Nippon Telegraph and Telephone Corporation

Ryo Nishimaki

Tetsutaro Kobayashi

Reo Yoshida

Koutarou Suzuki

Yuki Okano

Takashi Yamakawa

A digital watermark system that realizes digital watermark for a cryptographic function, including a memory and a processor configured to take as input a security parameter and generate a watermark embedding key for embedding information representative of a watermark in a circuit that realizes the cryptographic function, and a watermark extraction key for extracting information representative of the watermark from a circuit in which a watermark is embedded; take as input a master private key used for the cryptographic function, the watermark embedding key, and information representative of a watermark, and generate a circuit in which the watermark is embedded and that realizes the cryptographic function; and take as input the watermark extraction key and the circuit in which the watermark has been embedded, and extract information representative of a watermark from the circuit.

Digital watermark system, digital watermark method and program

An ID-based hash proof system configuration apparatus includes a processor, and a memory storing program instructions that cause the processor to receive a security parameter, and output a public parameter and a master private key by using a multi identity-based encryption (MIBE) setup algorithm and a key K randomly selected, receive the public parameter, the master private key, and an identifier, and output a private key by using a bit value r(1&#x2264;i&#x2264;n) that is selected, and a MIBE key generation algorithm, receive the public parameter and the identifier, and output a ciphertext and a key k by using a MIBE encryption algorithm, receive the public parameter and the identifier, and output a wrong ciphertext by using the MIBE encryption algorithm, and receive the public parameter, the private key, the identifier, and the ciphertext, and output the key k by using a MIBE decryption algorithm.

Identity-based hash proof system configuration apparatus, identity-based encryption apparatus, identity-based hash proof system configuration method and program

A transformation key generation apparatus has key generation means for receiving a decryption key sks of a first public key encryption scheme &#x3a3;s and a public key pkd of a second public key encryption scheme &#x3a3;d, and generating a transformation key utks&#x2192;d for transforming first ciphertext cts of the first public key encryption scheme &#x3a3;s into second ciphertext tct of the second public key encryption scheme &#x3a3;d by using a probabilistic circuit or function secret sharing.

Conversion key generation apparatus, encrypted text conversion apparatus, decryption apparatus, encrypted text conversion system, conversion key generation method, encrypted text conversion method, decryption method, and program

A communication terminal which is capable of reducing load of a server apparatus by reutilizing a message key to be used for encrypting a message is provided. The communication terminal includes a session key storage part which stores a session key which is shared with another communication terminal and which is not shared with the server apparatus, a message key generating part which generates a message key, a message key storage part which stores the message key to be reutilized in association with a message key identifier, a message encrypting part which generates a message encrypted text based on a common key cryptosystem using the message and the message key, a message key encrypting part which generates a message key encrypted text based on a common key cryptosystem which can perform re-encryption using the session key and the message key, and an encrypted text transmitting part which transmits a group identifier which is an identifier of a group to which an own terminal belongs, the message key encrypted text or the message key identifier, and the message encrypted text to the server apparatus.

Communication terminal, server apparatus, and program

There is provided an encrypted message search technique making it difficult to, at the time of searching for a message in a state of being encrypted, guess content of the search and a result of the search. There are included: an encrypted search secret key transmission step of a terminal generating an encrypted search secret key from a search secret key generated each time an update interval set in advance elapses and transmitting the encrypted search secret key to a server; a search secret key decryption step of the terminal decrypting the encrypted search secret key acquired from the server to obtain the search secret key; an encrypted message transmission step of the terminal transmitting an index set generated using information related to a message and a newest search secret key, and an encrypted message to the server; a query transmission step of the terminal transmitting a query set generated using a message search character string and the search secret key; and an encrypted message returning step of the server transmitting an encrypted message including elements of an index set corresponding to an element of the query set.

Encrypted message search method, message transmission/reception system, server, terminal and program

A communication terminal shares a session key with and sends cipher text to another communication terminal via a server device, including: a common key cipher text obtaining unit that encrypts a message based on a common key to obtain common key cipher text; a function computation result obtaining unit that computes the common key and the session key based on a predetermined first function to obtain a function computation result; a public key cipher text obtaining unit that encrypts the function computation result based on a public key to obtain public key cipher text; and a cipher text sending unit that sends the common key cipher text and the public key cipher text to the server device. The communication terminal can update data previously saved in a server to data that can be decrypted on the communication terminal side using an updated session key, without the server decrypting the data.

Communication terminals, server devices, and programs

A sharing apparatus independently shares a value corresponding to each element &#x3b8;(&#x3c8;, i, &#x3b2;)&#xb7;gof basis vectors b*(&#x3b8;) among each subset SUB(&#x3b1;) consisting of H(&#x3b1;) share management apparatuses PA(&#x3b1;, 1), . . . , PA(&#x3b1;, H(&#x3b1;)) to generate share information SH(&#x3c8;, i, &#x3b2;, &#x3b1;, h(&#x3b1;)) corresponding to each element &#x3b8;(&#x3c8;, i, &#x3b2;)&#xb7;g. The share management apparatus PA(&#x3b1;, h(&#x3b1;)) generates a share secret value DSH(&#x3c8;, &#x3b1;, h(&#x3b1;)) by performing a common calculation common in the subset SUB(&#x3b1;) on common information shared in the subset SUB(&#x3b1;) and the share information SH(&#x3c8;, i, &#x3b2;, &#x3b1;, h(&#x3b1;)). An acquisition apparatus generates reconstructed secret values SUBSK(&#x3c8;, &#x3b1;) for each subset SUB(&#x3b1;) by performing a reconstruction processing for the subset SUB(&#x3b1;) and generates generation information D*(&#x3c8;) from the reconstructed secret values SUBSK(&#x3c8;, &#x3b1;).

Secret sharing system, sharing apparatus, share management apparatus, acquisition apparatus, secret sharing method, program and recording medium

Hierarchical cryptography expressed in a general semiordered structure other than a tree structure is implemented. In information generation, random numbers &#x3c3;and (&#x3c3;)&#x3b5;Zare generated; main information k=&#x3c3;&#x3a3;vb*+b* is calculated; and derivation information k=&#x3c3;&#x3a3;vb*+b* is calculated for each j&#x3b5;w(v). In information derivation, random numbers &#x3c3;and (&#x3c3;)&#x3b5;Zare generated; main information k=&#x3c3;&#x3a3;uk+kis calculated; and derivation information k=&#x3c3;&#x3a3;uk+kis calculated for each j&#x3b5;w(v).

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

A secure secret sharing system is implemented. Shares SH(&#x3b1;, h(&#x3b1;)) are generated by secret sharing of secret information separately for each subset SUB(&#x3b1;); each of share management apparatuses PA(&#x3b1;, h(&#x3b1;)) generates a shared secret value DSH(&#x3b1;, h(&#x3b1;)) by performing a common operation to a corresponding share SH(&#x3b1;, h(&#x3b1;)) and common information containing a common value &#x3c3;(&#x3b1;) shared in each subset SUB(&#x3b1;); and an acquisition apparatus generates a reconstructed secret value SUBSK(&#x3b1;) by reconstruction processing for each subset SUB(&#x3b1;), using a plurality of shared secret values DSH(&#x3b1;, h(&#x3b1;)) corresponding to the same subset SUB(&#x3b1;), and generates generation information SK by using the reconstructed secret values SUBSK(&#x3b1;).

Secret sharing system, sharing apparatus, share management apparatus, acquisition apparatus, processing methods thereof, secret sharing method, program, and recording medium

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Musashino, Japan

Ryo Nishimaki