfies k Yj =Ï Yj Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b j *; * indicates an indeterminate character; the index v is v=(v 1 , . . . , v N-1 )ÎµI=(F q âª{*}) N-1 ; the index u is u=(u 1 , . . . , u N-1 )ÎµI=(F q âª{*}) N-1 ; w(v) is a set corresponding to the index v and w(v)={i|v i =*}; w(u) is a set corresponding to the index u and w(u)={i|u i =*}; w(u)âw(v); and v i =u i (iÎµ{1, . . . , Nâ1}\w(v)).

An information generation apparatus according to Claim 6 includes a random number generator adapted to generate a random number r Y ÎµZ q ; a first main information generator adapted to use the generated random number r Y to calculate first main information k Y that satisfies k Y =g 2 a (g 3 Î iÎµ{1, . . . , N-1}\w(Y) h i Yi ) rY ; a second main information generator adapted to use the generated random number r Y to calculate second main information g rY ; and a derivation information generator adapted to use the generated random number r Y to calculate derivation information k Yj that satisfies k Yj =h j rY for each element jÎµw(Y) of a set w(Y); where G and G T are cyclic groups having a prime number order q; g is a generator of the cyclic group G; the cyclic group G has a pairing function e: GÃGâG T , which makes g T =e(g, g) a generator of the cyclic group G T ; a is a random number selected at random from Z p ; g, g 1 =g a ÎµG, and g 2 , g 3 , h 1 , . . . , h N-1 ÎµG randomly selected from the cyclic group G are made publicly available as public keys; * indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; the set w(Y) corresponds to the index Y; and w(Y)={i|Y i =*}.

An information generation apparatus according to Claim 9 includes a random number generator adapted to generate a random number r u ÎµZ q ; a storage unit adapted to store main information k v serving as main information K Y or corresponding to an index v, derived from first main information k Y and derivation information k Yj , and derivation information k vj serving as derivation information k Yj or corresponding to the index v, derived from the derivation information k Yj ; a first main information deriving unit adapted to use the first main information k v and derivation information k vi , both of which are read from the storage unit, to calculate first main information k u corresponding to an index u, which satisfies k u =k v (Î iÎµw(v)\w(u) k vi ui ) (g 3 Î iÎµ{1, . . . , N-1}\w(v) h i vi Î iÎµw(v)\w(u) h i ui ) ru ; and a second main information deriving unit adapted to use the generated random number r u to calculate second main information g ru ; where G and G T are cyclic groups having a prime number order q; g is a generator of the cyclic group G; the cyclic group G has a pairing function e: GÃGâG T , which makes g T =e(g, g) a generator of the cyclic group G T ; a is a random number selected at random from Z p ; g, g 1 =g a ÎµG, and g 2 , g 3 , h 1 , . . . , h N-1 ÎµG randomly selected from the cyclic group G are made publicly available as public keys; * indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; a set w(Y) corresponding to the index Y is w(Y)={i|Y i =*}; r Y ÎµZ q is a random number; the first main information k Y corresponds to the index Y and satisfies k Y =g 2 a (g 3 Î iÎµ{1, . . . , N-1}\w(Y) h i Yi ) rY ; g rY is second main information corresponding to the index Y; the derivation information k Yj corresponds to the index Y and satisfies k Yj =h j rY ; * indicates an indeterminate character; the index v is v=(v 1 , . . . , v N-1 )ÎµI=(F q âª{*}) N-1 ; w(v) is a set corresponding to the index v and w(v)={i|v i =*}; the index u is u=(u 1 , . . . , u N-1 )ÎµI=(F q âª{*}) N-1 ; w(u) is a set corresponding to the index u and w(u)={i|u i =*}; set w(u)âset w(v); and v i =u i (iÎµ{1, . . . , Nâ1}\w(v)).

Effects of the Invention

In a structure having a parent node A, a parent node B, and a common child node C, it is possible to derive information of the common child node C from information of the parent node A and to derive information of the common child node C from information of the parent node B.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example functional block diagram of an information generation apparatus according to a first embodiment;

FIG. 2 is an example flowchart of information generation in the first embodiment;

FIG. 3 is an example flowchart of information derivation in the first embodiment;

FIG. 4 is an example functional block diagram of an information generation apparatus according to a second embodiment;

FIG. 5 is an example flowchart of information generation in the second embodiment; and

FIG. 6 is an example flowchart of information derivation in the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described below in detail.

