An efficient threshold key-insulated signature scheme

Abstract

To tackle the key-exposure problem in signature settings, this paper introduces a new cryptographic primitive named threshold key-insulated signature (TKIS) and proposes a concrete TKIS scheme For a TKIS system, at least k out of n helpers are needed to update a user's temporary private key. On the one hand, even if up to k−1 helpers are compromised in addition to the exposure of any of temporary private keys, security of the non-exposed periods is still assured. On the other hand, even if all the n helpers are compromised, we can still ensure the security of all periods as long as none of temporary private keys is exposed. Compared with traditional key-insulated signature (KIS) schemes, the proposed TKIS scheme not only greatly enhances the security of the system, but also provides flexibility and efficiency. Key words: threshold key-insulation, signature, random oracle model CLC number: TN 918, TP 301 Document code: A IntroductionWith the growing use of mobile devices allowing remote unprotected access, key exposures appear to be unavoidable. If private keys are exposed, all security guarantees are lost. To tackle the above problem, Dodis et al. [1] introduced a key insulation mechanism, which can protect private keys in public key cryptosystems. In a key-insulated cryptosystem, long-term keys (called helper keys) are kept in a physically-secure but computationally-limited device called helper. On the other hand, users store short-term private keys (called temporary private keys) in a powerful but insecure device where cryptographic computations happen.The key-insulated cryptosystem refreshes the temporary private keys at discrete time periods via interaction between the user and the helper, and the public key remains unchanged throughout the lifetime of the system. However, frequent updating of the temporary private key will also put the helper key in a higher risk

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