Proof Of Existence

Proof of Existence (PoE) is a decentralized mechanism for document notarization on the blockchain. It allows users to prove that specific data existed at a given point in time, without revealing the content itself. By using cryptographic hashes stored immutably on-chain, PoE provides a trustless, verifiable, and timestamped record of existence.

1. PoEv5

A minimal document notarization system for the Ethereum blockchain.

• Functionality:

  • Hashes document content using keccak256 (SHA-3).

  • Associates a hash with a Proof (description, sender, timestamp).

  • Allows one-time notarization per hash; immutable.

  • Enables verification and retrieval of notarized hashes.

• Limitations:

  • No revocation or modification.

  • No historical tracking or metadata updates.

2. PoEv7

A mid-level extension of the base contract with enhanced flexibility, allowing uncontrolled notarization and nullification, without strict access control.

• Key Features:

  • Allows notarization and nullification via content or direct hash.

  • Accepts custom notarizer or nullifier addresses—no sender ownership check.

  • Adds metadata (plaintext) to both notarization and nullification events.

  • Tracks proof changes (timestamp, block number, state).

  • Emits appropriate events (Notarized / Nullified).

• Differences from Base:

  • Includes proof revocation (nullify).

  • Supports metadata tagging for both creation and revocation.

  • Does not enforce that the original sender revokes the proof.

• Trade-offs:

  • Less secure due to absence of sender-based restrictions.

  • More suitable for open or delegated notarization scenarios (e.g., by a third party or organization).

3. PoEv9

A fully featured version introducing state history, access control, and full auditability.

• Advanced Features:

  • Tracks all changes to a proof as an array (Proof[]) per hash.

  • Differentiates between notarized and nullified states.

  • Restricts nullification to the original sender only.

  • Enforces non-empty content and non-null hashes.

• Proof Fields Extended:

  • blockNumber, isNotarized for on-chain and explorer visibility.

  • provider and timestamp for each state change.

• Interface Additions:

  • certify, cancel, and their *DocumentOnly variants.

  • getProof() returns the latest state.

  • getHistory() exposes the full state change log.

• Security & Traceability:

  • Strong guarantees of integrity, authorship, and revocation rights.

  • Ideal for systems requiring regulatory compliance or audit trails.

Summary Table