As an NFT collector, you should care about on-chain provenance. The most authentic provenance for an NFT is when it is initially minted directly from a creator’s wallet or a smart contract that the creator owns. However, with a few clever smart contract illusions, someone could manipulate NFT provenance using a technique known as Sleep Minting.

Sleep Minting is when a scammer mints an NFT directly to a famous creator’s wallet with permission to reclaim or pull the NFT back out of the creator’s wallet. This creates the appearance that (1) a creator authentically minted an NFT to themselves; and then (2) sent that NFT to a scammer. Based on “on-chain” provenance, the scammer can claim they own an NFT minted by a famous creator and sell it for a higher value.

How does this work technically? First, it is essential to understand how a smart contract stores NFT provenance and ownership. Anybody can query an NFT smart contract to determine who the current owner of an NFT is using the ownerOf(tokenId) function from the ERC-721 Standard. You could even query for an NFT owner at a specific block number by varying the eth_call RPC method parameters. However, the simplest way to see changes in ownership is to look at ERC-721 Transfer Event logs.

My a16z Crypto colleague Daren Matsuoka wrote a great Twitter thread about Event logs and how they work. A Transfer Event log is a message sent to the outside world by a smart contract containing details about an NFT transfer (who the NFT is transferring FROM, who the NFT is transferring TO, and the transferred TOKEN ID). Transfer Event logs provide an efficient way to check an NFT’s provenance.

As an NFT collector, you should care about on-chain provenance. The most authentic provenance for an NFT is when it is initially minted directly from a creator’s wallet or a smart contract that the creator owns. However, with a few clever smart contract illusions, someone could manipulate NFT provenance using a technique known as Sleep Minting.

Sleep Minting is when a scammer mints an NFT directly to a famous creator’s wallet with permission to reclaim or pull the NFT back out of the creator’s wallet. This creates the appearance that (1) a creator authentically minted an NFT to themselves; and then (2) sent that NFT to a scammer. Based on “on-chain” provenance, the scammer can claim they own an NFT minted by a famous creator and sell it for a higher value.

How does this work technically? First, it is essential to understand how a smart contract stores NFT provenance and ownership. Anybody can query an NFT smart contract to determine who the current owner of an NFT is using the ownerOf(tokenId) function from the ERC-721 Standard. You could even query for an NFT owner at a specific block number by varying the eth_call RPC method parameters. However, the simplest way to see changes in ownership is to look at ERC-721 Transfer Event logs.

My a16z Crypto colleague Daren Matsuoka wrote a great Twitter thread about Event logs and how they work. A Transfer Event log is a message sent to the outside world by a smart contract containing details about an NFT transfer (who the NFT is transferring FROM, who the NFT is transferring TO, and the transferred TOKEN ID). Transfer Event logs provide an efficient way to check an NFT’s provenance.