> ## Documentation Index
> Fetch the complete documentation index at: https://docs.teqoin.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Security Model

> Comprehensive security analysis and threat model for TeQoin L2

A complete analysis of TeQoin's security architecture, threat model, and security guarantees.

<Note>
  **TL;DR:**

  TeQoin inherits Ethereum's security through data availability on L1, fraud proofs for state validity, and economic incentives that make attacks unprofitable. Even with a malicious sequencer, user funds remain safe due to cryptographic proofs and decentralized verification.
</Note>

***

## 🎯 Security Guarantees

### What TeQoin Guarantees

<CardGroup cols={2}>
  <Card title="Fund Safety" icon="vault">
    **Your funds cannot be stolen**

    Even with malicious sequencer
  </Card>

  <Card title="State Validity" icon="check-circle">
    **All state transitions are valid**

    Invalid states are proven and reverted
  </Card>

  <Card title="Data Availability" icon="database">
    **All transaction data on L1**

    Users can always reconstruct state
  </Card>

  <Card title="Censorship Resistance" icon="shield">
    **Transactions cannot be censored**

    Force inclusion via L1
  </Card>

  <Card title="Liveness" icon="heartbeat">
    **System always operational**

    Can recover even if sequencer fails
  </Card>

  <Card title="No Custody" icon="key">
    **Self-custodial**

    Only you control your private keys
  </Card>
</CardGroup>

***

## 🏗️ Security Layers

### Defense in Depth

```mermaid theme={null}
graph TB
    A[User Funds] --> B[Layer 1: Cryptography]
    B --> C[Layer 2: Smart Contracts]
    C --> D[Layer 3: Fraud Proofs]
    D --> E[Layer 4: Economic Incentives]
    E --> F[Layer 5: Ethereum L1 Security]
    
    style A fill:#ff6b6b
    style F fill:#51cf66
```

<Steps>
  <Step title="Layer 1: Cryptographic Security">
    **Foundation: Math and cryptography**

    ```
        Private Key → Public Key → Address
        
        - ECDSA signatures (secp256k1)
        - Keccak-256 hashing
        - Merkle trees for state commitments
    ```

    **Guarantees:**

    * Only private key owner can sign transactions
    * Signatures cannot be forged
    * State roots cannot be faked

    **Attack resistance:**

    * Requires breaking ECDSA (computationally infeasible)
    * Would need to break SHA-256 class hashes
  </Step>

  <Step title="Layer 2: Smart Contract Security">
    **L1 contracts enforce rules**

    ```solidity theme={null}
        // L1 Bridge Contract
        - Holds all L2 ETH backing (locked)
        - Only releases with valid proof
        - Challenge period enforced
        - Immutable after deployment
    ```

    **Guarantees:**

    * Code is law (deterministic execution)
    * No admin keys can bypass rules
    * Audited by multiple firms
    * Battle-tested on Ethereum

    **Attack resistance:**

    * Would need to exploit smart contract bugs
    * Multiple audits reduce risk
    * Time-tested patterns used
  </Step>

  <Step title="Layer 3: Fraud Proof Security">
    **Invalid states are provably detected**

    ```
        Invalid State Submitted
        ↓
        Verifiers Detect Fraud
        ↓
        Fraud Proof Submitted
        ↓
        L1 Verifies Proof
        ↓
        Invalid State Reverted
    ```

    **Guarantees:**

    * Any invalid state can be proven wrong
    * Proof verified on-chain (trustless)
    * Malicious sequencer slashed
    * Correct state restored

    **Attack resistance:**

    * Would need all verifiers to collude
    * Economic incentive ensures verification
  </Step>

  <Step title="Layer 4: Economic Security">
    **Rational actors stay honest**

    ```
        Sequencer Stake: $10M
        Daily Revenue: $100K
        Annual Revenue: $36M
        
        Attack Gain: < $1M (gets caught)
        Attack Cost: $10M stake + $36M future revenue
        
        Result: Attack is irrational
    ```

    **Guarantees:**

    * Honest behavior is most profitable
    * Fraud is always caught (7-day period)
    * Penalties exceed any possible gain

