Abstract:
Secret sharing, a well-known cryptographic technique, introduced 40 years ago as a private and reliable variant of classical storage, has now become a major cryptographic primitive with numerous real-world applications. In this paper we consider the digital forensics aspects of secret sharing. We investigate the problem of framing which occurs when a coalition is able to calculate the share of a participant who does not belong to it. In the extreme case one authorized coalition can calculate shares of another authorized coalition and use the secret in some way blaming another authorized coalition for their action. In this context seniority plays an important role. We define seniority, which comes natural in the context of hierarchical access structures. Roughly speaking, our work shows that in an ideal secret sharing scheme an authorized coalition cannot frame participants who are less senior than all members of the coalition and is able to frame a participant who is more senior than at least one pivotal member of the coalition. We show that for any monotone access structure there exists a (non-ideal) frameproof secret sharing scheme.