Predicate Encryption

An overview of predicate encryption, which is a concept used in a first embodiment, will be described first.

DEFINITIONS

Terms and symbols to be used in the embodiments will be defined first.

Matrix: A matrix represents a rectangular arrangement of elements of a set in which an operation is defined. Not only elements of a ring but also elements of a group can form the matrix.

(â¢) T : Transposed matrix of ââ¢â

(â¢) â1 : Inverse matrix of ââ¢â

Logical AND

Logical OR

Z: Set of integers

k: Security parameter (kÎµZ, k>0)

{0, 1}*: Binary sequence having a desired bit length. An example is a sequence formed of integers 0 and 1. However, {0, 1}* is not limited to sequences formed of integers 0 and 1. {0, 1}* is a finite field of order 2 or its extention field.

{0, 1} Î¶ : Binary sequence having a bit length Î¶ (Î¶ÎµZ, Î¶>0). An example is a sequence formed of integers 0 and 1. However, {0, 1} Î¶ is not limited to sequences formed of integers 0 and 1. {0, 1} Î¶ is a finite field of order 2 (when Î¶=1) or an extention field obtained by extending the finite field by degree Î¶ (when Î¶>1).

(+): Exclusive OR operator between binary sequences. For example, the following is satisfied: 10110011(+)11100001=01010010.

F q : Finite field of order q, where q is an integer equal to or larger than 1. For example, the order q is a prime number of a power of a prime number. In other words, the finite field F q is a prime field or an extention field of the prime field, for example. When the finite field F q is a prime field, remainder calculations to modulus q can be easily performed, for example. When the finite field F q is an extention field, remainder calculations modulo an irreducible polynomial can be easily performed, for example. A specific method for configuring a finite field F q is disclosed, for example, in reference literature 1, âISO/IEC 18033-2: Information technologyâSecurity techniquesâEncryption algorithmsâPart 2: Asymmetric ciphersâ.

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TECHNICAL FIELD

BACKGROUND ART

The technology described in Non-patent literature 1 is a known conventional technology for hierarchical cryptography.

PRIOR ART LITERATURE

Non-Patent Literature

Non-patent literature 1: Craig Gentry, Alice Siverberg, âHierarchical ID-Based Cryptography,â ASIACRYPT 2002, pp. 548-566

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Means to Solve the Problems

Effects of the Invention

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example functional block diagram of an information generation apparatus according to a first embodiment;

FIG. 2 is an example flowchart of information generation in the first embodiment;

FIG. 3 is an example flowchart of information derivation in the first embodiment;

FIG. 4 is an example functional block diagram of an information generation apparatus according to a second embodiment;

FIG. 5 is an example flowchart of information generation in the second embodiment; and

FIG. 6 is an example flowchart of information derivation in the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described below in detail.

Predicate Encryption

An overview of predicate encryption, which is a concept used in a first embodiment, will be described first.

DEFINITIONS

Terms and symbols to be used in the embodiments will be defined first.

Matrix: A matrix represents a rectangular arrangement of elements of a set in which an operation is defined. Not only elements of a ring but also elements of a group can form the matrix.

(â¢) T : Transposed matrix of ââ¢â

(â¢) â1 : Inverse matrix of ââ¢â

Logical AND

Logical OR

Z: Set of integers

k: Security parameter (kÎµZ, k>0)

(+): Exclusive OR operator between binary sequences. For example, the following is satisfied: 10110011(+)11100001=01010010.

0 F : Additive unit element of the finite field F q

1 F : Multiplicative unit element of the finite field F q

Î´(i, j): Kronecker's delta function. When i=j, Î´(i, j)=1 F .

When iâ j, Î´(i, j)=0 F .

