SSUkey: A CPU-based solution protecting private keys on untrusted OS

Abstract

With more and more websites adopt private keys to authenticate users or sign digital payments in e-commerce, various solutions have been proposed to secure private keys – some of them employ extra specific hardware devices while most of them adopt security features provided by general OS. However, users are reluctant to extra devices and general OS is too complicated to protect itself, let alone the private keys on it. This paper proposes a software solution, SSUKey, adopting CPU security features to protect private keys against the vulnerabilities of OS. Firstly, threshold cryptography (TC) is employed to partition the private key into two shares and two Intel SGX enclaves on local client and remote server are used to secure the key shares respectively. Secondly, the two enclaves are carefully designed and configured to mitigate the vulnerabilities of Intel SGX, including side channel and rollback. Thirdly, an overall central private key management is designed to help users globally monitor the usage of private keys and detect abnormal behaviors. Finally, we implement SSUKey as a cryptography provider, apply it to file encryption and Transport Layer Security (TLS) download, and evaluate their performance. The experiment results show that the performance decline due to SSUKey is acceptable.