I Need this Back, Later! An Exploration of Practical Secret Sharing

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 (N=108) 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.