    **Attack resistance:**

    * Would require irrational economic behavior
    * Would need to sacrifice massive value
  </Step>

  <Step title="Layer 5: Ethereum L1 Security">
    **Inherit Ethereum's security**

    ```
        L1 Security:
        - $40B+ staked ETH
        - 1M+ validators worldwide
        - 15+ years of security research
        - Battle-tested consensus
    ```

    **Guarantees:**

    * L1 contracts cannot be manipulated
    * L1 data cannot be censored
    * L1 state is final

    **Attack resistance:**

    * Would need to attack Ethereum itself
    * Requires 51% of validators (\~\$20B)
  </Step>
</Steps>

***

## 🎭 Threat Model

### Attack Scenarios & Defenses

<AccordionGroup>
  <Accordion title="1. Malicious Sequencer Attempts Theft">
    **Attack:** Sequencer tries to steal user funds

    **Method:**

    ```
        Sequencer posts invalid state:
        - Claims Alice has 0 ETH (was 10 ETH)
        - Claims Sequencer has 10 ETH more
        
        State Root: MerkleRoot(malicious_state)
    ```

    **Defense:**

    ```
        1. Verifier downloads batch from L1
        2. Re-executes all transactions
        3. Computes correct state root
        4. State roots don't match!
        5. Verifier submits fraud proof
        6. L1 contract verifies proof
        7. Invalid state reverted
        8. Sequencer slashed ($10M loss)
        9. Alice keeps her 10 ETH
    ```

    **Result:** ✅ Attack fails, attacker loses stake
  </Accordion>

  <Accordion title="2. Sequencer Censors User Transactions">
    **Attack:** Sequencer refuses to include user's transactions

    **Method:**

    ```
        User submits withdrawal TX
        Sequencer ignores it indefinitely
        User cannot withdraw funds
    ```

    **Defense:**

    ```
        User's options:
        
        Option 1: Force Inclusion via L1
        - Submit TX directly to L1 contract
        - L1 contract forces sequencer to include
        - If sequencer refuses → slashed
        
        Option 2: Exit via L1
        - Submit Merkle proof of L2 balance to L1
        - L1 contract validates proof
        - Withdraw directly from L1 bridge
    ```

    **Result:** ✅ Censorship impossible long-term
  </Accordion>

  <Accordion title="3. Sequencer Goes Offline">
    **Attack:** Sequencer stops producing blocks (DoS)

    **Method:**

    ```
        Sequencer server crashes
        No new blocks produced
        Users cannot transact
    ```

    **Defense:**

    ```
        Short-term (hours):
        - Sequencer backup nodes activate
        - Automatic failover
        - Service continues
        
        Long-term (days):
        - Users submit forced transactions via L1
        - Users can exit directly to L1
        - New sequencer can be appointed
        
        State Recovery:
        - All data on L1 (data availability)
        - Anyone can reconstruct L2 state
        - New sequencer resumes from last state
    ```

    **Result:** ✅ System remains operational
  </Accordion>

  <Accordion title="4. Verifiers Collude with Sequencer">
    **Attack:** All verifiers agree to ignore fraud

    **Method:**

    ```
        Sequencer bribes all verifiers
        Sequencer posts invalid state
        No verifiers submit fraud proof
        Invalid state becomes final after 7 days
    ```

    **Defense:**

    ```
        Economic Reality:
        - Verifiers are permissionless (anyone can run)
        - Only need 1 honest verifier
        - Bribe cost: Must pay ALL potential verifiers
        - Includes: Every Ethereum user globally
        
        Cost to bribe everyone: Infinite
        Cost to run verifier: $200/month
        Fraud proof reward: $5M
        
        Result: Economically impossible to bribe everyone
        
        Even if 99.99% bribed:
        - 0.01% honest = attack fails
        - 1 honest verifier = attack fails
    ```

    **Result:** ✅ Attack requires bribing everyone (impossible)
  </Accordion>

  <Accordion title="5. L1 Contract Exploit">
    **Attack:** Find bug in L1 smart contracts

    **Method:**

    ```
        Attacker finds vulnerability
        Exploits to drain bridge funds
        Steals locked ETH
    ```

