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Overview

Protocol Requirements

  • Bridge attesters must stake at least 900 TAN as collateral as they manage bridge communication and off-chain data collection.
  • Bridge participants must stake at least 2,700 TAN as collateral as they store sensitive private key contributions.

Minimal staking amounts may be reduced in future.

Deposit Process

The deposit process in this bridge system is designed to be flexible and user-friendly. Users have the freedom to choose any bridge for their deposits. Each bridge sets its own flat fees for withdrawals, allowing users to select a bridge based on their fee preferences. To initiate a deposit, users request a deposit address from their chosen bridge. Once they receive this address, they can send their assets to it.

For Ethereum Virtual Machine (EVM) blockchains, an additional step is required. Users must submit their sender address before depositing assets. This step ensures that the system can accurately track and verify the origin of the deposited funds.

Withdrawal Process

Withdrawing assets from Tangent blockchain bridge system is equally straightforward. Users select a bridge for their withdrawal, which does not necessarily have to be the same bridge they used for depositing. After selecting a bridge, users send a withdrawal transaction. The system then processes this request and sends the assets to the user's specified address.

Security Measures

This system employs an N-of-N signature scheme, which utilizes Multi-Party Computation (MPC) capabilities. MPC allows for the creation of aggregated signatures or public keys, involving multiple participants in the asset bridge. This coordinated effort ensures robust security and makes it extremely difficult for any single participant to compromise the system.

Bridge participants do not communicate directly with one another; instead, the bridge's selected attester mediates all communications between participating nodes using asymmetric encryption. Certain Digital Signature Algorithms (DSAs) necessitate additional state management, such as temporary secret keys. Bridge selects a new random attester for each distinct operation.

Sensitive state information is generated by a randomly chosen participant and is protected from both the attester and other participants, including those who store this data, ensuring it cannot be used to access or alter intermediate messages while communication is in process.

Bridge Architecture

The bridge architecture consists of several key components:

  1. Attester: Acts as a coordinator, facilitating the transfer of assets between different blockchains and publishes off-chain transactions into the Tangent blockchain, ensuring that all relevant data is recorded on the blockchain.
  2. Participants: They hold a private key share, enabling them to create deposit addresses on other blockchains and sign transactions for withdrawals.

Bridge Revenue

Bridge attesters have the authority to set withdrawal fees in native tokens when they create a bridge. Attester is chosen to coordinate a bridge operation based on their minimal fee requirement. This means that if selected bridge does not provide adequate fee then it may fail to find an attester willing to coordinate it.

The distribution of these withdrawal fees is structured as follows:

  1. Bridge Attester's Share: The coordinating bridge attester receives at least 10% of the total fees.
  2. Bridge Participants' Share: The 60% minus network fees of remaining amount is allocated to the participants who signed the transaction.
  3. Other Attesters Share: Everything else goes to the attesters who submitted the confirmation transaction.

This fee structure ensures that all parties involved in the bridge process are incentivized and compensated appropriately for their roles in facilitating secure and efficient cross-chain transfers.

Participant Selection

To ensure unpredictability and fairness in the bridging process, participants are randomly selected into bridges. This random selection helps prevent any potential manipulation or bias in the asset transfer process.

Participant Groups

Each attester is responsible for configuring the size of the participant group when creating a dedicated bridge, which can range from 7 to 23 participants. This setup ensures a balance between security and practicality. Each participant also holds a secret share of every other participant within the group derived with Shamir Secret Sharing (SSS) pass. This design facilitates a high level of security and redundancy.

Participant Migration in Case of Failure

In the event of a failure, the system supports participant migration through an M-of-N migration scheme. To successfully migrate a private key share to another participant, at least 51% of participants must reach a consensus on the matter.

This approach ensures that the migration process is both secure and resilient, maintaining the integrity of the system even when faced with challenges.