A Key Recovery System Based on Password-protected Secret Sharing in a Permissioned Blockchain

In today’s fourth industrial revolution, various blockchain technologies are being actively researched. A blockchain is a peer-to-peer data-sharing structure lacking central control. If a user wishes to access stored data, she/he must employ a private key to prove ownership of the data and create a transaction. If the private key is lost, blockchain data cannot be accessed. To solve such a problem, public blockchain users can recover the key using a wallet program. However, key recovery in a permissioned blockchain (PBC) has been but little studied. The PBC server is Honest-but-Curious (HBC), and should not be able to learn anything of the user; the server should simply recover and store the key. The server must also be resistant to malicious attacks. Therefore, key recovery in a PBC must satisfy various security requirements. Here, we present a password-protected secret sharing (PPSS) key recovery system, protected by a secure password from a malicious key storage server of a PBC. We describe existing key recovery schemes and our PPSS scheme.