Ethereum Attestation Service is the most-used attestation primitive on EVM chains. H33-74 is what you would build if you needed attestation to survive any specific chain's failure.
Ethereum Attestation Service (EAS) provides a generic attestation primitive on Ethereum and other EVM chains. Attestations are on-chain records issued by an attester, optionally signed off-chain and submitted on-chain, with a schema registry that defines what each attestation type represents.
EAS is well-designed for its scope: attestations that live on EVM chains and are consumed by other EVM smart contracts. H33-74 was designed for a different scope: attestations that survive any specific chain and are consumed by auditors, regulators, and counterparties for operational evidence.
EAS attestations live in EVM chain state. The attestation is stored or referenced on the chain. Verification requires the chain. If the host chain becomes unavailable, deprecated, or compromised, the attestations on it become unavailable too. H33-74 attestations are 74-byte off-chain receipts that can be anchored to any chain or no chain. The chain holds a notarization pointer, not the attestation itself.
EAS uses ECDSA signatures from the attester's Ethereum account. These are pre-quantum signatures and will need to migrate before quantum-capable adversaries exist. H33-74 uses three independent post-quantum signature families on the receipt itself, so the receipt's integrity is post-quantum from the moment it is produced.
Verifying an EAS attestation requires the Ethereum (or other EVM) chain to be available and for the verifier to be able to query it. Verifying an H33-74 receipt requires the receipt, the public keys, and the open-source verifier. The chain is optional.
EAS assumes the consumer is in the Ethereum ecosystem and wants on-chain composability. H33-74 assumes the consumer is an auditor, regulator, counterparty, or internal compliance team that wants verifiable operational evidence regardless of which chain ecosystem they are in.
EAS is great when you are operating entirely inside Ethereum, when attestation consumers are other smart contracts, and when on-chain composability is the value being delivered.
H33-74 is great when attestation consumers are auditors, regulators, or counterparties outside the EVM ecosystem. When the audit horizon extends beyond any specific chain's lifetime. When post-quantum survivability matters. When the same receipt needs to be verifiable across chains that may not even exist yet at the time of receipt creation.
Chain portability is what makes H33-74 categorically different from chain-coupled attestation systems like EAS.
Chain Portability Why Chain Migration Shouldn't Exist