Proof of Storage Time: Efficiently Checking Continuous Data - PowerPoint PPT Presentation

Proof of Storage Time: Efficiently Checking Continuous Data Availability Gi Giuseppe At Ateniese Lo Long Chen hen Stevens Institute of Technology New Jersey Institute of Technology Mo Moham ammad ad Et Etemad ad Qi Qiang Ta Tang Stevens Institute of Technology New Jersey Institute of Technology

Outsourced Storage is a common practice Backup Data sharing Saving Cost

Example Case A hospital stores medical imaging data on the cloud Surgeons will consult these data during an emergency surgery A brief downtime will cause a serious medical accident! Co Continuous da data av availability is is cr cruci cial

Mission and Business Critical Applications Brief downtime may lead to serious negative consequences ◦ Lost of productivity ◦ Financial pain ◦ Damages to the business’ reputation

Threats to Continuous Availability Equipment Power outrages Malicious attackers failures

Cost of Continuous Availability More replications More hardware and software components More complex administration Co Continuous av availability mea means a hi high price ce !

Verify Continuous Availability A dishonest server would provide an inferior service The client who paid a high price must verify the continuous availability

Decentralized Storage Market File Data Owner Blockchain

Decentralized Storage Market File ! Data Owner Server • ! must be succinct Smart Contract • Verification must be cheap

Definition Proof of Construction Storage- time Instantiation

Proof of Construction Storage- time Instantiation

PoSt Framework Store Challenge Response

Security Definition Proof of Retrievability Proof of Storage-time Goa oal : Verify data availability Goa oal : Verify continuous availability Securi urity ty : Extractability Securi urity ty : Continuous extractability

Continuous Extractability File Stop at time point ! Adversary Extractor Record the current state in the memory

Definition Proof of Storage- time Instantiation

Naïve Attempts Proof of Retrievability •A challenge and response protocol •Only certify availability at the time a valid proof is processed Frequent PoR •Inefficient communication and verification •The client needs to be always online

Send PoR challenges in advance ◦ The prover may compute all PORs rapidly Unsuccessful and discard the data Attempts Send PoR challenges in the end ◦ The prover could keep data offline and retrieve them at the last moment

Filecoin’s proposal 1. Send PoR challenge ! " 2. Compute the PoR proof # " Problem: : 3. Let ! $ = &'(ℎ # " ◦ No concrete delay guarantee ◦ Verification is inefficient 4. Compute the PoR proof # $ 5. …… 6. Send back all ! * and # *

! " = $ & Ø To compute $ for honest guys takes time Verifiable almost % Delay Ø Malicious guy, even with parallel ability, can Function not get the result within time % Ø Anyone can efficiently verify the correctness of the evaluation with a proof &

Warm-up ! " Construction # " Given a PoR challenge ! " 1. VDF 2. Generate the PoR # " ! $ Compute ! $ , & $ = 3. ()*(# " ) # $ Generates the PoR # $ 4. 5. Etc. PoSt Proof Output all ! - , # - , & - 6.

Problem • The proof size is too large • Verification is inefficient

! " = $ Ø To compute $ for honest guys takes time Trapdoor almost % Delay Ø Malicious guy can not get $ within time % even with parallel computing Function ! ", '()*+,,( = $ Ø Anyone with trapdoor can compute $ within time significantly smaller than %

Main Construction Verification: ! " ! " ! " , $ " , ! % , $ % , … = ! " , $ " , ! % , $ % , … $ " $ " Aggregation Without Delay Delay ! % ()*ℎ(! " , $ " , ! % , $ % , … ) ! % = ()*ℎ(! " , $ " , ! % , $ % , … ) $ % $ % Public Validation .)/ = ()*ℎ(()*ℎ ! " , $ " , ! % , $ % , … )

Decentralized Storage Market File Data Owner Server !"# ℎ Verify !"# = &"'ℎ(ℎ) Smart Contract

Definition Proof of Construction Storage- time

Ver erification on Proof oof Stor oring Extremely Inherent Main left efficient cost concern Efficiency of Each Procedure

Storing Procedure Optimization Adopting Hash based PoRs Precomputation Accelerate the PoR by Parallel Computation Others…

Storing Benchmark 250 200 Setup time (min) 150 64 MB 128 MB 100 192 MB 50 256 MB 0 30 60 90 120 150 Data available time (day) Hourly data check up

PoSt can verify continuous data availability PoSt can be used to realize the decentralized storage market Summary Future work ◦ Optimization the storing procedure ◦ Make it stateless ◦ Achieve public verifiable ◦ More applications

Thank you for attention Gi Gius useppe At Ateniese Long C Chen Stevens Institute of New Jersey Institute of Technology Technology Mo Moha hammad Et Etemad Qi Qiang Ta Tang Stevens Institute of New Jersey Institute of Technology Technology