Cryptographic system

Patent metadata

Field	Value
Publication number	US-9722783-B2
Application number	US-201314421282-A
Country	US
Kind code	B2
Filing date	Jul 17, 2013
Priority date	Oct 19, 2012
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

An inner-product predicate encryption scheme with improved flexibility without a restriction that the dimensions of an attribute vector x → and a predicate vector v → should be equivalent. A ciphertext having an element c 0 and an element c t for each index t included in a set I x→ is decrypted with a decryption key having an element k 0 and an element k t for each index t included in a set I v→ by computing a product of pairing operations between corresponding pairs of basis vectors on the element c 0 and the element k 0 and on the element c t and the element k t .

First claim

The invention claimed is:

1. A cryptographic system comprising:
an encryption device; and
a decryption device,
wherein the encryption device includes a first processor programmed to perform functions of a ciphertext generation unit that generates a ciphertext having an element c 0 in which a value ω ˜ is set as a coefficient of a basis vector b 0,r , and an element c t in which attribute information x t is set as a coefficient of a basis vector b p and the value ω ˜ is set as a coefficient of a basis vector b q , for each index t included in a set I x→ , and
wherein the decryption device includes
a memory configured as a decryption key storage unit that stores a decryption key having an element k 0 and an element k t which are generated using a value s t and a value s 0 which is a sum of the value s t for each index t included in a set I v→ , the element k 0 being an element in which a value −s 0 is set as a coefficient of a basis vector b* 0,r corresponding to the basis vector b 0,r , the element k t being an element in which predicate information v t is set as a coefficient of a basis vector b* p corresponding to the basis vector b p and the value s t is set as a coefficient of a basis vector b* q corresponding to the basis vector b q , for each index t included in the set I v→ , and
a second processor programmed to perform functions of a decryption unit that decrypts the ciphertext generated by the ciphertext generation unit with the decryption key stored by the decryption key storage unit, the decryption unit decrypting the ciphertext by computing a product of pairing operations between corresponding pairs of the basis vectors on the element c 0 and the element k 0 and on the element c t and the element k t for each index t included in the set I v→ .

2. The cryptographic system according to claim 1 ,
wherein the ciphertext generation unit further generates an element c t in which information J which is assigned in advance to the index t is set as a coefficient of a basis vector b index , and
wherein the decryption key storage unit further generates an element k t in which information J′ having an inner-product of 0 with the information J which is assigned in advance to the index t is set as a coefficient of a basis vector b* index corresponding to the basis vector b index .

3. The cryptographic system according to claim 2 ,
wherein the ciphertext generation unit generates the element c 0 and the element c t as indicated in Formula 1,
wherein the decryption key storage unit stores the element k 0 and the element k t as indicated in Formula 2, and
wherein the decryption unit performs computation as indicated in Formula 3,

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Assignees

• Mitsubishi Electric Corp
• Nippon Telegraph & Telephone

Inventors

• Takashima Katsuyuki
• Okamoto Tatsuaki

Classifications

• H04L9/0866

  involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics · CPC title

• H04L9/0838 Primary

  Key agreement, i.e. key establishment technique in which a shared key is derived by parties as a function of information contributed by, or associated with, each of these (network architectures or network communication protocols for key exchange in a packet data network H04L63/061) · CPC title

• H04L9/007

  involving hierarchical structures · CPC title

• H04L9/0861

  Generation of secret information including derivation or calculation of cryptographic keys or passwords · CPC title

• G09C1/00

  Apparatus or methods whereby a given sequence of signs, e.g. an intelligible text, is transformed into an unintelligible sequence of signs by transposing the signs or groups of signs or by replacing them by others according to a predetermined system (cryptographic typewriters G09C3/00) · CPC title