Primary Source Attestation

Primary Source Attestation (PSA) is a cryptographic protocol that proves a piece of data existed at a specific time and has not been altered by anchoring a unique fingerprint of that data—its cryptographic hash—to a primary source of truth, most commonly a public blockchain like Ethereum or Bitcoin. This process creates an immutable, timestamped record that anyone can independently verify against the original data. The primary source's inherent properties—decentralization, immutability, and consensus—provide the trust layer, eliminating reliance on a single, potentially corruptible authority for verification.

The technical workflow involves several key steps. First, the data (e.g., a document, sensor reading, or software build) is processed through a cryptographic hash function like SHA-256, producing a deterministic, fixed-size hash. This hash is then published as a transaction to the chosen blockchain, where it is permanently recorded in a block. To verify the attestation later, a user recomputes the hash of the data in question and checks the blockchain for a transaction containing that exact hash. A match confirms the data's provenance and integrity from the attestation timestamp forward.

PSA is foundational for applications requiring tamper-evident records and proof of existence. Common use cases include securing software supply chains by attesting to build provenance, creating verifiable audit trails for legal documents, timestamping intellectual property, and validating the integrity of logs from IoT devices. It provides a trust-minimized alternative to traditional notarization or certificate authorities, as the verification logic is open and the trust is placed in the blockchain's consensus mechanism rather than a specific institution.

A critical distinction is that PSA verifies that data was attested, not what the data means. It proves integrity and existence but does not validate the content's correctness or truthfulness—a concept known as garbage in, garbage out. For example, a fraudulent contract can be attested just as easily as a legitimate one. Therefore, PSA is often combined with other systems, such as oracles for external data or zero-knowledge proofs for privacy, to create more comprehensive trust frameworks.

The architecture of PSA systems often involves components like attestation clients (to create hashes and submit transactions), smart contracts (to manage and log attestations on-chain), and verifier libraries (to allow easy off-chain checking). Standards are emerging to improve interoperability, such as encoding attestation metadata alongside the hash. This modular approach allows PSA to be integrated into broader decentralized identity systems, verifiable credentials, and data authenticity protocols, forming a core primitive for the verifiable web.

Primary Source Attestation (PSA) is a cryptographic protocol that enables a blockchain to trust and use data from an external, off-chain source by verifying its origin and integrity. It works by having a trusted attester—a designated entity or oracle node—cryptographically sign a data point at its source, creating a verifiable attestation. This attestation, which includes the data and the signature, is then submitted to the blockchain, where smart contracts can cryptographically verify the attester's signature against a known public key before consuming the data.

The process typically involves several key steps. First, the attester retrieves data directly from the primary source, such as a financial API, IoT sensor, or corporate database. The attester then creates a digital signature over a structured message containing the data, a timestamp, and often a unique identifier. This signature is generated using the attester's private key, cryptographically binding the data to that specific source and moment. The raw data and its signature are packaged into a standardized attestation format, like an Attestation Object, which is then broadcast to the blockchain network.

On-chain, a verifier smart contract receives the attestation. Its core function is to authenticate the data by checking the cryptographic signature against the known public key of the authorized attester. This verification proves the data originated from the expected source and has not been altered. Only after successful verification does the smart contract logic proceed, using the now-trusted data to execute transactions, trigger settlements, or update its state. This mechanism decouples data delivery (handled by oracles) from data verification (performed on-chain), creating a robust trust layer.

This architecture provides critical security properties. It establishes data provenance, offering a clear, auditable trail back to the primary source. It also ensures tamper-evidence, as any modification to the data after signing would cause verification to fail. Furthermore, by separating the roles of attester and blockchain, PSA allows for flexibility in data sourcing while maintaining the blockchain's security guarantees. Protocols like Ethereum Attestation Service (EAS) and Verifiable Credentials (VCs) are prominent implementations of this pattern.

Primary Source Attestation is fundamental to oracle design, enabling high-integrity use cases like decentralized finance (DeFi) price feeds, real-world asset (RWA) tokenization, and secure cross-chain messaging. By providing a standardized method for proof-of-origin, it moves beyond simple data delivery to a model of verifiable data, which is essential for building scalable, secure, and compliant decentralized applications that interact with the physical world and traditional systems.

The attestation flow begins at the primary source, which is the authoritative origin of the data. This is typically a full node or validator client running consensus software like Geth or Prysm. The source's core function is to execute a witness function—a deterministic piece of logic that queries its internal state to produce a specific, verifiable claim, such as the block hash at a given slot, the balance of an account, or the result of a smart contract call. This raw claim is the foundational data point for the entire attestation process.

Once the witness function generates the claim, the source cryptographically signs it using its private key, creating a digital signature. This signature is the cryptographic proof that the claim originated from that specific source. The signed claim, now an attestation, is packaged into a standard format—often using frameworks like EIP-712 for structured signing—and transmitted. Transmission can occur via direct API calls, through a decentralized oracle network's node software, or by posting to a public data availability layer, making the attestation available for collection and verification.

The final stage involves verification and aggregation. Off-chain verifiers or relayers receive the attestation and validate two critical elements: the cryptographic signature against the known public key of the source, and the logical consistency of the claim (e.g., does the attested block hash exist in the canonical chain?). For systems requiring higher security, multiple attestations for the same data point are aggregated using schemes like BLS signature aggregation, creating a single, robust proof that is then delivered to a destination contract or system, completing the flow from ground truth to actionable on-chain data.