Versioning CHAIN_HASH For Seamless Blockchain Upgrades

Understanding the Need for Versioned CHAIN_HASH

The CHAIN_HASH is a critical component in blockchain security, particularly within the context of sovereign-labs and the sovereign-sdk. Currently, any alteration to the RuntimeCall or Transaction types triggers a change in the Runtime::CHAIN_HASH. This seemingly simple update has significant implications: it invalidates all existing transactions on the data availability (DA) layer. This invalidation occurs because the CHAIN_HASH is integral to signature verification. In essence, the hash acts as a unique fingerprint for the blockchain state at a given point in time, and signatures are validated against this fingerprint. When the fingerprint changes, previously valid signatures become invalid, causing significant issues when upgrading the system. This can effectively halt a chain because old transactions will no longer be valid. It is a real problem for the system, and addressing it will result in better functionality and user experience.

Imagine a scenario where the runtime of your blockchain undergoes an upgrade. The introduction of new features, bug fixes, or performance enhancements invariably involves modifications to the transaction format or the call structure. These modifications, however small, lead to a change in the CHAIN_HASH. Consequently, all transactions that were valid before the upgrade become invalid afterward. This creates a critical hurdle for users who want to resync the chain after an upgrade or anyone attempting to access historical data. They will find that they are unable to execute the past transactions as these are rejected as invalid. This breaks the ability to verify all past transactions, which is a core tenet of blockchain technology, specifically with the immutability of the chain. To mitigate these issues, we need a robust solution that allows us to manage and support changes to CHAIN_HASH in a versioned manner.

To address this critical issue, we propose implementing a versioned CHAIN_HASH system. At its core, this solution involves storing historical CHAIN_HASH values. This would create a mapping from rollup height to a new chain hash. Resyncing the chain will use the appropriate chain hash for each block to verify the signatures of old transactions. This will enable users to resync the chain even when the active chain hash is different. Without such a solution, blockchain upgrades become far more complex and risky, potentially leading to significant downtime and data loss. This also makes the process of upgrading significantly smoother. With versioning, the upgrades become much more transparent and less risky. This will give users more confidence in the system, and will increase adoption and use.

This approach aligns with the core principles of blockchain technology, ensuring that historical transactions remain valid and verifiable, even as the system evolves. By maintaining a history of CHAIN_HASH values, we can ensure that users can always verify the integrity of the blockchain, regardless of the version of the runtime they are using. This approach is more complex to implement at first, but is a worthy trade off for a more reliable, trustworthy, and upgradeable system.

Key Considerations for Implementation

Implementing a versioned CHAIN_HASH system involves several key considerations. Firstly, we must address the automatic generation of the chain hash at build time. Currently, the CHAIN_HASH is generated automatically during the build process, which simplifies the process. But, with versioning, this will require manual specification of older hashes, most likely through configuration files. This means developers must meticulously track and configure these hashes as part of the upgrade process. This also means users need to update their configuration files whenever an upgrade occurs, increasing the complexity of the deployment process.

Secondly, we need to take ZK (Zero-Knowledge) provers into account. ZK provers are an essential part of the system, and ensuring that they are compatible with the new versioned system will be key to success. This may involve using separate binaries for each upgrade height and establishing a coordination mechanism to manage these binaries. This approach ensures compatibility between ZK provers and different blockchain versions. The different binaries will need to be configured for each version of the blockchain. This will be more complex in that ZK provers are designed to work with very specific conditions. Introducing new versions introduces a whole new set of configurations, which can be very tedious.

Another significant point is whether the historical CHAIN_HASH values should be stored on-chain. Saving the hashes on-chain could allow the reuse of the same ZK binary. But, if the information is stored on-chain, update permissions need to be managed carefully. Another thing to consider is whether the CHAIN_HASH is available within the transaction execution context. If it is available, could updates be permissionless, with penalties imposed for incorrect updates? This could allow the runtime to access the historical hashes through a new capability. This is the optimal solution but the most complex. It is complex because of all the conditions that could be potentially affected by incorrect updates.

Careful consideration of these elements is important for a successful implementation. By thoughtfully addressing these key aspects, we can create a versioned CHAIN_HASH system that is both secure and efficient, ensuring the long-term viability and upgradability of the blockchain. This will allow the system to be much easier to maintain, and will increase the value of the system to its users. The value of this upgrade cannot be understated, and will be essential for the long-term success of the project.

Proposed Solutions and Trade-offs

One potential solution is to store the historical CHAIN_HASH values on-chain. This could allow for a more streamlined resync process and potentially enable the reuse of the same ZK binary across different versions. However, this approach introduces challenges related to update permissions. Ensuring the integrity and security of the on-chain hash storage is paramount, so we need to carefully manage the update permissions.

One possible method involves implementing a permissioned update mechanism, where only authorized actors or smart contracts can modify the hash values. This approach provides a degree of control, reducing the risk of unauthorized modifications. However, it also introduces a potential single point of failure and could lead to delays or disruptions if the authorized actors are unavailable or compromised. Alternatively, we could explore a permissionless update mechanism, where any participant can submit a new hash. The introduction of penalties for incorrect updates can provide an incentive for accuracy. This could be achieved through slashing mechanisms or reputation systems. If the CHAIN_HASH is made available within the transaction execution environment, it would enable the runtime to access the historical hashes through a new capability.

The trade-offs here include complexity of implementation versus flexibility and decentralization. The on-chain storage approach necessitates careful planning regarding update mechanisms. The choice between permissioned and permissionless updates involves weighing the balance between security and usability. With permissioned updates, the system can be more secure, but the upgrades may be more difficult. With permissionless upgrades, the system is more flexible, but there is more security risk.

Another consideration involves the use of separate ZK binaries for different upgrade heights. This approach provides a more robust solution as it eliminates the need for compatibility between ZK provers and different blockchain versions. This however introduces complexity in managing and coordinating these separate binaries. Developers must ensure that each binary is correctly configured and deployed for each version of the blockchain. They will also need to consider the overhead of maintaining multiple binaries and the potential for increased storage requirements.

Conclusion and Future Steps

The implementation of a versioned CHAIN_HASH system is a critical step towards improving the resilience and upgradeability of sovereign-labs and the sovereign-sdk. This is not just a desirable feature; it is a necessity for the long-term success of the system. By carefully considering the implications of each approach, we can build a robust and reliable system that meets the needs of users and developers. This will also ensure that our blockchain remains adaptable and secure in the face of evolving threats and technological advancements.

The key takeaway is that the benefits of versioning CHAIN_HASH outweigh the costs. Although it adds complexity in the short term, it provides long-term advantages in terms of data integrity, upgrade flexibility, and overall system reliability. Moving forward, the development team must prioritize the design and implementation of a versioned CHAIN_HASH system. This will ensure that the blockchain remains robust, reliable, and adaptable in the face of evolving challenges and technological advancements. This will also give users more confidence in the long-term viability of the system, and will increase adoption and use.

Further steps include detailed analysis of on-chain and off-chain storage options. We need to decide which method is best for each deployment, depending on the circumstances. We also need to evaluate the different upgrade mechanisms. Detailed analysis of the risks and benefits of each will be essential to ensure we develop a high quality and high reliability system. This also requires extensive testing to ensure all potential vulnerabilities are identified and addressed. Once a solution is selected and thoroughly tested, the implementation phase can begin, followed by deployment and continuous monitoring. The key to successfully implementing the versioned CHAIN_HASH system is to address all potential issues proactively. This will give users and developers more confidence in the system, and will ultimately drive success.

For more in-depth information on blockchain security and best practices, check out the resources from the OWASP website.