Sign NFTs


FIP-27 has introduced the ability to use a FIO Crypto Handle (aka FIO Address) to sign NFTs. An NFT is considered signed, when the owner of the FIO Crypto Handle maps the NFT’s contract address and token ID on specific chain to their FIO Crypto Handle. This acts as an attestation that they created the NFT. If the FIO Crypto Handle is known, e.g. artist publishes it on their twitter, website, etc., the attestation can act as a signature of the specific NFT.

In addition, the artist can also append the hash of the asset (e.g. image, video, etc.) to ensure that the NFT points to the actual art work. This is important given that the files associated with the NFT are not always recorded on a permanent and verifable storage.

How to sign an NFT

To sign an NFT, use the addnft action and supply:

parameter description
chain_code Alphanumeric chain code as described in FIP-15, e.g. ETH for Ethereum
contract_address Public address of the smart contract which has minted the NFT, e.g. 0x12f28e2106ce8fd8464885b80ea865e98b465149 for Beeple Special Edition contract.
token_id Token ID of the specific token on the smart contract provided, e.g. 100010001. It may be left blank to “sign” all tokens of that contract.
url NFT asset url, e.g. link to the image.
hash SHA256 hash of the NFT asset.
metadata Currently only creator url is supported, e.g. artist’s website, in a JSON format like this: “{"creator_url":""}”

How to change NFTs

  • To change chain_code, contract_address, or token_id, first remove the NFT, then add it back in.
  • To change any other value, resubmit addnft action with new parameters.

How to remove NFTs

To remove NFTs association from FIO Crypto Handle use the remnft to remove individual NFTs or remallnfts to remove all NFTs.

Fetch NFT signatures

The following getter methods are available to fetch NFT signatures

Method Description
/get_nfts_fio_address Returns a list of NFTs which were signed by the supplied FIO Crypto Handle. It’s best used to display all NFTs signed by a known FIO Crypto Handle, e.g. FIO Crypto Handle advertised by an artist as theirs.
/get_nfts_contract Returns a list of NFTs which match the supplied chain_code, contract_address, and token_id. It’s best used to return a list of signatures for a specific token on a specific chain and smart contract, e.g. to validate it has been signed by a known FIO Crypto Handle. Currently, if an NFT is signed with blank token_id, querying for a specific token ID will not return that signature. It’s therefore advisable to query both for specific token_id as well as blank token_id to return any signatures at the smart contract level. Please note that multiple signatures may be returned for the same NFT.
/get_nfts_hash Returns a list of NFTs which contain the supplied NFT asset hash. It’s best used to see if a specific image has been signed as an NFT and which specific NFT contains it.