A network system using a threshold secret sharing method

摘要

In a data encryption/decryption method including an encryption step and a decryption step. In the encryption step (Fig. 2), there are prepared n pairs of secret keys (d1 to d4) and public keys (Q1 to Q4) in a public-key cryptographic scheme, where n is a positive integer. A new key is generated in accordance with at least one of the public keys. Data is encrypted in a common-key cryptographic scheme by use of the new key. There is prepared a (k,n) threshold logic (k is an integer equal to or less than n) having terms associated with the new key and the n public keys. A calculation of the threshold logic is conducted by use of the new key and the n public keys, and encrypted data and a result of the calculation of the threshold logic are stored. In the decryption step (Fig. 3), the new key is restored from k secret keys selected from the n secret keys and the stored result of the threshold logic calculation in accordance with a threshold reverse logic corresponding to the threshold logic and stored data is decrypted by the restored key in the common-key cryptographic scheme.