Increasing the lifetime of a key: A comparative analysis of the security of re-keying techniques

Abstract

Rather than use a shared key directly to cryptographically process (e.g. encrypt or authenticate) data one can use it as a master key to derive subkeys, and use the subkeys for the actual cryptographic processing. This popular paradigm is called re-keying, and the expectation is that it is good for security. In this paper we provide concrete security analyses of various re-keying mechanisms and their usage. We show that re-keying does indeed “increase” security, effectively extending the lifetime of the master key and bringing significant, provable security gains in practical situations. We quantify the security provided by different rekeying processes as a function of the security of the primitives they use, thereby enabling a user to choose between different re-keying processes given the constraints of some application.