Accessing Block Hash
Last updated
Last updated
Block hashes are the cryptographic representations of a block's content. They encapsulate the entirety of a block's information, primarily its block header. When it comes to storage proofs, accessing the relevant block hash is the critical first step in affirming the integrity and authenticity of any on-chain data. It sets the stage for all subsequent verification processes in the .
Smart contracts can retrieve these block hashes in various ways, each with its own trade-offs and considerations. Let’s explore some common methods:
Smart contracts can natively utilize the BLOCKHASH opcode to fetch hashes of the most recent 256 blocks in the Ethereum Virtual Machine (EVM). While straightforward, this method is restricted to a limited timeframe, and accessing older blocks becomes challenging.
This limitation prevents developers from injecting proofs of arbitrary on-chain data into their smart contracts, as they cannot easily verify inclusion proofs against historical block hashes.
Alternately, an off-chain actor could forward block hashes on-chain. However, this approach introduces latency and usually requires trusting a third party, a committee or similar. Additionally, it potentially introduces vulnerabilities tied to economic incentives or adversarial behaviours.
The Historical Block Hash Accumulator can be used to circumvent these issues. It enables on-chain smart contracts to derive older block hashes by validating them against a stored accumulator root (MMR Root). The methodology eliminates the need to trust external actors and widens the accessible range of block hashes without sacrificing security.
