Key agreement system, shared-key generation apparatus, and shared-key recovery apparatus

Abstract

Provided is a content distribution system that prevents different keys to be derived between an encryption apparatus and a decryption apparatus. A random-number generating unit 112, in an encryption apparatus 110, generates a random number s. A first function unit 113 generates a functional value G(s) of the random number s, and generates a random-number value u and a shared key K from the functional value G(s). An encryption unit 114 generates a first cipher text c1 of the random number s, using a public-key polynomial h and the random-number value u. A decryption unit 123, in a decryption apparatus 120, decrypts the first cipher text c1 using a secret-key polynomial f, to generate a decryption random number s' A second function unit 126 generates a functional value G(s') of the decryption random number s', and generates a random-number value u' and a shared key K'from the functional value G(s' ). A comparison unit 127 generates a first re-cipher text c1', using the random-number value u' and the shared key K', and outputs the shared key K' if the first cipher text c1 is equal to the first re-cipher text c1'.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a cryptographic technology used as an information security technology. The present invention particularly relates to a technology of distributing a key under a condition that any third party cannot know the content of the key.[0003] 2. Description of Related Art[0004] Conventionally, the public-key cryptosystem has been used for transmitting information from a transmission apparatus to a reception apparatus in secrecy.[0005] In the public-key cryptosystem, a transmission apparatus encrypts a communication content using the public key of a reception apparatus, and sends the encrypted communication content to the reception apparatus. The reception apparatus receives the encrypted communication content, and decrypts the encrypted communication content using a secret key, thereby obtaining the original communication content (e.g. refer to the non-patent reference 1).[0006] In the year of 1996, the NTRU cryptosystem ...

AI Technical Summary

Benefits of technology

[0048] The object of the present invention, in view of the above-described problems, is to provide a key agreement system, a shared-key generation apparatus, a shared-key recovery apparatus, a shared-key generating method, a shared-key recovery method, a shared-key generating program, and a shared-key recovery program, which prevents derivation of different keys between the shared-key generation apparatus and the shared-key recovery apparatus.

[0119] According to this construction, the shared-key recovery apparatus decrypts the received encrypted content, using the outputted decryption shared key, to generate a decrypted content. Therefore, there is an effect that a content is received from the shared-key generation apparatus, in secrecy.

Problems solved by technology

However, the mentioned processes have a possibility of yielding decrypted text that is different from the original plaintext.

On the contrary, other reception apparatuses that do not know about the secret key sk cannot obtain the element s from the cipher text C, even if they have acquired the public key pk and received the cipher text C. This means that these reception apparatuses cannot derive the same shared key K as that derived by the transmission apparatus.

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