E: Elliptic curve defined on the finite field F q . It is defined as a special point O called the point of infinity plus a set of points (x, y) satisfying x, yÎµF q and the Weierstrass equation in an affine coordinate system

y 2 +a 1 xy+a 3 y=x 3 +a 2 x 2 +a 4 x+a 6 ââ(1)

where a 1 , a 2 , a 3 , a 4 , a 6 ÎµF q . A binary operation + called an elliptic addition can be defined for any two points on the elliptic curve E, and a unary operation â called an elliptic inverse can be defined for any one point on the elliptic curve E. It is well known that a finite set of rational points on the elliptic curve E forms a group with respect to the elliptic addition. It is also well known that an operation called an elliptic scalar multiplication can be defined with the elliptic addition. A specific operation method of elliptic operations such as the elliptic addition on a computer is also well known. (For example, see reference literature 1, reference literature 2, âRFC 5091: Identity-Based Cryptography Standard (IBCS) #1: Supersingular Curve Implementations of the BF and BB1 Cryptosystemsâ, and reference literature 3, Ian F. Blake, Gadiel Seroussi, and Nigel P. Smart, âElliptic Curves in Cryptographyâ, Pearson Education, ISBN 4-89471-431-0.)

A finite set of rational points on the elliptic curve E has a subgroup of order p (pâ§1). When the number of elements in a finite set of rational points on the elliptic curve E is #E and p is a large prime number that can divide #E without a remainder, for example, a finite set E[p] of p equally divided points on the elliptic curve E forms a subgroup of the finite set of rational points on the elliptic curve E. The p equally divided points on the elliptic curve E are points A on the elliptic curve E which satisfy the elliptic scalar multiplication pA=O.

G 1 , G 2 , G T : Cyclic groups of order q. Examples of the cyclic groups G 1 and G 2 include the finite set E[p] of p equally divided points on the elliptic curve E and subgroups thereof. G 1 may equal G 2 , or G 1 may not equal G 2 . Examples of the cyclic group G T include a finite set constituting an extention field of the finite field F q . A specific example thereof is a finite set of the p-th root of 1 in the algebraic closure of the finite field F q .

In the embodiments, operations defined on the cyclic groups G 1 and G 2 are expressed as additions, and an operation defined on the cyclic group G T is expressed as a multiplication. More specifically, ÏÂ·Î©ÎµG 1 for ÏÎµF q and Î©ÎµG 1 means that the operation defined in the cyclic group G 1 is applied to Î©ÎµG 1 Ï times, and Î© 1 +Î© 2 ÎµG 1 for Î© 1 , Î© 2 ÎµG 1 means that the operation defined in the cyclic group G 1 is applied to Î© 1 ÎµG 1 and Î© 2 ÎµG 1 . In the same way, ÏÂ·Î©ÎµG 2 for ÏÎµF q and Î©ÎµG 2 means that the operation defined in the cyclic group G 2 is applied to Î©ÎµG 2 , times, and Î© 1 +Î© 2 ÎµG 2 for Î© 1 , Î© 2 ÎµG 2 means that the operation defined in the cyclic group G 2 is applied to Î© 1 ÎµG 2 and Î© 2 ÎµG 2 . In contrast, Î© Ï ÎµG T for ÏÎµF q and Î©ÎµG T means that the operation defined in the cyclic group G T is applied to Î©ÎµG T Ï times, and Î© 1 Â·Î© 2 ÎµG T for Î© 1 , Î© 2 ÎµG T means that the operation defined in the cyclic group G T is applied to Î© 1 ÎµG T and Î© 2 ÎµG T .

G 1 n+1 : Direct product of (n+1) cyclic groups G 1 (nâ§1)

G 2 n+1 : Direct product of (n+1) cyclic groups G 2

g 1 , g 2 , g T : Generators of the cyclic groups G 1 , G 2 , G T

V: (n+1)-dimensional vector space formed of the direct product of the (n+1) cyclic groups G 1

V*: (n+1)-dimensional vector space formed of the direct product of the (n+1) cyclic groups G 2

e: Function (bilinear function) for calculating a non-degenerate bilinear map that maps the direct product G 1 n+1 ÃG 2 n+1 of the direct product G 1 n+1 and the direct product G 2 n+1 to the cyclic group G T . The bilinear function e receives (n+1) elements Î³ L (L=1, . . . , n+1) (nâ§1) of the cyclic group G 1 and (n+1) elements Î³ L *(L=1, . . . , n+1) of the cyclic group G 2 and outputs one element of the cyclic group G T .

e:G 1 n+1 ÃG 2 n+1 âG T ââ(2)

The bilinear function e satisfies the following characteristics:

Bilinearity: The following relationship is satisfied for all Î 1 ÎµG 1 n+1 , Î 2 ÎµG 2 n+1 , and Î½, ÎºÎµF q

e (Î½Â·Î 1 ,ÎºÂ·Î 2 )= e (Î 1 ,Î 2 ) Î½Â·Îº ââ(3)

Non-degeneracy: This function does not map all

Î 1 ÎµG 1 n+1 ,Î 2 ÎµG 2 n+1 ââ(4)

onto the unit element of the cyclic group G T .

