Two‐level security for message sequences

We consider a scenario where a sequence of messages must be protected and the security requirement is that, the most recent message has high level of security while past messages could be secured at a lower level. We assume the adversary is an eavesdropping adversary and has unlimited computational power. The motivation for this problem is situations where sensitivity of messages reduce over time, and this could be used to reduce the overall required key length of the system. The aforementioned requirements suggest dynamic security level for a message: when it is the last message in the sequence, it enjoys a high level of security, but as soon as a new message arrives, its security is decreased to a second lower level.We formalize security of this scenario, construct an encryption system with provable security, and show that the required key length in some sense (that will be explained) is optimal. We discuss our results and directions for future research. Copyright © 2016 John Wiley & Sons, Ltd. We consider a scenario where a sequence of messages must be protected and the security requirement is that, the most recent message has high level of security while past messages could be secured at a lower level. We assume the adversary is an eavesdropping adversary and has unlimited computational power. We formalize security of this scenario, construct an encryption system with provable security, and show that the required key length is optimal.