    **Defense:**

    ```
        Prevention:
        - Multiple security audits
        - Formal verification
        - Bug bounty program ($1M+ rewards)
        - Gradual rollout (start small)
        - Circuit breakers
        
        If exploit found:
        - Pause mechanism activated
        - Governance can upgrade
        - Insurance fund covers losses
        - Community recovery process
    ```

    **Result:** ⚠️ Low risk but possible (mitigated heavily)
  </Accordion>

  <Accordion title="6. 51% Attack on Ethereum L1">
    **Attack:** Attacker controls Ethereum consensus

    **Method:**

    ```
        Attacker acquires 51% of Ethereum validators
        Reverts L1 transactions
        Manipulates L1 data
    ```

    **Defense:**

    ```
        Reality:
        - Would need ~$20B to acquire 51%
        - Would destroy ETH value (self-defeating)
        - Ethereum social consensus would fork
        - Attack detection and response
        
        If this happens:
        - TeQoin is compromised
        - So is all of Ethereum
        - So is all of DeFi
        - Economic apocalypse
    ```

    **Result:** ⚠️ Inherits Ethereum's security assumptions
  </Accordion>
</AccordionGroup>

***

## 💰 Economic Security Analysis

### Cost-Benefit for Attackers

<Tabs>
  <Tab title="Attack Costs">
    **What would attacks cost?**

    | Attack Type                 | Cost                           | Success Probability     |
    | --------------------------- | ------------------------------ | ----------------------- |
    | **Steal funds (sequencer)** | $10M stake + $36M/year revenue | 0% (fraud proof)        |
    | **Censor transactions**     | \$10M stake + reputation       | 0% (force inclusion)    |
    | **Bribe all verifiers**     | Infinite (permissionless)      | 0% (need everyone)      |
    | **51% Ethereum**            | \$20B+                         | \~0% (social consensus) |
    | **Smart contract exploit**  | Research time + \$1M bounty    | 1% (audited)            |

    **Takeaway:** All attacks are either impossible or economically irrational
  </Tab>

  <Tab title="Defender Incentives">
    **Why people defend the system:**

    **Sequencer:**

    ```
        Honest Revenue: $36M/year
        Dishonest Gain: -$10M (slashed)
        
        Incentive: Stay honest
    ```

    **Verifiers:**

    ```
        Cost: $2,400/year
        Fraud Proof Reward: $5M (one-time)
        Expected Value: Highly positive
        
        Incentive: Monitor actively
    ```

    **Users:**

    ```
        Benefit: Secure funds
        Cost: None (just use it)
        
        Incentive: Use TeQoin
    ```

    **Ethereum Validators:**

    ```
        Benefit: L2 usage increases ETH value
        Cost: None (L2 pays for L1 security)
        
        Incentive: Support L2s
    ```
  </Tab>

  <Tab title="Nash Equilibrium">
    **Game theory stable state:**

    ```
        Players: Sequencer, Verifiers, Users
        
        Strategies:
        - Sequencer: [Honest, Dishonest]
        - Verifiers: [Monitor, Ignore]
        - Users: [Use, Don't Use]
        
        Payoff Matrix (simplified):
        
                            Verifiers Monitor
        Sequencer Honest:   (High, Medium, High)
        Sequencer Dishonest:(-∞, High, Medium)
        
                            Verifiers Ignore
        Sequencer Honest:   (High, Low, High)
        Sequencer Dishonest:(High, Low, -∞)
        
        Nash Equilibrium: (Honest, Monitor, Use)
        
        - Sequencer: Stay honest (maximizes profit)
        - Verifiers: Monitor (profitable)
        - Users: Use system (secure)
        
        No player benefits from deviating!
    ```
  </Tab>
</Tabs>

***

## 🔐 Security Assumptions

### What We Trust

<Tabs>
  <Tab title="Cryptographic Assumptions">
    **We assume these are secure:**