Computability: There exists an algorithm for efficiently calculating e(Î 1 , Î 2 ) for all Î 1 ÎµG 1 n+1 , Î 2 ÎµG 2 n+1 .

In the embodiments, the following function for calculating a non-degenerate bilinear map that maps the direct product G 1 ÃG 2 of the cyclic group G 1 and the cyclic group G 2 to the cyclic group G T constitutes the bilinear function e.

Pair: G 1 ÃG 2 âG T ââ(5)

The bilinear function e receives an (n+1)-dimensional vector (Î³ 1 , . . . , Î³ n+1 ) formed of (n+1) elements Î³ L (L=1, . . . , n+1) of the cyclic group G 1 and an (n+1)-dimensional vector (Î³ 1 *, . . . , Î³ n+1 *) formed of (n+1) elements Î³ L * (L=1, . . . , n+1) of the cyclic group G 2 and outputs one element of the cyclic group G T .

e=Î L=1 n+1 Pair(Î³ L ,Î³ L *)ââ(6)

The bilinear function Pair receives one element of the cyclic group G 1 and one element of the cyclic group G 2 and outputs one element of the cyclic group G T , and satisfies the following characteristics:

Bilinearity: The following relationship is satisfied for all Î© 1 e G 1 , Î© 2 ÎµG 2 , and Î½, ÎºÎµF q

Pair(Î½Â·Î© 1 ,ÎºÂ·Î© 2 )=Pair(Î© 1 ,Î© 2 ) Î½Â·Îº ââ(7)

Non-degeneracy: This function does not map all

Î© 1 ÎµG 1 , Î© 2 ÎµG 2 ââ(8)

onto the unit element of the cyclic group G T .

Computability: There exists an algorithm for efficiently calculating Pair(Î© 1 , Î© 2 ) for all Î© 1 ÎµG 1 , Î© 2 ÎµG 2 .

A specific example of the bilinear function Pair is a function for performing a pairing operation such as Weil pairing or Tate pairing. (See reference literature 4, Alfred. J. Menezes, âElliptic Curve Public Key Cryptosystemsâ, Kluwer Academic Publishers, ISBN 0-7923-9368-6, pp. 61-81, for example.) A modified pairing function e(Î© 1 , phi(Î© 2 )) (Î© 1 ÎµG 1 , Î© 2 ÎµG 2 ) obtained by combining a function for performing a pairing operation, such as Tate pairing, and a predetermined function phi according to the type of the elliptic curve E may be used as the bilinear function Pair (see reference literature 2, for example). As the algorithm for performing a pairing operation on a computer, the Miller algorithm (see reference literature 5, V. S. Miller, âShort Programs for Functions on Curvesâ, 1986, http://crypto.stanford.edu/miller/miller.pdf) or some other known algorithm can be used. Methods for configuring a cyclic group and an elliptic curve used to efficiently perform a pairing operation have been known. (For example, see reference literature 2; reference literature 6, A. Miyaji, M. Nakabayashi, and S. Takano, âNew Explicit Conditions of Elliptic Curve Traces for FR Reductionâ, IEICE Trans. Fundamentals, Vol. E84-A, No. 5, pp. 1234-1243, May 2001; reference literature 7, P. S. L. M. Barreto, B. Lynn, M. Scott, âConstructing Elliptic Curves with Prescribed Embedding Degreesâ, Proc. SCN '2002, LNCS 2576, pp. 257-267, Springer-Verlag. 2003; and reference literature 8, R. Dupont, A. Enge, F. Morain, âBuilding Curves with Arbitrary Small MOV Degree over Finite Prime Fieldsâ, http://eprint.iacr.org/2002/094/).

a i (i=1, . . . , n+1): (n+1)-dimensional basis vectors having (n+1) elements of the cyclic group G 1 as elements. An example of the basis vectors a i is an (n+1)-dimensional basis vector having Îº 1 Â·g 1 ÎµG 1 as an i-dimensional element and the unit element (expressed as â0â in additive expression) of the cyclic group G 1 as the remaining n elements. In that case, the elements of the (n+1)-dimensional basis vectors a i (i=1, . . . , n+1) can be listed as follows:

