International Association
for Cryptologic Research

Blockchain, which is a useful tool for providing data integrity, has emerged as an alternative to centralized servers. Concentrating on the integrity of the blockchain, many applications have been developed. Specifically, a blockchain can be utilized in proving the user's identity using its strong integrity. However, since all data in the blockchain is publicly available, it can cause privacy problems if the user's identity is stored in the blockchain unencrypted. Although the encryption of the private information can diminish privacy problems in the blockchain, it is difficult to transparently utilize encrypted user information in the blockchain. To provide integrity and privacy of user information simultaneously in the blockchain, we propose a SIMS (Self-Sovereign Identity Management System) framework based on a zk-SNARK (zero-knowledge Succinct Non-interactive ARgument of Knowledge). In our proposed SIMS, the user information is employed in a privacy-preserving way due to the zero-knowledge property of the zk-SNARK. We construct a SIMS scheme and prove its security. We describe applications of SIMS and demonstrate its practicality through efficient implementations.