Keys in the Clouds: Auditable Multi-device Access to Cryptographic Credentials Arseny Kurnikov Andrew Paverd Aalto University, Finland Aalto University, Finland
[email protected] [email protected] Mohammad Mannan N. Asokan Concordia University, Canada Aalto University, Finland
[email protected] [email protected] ABSTRACT 1 INTRODUCTION Personal cryptographic keys are the foundation of many secure Personal cryptographic keys are the foundation of many secure services, but storing these keys securely is a challenge, especially if services, such as signing or decrypting emails, signing code, authen- they are used from multiple devices. Storing keys in a centralized ticating to remote servers, or decrypting cloud storage. However, location, like an Internet-accessible server, raises serious security storing personal cryptographic keys securely often proves to be dif- concerns (e.g. server compromise). Hardware-based Trusted Execu- ficult for users, especially when keys must be usable from multiple tion Environments (TEEs) are a well-known solution for protecting devices (e.g. PCs, smartphones, and tablets). Although we already sensitive data in untrusted environments, and are now becoming have various approaches for protecting personal cryptographic available on commodity server platforms. keys, these have various limitations: Although the idea of protecting keys using a server-side TEE Password only: keys stored directly on the user’s device may be is straight-forward, in this paper we validate this approach and compromised by malicious software on the device. Even if the keys show that it enables new desirable functionality. We describe the are protected by a password, either the password or the decrypted design, implementation, and evaluation of a TEE-based Cloud Key key could be captured by malicious software (see e.g.