Add NFT key contract article (#1910)

* Update nft-keys.md

docs/2.build/1.chain-abstraction/nft-keys.md

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+---
+id: nft-chain-keys
+title: NFT Chain Keys Smart Contract
+sidebar_label: NFT Chain Keys Contract
+---
+
+The NFT Chain Keys smart contract makes the ownership of remote accounts both provable and transferrable. This new paradigm allows you to create new end-user experiences that leverage provable and transferrable remote accounts as a core primitive. 
+
+## Contract overview
+
+The [MPC Account Recovery smart contract](https://github.com/near/mpc-recovery) provides a [`sign`](https://github.com/near/mpc-recovery#sign) method that accepts a `path` parameter. This allows one predecessor account to have access to an effectively unlimited number of MPC keys.
+
+The NFT Chain Keys contract takes advantage of this property and allows secure transfers of MPC keys between users, using the [NEP-171 NFT contract standard](https://nomicon.io/Standards/Tokens/NonFungibleToken/Core).
+The contract also implements new functionality to enable chain key management features.
+
+:::info
+
+The essence of Multi-Party Computation (MPC) is to enable independent parties to perform shared computations on private information without revealing secrets to each other.
+
+:::
+
+### Standards
+
+Besides the NEP-171 contract standard, the NFT Chain Keys contract complies with a full suite of NEP standards:
+
+- [NEP-145: Storage Management](https://nomicon.io/Standards/StorageManagement)
+- [NEP-171: NFT Core](https://nomicon.io/Standards/Tokens/NonFungibleToken/Core)
+- [NEP-177: Metadata](https://nomicon.io/Standards/Tokens/NonFungibleToken/Metadata)
+- [NEP-178: Approval Management](https://nomicon.io/Standards/Tokens/NonFungibleToken/ApprovalManagement)
+- [NEP-181: Enumeration](https://nomicon.io/Standards/Tokens/NonFungibleToken/Enumeration)
+
+## Usage
+
+Please refer to the smart contract [GitHub documentation](https://github.com/near/multichain-gas-station-contract/blob/master/nft_key/README.md) for usage information:
+
+- [Creating new key tokens](https://github.com/near/multichain-gas-station-contract/tree/master/nft_key#creating-new-key-tokens): mint unlimited new NFT chain keys, as long as the account has sufficient storage.
+- [Issuing signatures](https://github.com/near/multichain-gas-station-contract/tree/master/nft_key#issuing-signatures): generate new signatures based on a submitted payload.
+- [Approvals](https://github.com/near/multichain-gas-station-contract/tree/master/nft_key#approvals): implement a separate set of approval management functions for using NFTs, which operate similarly to NEP-178.
+
+
+---
+
+## Use Cases for NFT Keys
+
+:::info Disclaimer
+The ideas presented in this section are just initial concepts, and shouldn’t be considered as fully fledged solutions.
+:::
+
+### Remote Account Marketplace
+
+NFT Keys enable users to buy, sell, and trade remote accounts within a marketplace-style application.
+For instance, _Alice_, possessing a set of remote accounts with value and history, can mint an NFT key and list these accounts for sale on the marketplace.
+Potential buyers, like _Bob_, can browse the value of _Alice’s_ accounts and choose to make a purchase.
+If _Bob_ decides to proceed, they would simply need to acquire ownership of the original NFT key from _Alice_ in exchange for payment, such as in `$NEAR`.
+Once the transaction is completed, ownership of the accounts transfers to _Bob_.
+
+### Bridgeless Multi-Chain DEX
+
+You can create a Multi-chain DEX without bridging by combining Chain Signatures with NFT Keys.
+Users wishing to swap asset `$A` for asset `$B` would initiate the swap on the bridgeless DEX.
+Supported by liquidity providers (Automated Market Makers) across multiple chains, the DEX facilitates these swaps.
+Here's how it works:
+
+- A user proposes the swap, specifying asset `$A` in remote `account X` for asset `$B` in remote `account Y`.
+- The liquidity provider receives asset `$A` from the user and sends the equivalent amount of asset `$B` to a newly created remote `account Y`, along with a minted NFT key.
+- The NFT key is then sent to the user to complete the swap.
+
+Although liquidity providers still need to leverage bridging to settle assets between different pools, users of this exchange type are exposed to reduced bridge risk.

website/sidebars.js

@@ -138,6 +138,7 @@ const sidebar = {
         'build/chain-abstraction/fastauth-sdk',
         'build/chain-abstraction/chain-signatures',
         'build/chain-abstraction/wallet',
+        'build/chain-abstraction/nft-chain-keys',
         {
           "Multichain Gas Relayer": [
             "build/chain-abstraction/multichain-gas-relayer/multichain-server",