Privacy-Preserving Delegatable Proofs of Storage based on Privately
Verifiable Proofs of Storage
Abstract
In ESORICS’16, Xu et al. introduced a new notion called delegatable
proofs of storage (delegatable POS, DPOS), which strikes a balance
between privately verifiable POS (PriPOS) and publicly verifiable POS
(PubPOS). Their scheme offers efficiency similar to PriPOS while
allowing third-party auditors to verify file integrity, with auditors
being revocable and replaceable, thus approximating PubPOS. Later in
2018, Yang et al. enhanced the scheme with data dynamic and
privacy-preserving features. However, the scheme’s design is intricate,
introduces new hardness assumptions, and has the potential for improved
computational efficiency. Our work explores the connections between
PriPOS and DPOS, proposing a generic construction that could construct
DPOS schemes directly from PriPOS ones. Our generic construction removes
the need for new designs or additional assumptions, retains PriPOS’s
efficiency, and avoids the overhead of re-downloading files. We formally
prove the security of our generic construction and showcase it by
instantiating a DPOS scheme based on a classical PriPOS scheme, which
concretely shows key advantages. The proposed scheme uses standard
primitives like pseudo-random functions, avoids costly pairings, and
optimizes computational and communication costs. Furthermore, our
generic construction seamlessly accommodates the extension of DPOS
schemes to incorporate advanced features. Specifically, we enhance the
base DPOS scheme with random masks to achieve a privacy-preserving DPOS
scheme and integrate Index Management Tree (IMT) to develop a dynamic
DPOS scheme, which reduces update complexity to O ( log n ) .