Shadow Swap Protocol

A privacy-preserving Atomic Bridge between Zcash and Starknet featuring shielded pools with HTLC support and a privacy-focused ERC20 token.

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🔒 Deployed Contracts

Contract	Address
FastPool	0x01749627bb08da4f8c3df6c55045ac429abdceada025262d4c51430d643db84e
StandardPool	0x05cf3a281b3932cb4fec5648558c05fe796bd2d1b6e75554e3306c4849b82ed8
VeilToken	0x02e90f89aecddf3f6b15bd52286a33c743b684fa8c17ed1d7ae57713a81459e1

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📋 Contract Overview

VeilToken

A privacy-enhanced ERC20 token that emits commitment-based events instead of exposing actual addresses.

Features:

• Fixed supply: 21,000,000 VEIL
• 18 decimals
• Poseidon hash-based commitments for transfer/approval events
• Standard ERC20 interface

Key Functions:

• transfer() / transfer_from() - Transfer tokens with privacy commitments
• approve() - Approve spending with commitment tracking
• balance_of() / total_supply() - Standard ERC20 queries

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FastPool

A shielded pool optimized for fast withdrawals with $10K deposit limit per transaction.

Features:

• ✅ Merkle tree-based privacy (100 root history)
• ✅ Virtual HTLCs for atomic swaps
• ✅ Multi-token support
• ✅ Deposit limit: 10,000 tokens max
• ✅ Timelock range: 1 hour - 7 days
• ✅ Reentrancy protection

Key Functions:

• deposit() - Deposit tokens with commitment
• create_htlc() - Create hash time-locked contract
• withdraw() - Withdraw with secret or after timelock
• update_merkle_root() - Update privacy set (owner only)

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StandardPool

Full-featured shielded pool with unlimited deposits for maximum privacy and flexibility.

Features:

• ✅ Merkle tree-based privacy (100 root history)
• ✅ Virtual HTLCs for atomic swaps
• ✅ Multi-token support
• ✅ No deposit limits
• ✅ Timelock range: 1 hour - 7 days
• ✅ Reentrancy protection

Key Functions:

• deposit() - Deposit tokens with commitment (unlimited)
• create_htlc() - Create hash time-locked contract
• withdraw() - Withdraw with secret or after timelock
• update_merkle_root() - Update privacy set (owner only)

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🔐 Privacy Model

Deposits:

• Users deposit tokens with a Poseidon hash commitment
• Commitments are added to a Merkle tree
• No link between depositor and withdrawal address

Withdrawals:

• Prove Merkle inclusion without revealing which leaf
• Nullifiers prevent double-spending
• HTLCs enable cross-chain atomic swaps

HTLCs:

• Hash-locked: Requires secret preimage to claim
• Time-locked: Refundable after expiration
• Virtual: No on-chain token lock (managed by owner)

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🚀 Usage

Deposit Flow

1. Approve token to pool contract
2. Generate commitment: Poseidon(secret, nullifier)
3. Call deposit(token, commitment, amount)
4. Wait for Merkle root update

Withdrawal Flow

1. Owner creates HTLC with nullifier proof
2. Recipient provides secret to withdraw
3. Or original user reclaims after timelock

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⚠️ Security Notes

• Owner-controlled: HTLCs and root updates require owner signature
• Emergency functions: Owner can withdraw funds if needed
• Nullifier protection: Each nullifier can only be spent once
• Timelock bounds: HTLCs must expire between 1 hour and 7 days
• FastPool limit: Max 10,000 tokens per deposit

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📜 License

Apache 2.0

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🛠️ Built With

• Cairo - Smart contract language
• OpenZeppelin - Security components
• Poseidon - Zero-knowledge friendly hashing
• Starknet - Ethereum L2 scaling solution