    ✅ **ECDSA (secp256k1)**

    * Used for signatures
    * Same as Bitcoin/Ethereum
    * No known attacks

    ✅ **Keccak-256 (SHA-3)**

    * Used for hashing
    * Cryptographically secure
    * Collision resistant

    ✅ **Merkle Trees**

    * State commitments
    * Mathematically proven
    * Tamper-evident

    **Risk:** Cryptography is broken
    **Likelihood:** Extremely low (decades of research)
    **Impact:** All of crypto breaks (not just TeQoin)
  </Tab>

  <Tab title="Ethereum L1 Security">
    **We assume Ethereum is secure:**

    ✅ **Consensus**

    * Proof of Stake works
    * 1M+ validators
    * \$40B+ staked

    ✅ **EVM**

    * Smart contracts execute correctly
    * No consensus bugs
    * Deterministic execution

    ✅ **Data Availability**

    * L1 data is always available
    * Cannot be censored
    * Validators honest majority

    **Risk:** Ethereum is compromised
    **Likelihood:** Very low (most secure blockchain)
    **Impact:** All Ethereum L2s affected
  </Tab>

  <Tab title="Economic Assumptions">
    **We assume rational economic behavior:**

    ✅ **Rational Actors**

    * People maximize profit
    * Don't destroy value irrationally
    * Follow economic incentives

    ✅ **Market Efficiency**

    * Fraud proof rewards attract verifiers
    * Competition ensures verification
    * Prices reflect information

    ✅ **No Infinite Resources**

    * Attackers have budget limits
    * Can't bribe everyone
    * Can't sustain losses indefinitely

    **Risk:** Irrational actors with unlimited funds
    **Likelihood:** Very low (markets are rational)
    **Impact:** Could enable certain attacks
  </Tab>

  <Tab title="What We DON'T Trust">
    **System is secure WITHOUT trusting:**

    ❌ **Sequencer**

    * Assume potentially malicious
    * Fraud proofs ensure validity
    * Economic penalties deter attacks

    ❌ **Any Single Verifier**

    * Permissionless verification
    * Only need 1 honest verifier
    * Economic incentive ensures many

    ❌ **TeQoin Team**

    * Cannot access user funds
    * Cannot bypass L1 contracts
    * Cannot censor indefinitely

    **This is trustless security!**
  </Tab>
</Tabs>

***

## 🛡️ Security Best Practices

### For Users

<CardGroup cols={2}>
  <Card title="Secure Your Private Key" icon="key">
    **Critical:**

    * Use hardware wallet (Ledger, Trezor)
    * Never share private key
    * Backup seed phrase securely
    * Use strong passwords
  </Card>

  <Card title="Verify Transactions" icon="magnifying-glass">
    **Before signing:**

    * Check recipient address
    * Verify amount
    * Review contract interactions
    * Check network (L1 vs L2)
  </Card>

  <Card title="Use Official Interfaces" icon="shield-check">
    **Only trust:**

    * [https://bridge.teqoin.io](https://bridge.teqoin.io)
    * [https://rpc.teqoin.io](https://rpc.teqoin.io)
    * Official documentation
    * Verified contract addresses
  </Card>

  <Card title="Start Small" icon="coins">
    **Test first:**

    * Send small amount initially
    * Verify it arrives
    * Then send larger amounts
    * Don't risk everything at once
  </Card>
</CardGroup>

### For Developers

<CardGroup cols={2}>
  <Card title="Audit Your Contracts" icon="magnifying-glass-chart">
    **Before mainnet:**

    * Multiple security audits
    * Formal verification if possible
    * Bug bounty program
    * Test on testnet extensively
  </Card>

  <Card title="Handle Reorgs" icon="arrows-rotate">
    **L2 blocks can reorg:**

    * Wait for L1 finality (7 days)
    * For soft finality, wait 5-10 blocks
    * Don't assume instant finality
    * Handle reorg scenarios
  </Card>

  <Card title="Validate Inputs" icon="check">
    **Never trust user input:**

    * Validate all addresses
    * Check amount bounds
    * Verify signatures
    * Sanitize data
  </Card>

  <Card title="Plan for Emergencies" icon="triangle-exclamation">
    **Emergency procedures:**

    * Pause mechanisms
    * Upgrade paths
    * Recovery procedures
    * Communication plans
  </Card>
</CardGroup>

