Proactive Security: Long-term protection against break-ins

Proactive security provides a method for maintaining the overall security of a system, even when individual components are repeatedly broken into and controlled by an attacker. In particular it provides for automated recovery of the security of individual components, avoiding the use of expensive and inconvenient manual processes (unless perhaps when an ongoing attack is detected). The technique calls for the distribution of trust among several components (servers), together with periodic refreshments of the sensitive data held by the servers. This way, the proactive approach guarantees uninterrupted security as long as not too many servers are broken into at the same time. We describe the proactive approach and review some algorithms, implementations, and applications. We elaborate on two of the most important results: proactive signatures and proactive secure communication. Proactive signatures provide a solution for long-lived secret keys, such as the key of a certi cation authority. Proactive secure communication ensures secrecy and authenticity of communication, with automated refresh of the secret keys.