Cross-Chain Messaging

Cross-chain messaging is the foundation of TAC’s hybrid dApp functionality. It enables secure communication between TON users and EVM smart contracts through a structured system of message creation, validation, and execution. Understanding this messaging system helps developers build more effective applications and troubleshoot issues when they arise.

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Message Lifecycle Overview

Every cross-chain operation in TAC follows a predictable lifecycle that ensures security and reliability while maintaining reasonable performance for application use cases.

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Message Structure

Cross-chain messages contain all the information needed for secure validation and execution across different blockchain architectures.

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Core Message Components

Every message includes essential metadata and operation-specific data:

{
  timestamp: 1640995200,              // TON blockchain timestamp
  target: "0x742d35Cc6473...",        // Target smart contract address
  methodName: "swapTokens(bytes,bytes)", // Method signature
  arguments: "0x1234...",             // Encoded method parameters
  caller: "EQAbc123...",              // Original TON caller address
  mintTokens: [...],                  // Tokens to mint on TAC EVM
  unlockTokens: [...]                 // Tokens to unlock from previous operations
}

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TAC Header Information

The TON Adapter automatically augments messages with additional metadata that proxy contracts receive:

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Parameter Encoding

Application-specific parameters are encoded using standard Ethereum ABI encoding:

// Example: DEX swap parameters
const abi = new ethers.AbiCoder();
const swapParams = abi.encode(
  ["tuple(address,address,uint256,uint256,address,uint256)"],
  [[tokenIn, tokenOut, amountIn, minAmountOut, recipient, deadline]]
);

This encoding ensures that EVM proxy contracts can decode parameters correctly while maintaining compatibility with standard Ethereum tooling.

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Validation Process

The TON Adapter employs multiple layers of validation to ensure message integrity and prevent malicious activity.

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Asset Verification

• Transfer Validation: Sequencers verify that actual token transfers match the amounts specified in cross-chain messages. This prevents attempts to claim false transfer amounts or access unauthorized funds.

• Balance Checking: User balances are validated against requested operations to ensure sufficient assets are available for the intended operation.

• Metadata Consistency: Token information and operation parameters are cross-referenced to ensure consistency throughout the validation process.

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Cryptographic Validation

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Epoch-Based Processing

TAC organizes message processing into time-based epochs that provide structure and predictability to cross-chain operations.

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Epoch Structure

Deterministic Timing: Each epoch is calculated using a precise formula that ensures all sequencers work with the same time boundaries:

EpochId = (currentTime - protocolDeployTime) / epochDuration

Processing Windows: Messages are collected and processed within specific timeframes:

[protocolDeployTime + EpochId × epochDuration,
 protocolDeployTime + (EpochId + 1) × epochDuration]

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Benefits of Epoch Processing

• Ordered Processing: All sequencers process the same set of messages in each epoch, preventing timing-based attacks and ensuring consistency.

• Batch Efficiency: Processing messages in batches is more efficient than individual handling and provides better consensus guarantees.

• Predictable Latency: Users and applications can estimate processing times based on epoch duration and current network status.

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Message Types and Flows

Different types of cross-chain operations follow distinct patterns that affect how messages are structured and processed.

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One-Way Messages (TON → TAC)

• Simple Operations: Basic token transfers, contract calls that don’t require return values, or operations where results remain on the EVM side.

• Message Flow: TON user → TON Adapter → Sequencer validation → EVM execution → Completion notification.

• Use Cases: Token deposits, simple contract interactions, or operations where users only need confirmation of completion.

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Round-Trip Messages (TON → TAC → TON)

• Complex Operations: Operations that generate results or assets that need to be returned to the original TON user.

• Extended Flow: Includes an additional return path where EVM proxy contracts create new messages to send results back through the TON Adapter.

• Use Cases: Token swaps, liquidity operations, or any interaction where users expect to receive different assets or data back.

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Rollback Operations

• Automatic Triggers: Failed executions on either chain automatically trigger rollback message creation to return assets safely.

• Asset Protection: Rollback messages ensure that locked or transferred assets are returned to users when operations cannot complete successfully.

• Special Processing: Rollback messages receive priority processing to minimize the time users wait for asset recovery.

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Error Handling and Recovery

TAC’s messaging system includes comprehensive error handling mechanisms that protect user assets and provide clear feedback about operation status.

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Failure Detection

Execution Monitoring: The system continuously monitors message execution on target chains and detects various types of failures.

Timeout Handling: Messages that don’t complete within expected timeframes trigger automatic timeout procedures.

Validation Failures: Messages that fail validation at any stage are rejected before execution to prevent resource waste.

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Recovery Mechanisms

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Message Security Guarantees

The cross-chain messaging system provides strong security guarantees through multiple redundant mechanisms.

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Economic Security

• Stake Requirements: Sequencers must stake significant collateral to participate in message validation, creating strong financial incentives for honest behavior.

• Slashing Mechanisms: Provably incorrect behavior results in automatic collateral slashing, making attacks economically unattractive.

• Reward Alignment: Performance-based rewards encourage reliable operation and continued network participation.

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Technical Security

• Consensus Thresholds: High consensus requirements (3/5 within groups, multiple groups for network consensus) make coordination attacks extremely difficult.

• Cryptographic Verification: Merkle proofs and digital signatures provide mathematical guarantees of message integrity and authenticity.

• Redundant Validation: Multiple independent parties validate each message, preventing single points of failure or manipulation.

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Performance Characteristics

Understanding the performance characteristics of cross-chain messaging helps developers set appropriate expectations and design better user experiences.

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Best Practices for Developers

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What’s Next?

Understanding cross-chain messaging and fee structures provides the foundation for exploring specific operational aspects of TAC’s hybrid dApp system.