(

Îº

Â·

â¦

â¢

)

â¢

(

Îº

Â·

â¦

â¢

)

â¢

â¦

â¢

(

â¦

â¢

Îº

Â·

)

(

)

Here, Îº 1 is a constant formed of an element of the finite field F q other than the additive unit element 0 F . An example of Îº 1 ÎµF q is Îº 1 =1 F . The basis vectors a i are orthogonal bases. Each (n+1)-dimensional vector having (n+1) elements of the cyclic group G 1 as elements is expressed by a linear sum of (n+1)-dimensional basis vectors a i (i=1, . . . , n+1). Therefore, the (n+1)-dimensional basis vectors a i span the vector space V, described earlier.

a i * (i=1, . . . , n+1): (n+1)-dimensional basis vectors having (n+1) elements of the cyclic group G 2 as elements. An example of the basis vectors a i * is an (n+1)-dimensional basis vector having Îº 2 Â·g 2 ÎµG 2 as an i-dimensional element and the unit element (expressed as â0â in additive expression) of the cyclic group G 2 as the remaining n elements. In that case, the elements of the (n+1)-dimensional basis vectors a i * (i=1, . . . , n+1) can be listed as follows:

(

Îº

Â·

â¦

â¢

)

â¢

(

Îº

Â·

â¦

â¢

)

â¢

â¦

â¢

(

â¦

â¢

Îº

Â·

)

(

)

Here, Îº 2 is a constant formed of an element of the finite field F q other than the additive unit element 0 F . An example of Îº 2 ÎµF q is Îº 2 =1 F . The basis vectors a i * are orthogonal bases. Each (n+1)-dimensional vector having (n+1) elements of the cyclic group G 2 as elements is expressed by a linear sum of (n+1)-dimensional basis vectors a i * (i=1, . . . , n+1). Therefore, the (n+1)-dimensional basis vectors a i * span the vector space V*, described earlier.

The basis vectors a i and the basis vectors a i * satisfy the following expression for an element Ï=Îº 1 Â·Îº 2 of the finite field F q other than 0 F :

e ( a i ,a j *)= g T ÏÎ´(i,j) ââ(11)

When i=j, the following expression is satisfied from Expressions (6) and (7).

e â¡

(

a i

a j *

)

â¢

Pair â¡

(

Îº 1

Â·

g 1

Îº

Â·

g 2

)

Â·

Pair â¡

(

0 , 0

)

Â· â¦ Â·

Pair â¡

(

0 , 0

)

â¢

Pair â¡

(

g 1

g 2

)

Îº â¢

â¢ 1 â¢ Îº â¢

â¢ 2

Â·

Pair â¡

(

g 1

g 2

)

0 Â· 0

Â· â¦ Â·

Pair â¡

(

g 1

g 2

)

0 Â· 0

â¢

Pair â¡

(

g 1

g 2

)

Îº â¢

â¢ 1 â¢ Îº â¢

â¢ 2

g T Ï

When iâ j, e(a i , a j *) does not include Pair(Îº 1 Â·g 1 , Îº 2 Â·g 2 ) and is the product of Pair (Îº 1 Â·g 1 , 0), Pair (0, Îº 2 Â·g 2 ), and Pair(0, 0). In addition, the following expression is satisfied from Expression (7).

Pair( g 1 ,0)=Pair(0, g 2 )=Pair( g 1 ,g 2 ) 0

Therefore, when iâ j, the following expression is satisfied.

e ( a i ,a j *)= e ( g 1 , g 2 ) 0 =g T 0

Especially when Ï=Îº 1 Â·Îº 2 =1 F (for example, Îº 1 =Îº 2 =1 F ), the following expression is satisfied.

e ( a i ,a j *)= g T Î´(i,j) ââ(12)

Here, g T 0 =1 is the unit element of the cyclic group G T , and g T 1 =g T is a generator of the cyclic group G T . In that case, the basis vectors a i and the basis vectors a i * are dual normal orthogonal bases, and the vector space V and the vector space V* are a dual vector space that constitutes bilinear mapping (dual pairing vector space (DPVS)).

