Briefing
The research addresses the systemic censorship vulnerability in Proposer-Builder Separation (PBS) by introducing a two-tiered block construction architecture that mandates publicly verifiable decryption, ensuring transaction inclusion integrity. The core breakthrough is a cryptographic primitive that forces the block executor to broadcast a proof of correct decryption alongside the decrypted transaction set, enabling any network entity to validate the process and detect malicious denial-of-service attempts. This mechanism fundamentally re-architects the trust model between block proposers and builders, providing a provable defense against transaction censorship and enhancing the overall security and fairness of decentralized transaction ordering.
Context
The prevailing architectural solution to mitigate Maximal Extractable Value (MEV), Proposer-Builder Separation (PBS), introduced a critical, foundational security gap. In prior encrypted mempool schemes, the block builder or executor, upon receiving encrypted transactions, was tasked with their decryption and inclusion. The established theoretical limitation was the verifiability of the decryption process ; a malicious executor could simply deny the inclusion of a specific, targeted transaction, claiming a decryption error or an invalid transaction, exploiting the fact that the transaction was in plain format post-decryption. This unverifiable denial of service created an avenue for systemic transaction censorship.
Analysis
The paper’s core mechanism integrates a verifiable decryption primitive into the two-tiered Builder/Executor architecture. The process begins with users submitting encrypted transactions. The Builder aggregates these into an encrypted block and commits to it. When the Executor receives the encrypted block, the novel step is that the Executor must not only decrypt the block but also generate a decryption integrity check → a cryptographic proof that the decryption was performed correctly and that the resulting plaintext transactions are exactly those included in the block.
This proof is then broadcasted to the network. This public broadcast allows any validator or monitoring node to verify the correctness of the decryption against the initial encrypted commitment. The mechanism fundamentally differs from previous approaches by shifting the security from a trust-based assumption of honest decryption to a mathematically verifiable assertion of correct decryption, thereby eliminating the possibility of undetected, targeted transaction exclusion.
Parameters
- Decryption Integrity Check Duration → High efficiency suitable for real-time applications. The system’s viability hinges on the cryptographic overhead of generating and verifying the decryption proof being negligible relative to block time.
- Architectural Tiers → Two (Builder and Executor). This separation of block construction and execution roles is secured by the new verifiable primitive.
- Adversarial Target → Denial of Inclusion/Censorship. The mechanism specifically targets and mitigates the malicious act of a block producer rejecting a valid, decrypted transaction.
Outlook
This verifiable decryption mechanism establishes a new baseline for censorship resistance in modular blockchain architectures. The immediate next step involves optimizing the cryptographic primitive to minimize the computational overhead of the decryption integrity check, potentially through advanced zero-knowledge techniques. Strategically, this work paves the way for truly fair transaction ordering and private mempools, unlocking real-world applications in 3-5 years where high-value, latency-sensitive DeFi operations can be executed with provable fairness, without the risk of predatory MEV or political censorship at the block production layer.
