Native Privacy with UNO Protocol

pub enum PrivacyLevel {
    /// Public (default)
    /// Sender, receiver, and amount all visible
    Public,
 
    /// Amount Hidden
    /// Sender and receiver visible, amount encrypted
    AmountHidden,
 
    /// Full Private
    /// Amount and receiver encrypted, only sender visible
    FullPrivate,
}

Problem: Other players can see bet sizes and copy strategies

Solution: AmountHidden transfer
- Game contract sees you placed a bet
- Other players cannot see the amount
- Prevents copy-trading and front-running

Problem: Salary payments on public chains expose compensation

Solution: AmountHidden transfer
- HR system records payment made
- Employees cannot see each other's pay
- Auditors can verify with proof

Problem: Large transfers attract unwanted attention

Solution: FullPrivate transfer
- Only sender identity is public
- Amount and recipient are encrypted
- Reduces targeting risk

pub struct UnoTransfer {
    /// Privacy level
    pub privacy_level: PrivacyLevel,
 
    /// Sender (always visible for debit)
    pub sender: Address,
 
    /// Encrypted receiver (FullPrivate mode)
    pub encrypted_receiver: Option<Vec<u8>>,
 
    /// Visible receiver (AmountHidden mode)
    pub receiver: Option<Address>,
 
    /// Encrypted amount (Twisted ElGamal)
    pub encrypted_amount: Vec<u8>,
 
    /// Zero-knowledge proof
    pub zk_proof: ZKProof,
 
    /// Nullifier (prevents double-spend)
    pub nullifier: Hash,
 
    /// Asset type
    pub asset: Hash,
}

pub struct ZKProof {
    /// Proof type (Bulletproofs or PLONK)
    pub proof_type: ProofType,
 
    /// Proof data
    pub proof_data: Vec<u8>,
}
 
// The ZK proof guarantees:
// 1. Sender has sufficient balance
// 2. Transfer amount > 0
// 3. New balances are correctly calculated
// 4. No tokens created from nothing

// Shield 1000 TOS into encrypted balance
let shield_tx = ShieldTransfer {
    amount: 1000_00000000,  // Public amount going in
    asset: TOS_ASSET,
    // Amount becomes encrypted in UNO balance
};

let uno_tx = UnoTransfer {
    privacy_level: PrivacyLevel::AmountHidden,
    sender: my_address,
    receiver: Some(recipient),
    encrypted_amount: encrypt(1000_00000000),
    zk_proof: generate_proof(my_uno_balance, amount),
    nullifier: generate_nullifier(),
    asset: TOS_ASSET,
};

// Unshield 500 TOS from encrypted balance
let unshield_tx = UnshieldTransfer {
    encrypted_amount: my_encrypted_500,
    zk_proof: generate_unshield_proof(),
    nullifier: generate_nullifier(),
    // 500 TOS appears in public balance
};

pub enum FeeType {
    /// Pay with public TOS (fee goes to miners)
    TOS = 0,
 
    /// Pay with Energy (gas-free)
    Energy = 1,
 
    /// Pay with UNO balance (burned)
    UNO = 2,
}

/// Nullifier mechanism
/// Each encrypted output can only be spent once
fn check_double_spend(nullifier: Hash) -> bool {
    if nullifier_set.contains(nullifier) {
        return false; // Already spent
    }
    nullifier_set.insert(nullifier);
    true
}

/// Optional compliance proof
pub struct ComplianceProof {
    /// Prove transaction meets AML rules
    pub aml_proof: ZKProof,
 
    /// Prove identity verified (without revealing identity)
    pub kyc_proof: ZKProof,
 
    /// Prove amount within limits
    pub limit_proof: ZKProof,
}
 
// Can prove: "I am a verified user and amount < $10,000"
// Without revealing: actual identity or exact amount

pub mod PrivacyTransferSyscall {
    /// Execute private transfer
    pub fn private_transfer(tx: UnoTransfer) -> Result<Hash, TransferError>;
 
    /// Verify ZK proof
    pub fn verify_proof(proof: &ZKProof) -> bool;
 
    /// Check if nullifier is already used
    pub fn is_nullifier_used(nullifier: Hash) -> bool;
 
    /// Get encrypted balance
    pub fn get_encrypted_balance(
        account: Address,
        asset: Hash,
    ) -> EncryptedBalance;
}

/// Private betting - hide bet amounts from other players
fn place_private_bet(player: Address, choice: u8) {
    // Get amount from caller's encrypted balance
    let encrypted_amount = get_call_value_encrypted();
 
    // Transfer privately to game contract
    let bet_tx = UnoTransfer {
        privacy_level: PrivacyLevel::AmountHidden,
        sender: player,
        receiver: Some(game_contract),
        encrypted_amount,
        zk_proof: get_caller_proof(),
        ..
    };
 
    // Other players can see someone bet, but not the amount
    private_transfer(bet_tx)?;
 
    // Store encrypted bet for later settlement
    store_private_bet(player, encrypted_amount, choice);
}