Sharing encryption keys secretly can be useful to protect the availability and confidentiality of redundant encrypted backups. Key shares may be distributed and managed conveniently online, or offline with security benefits. We carried out a field study in order to learn how practical secret sharing is in the offline case using two form factors as carriers of share information: paper printouts and key tags. Our findings suggest that offline sharing is practical but slow. The form factor did not have a significant effect on retrieval success. Perhaps other parameters may be optimized instead such as convenience and costs of share production. We used k = 3, n = 5 as the secret sharing parameters in our study. This appears to suffice in many cases but we also found that increasing n and k is recommendable in practice because the safety and security margin was thin in our study.

Commercial trusted third parties (TTPs) may increase their bottom line by watering down their validation procedures because they assume no liability for lapses of judgement. Consumers bear the risk of misplaced trust. Reputation loss is a weak deterrent for TTPs because consumers do not choose them - web shops and browser vendors do. At the same time, consumers are the source of income of these parties. Hence, risks and rewards are not well-aligned. Towards a better alignment, we explore the brokering of connection insurances and transaction insurances, where consumers get to choose their insurer. We lay out the principal idea how such a brokerage might work at a technical level with minimal interference with existing protocols and mechanisms, we analyze the security requirements and we propose techniques to meet these requirements.