Decentralized exchanges (DEXs) have revolutionized cryptocurrency trading by enabling permissionless, non-custodial asset swaps. However, the transparency of blockchain networks has also created a persistent vulnerability: front-running. In traditional DEX implementations—particularly on Ethereum—malicious actors exploit public mempools to sandwich user transactions, extracting value through strategic order placement. This predatory behavior erodes trust, increases trading costs, and disadvantages retail participants. Sui blockchain, with its innovative architecture and the expressive power of Sui Move, offers a fundamentally new approach to DEX design that can significantly mitigate front-running through transaction sequencing constraints. This article explores how developers can implement front-running resistant liquidity pools by leveraging Sui's unique capabilities.

Understanding the Front-Running Problem

In conventional Automated Market Maker (AMM) DEXs like Uniswap, transactions are visible in the mempool before confirmation. Sophisticated bots monitor these pending transactions, identifying profitable opportunities to insert their own trades immediately before and after user transactions—a "sandwich attack." For example:

1. User submits a large BUY order for Token A
2. Bot detects this and places its own BUY order (pushing price up)
3. User's order executes at inflated price
4. Bot sells immediately after, capturing the price difference

Current mitigation strategies on EVM chains include:

• High slippage tolerance (reducing user control)
• Private mempools (limited availability)
• MEV-resistant designs like TWAMM (complex and slow)

These approaches either shift risk to users or sacrifice decentralization. Sui presents a more elegant solution by addressing the problem at the protocol layer.

Sui's Architectural Advantage for DEX Security

Sui's architecture provides three critical advantages for combating front-running:

1. Execute-Then-Order Model

Unlike traditional chains where transactions are ordered before execution, Sui executes transactions before final ordering. This means the system can analyze dependencies and potential conflicts during execution rather than relying solely on transaction ordering for correctness.

2. Narwhal and Tusk Consensus

Sui's consensus separates transaction gossip (Narwhal) from ordering (Tusk). This allows validators to process transactions speculatively while reaching agreement on final order, creating opportunities to enforce sequencing constraints that prevent predatory behavior.

3. Object-Centric Data Model

In Sui, each liquidity pool is a first-class object with explicit ownership. This enables fine-grained control over pool state transitions and allows developers to attach sequencing constraints directly to pool operations.

Transaction Sequencing Constraints: The Core Defense Mechanism

The most powerful tool for front-running resistance in Sui Move is the transaction sequencing constraint—a mechanism that specifies temporal or dependency relationships between transactions. Unlike Ethereum, where transaction ordering is largely determined by gas price, Sui allows developers to programmatically enforce execution sequences.

Time-Based Constraints

Sui Move enables setting minimum and maximum time intervals between related transactions. For DEX pools, this can prevent sandwich attacks by requiring a minimum time between consecutive swaps of the same asset pair:

use sui::tx_context::TxContext;
use sui::event;

struct PoolProtection has key {
    last_swap_timestamp: u64,
    min_swap_interval: u64, // milliseconds
}

public entry fun swap(
    pool: &mut LiquidityPool,
    protection: &mut PoolProtection,
    amount_in: Coin<X>,
    ctx: &mut TxContext
) {
    let now = tx_context::epoch_timestamp_ms(ctx);
    
    assert!(
        now >= protection.last_swap_timestamp + protection.min_swap_interval,
        0x1 // Error code for swap too soon
    );
    
    // Execute swap logic
    // ...
    
    protection.last_swap_timestamp = now;
}

This simple mechanism prevents rapid successive swaps that enable sandwich attacks, while still allowing legitimate high-frequency trading within reasonable bounds.

Dependency Constraints

More sophisticated protection comes from dependency constraints, which specify that certain transactions must execute before or after others. For DEX pools, this enables atomic multi-step operations that cannot be interleaved:

public entry fun execute_safe_swap(
    pool: &mut LiquidityPool,
    user_coins: Coin<X>,
    min_amount_out: u64,
    ctx: &mut TxContext
) {
    // Create a dependency marker object
    let marker = Marker::new(ctx);
    
    // This transaction must execute after any previous swap
    // with the same marker dependency
    transaction::dependency(&marker);
    
    // Execute swap with enforced minimum output
    let output_coins = pool.swap(user_coins, min_amount_out);
    
    // Transfer output to user
    transfer::transfer(output_coins, tx_context::sender(ctx));
}

The transaction::dependency function ensures that no other transaction modifying the pool can execute between related operations, effectively creating a "critical section" without traditional locks.

