Chia Network has always been at the forefront of eco-friendly and decentralized blockchain technology. As the landscape evolves, so too must the core mechanisms that secure our network. Today, we’re excited to provide an overview of a significant upgrade coming to the Chia blockchain: a proposed new Proof of Space protocol designed to enhance security, improve energy efficiency, and establish a durable foundation for the future. This isn’t just an incremental change; it’s a fundamental evolution in how Chia securely achieves consensus, addressing key challenges and paving the way for long-term sustainability. Watch Dr Nick’s overview of the new proof of space format here.
The Motivation for Change:
The current Proof of Space has served Chia well, but as detailed in CHIP-48, several key motivations drive this transition:
- Addressing Energy Consumption: While Chia’s original PoS is significantly greener than Proof of Work, the emergence of highly optimized compressed plots has introduced increased ongoing energy demands. The new PoS is engineered to mitigate this, shifting the energy cost towards the initial plotting phase rather than continuous harvesting.
- Strengthening Rental Attack Resistance: The increasing power and accessibility of high-performance computing, particularly GPUs, presents a potential risk of rental attacks. The new PoS incorporates robust defenses to significantly increase the cost and difficulty for attackers to simulate a majority of the network’s space.
- Enhancing Plot Stability: The proliferation of various plot formats has created fragmentation and uncertainty for farmers. This new standard aims to provide a long-term, stable plot format with a high Plot Stability Index (PSI), reducing the need for frequent replotting and increasing confidence in plot longevity.
This proposed upgrade is poised to benefit the entire Chia ecosystem by fostering a more secure, energy-efficient, and streamlined farming environment. It also aims to improve plotting accessibility and efficiency, even for lower-end hardware.
Introducing the New Proof of Space: The Quality Chain in Action
At the heart of this new PoS lies a novel concept: the Quality Chain. This innovative mechanism fundamentally changes how storage space contributes to consensus. Instead of continuous, energy-intensive processes, the majority of the security work is concentrated in the infrequent event of winning a block or a pool partial. This means that for honest farmers, the ongoing energy expenditure will be minimal.
Here’s a simplified look at how it works:
- Challenge and Proof Fragment: The network issues a challenge, which filters for specific Proof Fragments within a farmer’s plot. These Proof Fragments are bit-dropped and encrypted fragments of proofs.
- Chain Links: Matching Proof Fragments form Chain Links, connecting different parts of the plot.
- Building the Quality Chain: These Chain Links are then used to build a Quality Chain. This chain is constructed by a process that makes it computationally expensive for attackers to manipulate through bit-dropping.
- Winning Proof: Only if a Quality Chain meets the network’s difficulty threshold (for a block win) or a pool’s difficulty (for a partial) is the full proof reconstructed and submitted.
This approach introduces bit-drop saturation, a point where the computational cost of trying to reconstruct dropped bits to gain an advantage becomes higher than simply creating a full, honest plot. Furthermore, a tunable plot difficulty parameter allows for adjusting the plotting effort, enhancing resistance to grinding attacks without increasing the ongoing demands on harvesters or solvers.
Key Design Principles and Improvements:
The new Proof of Space incorporates several key design principles that contribute to its enhanced security and efficiency:
- Leaf-First Challenges and Proof Fragments: Challenges now target the leaves of the plot structure (where Proof Fragments reside), and the sorted nature of these Proof Fragments prevents attackers from easily exploiting neighboring data.
- Bipartite Pairing: The way data is paired within the plot structure prevents attackers from “flipping” entries for compression advantages.
- Benes Compression with Partitioned Tables: A novel compression algorithm, Benes, is employed for efficient data storage. To ensure accessibility for all farmers, partitioned tables allow for processing this compression in smaller, manageable chunks, even on systems with limited RAM.
- Smaller Plot Sizes: The new format utilizes only three core tables, resulting in significantly smaller plot sizes (e.g., ~1.6 GiB for k28), which can improve accessibility and reduce initial plotting time for some.
