SV2 Extensions for Payout Verification and Job Size at Scale

However, this development only solves one part of the problem; miners still need to trust pools regarding the payout split until a block is found. The current implementation does not allow for verification of the payout split prior to the discovery of a block nor does it maintain a consistent job size as payout structures become more complex.

To address these gaps, Tessera, a suite comprising two specific Stratum V2 extensions named Pactum and Axiom, has been developed. These extensions are designed to enhance transparency and scalability in mining operations. Pactum introduces a mechanism where a pool can commit to a specific payout division via a signed message using BIP340 Schnorr signatures over secp256k1. This signature is linked directly to the session's mining job token, enabling verification of the payout rule before a block is mined. This effectively makes the commitment a verifiable contract rather than an internal unverifiable promise.

On the other hand, Axiom deals with the scalability issue related to the increasing size of coinbase transactions as more payout addresses are added. It introduces a method of coinbase midstate compression, creating a 32-byte hash that represents the structure of a coinbase transaction's payout outputs. This hash is computed upstream, allowing the mining device to continue working with a consistent job size of 32 bytes regardless of the number of payout outputs. This approach prevents the job size from expanding, which is crucial for resource-constrained ASIC firmware.

Despite these advancements, the real-world application of these extensions is still in its nascent stages. Currently, there is a working prototype Job Declaration Server that has been tested against the reference Stratum V2 Job Declaration Client, which tolerates but does not act on the Pactum extension due to lacking extension-negotiation logic. This highlights a potentially significant gap in the existing reference implementation, which may need addressing to fully utilize these new extensions.

The repository for Tessera, which includes these developments, can be accessed here: sweethashio/Tessera: Tessera SV2 Suite. This effort marks a step towards solving the remaining trust issues in non-custodial mining pools by making the payout process transparent and scalable. Further discussions and development will likely focus on integrating these solutions into production environments and enhancing compatibility with existing systems.