VESPo: Verified Evaluation of Secret Polynomials (with application to dynamic proofs of retrievability)

Proofs of Retrievability are protocols which allow a Client to store data remotely and efficiently ensure, via audits, that the entirety is still intact. Dynamic (DPoR) also support efficient retrieval update any small portion data. We propose novel protocol for arbitrary outsourced storage achieves both low remote size audit complexity. A key ingredient, can be intrinsic interest, reduces evaluating secret polynomial at given public points, when (encrypted) stored on an untrusted Server. The Server performs evaluations returns associated certificates. check correct using certificates some pre-computed keys, more than re-evaluating polynomial. Our two important features: itself encrypted Server, it dynamically updated by changing individual coefficients cheaply without redoing entire setup. methods rely linearly homomorphic encryption pairings, our implementation shows good performance with millions coefficients, DPoR terabytes For instance, 1TB database, compared state art, we reduce 5000x, communication 20x, client-side time 2x, cost one order magnitude increase in server-side time.