Comparison to the Original Proof of Space:
The original Chia Proof of Space, as detailed in the initial Proof of Space Construction, laid a groundbreaking foundation for secure, storage-based consensus. However, the new Proof of Space architecture introduces significant departures in its design to address evolving security concerns and efficiency goals. Here’s a breakdown of the key differences:
- Number of Tables: The original PoS construction utilized seven tables in its plotting process. The new Proof of Space significantly reduces this complexity, employing a design where 5 tables are constructed but only three core tables are retained in the final plot. This reduction in table count contributes to smaller plot sizes and a streamlined plotting process.
- Matching Functions and Structure: The original design relied on a series of matching functions across the seven tables, with a forward propagation and backpropagation phase to determine and refine matches. The new PoS introduces a fundamentally different approach with Proof Fragments and the Quality Chain. Instead of extensive sequential table matching, the new design primarily uses linked bit-dropped and encrypted Proof Fragments, with security now focused on their properties and the chaining mechanism, even though some limited sequential matching persists.
- Plotting Process: The original plotting algorithm involved distinct phases: Forward Propagation, Backpropagation, Compression (using Delta format and ANS encoding), and Checkpoints. The new PoS, while still involving a plotting phase, utilizes a different set of techniques, including the generation and sorting of Proof Fragments, and the creation of partitioned tables optimized for Benes compression. The concept of a Quality Chain is central to the new design and absent in the original.
- Final Disk Format: The original PoS resulted in a final disk format comprising the original value table, five tables storing positions to the previous table, a table for final outputs, and checkpoint tables. The new PoS has a more compact final format due to the reduced number of core tables and the use of Benes compression within partitioned tables.
- Proof Retrieval and Quality String: The original proof retrieval process involved traversing back through the seven tables. The quality string was derived from specific values within the retrieved proof, with a defined “plot ordering” that differed from the “proof ordering.” The new PoS retrieves proofs based on the Quality Chain and the associated Proof Fragment. The quality evaluation is tied to the successful construction and validation of this chain against a difficulty target.
- Compression Techniques: The original PoS employed Delta formatting and ANS encoding to compress positional data between tables. The new PoS leverages Benes compression, a novel algorithm particularly effective for plot-structured data, within its partitioned table architecture.
- Security Focus: While the original PoS considered resistance to Hellman attacks and cycle attacks, the new design places a strong emphasis on bit-drop saturation and a tunable plot difficulty to counter compression and rental attacks. The Quality Chain itself is a key security feature not present in the original design.
- Plot Size and HDD Activity: The original PoS aimed for large plot sizes to deter grinding attacks. The new PoS allows for significantly smaller minimum plot sizes while relying on plot difficulty and other mechanisms to maintain security. The impact on HDD activity is also managed differently, resulting in more sequential disk load and fewer disk seeks per plot to balance performance and accessibility.
In essence, the new Proof of Space represents a fundamental change to only one component of Chia’s consensus mechanism, Proofs of Time and the components pinning Proofs of Space and Proofs of Time together are not changing. While building upon the principles of using storage space for security, it introduces novel concepts like the Quality Chain and Proof Fragments, employs advanced compression techniques like Benes within a partitioned structure, and focuses on different attack vectors and efficiency considerations compared to the original seven-table design. This evolution aims to create a more resilient, energy-efficient, and stable foundation for the Chia blockchain’s future.
The Transition: A Phased Approach
Implementing such a fundamental change requires a carefully managed transition. As outlined in CHIP-49, a hard fork will be necessary to activate the proposed new Proof of Space. This will be accompanied by a phased replotting period, during which legacy plots will gradually be deprecated. Chia Network will provide production-level plotters and harvesters well in advance of the hard fork to ensure a smooth transition for the community.
Looking Ahead:
This new Proof of Space marks a crucial step in the evolution of Chia Network. By addressing the challenges of energy efficiency, rental attack risks, and plot stability, we are building a more secure, sustainable, and future-proof blockchain. We encourage the community to explore the technical details in the linked CHIPs and participate in discussions as we move towards this exciting new era for Chia.
More details about the timeline are available in our overview blog and associated CHIP-49.
Conclusion:
The introduction of the new Proof of Space is a testament to Chia Network’s commitment to innovation and long-term vision. By embracing advancements in cryptographic techniques and addressing the evolving challenges in the blockchain space, we are laying a stronger foundation for a green, decentralized digital currency. This upgrade promises a more secure, efficient, and stable Chia network for years to come.