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Follow these best practices to maximize your security and privacy when using Privacy Cash.

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Transaction Security

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Keep Your Secrets Safe

Never share your note secrets: Each deposit generates a secret note. Anyone with this secret can withdraw your funds. Treat it like a private key.

Store Secrets Offline

Keep your note secrets in a secure, offline location. Hardware wallets or encrypted files are recommended.

Use Multiple Notes

Split large amounts across multiple deposits to reduce risk and improve privacy.

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Verify Transaction Details

Always verify transaction parameters before signing:
  • Recipient address: Ensure the withdrawal address is correct
  • Amount: Confirm deposit/withdrawal amounts match your intent
  • Fees: Check that fees are within expected ranges (0.25% for withdrawals)
  • Token type: Verify you’re transacting with the correct SPL token

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Privacy Best Practices

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Timing and Anonymity Set

Wait Before Withdrawing

For maximum privacy, wait for multiple other deposits before withdrawing. A larger anonymity set makes linking deposits to withdrawals more difficult.
Recommendations:
  • Minimum wait: Wait for at least 10-20 other deposits in the same denomination
  • Different amounts: Avoid depositing and withdrawing the exact same amount
  • Time variation: Don’t withdraw at predictable intervals

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Network Privacy

Use VPN or Tor

Protect your IP address when interacting with the protocol to prevent network-level correlation.

Different Wallets

Consider using separate wallets for deposits and withdrawals to enhance privacy.

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Amount Management

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Deposit Limits

Current Limits:
  • SOL: Maximum 1,000 SOL per deposit
  • SPL Tokens: Limits vary by token (set by protocol authority)
These limits protect against large-scale attacks and ensure system stability.Reference: lib.rs:78, lib.rs:267-272

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Breaking Up Large Amounts

For amounts exceeding deposit limits or for better privacy:
  1. Split deposits: Break large amounts into multiple smaller deposits
  2. Use different denominations: Vary the amounts to avoid patterns
  3. Stagger timing: Space out deposits over time
  4. Mix tokens: Consider using multiple token types if appropriate

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Relayer Safety

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Using Relayers for Withdrawals

Relayer Best Practices

Relayers enable withdrawals to fresh addresses without linking to your deposit wallet.
When using relayers:
Verify relayer fees: Relayers charge a service fee on top of the protocol’s 0.25% withdrawal fee. Check that the total fee is reasonable before proceeding.
  • Use reputable relayers with transparent fee structures
  • Understand that relayers know the withdrawal address (but not the deposit)
  • Consider using multiple relayers for different withdrawals
  • Verify the relayer’s smart contract is correctly implemented

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Smart Contract Interaction

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Verifying Program Deployment

Before interacting with Privacy Cash, verify the on-chain program:Program ID (Mainnet):
9fhQBbumKEFuXtMBDw8AaQyAjCorLGJQiS3skWZdQyQD
Verified Hash:
c6f1e5336f2068dc1c1e1c64e92e3d8495b8df79f78011e2620af60aa43090c5
Use Solana verification tools to ensure the deployed program matches the audited source code.

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Approved Tokens Only

Token Allowlist

Only use approved SPL tokens listed in the protocol documentation.
Mainnet Approved Tokens:
  • USDC (Circle)
  • USDT (Tether)
  • ORE
  • ZEC (Zcash)
  • stORE (Staked ORE)
  • jlUSDC (Jupiter LP USDC)
  • jlWSOL (Jupiter LP Wrapped SOL)
Reference: lib.rs:52-60
Attempting to use non-approved tokens will result in transaction failure. The protocol enforces a strict allowlist for security.

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Fee Management

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Understanding Fee Structure

Deposits

Free - No protocol fees for deposits (0%)

Withdrawals

0.25% - Standard withdrawal fee (25 basis points)
Reference: lib.rs:91-92

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Fee Error Margin

The protocol allows a 5% error margin on fees to accommodate minor calculation differences: 
Minimum acceptable fee = Expected fee × (1 - 5%)
                      = Expected fee × 0.95
This prevents legitimate transactions from failing due to rounding errors while still protecting against fee manipulation. Reference: lib.rs:93, utils.rs:148-212

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Operational Security

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Wallet Security

Hardware Wallets

Use hardware wallets for signing transactions when possible.

Multi-Signature

For large amounts, consider using multi-signature wallets for deposits.

Fresh Addresses

Withdraw to fresh addresses that haven’t been publicly linked to you.

Regular Audits

Periodically review your notes and transactions for any anomalies.

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Backup Your Data

Critical: Back up all transaction data, including:
  • Note secrets and commitments
  • Merkle tree paths
  • Transaction hashes
  • Encrypted output data
Loss of this data means permanent loss of funds.
Backup recommendations:
  • Store encrypted backups in multiple secure locations
  • Use different encryption keys for different backups
  • Test recovery procedures periodically
  • Consider using secret-sharing schemes (e.g., Shamir’s Secret Sharing)

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Monitoring and Alerts

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Track Your Transactions

Monitor these events:
  • CommitmentData: Emitted when SOL deposits/withdrawals create new commitments
  • SplCommitmentData: Emitted for SPL token transactions
These events help you track the state of the Merkle tree and verify your transactions were included.Reference: lib.rs:351-361, lib.rs:505-517

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Merkle Root History

The protocol maintains a history of 100 recent Merkle roots:
  • Transactions can reference any root from this history
  • Older roots are automatically pruned from the history
  • If your proof references a root outside the history window, the transaction will fail
Time-sensitive withdrawals: If you generate a proof but don’t submit it for an extended period, the referenced root may be pruned from history. Always submit proofs promptly after generation.Reference: merkle_tree.rs:79-105, lib.rs:80

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Common Pitfalls to Avoid

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Transaction Failures

Double-Spend Attempts

Using the same nullifier twice will cause automatic transaction failure.

Invalid Proofs

Ensure your zero-knowledge proof is correctly generated for the current circuit.

Unknown Roots

Verify your Merkle root is still in the 100-entry history before submitting.

Insufficient Funds

Ensure the pool has enough liquidity for your withdrawal plus fees.

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Privacy Leaks

Avoid these common privacy mistakes:
  1. Same-amount patterns: Don’t deposit and withdraw identical amounts
  2. Immediate withdrawals: Wait for more deposits to increase anonymity set
  3. Address reuse: Don’t withdraw to previously used addresses
  4. Metadata correlation: Use different timestamps, gas prices, and wallet addresses
  5. Social correlation: Don’t discuss specific deposits/withdrawals publicly

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Emergency Procedures

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If You Lose Your Note Secret

Funds are irrecoverable: If you lose your note secret and have no backup, your funds cannot be recovered. There is no password reset or recovery mechanism.

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If You Suspect Compromise

If you believe your note secret may be compromised:
  1. Immediately withdraw: If possible, withdraw to a new, secure address
  2. Use a relayer: Consider using a relayer to avoid exposing your IP
  3. Monitor the chain: Watch for unauthorized withdrawal attempts
  4. Secure new funds: Use different wallets and secrets for future deposits

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Additional Resources

Security Audits

Review comprehensive security audits by multiple firms

Safety Features

Learn about built-in protocol security mechanisms

GitHub Repository

Examine the open-source code yourself

SDK Documentation

Integrate Privacy Cash safely into your application

Build docs developers (and LLMs) love

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