Documentation

Privacy-Enhanced Cross-Chain Bridge Protocol

Executive Summary

Zejak is a privacy-preserving cross-chain protocol that leverages Zcash's battle-tested shielded pool infrastructure to provide anonymous transaction routing for Solana users. By combining meme culture with functional privacy technology, Zejak enables users to break on-chain linkability between sender and recipient addresses through a three-phase bridge architecture.

Problem Statement

Current blockchain transactions on transparent chains like Solana create permanent, publicly auditable links between wallet addresses. While beneficial for transparency, this creates privacy concerns for users who wish to:

  • Break transaction history linkage
  • Prevent address clustering and profiling
  • Maintain financial privacy in legitimate use cases
  • Protect against front-running and MEV exploitation

Solution Architecture

Core Mechanism

Zejak implements a privacy-enhanced bridge protocol utilizing Zcash's shielded pool as an anonymity mixer:

Sender (SOL) → Zejak Vanity Address → Zcash Shielded Pool → Recipient (SOL)

Three-Phase Protocol

Phase 1: Deposit (Solana → Zcash)

  • User sends SOL to a Zejak vanity address (e.g., Zejak7a9f...)
  • Zejak bridge contract locks the SOL and generates a unique deposit identifier
  • A corresponding amount of ZEC is minted/released from the bridge liquidity pool
  • ZEC is sent to a Zcash shielded address (z-address)

Phase 2: Anonymity Set Expansion (Zcash Shielded Pool)

  • Funds remain in the shielded pool for a configurable mixing period
  • Zero-knowledge proofs obscure the link between input and output transactions
  • Transactions are mixed with other users' shielded transactions
  • The larger the anonymity set, the stronger the privacy guarantees

Phase 3: Withdrawal (Zcash → Solana)

  • After the mixing period, ZEC is withdrawn from the shielded pool
  • Zcash bridge component burns/locks the ZEC
  • SOL is released from the destination bridge contract
  • Funds arrive at the user's specified recipient address with no on-chain link to the original sender

Technical Components

1. Solana Bridge Contracts

zejak_deposit_program
├── deposit_instruction
│   ├── validate_signature
│   ├── lock_sol_tokens
│   └── emit_bridge_event
└── withdrawal_instruction
    ├── verify_zcash_proof
    ├── unlock_sol_tokens
    └── transfer_to_recipient

Key Features:

  • Program Derived Addresses (PDAs) for secure fund custody
  • Multi-signature bridge authority
  • Rate limiting and withdrawal delays for security
  • Event emission for bridge indexers

2. Zcash Integration Layer

zcash_bridge_service
├── shielded_pool_manager
│   ├── z_address_generation
│   ├── shielded_transaction_creation
│   └── note_commitment_tracking
├── bridge_validator
│   ├── proof_verification
│   └── consensus_mechanism
└── liquidity_pool
    ├── zec_reserves
    └── dynamic_fee_calculator

Key Features:

  • Utilization of Zcash Sapling/Orchard shielded pools
  • Zero-knowledge proof generation and verification
  • Bridge oracle network for cross-chain state verification
  • Liquidity management with yield generation

3. Zejak Vanity Address System

vanity_address_generator
├── pattern_matching
│   └── "Zejak" prefix branding
├── keypair_management
│   └── secure_key_derivation
└── address_registry
    └── on_chain_mapping

Key Features:

  • Deterministic vanity address generation
  • Hierarchical Deterministic (HD) wallet structure
  • User-friendly address formats (Zejak7a9f...)
  • QR code generation for easy sharing

Privacy Guarantees

Anonymity Set

  • Minimum mixing period: 10 minutes - 1 hour
  • Anonymity set size: Depends on protocol usage; minimum 10 concurrent users
  • Privacy level: Computational privacy via zero-knowledge proofs

Security Assumptions

  • Cryptographic: Relies on Zcash's zk-SNARK security (Groth16/Halo2)
  • Bridge integrity: Multi-party computation for bridge operations
  • Network assumptions: Honest majority of bridge validators

Transaction Flow

1. User initiates deposit:

  • Amount: X SOL
  • Destination: User's recipient address (encrypted)
  • Fee: 0.5% + network fees

2. Bridge locks SOL:

  • SOL locked in PDA
  • Event emitted with deposit_id
  • ZEC released from liquidity pool

3. Zcash mixing:

  • Funds enter shielded pool
  • Minimum 10-minute delay
  • Multiple hops within pool (optional)

4. Withdrawal process:

  • User submits withdrawal proof
  • Bridge validates ZK proof
  • SOL released to recipient address

Fee Structure

Bridge Fee

0.3-0.5%

of transaction amount

Solana Network

~0.000005

SOL per transaction

Zcash Network

~0.0001

ZEC per transaction

Priority mixing: Optional 0.2% fee for faster processing

API Endpoints

// Deposit
POST /api/deposit
{
  amount: number,
  recipient: string (encrypted),
  mixingDuration: number (minutes)
}

// Get status
GET /api/status/:depositId

// Withdraw
POST /api/withdraw
{
  depositId: string,
  proof: ZKProof,
  recipient: string
}

Security Considerations

Attack Vectors & Mitigations

Bridge validator collusion

Implement threshold cryptography (5-of-9 multisig)

Timing analysis

Random delays and batching

Amount correlation

Support for amount splitting and round numbers

Front-running

Commit-reveal scheme for withdrawals

Smart contract exploits

Multi-phase audits and bug bounty program

Get Started

Ready to protect your privacy? Head to the dashboard to generate your first Zejak vanity address and start receiving private payments.