Common key encryption device

Abstract

The present invention provides an encryption and decryption device and an extended key generation device, method and recording medium. In the extended key generation unit of the encryption apparatus of the common key encryption method that uses the extended key in the reverse order during encryption and decryption, two cyclic functions f equal to the number of stages of the first stage and the stage number of the last stage are set. 1 and f n+1 are set to be inverse functions of each other. In this way, since the expansion key generation at the time of encryption and the expansion key generation at the time of decryption are basically the same, the expansion keys can be generated immediately and one by one in the order of use by using the public key as input at the time of encryption and at the time of decryption, which can avoid Generates a delay for generating extended keys, and can perform key generation on-the-fly.

Description

technical field [0001] This application is based on and claims the priority of prior Japanese Patent Application No. 2000-211686 filed on July 12, 2000, the entire contents of which are hereby incorporated by reference. [0002] The present invention relates to an encryption device, a decryption device, an extended key generation device, an extended key generation method, and a recording medium that use a plurality of extended keys in reverse order for encryption and decryption. Background technique [0003] Encryption technology is becoming more and more important for the security control of electronic information, especially copyright-related information, confidential information, or private information. Encryption is actually utilized in various forms in various fields. [0004] There are various encryption methods, one of which is public key encryption. The public key encryption method is a method in which decryption is performed using the same key...

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Problems solved by technology

[0020] However, since the same extended key R n The time that is not required for the generation process of , there is a problem of delay before starting decryption

[0021] As mentioned above, in the prior art, since the extended keys cannot be generated in the reverse order, all the extended keys need to be generated and stored before the decryption process, but there is a problem that, for example, in a poor hardware environment like an IC card, all the keys required for decryption are not stored. Problems with the remaining storage area for extended keys

[0022] In order to avoid this problem by key generation at any time, it is necessary to temporarily perform the same extended key generation process as in the encryption, obtain the output value obtained by applying the round function in the final cycle, and apply the output value in the reverse direction of the cycle in advance. The inverse function of each round function, but at this time there is also the problem that the delay before starting decryption cannot be avoided

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