Every H33-74 attestation is permanently recorded on Bitcoin mainnet via OP_RETURN. 32 bytes on-chain. 42 bytes off-chain. Immutable. Independently verifiable by anyone with a block explorer.
Bitcoin mainnet attestation is the process of writing a cryptographic commitment to the Bitcoin blockchain so that it can never be altered, deleted, or disputed. H33 uses this mechanism to anchor every H33-74 proof to the most secure, longest-running, most battle-tested distributed ledger in existence.
The attestation is not a smart contract. It is not a token. It is not a side chain. It is a raw OP_RETURN output embedded in a standard Bitcoin transaction. The data is part of the block. The block is part of the chain. The chain is secured by the cumulative proof-of-work of every miner on the network since 2009.
This is the simplest possible anchoring mechanism. There is no execution risk. There is no smart contract vulnerability surface. There is no governance token. There is no upgrade path that can retroactively change what was recorded. Once a hash is in a Bitcoin block, it stays there.
Every H33-74 attestation produces exactly 74 bytes of proof material. This is not a compressed version of a larger proof. It is the proof. The 74 bytes are split across two storage layers, each serving a distinct purpose.
| Component | Size | Location | Purpose |
|---|---|---|---|
| SHA3-256 commitment hash | 32 bytes | Bitcoin mainnet (OP_RETURN) | Immutable public anchor |
| Signature metadata | 42 bytes | Off-chain (Cachee) | Verification context |
| Total | 74 bytes | Complete attestation |
The 32-byte on-chain component is a SHA3-256 hash that commits to the full attestation payload. SHA3-256 is a post-quantum secure hash function — no known quantum algorithm provides more than a quadratic speedup against it, and at 256 bits, the security margin remains well above any projected threat.
The 42-byte off-chain component contains the metadata needed to reconstruct and verify the proof: the signature scheme identifiers, the timestamp, and the verification pointers. This data is stored in Cachee, H33's post-quantum attested caching layer, where every entry is itself cryptographically verified.
This is not a hypothetical. H33-74 attestations are live on Bitcoin mainnet. You can inspect the transaction yourself using any block explorer. The OP_RETURN output contains the raw SHA3-256 commitment hash.
The SHA3-256 hash committed to Bitcoin is a binding commitment over the full attestation payload. The payload itself includes every component needed to establish what was attested, when, and by what cryptographic mechanism.
The SHA3-256 digest of the complete attestation data. This is the value written to Bitcoin. Any change to any field in the payload produces a completely different hash.
The attestation is signed using three independent post-quantum signature schemes based on three independent hardness assumptions: MLWE lattices, NTRU lattices, and hash-based signatures. An attacker must break all three simultaneously.
The exact time of attestation and its position in the hash chain. This establishes ordering — proof A came before proof B — independent of any external clock.
Which system produced the attestation and under what context. This allows multi-tenant verification without exposing the underlying data that was attested.
This verification process requires no special software, no API key, no account, and no trust in H33. The Bitcoin blockchain is a public ledger. The SHA3-256 hash function is a public standard. Anyone can recompute the hash and compare it to the on-chain value.
If the hash matches, the attestation has not been tampered with since the moment it was anchored. The Bitcoin block timestamp provides an upper bound on when the attestation was created. The cumulative proof-of-work behind that block provides the security guarantee.
H33 chose Bitcoin for attestation anchoring because of three properties that no other system provides simultaneously.
Bitcoin has never had a successful rollback of a confirmed transaction in its 17-year history. The cumulative proof-of-work behind any given block makes retroactive alteration computationally infeasible. No governance committee, no foundation, no single entity can rewrite the chain.
OP_RETURN is a simple, non-executable output. There is no smart contract to audit, no execution logic to exploit, no reentrancy vulnerability, no gas estimation error. The data is stored. That is all it does. The attack surface is the Bitcoin protocol itself, which has the longest track record of any blockchain.
Bitcoin is supported by every major block explorer, every major wallet, and every major blockchain analysis tool. There is no vendor lock-in. There is no proprietary chain. The verification infrastructure already exists and has been battle-tested by an entire industry for nearly two decades.
OP_RETURN is the correct mechanism. It is non-spendable by design. It does not bloat the UTXO set. It is prunable by nodes that do not need it. It is the mechanism specifically intended by the Bitcoin protocol for embedding small amounts of data. H33 uses it exactly as designed.
When H33 attests a computation, a biometric match, an AI decision, or a compliance control, the attestation is not just signed and stored. It is anchored to a global, adversarial, permissionless ledger that has resisted every attack for 17 years.
This means your evidence is not dependent on H33's servers remaining online. It is not dependent on H33 as a company continuing to exist. It is not dependent on any single jurisdiction's legal framework. The proof is on Bitcoin. Bitcoin does not have a terms of service.
If you are an insurer, a regulator, or an auditor, this is what you want: evidence that cannot be retroactively fabricated, stored in a system that the attestor does not control.
7 patents pending. 300+ patent claims. The H33-74 attestation architecture, including the Bitcoin anchoring mechanism and the three-key post-quantum signature bundle, is protected by pending patent applications covering the full attestation pipeline.