Undetachable Threshold Signatures

Abstract

A major problem of mobile agents is their inability to authenticate transactions in a hostile environment. Users will not wish to equip agents with their private signature keys when the agents may execute on untrusted platforms. Undetachable signatures were introduced to solve this problem by allowing users to equip agents with the means to sign signatures for tightly constrainedtransactions, using information especially derived from the user private signature key. However, the problem remains that a platform can force an agent to commit to a sub-optimal transaction. In parallel with the work on undetachable signatures, much work has been performedon thresholdsignature schemes, which allow signing power to be distributed across multiple agents, thereby reducing the trust in a single entity. We combine these notions and introduce the concept of an undetachable threshold signature scheme, which enables constrainedsigning power to be distributed across multiple agents, thus reducing the necessary trust in single agent platforms. We also provide an RSA-based example of such a scheme basedon a combination of Shoup’s thresholdsignature scheme, [1] and Kotzanikolaou et al’s undetachable signature scheme, [2].

The work reportedin this paper has formed part of the Software Based Systems area of the Core 2 Research Programme of the Virtual Centre of Excellence in Mobile & Personal Communications, Mobile VCE, www.mobilevce.com, whose funding support, including that of the EPSRC, is gratefully acknowledged. More detailed technical reports on this research are available to Industrial Members of Mobile VCE.