Proof of Spacetime

2.3.0 Proof of Spacetime (PoSt)

Proof of Spacetime (PoSt) plays a pivotal role in Candao’s consensus model, ensuring that data remains stored over an agreed period. While Proof of Replication (PoRep) confirms that data is uniquely and correctly stored, PoSt continuously checks whether the storage provider maintains that data for the required duration. This combination of time-bound and replication-based proofs provides a robust system for maintaining data integrity, availability, and trust in a decentralized cloud.

PoSt operates by issuing periodic challenges to storage providers. These challenges require the providers to prove that they are still storing the correct data, ensuring long-term availability.

• Continuous Data Availability: The primary function of PoSt is to verify that the data remains accessible throughout the agreed storage period. It ensures that data is not simply stored at one point in time, but remains accessible for future retrieval.

• Challenge-Response Protocol: Validators, who are responsible for ensuring data availability, issue randomized challenges to storage providers. These challenges require the provider to prove, through cryptographic methods, that they are still holding the correct data. Since an encrypted version of the file is stored, users cannot access the original file contents.

• Spacetime Proofs: In response to these challenges, storage providers generate a spacetime proof, a cryptographic representation that confirms the ongoing storage of data. These proofs are verified by validators and recorded on the CDO-Chain.

2.3.1 Technical Breakdown of Proof of Spacetime

PoSt is implemented in several steps, ensuring a secure and reliable verification of data availability over time:

• Initial Storage Agreement: When a storage provider agrees to store data, the contract begins with the generation of a Proof of Replication (PoRep), confirming that a unique encrypted replica of the data is securely stored. This marks the start of the storage term.

• Randomized Challenges: Validators issue randomized challenges at intervals throughout the storage term. These challenges require the storage provider to demonstrate that they still hold the replicated data. The randomness of these challenges ensures that the provider cannot predict or manipulate when they will need to prove their data availability.

• Generating Spacetime Proofs: Upon receiving a challenge, the storage provider must generate a spacetime proof. This proof is a cryptographic record that shows the provider has consistently stored the data for the agreed-upon time. Spacetime proofs are designed to be lightweight and efficient, ensuring that they can be generated and verified quickly. They can not be replayed and they are time limited.

• Verifying Spacetime Proofs: Validators verify the spacetime proof provided by the storage provider. If the proof is valid, the provider is rewarded with CDO tokens from the Ecosystem Rewards Pool. If the provider fails to produce a valid proof, penalties are applied, which at worst can include the slashing of staked collateral (CDO tokens).

• On-Chain Recording: Once verified, the spacetime proof is recorded on the CDO-Chain. This immutable record ensures transparency and accountability, as all proof verifications are publicly accessible.

2.3.2. Benefits of Proof of Spacetime

The Proof of Spacetime mechanism offers several benefits to both the Candao network and its users:

• Ensures Long-Term Data Availability: PoSt guarantees that data is stored for the duration of the agreed contract, offering users confidence that their files will be available when needed.

• Mitigates Data Loss: By continuously challenging storage providers to prove they are holding the data, PoSt minimizes the risk of data loss. Providers are incentivized to invest in high-quality storage infrastructure to meet the network’s requirements.

• Scalable Verification: PoSt is designed to be scalable, allowing for the verification of large volumes of data across a growing network without requiring excessive computational resources. This makes the system suitable for handling the increasing demand for decentralized cloud.

• Decentralized Security: PoSt enhances the security of the Candao network by decentralizing the verification process. No single entity controls the challenges or proofs, ensuring that the network remains trustless and resilient against attacks. Users do not have to trust a single entity for the safe keeping of their data.

2.3.3 Security Considerations in PoSt

Security is a top priority for the Candao network, and PoSt plays a critical role in maintaining it:

• Protection Against Sybil Attacks: PoSt, combined with the staking of CDO tokens, helps protect the network from Sybil attacks, where malicious actors create multiple fake identities to undermine the system. By requiring significant collateral and frequent proofs of storage, the network ensures that only legitimate providers can participate.

• Data Integrity and Confidentiality: PoSt works alongside encryption and zk-SNARKs, to ensure that storage proofs are confidential. This prevents unauthorized access to the data while still allowing validators to verify its continued existence.

• Geo-Distribution of Storage Providers: To further enhance security, Candao ensures through a reward mechanism that storage providers are distributed across different geographic regions. This minimizes the risk of localized attacks or natural disasters compromising the network.

2.3.4. Future Enhancements to Proof of Spacetime

As the Candao network evolves, there are several avenues for improving PoSt:

• Improved Validator Algorithms: Candao could implement more advanced algorithms for generating and verifying spacetime proofs, reducing the time and resources required for validation. Verification of encrypted data integrity over a large scale decentralized network is an ongoing engineering problem.

• Multi-Level PoSt: In a multi-level PoSt system, storage providers would be categorized into tiers based on their performance and the sensitivity of the data they store. Providers with better performance or who store more critical data could receive higher rewards and more stringent challenges.