***

## 📊 Security Comparison

### TeQoin vs Other L2s

| Security Aspect       | TeQoin        | Optimism      | Arbitrum      | zkSync        | Polygon    |
| --------------------- | ------------- | ------------- | ------------- | ------------- | ---------- |
| **Data Availability** | L1            | L1            | L1            | L1            | Sidechain  |
| **Validity Proofs**   | Fraud Proofs  | Fraud Proofs  | Fraud Proofs  | ZK Proofs     | None       |
| **Withdrawal Time**   | 7 days        | 7 days        | 7 days        | Hours         | Instant    |
| **Sequencer**         | Centralized\* | Centralized\* | Centralized\* | Centralized\* | Validators |
| **EVM Compatibility** | 100%          | 100%          | 99%+          | \~95%         | 100%       |
| **Security Level**    | Ethereum      | Ethereum      | Ethereum      | Ethereum      | Lower      |

\*Decentralization roadmap planned

**Key Takeaway:** TeQoin has Ethereum-grade security through L1 data availability and fraud proofs

***

## 🔬 Formal Security Properties

### Mathematical Guarantees

<AccordionGroup>
  <Accordion title="Safety">
    **Nothing bad ever happens**

    **Formal property:**

    ```
        ∀ state S: 
          validStateTransition(S_prev, TX, S_new) ∨ 
          ∃ fraudProof: proves_invalid(S_new)
    ```

    **In English:**
    For any state transition, either:

    1. It's valid according to EVM rules, OR
    2. There exists a fraud proof proving it's invalid

    **Result:** Invalid states cannot persist
  </Accordion>

  <Accordion title="Liveness">
    **Something good eventually happens**

    **Formal property:**

    ```
        ∀ transaction TX: 
          eventually(TX_included_in_block) ∨ 
          user_can_force_include(TX)
    ```

    **In English:**
    For any transaction, either:

    1. It will eventually be included by sequencer, OR
    2. User can force inclusion via L1

    **Result:** Transactions cannot be censored forever
  </Accordion>

  <Accordion title="Data Availability">
    **All data is always available**

    **Formal property:**

    ```
        ∀ L2_block B: 
          ∃ L1_calldata D: contains(D, all_transactions(B))
    ```

    **In English:**
    For every L2 block:

    * Transaction data exists on L1
    * Available to all participants
    * Cannot be hidden or deleted

    **Result:** State can always be reconstructed
  </Accordion>
</AccordionGroup>

***

## 🎯 Security Guarantees Summary

### What You Can Trust

<Steps>
  <Step title="Your Funds Are Safe">
    ✅ Cannot be stolen by sequencer\
    ✅ Cannot be frozen indefinitely\
    ✅ Can always be withdrawn (7 days)\
    ✅ Protected by Ethereum L1 security
  </Step>

  <Step title="State is Valid">
    ✅ All state transitions follow EVM rules\
    ✅ Invalid states are proven and reverted\
    ✅ Economic incentive ensures verification\
    ✅ Fraud proofs work automatically
  </Step>

  <Step title="Censorship Resistant">
    ✅ Transactions cannot be censored permanently\
    ✅ Can force inclusion via L1\
    ✅ Can exit system anytime\
    ✅ Sequencer slashed for censorship
  </Step>

  <Step title="Trustless">
    ✅ Don't need to trust sequencer\
    ✅ Don't need to trust verifiers\
    ✅ Don't need to trust TeQoin team\
    ✅ Only trust math and economics
  </Step>
</Steps>

***

## 📚 Additional Resources

<CardGroup cols={2}>
  <Card title="Fraud Proofs" icon="shield-halved" href="/architecture/fraud-proofs">
    How fraud detection works
  </Card>

  <Card title="Optimistic Rollup" icon="layer-group" href="/architecture/optimistic-rollup">
    Core technology explained
  </Card>

  <Card title="Sequencer Design" icon="server" href="/architecture/sequencer">
    Block production system
  </Card>

  <Card title="Challenge Period" icon="clock" href="/bridge/challenge-period">
    Why withdrawals take 7 days
  </Card>
</CardGroup>

***