# Payment Privacy and On-Chain Transparency

Blockchain technology records every transaction publicly on a distributed ledger. This means all payment transfers through Numpay are permanently visible on-chain, including sender and receiver wallet addresses, transferred amounts, and timestamps. However, Numpay is designed to separate user identity from on-chain data to preserve privacy while maintaining transparency and auditability.

### On-Chain Data Exposure

| Data Field           | Visibility          | Privacy Impact                               |
| -------------------- | ------------------- | -------------------------------------------- |
| Wallet Address       | Public              | Pseudonymous; no direct personal info        |
| Transaction Amount   | Public              | Revealed unless privacy enhancements applied |
| Timestamp            | Public              | Records timing of transaction                |
| Identifier Hash      | Public (hashed)     | One-way hashed, irreversible                 |
| Personal Identifiers | Not stored on-chain | Encrypted off-chain, never revealed on-chain |

Wallet addresses act as pseudonyms rather than real identities. The link between a user’s phone number and their wallet address is stored as a cryptographic hash on-chain. Due to the irreversible nature of hashing algorithms (e.g., SHA-256, Keccak-256), on-chain data cannot be reverse-engineered to reveal actual identifiers.

### Identity Decoupling and Privacy Model

Numpay’s design principle is to minimize correlation risk between on-chain wallet addresses and off-chain user identifiers. This is achieved through:

* **Off-Chain Attestation:** Verification and binding of identifiers occur off-chain using encrypted proofs, which are then represented as non-reversible hashes on-chain.
* **User-Controlled Wallets:** Private keys remain with users; no centralized system holds identity mappings in a reversible form.
* **Encrypted Metadata:** Any additional user data is encrypted using asymmetric cryptography, ensuring only authorized parties can decrypt it.

### Privacy Enhancement Techniques

While blockchain transparency supports audit and compliance, some use cases require stronger privacy guarantees. Numpay includes optional privacy features planned for future releases.

| Technique                         | Description                                                                                 | Privacy Benefit                    | Trade-Offs                                                       |
| --------------------------------- | ------------------------------------------------------------------------------------------- | ---------------------------------- | ---------------------------------------------------------------- |
| Stealth Addresses                 | Generate a new, one-time-use address per transaction                                        | Prevents address reuse and linkage | Increased complexity for key management and transaction tracking |
| Zero-Knowledge Proofs (zk-Proofs) | Cryptographic proofs that confirm transaction validity without revealing amounts or parties | Masks transaction details          | Computationally intensive; may increase gas costs                |
| Transaction Mixing (CoinJoins)    | Combines multiple transactions to obscure origin and destination                            | Hides transaction flow patterns    | Requires user coordination and trust assumptions                 |

### Comparison With Other Privacy Models

| Feature                    | Numpay Base Layer                       | Public Blockchains (e.g., Ethereum) | Privacy-Focused Chains (e.g., Zcash, Monero) |
| -------------------------- | --------------------------------------- | ----------------------------------- | -------------------------------------------- |
| Identity Linkage           | Pseudonymous with off-chain binding     | Pseudonymous, no identity binding   | Privacy by default, no address reuse         |
| Transaction Amount Privacy | Visible unless privacy features enabled | Fully visible                       | Fully shielded                               |
| User Control of Keys       | Full control                            | Full control                        | Full control                                 |
| Compliance Compatibility   | Designed for optional transparency      | Low                                 | Complex                                      |

### Summary

* All payments are recorded publicly but with wallet addresses only, not names.
* Identifiers are cryptographically hashed, preventing reverse lookup on-chain.
* Optional privacy layers will provide stronger anonymity when needed, balancing transparency and privacy.
* Users maintain control over keys and identity data, limiting exposure risks.
* Numpay’s approach balances auditability, user privacy, and regulatory compliance better than standard public blockchains.


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