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Chain Signatures enable NEAR accounts, including smart contracts, to sign and execute transactions across many blockchain protocols. This unlocks the next level of blockchain interoperability by giving ownership of diverse assets, cross-chain accounts, and data to every single NEAR account. Chain Signatures Overview
While you can sign transactions for any network using EdDSA or ECDSA keys, each chain signs transactions differently.Our example implementations show you how to sign transactions for:
  • Bitcoin
  • Ethereum and all EVM chains (Base, BNB Chain, Avalanche, Polygon, Arbitrum, and more)
  • Solana
  • Cosmos chains
  • XRP Ledger
  • Aptos
  • Sui

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Benefits

Integration with Chain Signatures brings many benefits to Web3 developers:

Single Account

Manage interactions with external blockchains from one NEAR account, simplifying key management and reducing the need for multiple wallets.

Reduced Overhead

Write smart contracts on NEAR that directly sign cross-chain transactions, cutting down on code redundancy and potential points of failure.

Secure Signing

Decentralized MPC signing process means no single entity controls the signing key, reducing centralization risks.
Keep in mind that Chain Signatures is a “one way” solution to sign and execute outbound transactions happening on other blockchains. If you’re looking to access states on external blockchains, check out Omnibridge.

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Use Cases

The Chain Signatures architecture provides a decentralized method to interact with multiple blockchains from one NEAR account.

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Bitcoin DeFi

Developers can build decentralized finance (DeFi) applications on NEAR while directly leveraging Bitcoin liquidity. The business logic resides on NEAR, while BTC is used for actual payments.
  • Atomic Swaps: Facilitate trustless, instant exchanges between Bitcoin and other cryptocurrencies
  • Payment Processing: Receive Bitcoin payments with native transfers to Chain Signature derived accounts
  • Lending Platforms: Use smart contracts on NEAR for interest calculations, borrowing, and repayments
  • DeFi Protocols: Control payment flow and execute Bitcoin transactions through NEAR contracts

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Cross-Chain NFT Platforms

Create NFT marketplaces on NEAR where users purchase NFTs using external cryptocurrencies:
  • Process BTC/ETH payments via Chain Signatures and Omnibridge
  • Handle NFT minting and trading logic on NEAR
  • Mint NFTs on multiple blockchains using Chain Signatures

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How It Works

Controlling accounts and their assets on other blockchain platforms is made possible through the interaction between three elements:
1

Derivation Paths

A deterministic way to derive foreign addresses from one NEAR account. Each path creates a unique address that only your NEAR account can control.
2

Multichain Smart Contract

The v1.signer contract receives requests to sign transactions for other blockchains.
3

MPC Service

A decentralized third-party service providing signatures to the contract through threshold cryptography.
Chain Signatures Flow

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Derivation Paths: One Account, Multiple Chains

Chain Signatures link NEAR accounts to addresses in other blockchains using Additive Key Derivation. These keys are generated using derivation paths. A derivation path is simply a string (e.g., ethereum-1, ethereum-2) that in conjunction with the NEAR account derives a unique address on the target blockchain. 
example.near + ethereum-1 = 0x1b48b83a308ea4beb845db088180dc3389f8aa3b
example.near + ethereum-2 = 0x99c5d3025dc736541f2d97c3ef3c90de4d221315
example.near + bitcoin-1  = bc1q...
In practice, the external address is deterministically derived using the NEAR address (example.near), the path (ethereum-1), and the MPC service’s public key.

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Multichain Smart Contract

The v1.signer contract has a sign method that takes three parameters:
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payload
string
required
The transaction or transaction hash to be signed for the target blockchain
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path
string
required
The derivation path that identifies the account to be used to sign the transaction
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domain_id
integer
required
Identifies the signature scheme: 0 for Secp256k1 (Bitcoin, Ethereum) or 1 for Ed25519 (Solana, Aptos)
Example: A user could request a signature to send 0.1 ETH to 0x060f1... using the ethereum-1 account with 0 (Secp256k1) as domain ID. After a request is made, the sign method yields execution while the MPC signing service signs the transaction. Once ready, the contract resumes and returns the signature.
The sign method supports both Secp256k1 and Ed25519 signature schemes, enabling signing for the vast majority of well-known blockchains. MPC participants can add more signature schemes via the vote_add_domains method.

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Multi-Party Computation Service

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. NEAR’s MPC service is comprised of several independent nodes, none of which can sign by itself, but instead create signature-shares that are aggregated through multiple rounds to jointly sign a transaction. Currently, the service is composed of 8 independent nodes. The set of participating nodes can be extended with the vote_new_parameters method if enough active nodes vote for it.
1

Listen for Requests

The MPC service continuously listens for signature requests (calls to the sign method on v1.signer).
2

Joint Signing

When detected, nodes jointly derive a signature for the payload using the account identified by the path.
3

Store Signature

Once complete, the service calls the v1.signer contract to store the resulting signature.
A Custom MPC Service: Generally, MPC signing services work by sharing a master key, which needs to be re-created each time a node joins or leaves. NEAR’s MPC service allows for nodes to safely join and leave without needing to re-derive a master key.

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Concluding Remarks

Chain Signatures are a powerful tool that allows NEAR accounts to control accounts on other blockchains. This is a fundamental step towards enabling true ownership of cross-chain data and assets. For the user, the process is made completely on-chain, since they only need to make a call to a smart contract and wait for the response. Thanks to derivation paths, a single NEAR account can control multiple accounts on different blockchains, and thanks to the MPC service, the user can be sure that nobody but themselves can request signatures for those accounts.

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Next Steps

Getting Started Guide

Learn how to implement Chain Signatures in your application

Implementation Examples

View code examples for different blockchains

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