RECOVERY METHOD FOR PRIVATE KEY AND STORAGE METHOD

PROBLEM TO BE SOLVED: To provide a recovery method for private key and its storage method that securely stores a private key and securely and surely realizes key recovery when the private key is lost. SOLUTION: A computer A100 possessing a private key A12 selects credible computers B110 and C120 in advance, after its own private key A12 is encrypted by using a public key C26 of the computer C120, the computer A100 transmits the encrypted public key to the other computer B110, which securely stores the key as an encrypted private key C(A) 36. When the computer A100 loses the private key A12, the computer A100 acquires the encrypted private key C(A) 36 from the computer B110 and transmits it to the computer C120, uses the private key C41 of the computer C120 to decode it into the original private key A12 and the computer C120 transmits the decoded private key A12 to the computer A100 of the possessor to realize key recovery of the private key A12.