A: An (n+1) row by (n+1) column matrix having the basis vectors a i (i=1, . . . , n+1) as elements. When the basis vectors a i (i=1, . . . , n+1) are expressed by Expression (9), for example, the matrix A is as follows:

(

â®

)

(

Îº

Â·

â¦

Îº

Â·

â®

â±

â¦

Îº

Â·

)

(

)

A*: An (n+1) row by (n+1) column matrix having the basis vectors a i * (i=1, . . . , n+1) as elements. When the basis vectors a i * (i=1, . . . , n+1) are expressed by Expression (10), for example, the matrix A* is as follows:

(

â¢

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)

(

Îº

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â¦

Îº

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â®

â±

â¦

CLAIMS

Claims ( 13 )

What is claimed is:

1. An information generation apparatus comprising:

a processor;

a random number generator, implemented by the processor, adapted to generate a random number Ï Y ÎµZ q and a random number Ï Yj ÎµZ q corresponding to each element jÎµw(Y) of a set w(Y);

a main information generator, implemented by the processor, adapted to use the generated random number Ï Y to calculate main information k Y that satisfies k Y =Ï Y Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b N *; and

a derivation information generator, implemented by the processor, adapted to use the generated random number Ï Yj to calculate derivation information k Yj that satisfies k Yj =Ï Yj Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b j * for each element jÎµw(Y) of the set w(Y);

where e is a non-degenerate, bilinear function that outputs one element of a cyclic group G T in response to inputs of N elements Î³ L (L=1, . . . , N) (Nâ§2) of a cyclic group G 1 and N elements Î³ L * (L=1, . . . , N) of a cyclic group G 2 ; b i ÎµG 1 N (i=1, . . . , N) is an N-dimensional basis vector having N elements of the cyclic group G 1 as elements; b j *ÎµG 2 N (j=1, . . . , N) is an N-dimensional basis vector having N elements of the cyclic group G 2 as elements; a function value obtained when each element of the basis vector b i ÎµG 1 N (i=1, . . . , N) and each element of the basis vector b j *ÎµG 2 N (j=1, . . . , N) are put into the bilinear function e is represented by g T ÏÂ·Î´(i,j) ÎµG T , using a Kronecker's delta function in which Î´(i, j)=1 F when i=j and Î´(i, j)=0 F when iâ j; 0 F is an additive unit element of a finite field F q ; 1 F is a multiplicative unit element of the finite field F q ; Ï is an element of the finite field F q , other than 0 F ; and g T is a generator of the cyclic group G T ; and

* indicates an indeterminate character, an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 , the set w(Y) corresponds to the index Y, and w(Y)={i|Y i =*}.

2. The information generation apparatus according to claim 1 ,

wherein the random number generator further generates a random number Ï u ÎµZ q ,

the information generation apparatus comprising:

a storage device adapted to store main information k v corresponding to an index v and derivation information k vj corresponding to the index v; and

a main information deriving unit, implemented by the processor, adapted to use the main information k v and derivation information k vi , both of which are read from the storage device, and the generated random number Ï u to calculate main information k u corresponding to an index u, which satisfies k u =Ï u Î£ iÎµw(v)\w(u) u i k vi +k v ;

where * indicates an indeterminate character; the index v is v=(v 1 , . . . , v N-1 )ÎµI=(F q âª{*}) N-1 ; w(v) is a set corresponding to the index v and w(v)={i|v i =*}; the index u is u=(u 1 , . . . , u N-1 )ÎµI=(F q âª{*}) N-1 ; w(u) is a set corresponding to the index u and w(u)={i|u i =*}; w(u)âw(v); and v i =u i (iÎµ{1, . . . , Nâ1}\w(v)).

3. The information generation apparatus according to claim 2 , wherein the random number generator further generates a random number Ï uj ÎµZ q , corresponding to each element jÎµw(u) of the set w(u);

the information generation apparatus further comprising:

a derivation information deriving unit, implemented by the processor, adapted to use the derivation information k vj read from the storage device and the generated random number Ï uj to calculate derivation information k uj corresponding to the index u, which satisfies k uj =Ï uj Î£ iÎµw(v)\w(u) u i k vi +k vj , for each element jÎµw(u) of the set w(u).

