# VerifiedExistence ![](https://1282211561-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M6_qRninsmdOoJ_i5U_%2F-M9s_uRHfRI7SqpxjjfU%2F-M9sdwm5Wl21z8hvzUFk%2FVerifiedExistence%20bg2.png?alt=media\&token=f3b41beb-765a-41b6-8339-adda65e45b88) ## Intro This [smart contract](https://github.com/swarmfund/swarm-open-tools/tree/master/VerifiedExistence) 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: * Deploy contract via [Remix](https://remix.ethereum.org/) * Use contract interaction via [Etherscan](https://etherscan.io) * Create doc/string hashes using [Hash Calculator](https://www.pelock.com/products/hash-calculator) * `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 get`proofHash, timestamp, description\` ## Notable Functions **Read Functions** | Function | Description | | ----------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `getProofIdByHash()` | query with `proofHash` and get `tokenId` | | `getProofData()` | query with `tokenId` and get `proofHash, timestamp, description` | | `getProofConfirmationCount()` | query with `tokenId` and get `confirmation count` | | `getProofIdByHash()` | query with `proofHash` and get `tokenId` | | `isConfirmedBy()` | check whether a specific `address` confirmed a `proof` / `tokenId` | | `balanceOf()` | number of tokens the `address` owns | | `ownerOf()` | get the `address` who owns a `tokenId` | | `safeTransferFrom()` | transfer Proofs `address from`, `address to`, `tokenId` | | `tokenOfOwnerByIndex()` | `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 | | `totalSupply()` | get the current supply of `proofs` in existence; burnt/deleted not included | **Write Functions** | Function | Description | | --------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `addProof()` | 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 | | `deleteProof()` | write `tokenId`, deletes proof/token; only the address holding a proof token can burn it, not any `default_admin` or `proof_whitelisted` | | `addConfirmation()` | write `tokenId` add confirmation of the data; requires being whitelisted; creates an event | | `transferFrom()` | `address from`, `address to`, `tokenId` // do not use, unsafe | | `approve()` | `address to`, `tokenId`) // give “address to" the right to transfer ownership of a proof the contract owns | | `setApprovalForAll()` | `address operator`, `bool _approved` // gives "address to" the right to transfer ownership of all proofs the sender owns | | `grantRole()` | `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` with`0x0000000000000000000000000000000000000000000000000000000000000000`, `Proof_Whitelisted` with `0xf555e1ec80c58c7664dc73d872d3ef6e07bdd9c5ba6b3bf7a91ffaa413b8dac5`, `Confirm_Whitelisted` with `0x53eebd7fe83ace838d6b0a9d4f111237deb02359c62b25f1025613d537b2379b` | | `batchGrantRole()` | `hash of role`, `addresses [0x..., 0x...]` to grant certain role to multiple addresses | | `revokeRole()` | 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](https://etherscan.io/address/0xdc95ed11e88d44f4e6ece3c959034646e7917b15#code) 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) * listed in this [repo](https://github.com/swarmfund/swarm-network-governance/tree/master/SCVs); text between \ and \ tags is hashed * create `proofs` using hash and title; send it to a Swarm Council wallet; e.g [`proof (SCV_1587031154_Decision regarding_April_Voting_Period.md)`](https://etherscan.io/tx/0xf9363a3dc08a1927cdbe5e90c83c96bfd80012296bdad6821193a15a4f08460e) ### 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