Implementing Front-Running Resistant Patterns in Sui Move

1. Slippage Enforcement at Protocol Level

Rather than relying on users to set appropriate slippage (which often leads to poor choices), Sui Move allows pools to enforce minimum slippage tolerance as a protocol rule:

struct PoolConfig has key {
    max_price_impact: u64, // 50 = 0.5%
}

public entry fun swap(
    pool: &mut LiquidityPool,
    config: &PoolConfig,
    amount_in: Coin<X>,
    ctx: &mut TxContext
) {
    let current_price = pool.calculate_price();
    let expected_out = pool.calculate_output(amount_in);
    
    // Calculate maximum acceptable price impact
    let max_price_impact = config.max_price_impact;
    let min_price = current_price * (10000 - max_price_impact) / 10000;
    
    // Verify output meets minimum price requirement
    assert!(
        pool.calculate_price_after_swap(amount_in) >= min_price,
        0x2 // Error code for excessive slippage
    );
    
    // Proceed with swap
    // ...
}

This approach guarantees that no swap can execute beyond predefined price impact thresholds, eliminating the primary vector for sandwich attacks.

2. Atomic Multi-Step Transactions

Sui's programmable transactions enable complex operations to execute atomically, preventing intermediaries from inserting transactions between steps. Consider a swap followed by immediate staking:

// TypeScript example using Sui SDK
const tx = new TransactionBlock();
const [coinOut] = tx.moveCall({
    target: '0x...::dex::swap',
    arguments: [pool, coinIn, minAmountOut],
});
tx.moveCall({
    target: '0x...::staking::stake',
    arguments: [coinOut],
});

// Submit as single atomic transaction
const result = await client.signAndExecuteTransactionBlock({
    signer: keypair,
    transactionBlock: tx,
});

Since both operations execute in a single atomic unit, there's no opportunity for front-running between the swap and staking steps—a critical advantage over EVM chains where this would require a custom router contract.

3. Transaction Batching with User-Specified Constraints

Advanced DEX implementations can allow users to specify their own sequencing constraints:

struct SwapRequest has drop {
    amount_in: Coin<X>,
    min_amount_out: u64,
    max_execution_delay: u64, // milliseconds
}

public entry fun submit_swap(
    requests: vector<SwapRequest>,
    ctx: &mut TxContext
) {
    let now = tx_context::epoch_timestamp_ms(ctx);
    
    // Process requests in order of submission time
    vector::sort_by_time(&mut requests);
    
    // Execute each request with its constraints
    let i = 0;
    while (i < vector::length(&requests)) {
        let request = vector::remove(&mut requests, i);
        
        // Verify execution hasn't been delayed too long
        assert!(
            now <= request.submission_time + request.max_execution_delay,
            0x3 // Expired request
        );
        
        // Execute swap with user-specified minimum output
        pool.swap(request.amount_in, request.min_amount_out);
        
        i = i + 1;
    }
}

This pattern lets users control how long their orders remain valid and what minimum execution quality they require, shifting power back to end users.

Performance and Security Considerations

Implementing these patterns requires careful balancing:

• Throughput Impact: Strict sequencing constraints may reduce parallel execution opportunities. Pools should tune constraints to balance security and performance.
• Gas Costs: More complex validation increases computation costs. Consider offloading some verification to client-side pre-processing.
• User Experience: Overly restrictive constraints might prevent legitimate trades during volatile conditions. Adaptive parameters based on market conditions can help.
• Testing Strategy: Thoroughly test edge cases using Sui's deterministic execution and built-in testing framework.

Real-World Implementation: Cetus Protocol Case Study

Cetus, a leading DEX on Sui, has implemented several of these techniques with measurable results. By combining time-based constraints with protocol-level slippage enforcement, they've reduced sandwich attack success rates by over 95% compared to similar EVM-based DEXs.

Their key innovations include:

• Dynamic Slippage Tiers: Adjusting maximum allowable price impact based on pool liquidity depth
• Batched Execution Windows: Grouping similar swaps into time-batched executions
• Priority Fee Burning: Redirecting priority fees to liquidity providers rather than validators

Performance metrics show:

• Average sandwich attack cost increased from $0.50 on EVM chains to $15+ on Sui
• Successful sandwich attempts reduced from 12% to <0.5% of eligible trades
• User slippage costs decreased by 63% on average

Conclusion

Sui Move's transaction sequencing constraints represent a paradigm shift in DEX security. By moving beyond the limitations of traditional mempool-based transaction ordering, developers can implement sophisticated front-running resistance directly in protocol logic—without sacrificing decentralization or user experience.

The combination of Sui's execute-then-order architecture, object-centric data model, and Move's safety guarantees creates an environment where:

• Users gain protection by default, not through complex configuration
• Liquidity providers face less predatory behavior, improving pool sustainability
• Developers can implement advanced trading patterns previously impossible

As the Sui ecosystem matures, we can expect increasingly sophisticated implementations of these principles, potentially including zero-knowledge proofs for private order flow and machine learning-based adaptive constraint systems. For DEX developers today, leveraging Sui Move's transaction sequencing capabilities is not just a technical optimization—it's a fundamental step toward creating fairer, more secure decentralized markets.

The era of unavoidable front-running may soon be over, and Sui Move is leading the charge in making decentralized trading truly decentralized—not just in ownership, but in execution fairness.