4. An information generation apparatus comprising:

a storage device adapted to store main information k v serving as main information k Y or corresponding to an index v, derived from the main information k Y and derivation information k Yj , and derivation information k vj serving as the derivation information k Yj or corresponding to the index v, derived from the derivation information k Yj ;

a processor;

a random number generator, implemented by the processor, adapted to generate a random number Ï u ÎµZ q ; and

a main information deriving unit, implemented by the processor, adapted to use the main information k v and derivation information k vi , both of which are read from the storage unit, and the generated random number Ï u to calculate main information k u corresponding to an index u, which satisfies k u =Ï u Î£ iÎµw(v)\w(u) u i k vi +k v ;

* indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; a set w(Y) corresponding to the index Y is w(Y)={i|Y i =*}; Ï Y ÎµZ q is a random number; Ï Yi ÎµZ q is a random number corresponding to each element jÎµw(Y) of the set w(Y); the main information k Y corresponds to the index Y and satisfies k Y =Ï Y Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b N *; and the derivation information k Yi corresponds to the index Y and satisfies k Yj =Ï Yj Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *b j *;

* indicates an indeterminate character; the index v is v=(v 1 , . . . , v N-1 )ÎµI=(F q âª{*}) N-1 ; the index u is u=(u 1 , . . . , u N-1 )ÎµI=(F q âª{*}) N-1 ; w(v) is a set corresponding to the index v and w(v)={i|v i =*}; w(u) is a set corresponding to the index u and w(u)={i|u i =*}; w(u)âw(v); and v i =u i (iÎµ{1, . . . Nâ1}\w(v)).

5. The information generation apparatus according to claim 4 , wherein the random number generator further generates a random number Ï uj ÎµZ q , corresponding to each element jÎµw(u) of the set w(u);

the information generation apparatus further comprising:

a derivation information deriving unit, implemented by the processor, adapted to use the derivation information k vj read from the storage device and the generated random number Ï uj to calculate derivation information k uj that satisfies k uj =Ï uj Î£ iÎµw(v)\w(u) u i k vi +k vj for each element jÎµw(u) of the set w(u).

6. An information generation apparatus comprising:

a processor;

a random number generator, implemented by the processor, adapted to generate a random number r Y ÎµZ q ;

a first main information generator, implemented by the processor, adapted to use the generated random number r Y to calculate first main information k Y that satisfies k Y =g 2 a (g 3 Î iÎµ{1, . . . , Nâ1}\w(Y) h i Yi ) rY ;

a second main information generator, implemented by the processor, adapted to use the generated random number r Y to calculate second main information g rY ; and

a derivation information generator, implemented by the processor, adapted to use the generated random number r Y to calculate derivation information k Yj that satisfies k Yj =h j rY for each element jÎµw(Y) of a set w(Y);

where G and G T are cyclic groups having a prime number order q; g is a generator of the cyclic group G; the cyclic group G has a pairing function e: GÃGâG T , which makes g T =e(g, g) a generator of the cyclic group G T ; a is a random number selected at random from Z p ; and g, g 1 =g a ÎµG, and g 2 , g 3 , h 1 , . . . , h N-1 ÎµG randomly selected from the cyclic group G are made publicly available as public keys; and

* indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; the set w(Y) corresponds to the index Y; and w(Y)={i|Y i =*}.

7. The information generation apparatus according to claim 6 , wherein the random number generator further generates a random number r u ÎµZ q ,

the information generation apparatus comprising:

a storage device adapted to store first main information k v corresponding to an index v, second main information g r , and derivation information k vj corresponding to the index v;

a first main information deriving unit, implemented by the processor, adapted to use the first main information k v and derivation information k vi , both of which are read from the storage device, to calculate first main information corresponding to an index u, which satisfies k u =k v (Î iÎµw(v)\w(u) k vi ui )(g 3 Î iÎµ{1, . . . , N-1}\w(v) h i vi Î iÎµw(v)\w(u) h i ui ) ru ; and

a second main information deriving unit, implemented by the processor, adapted to use the generated random number r u to calculate second main information g ru ;

where * indicates an indeterminate character; the index v is v=(v 1 , . . . , v N-1 )ÎµI=(F q âª{*}) N-1 ; w(v) is a set corresponding to the index v and w(v)={i|v i =*}; the index u is u=(u 1 , . . . , u N-1 )ÎµI=(F q âª{*}) N-1 ; and w(u) is a set corresponding to the index u and w(u)={i|u i =*}; w(u)âw(v); and v i =u i (iÎµ{1, . . . , â1}\w(v)).

