# Key (NFT-based)

The Sentry Key is a unique, non-fungible token (NFT) that is required to operate a Sentry Node in the Xai network. The Sentry Key serves as a proof of eligibility for a node to submit claims and receive rewards. It is minted by sending the correct amount of Ether or equivalent value in fiat or other ERC20 currencies that the mint contract accepts, and the price for minting is determined by an increasing threshold system.

The Sentry Key plays a crucial role in the Referee contract. When a node wants to submit an assertion to a challenge, it must provide its Sentry Key ID. The Referee contract checks if the Sentry Key is valid and if the node is either the owner of the Sentry Key or an approved operator. If these conditions are met, the key's assertion is submitted to the challenge.

When the next challenge occurs the Referee contract will make rewards available for Sentry Keys that submitted assertions for the previous challenge.

In summary, the Sentry Key is a key component in the Xai network that regulates the operation of Sentry Nodes, the submission of assertions, and the distribution of rewards.


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