This smart contract is meant to:

Create proofs of the existence of a Hash (representing some document or text), thus verify their existence

  • Owner (and whitelisted others) can create new proofs, like verified time-based document watermarks on the blockchain

  • Contract creates proofs as NFT/ERC721, which can be sent to a recipient address

  • Whitelisted others can add confirmations for proofs

  • Roles:

    • default_admin: contract deployer set as default, can be transferred; is allowed to grant/revoke all roles (admins + whitelists)

    • proof_whitelisted: add/delete proofs; admins are not automatically whitelisted, so that needs to be added if desired

    • confirm_whitelisted: add/delete confirmations of proofs

  • Note: Recipient wallets need to be able to handle ER721. For safety reasons, it is not possible to send a token to a contract that does not explicitly support it.

tl/dr instructions

  • Tools:

  • proofs

    • whitelist deployment address plus any group of addresses with grantRole() as Proof_Whitelisted using 0xf555e1ec80c58c7664dc73d872d3ef6e07bdd9c5ba6b3bf7a91ffaa413b8dac5

    • create new proof with addProof() using proofHash (hash of a document, file, string, etc.), string (any description of the hash) and the address where the proofHash shall be sent to

    • (If you hold the proof in your address) you can delete it by using deleteProof()

  • confirmation of proofs

    • whitelist any group of addresses with grantRole() as Confirm_Whitelisted with 0x53eebd7fe83ace838d6b0a9d4f111237deb02359c62b25f1025613d537b2379b

    • create new confirmation of a proof with addConfirmation() using tokenId

  • Review proof data

    • Query either using getProofData() and/or getProofIdByHash() to getproofHash, timestamp, description`

Notable Functions

Read Functions




query with proofHash and get tokenId


query with tokenId and get proofHash, timestamp, description


query with tokenId and get confirmation count


query with proofHash and get tokenId


check whether a specific address confirmed a proof / tokenId


number of tokens the address owns


get the address who owns a tokenId


transfer Proofs address from, address to, tokenId


address owner, index (uint256) // index is a 1..n numbering of proofs owned by the address. Use this to get all proofs owned by an address, in combination with balanceOf to get the count


get the current supply of proofs in existence; burnt/deleted not included

Write Functions




write proofHash (0x{hash}) (hash of a document, file, string, etc.), string (any description of the hash; length only affects gas), address (where the NFT/ERC721 is being sent to); contract returns tokenId; Fails if hash already exists; Requires being whitelisted; creates an ERC721 and a custom event


write tokenId, deletes proof/token; only the address holding a proof token can burn it, not any default_admin or proof_whitelisted


write tokenId add confirmation of the data; requires being whitelisted; creates an event


address from, address to, tokenId // do not use, unsafe


address to, tokenId) // give “address to" the right to transfer ownership of a proof the contract owns


address operator, bool _approved // gives "address to" the right to transfer ownership of all proofs the sender owns


hash of role, addresses ["0x...", "0x..."] to grant certain role to certain address; hashes of the roles are const in the contract: Default_Admin_Role with0x0000000000000000000000000000000000000000000000000000000000000000, Proof_Whitelisted with 0xf555e1ec80c58c7664dc73d872d3ef6e07bdd9c5ba6b3bf7a91ffaa413b8dac5, Confirm_Whitelisted with 0x53eebd7fe83ace838d6b0a9d4f111237deb02359c62b25f1025613d537b2379b


hash of role, addresses [0x..., 0x...] to grant certain role to multiple addresses


same as grantRole only reverse

Swarm - Example Use Cases

Core initial use case

The Swarm Council can publish protocols of decisions taken on GitHub and verify the Hash via VerifiedExistence:

  • Dedicated contract for VerifiedExistence for Swarm Network

  • Contract owner and proof_whitelisted is multisig with council members (tbd)

  • Council published documents with hashes;

  • Create Proof (Hash + meta data) and proof NFT / ERC721 is sent to dedicated wallet (e.g. Gnosis Safe, which allows ERC721 to be kept as “Collectibles”)

  • Example: Swarm Council Votes (SCVs)

Other potential use cases:

Proof of Masternode

  • Smart contract, which tracks verified Masternodes, could be added to proof_whitelisted of a contract put in place by council

  • A smart contract / person / process could keep track of active masternodes and create/delete corresponding proofs and send proof NFTs to masternode wallets

  • Masternode distributions could be using NFTs held as basis for reward distribution

  • Masternodes could be confirming various actions of the Council contract

Masternodes could be added as confirm_whitelisted

  • Can then add supporting votes (confirmations) to certain actions