8. The information generation apparatus according to claim 7 , further comprising a derivation information deriving unit, implemented by the processor, adapted to use the derivation information k vi read from the storage device and the generated random number r u to calculate derivation information k uj that satisfies k uj =k vj h j ru for element jÎµw(u) of the set w(u).

9. An information generation apparatus comprising:

a processor;

a random number generator, implemented by the processor, adapted to generate a random number r u ÎµZ q ;

a storage device adapted to store main information k v serving as main information K Y or corresponding to an index v, derived from first main information k Y and derivation information k Yj , and derivation information k vj serving as derivation information k Yj or corresponding to the index v, derived from the derivation information k Yj ;

a first main information deriving unit, implemented by the processor, adapted to use the first main information k v and derivation information k vi , both of which are read from the storage device, to calculate first main information k u corresponding to an index u, which satisfies k u =k v (Î iÎµw(v)\w(u) k vi ui )(g 3 Î iÎµ{1, . . . , N-1}\w(v) h i vi Î iÎµw(v)\w(u) h i ui ) ru ; and

a second main information deriving unit, implemented by the processor, adapted to use the generated random number r u to calculate second main information g ru ;

* indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; and a set w(Y) corresponding to the index Y is w(Y)={i|Y 1 =*};

r Y ÎµZ q is a random number; the first main information k Y corresponds to the index Y and satisfies k Y =g 2 a (g 3 (Î iÎµ{1, . . . , N-1}\w(v) h i Yi ) rY ; g rY is second main information corresponding to the index Y; and the derivation information k Yj corresponds to the index Y and satisfies k Yj =h j rY ; and

* indicates an indeterminate character; the index v is v=(v 1 , . . . , v N-1 )ÎµI=(F q âª{*}) N-1 ; w(v) is a set corresponding to the index v and w(v)={i|v i =*}; the index u is u=(u 1 , . . . , u N-1 )Îµ=I(F q âª{*}) N-1 ; w(u) is a set corresponding to the index u and w(u)={i|u i =*}; set w(u)âset w(v); and v i =u i (iÎµ{1, . . . , Nâ1}\w(v)).

10. The information generation apparatus according to claim 9 , further comprising a derivation information deriving unit, implemented by the processor, adapted to use the derivation information k vi read from the storage device and the generated random number r u to calculate derivation information k uj that satisfies k uj =k vj h j ru for element jÎµw(u) of the set w(u).

11. An information generation method, implemented by an information generation apparatus having a processor, comprising:

generating, in a random number generator, a random number Ï Y ÎµZ q and a random number Ï Yj ÎµZ q corresponding to each element jÎµw(Y) of a set w(Y);

using, in a main information generator, the generated random number Ï Y to calculate main information k Y that satisfies k Y =Ï Y Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b N *; and

using, in a derivation information generator, the generated random number Ï Yj to calculate derivation information k Yj that satisfies k Yj =Ï Yj Î£ iÎµ{1, . . . , N-1}\w(Y) Y i b i *+b j * for each element jÎµw(Y) of the set w(Y);

* indicates an indeterminate character, an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 , and the set w(Y) corresponds to the index Y and w(Y)={i|Y i =*}.

12. An information generation method, implemented by an information generation apparatus having a processor, comprising:

generating, in a random number generator, a random number r Y ÎµZ q ;

using, in a first main information generator, the generated random number r Y to calculate first main information k Y that satisfies k Y =g 2 a (g 3 Î iÎµ{1, . . . , N-1}\w(Y) h i Yi ) rY ;

using, in a second main information generator, the generated random number r Y to calculate second main information g rY ; and

using, in a derivation information generator, the generated random number r Y to calculate derivation information k Yj that satisfies k Yj =h j rY for each element jÎµw(Y) of a set w(Y);

* indicates an indeterminate character; an index Y is Y=(Y 1 , . . . , Y N-1 )ÎµI=(F q âª{*}) N-1 ; and the set w(Y) corresponds to the index Y and w(Y)={i|Y i =*}.

13. A non-transitory computer-readable recording medium having stored thereon an information generation program that causes a computer to function as each unit of the information generation apparatus according to any one of claims 1 to 10 .

US13/258,165

2009-04-24

2010-04-23

Information generation apparatus, method, program, and recording medium for deriving a decryption key from another decryption key

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