# Data Handling and Identifier Protection

### What Data Is Collected (and What Isn’t)

Numpay is designed with minimal data exposure in mind. The system does not collect or store personal data in any raw or plaintext format. Instead, it uses cryptographic methods to link identifiers like phone numbers to blockchain wallet addresses without revealing the original input.

### On-Chain Data

The only data written to the blockchain includes:

* Public wallet addresses
* Hashed representations of user identifiers (e.g. SHA-256 or Keccak-256 hashes)
* Encrypted metadata needed to verify ownership of an identifier
* Transaction history (inherent to public blockchains)

No plain email addresses or phone numbers are stored or exposed on-chain. Hashes are one-way and irreversible. This means that even if someone reads the blockchain, they cannot reverse-engineer the original email or phone number.

### Off-Chain Data

To link a phone number or email to a wallet, Numpay uses an off-chain verifier. This service:

* Receives the user’s identifier (phone) temporarily
* Sends a verification code (OTP)
* On success, issues a signed attestation confirming the identifier belongs to the user

This process happens off-chain. Once the attestation is generated, the verifier does not retain the original identifier. The signed proof is then submitted to the blockchain, where it’s used to validate identity without exposing personal data.

### Hashing and Encryption

When an identifier is submitted:

1. It is hashed using a secure algorithm (e.g. SHA-256)
2. The hash is then linked to a wallet address inside a smart contract
3. Optional metadata can be encrypted using the wallet's public key and stored for future validation

This ensures that:

* Identifiers are not human-readable at any point on-chain
* Only the user can decrypt or verify the encrypted metadata
* No central authority can track or reconstruct user identity from blockchain data

### Key Points

* We do not store raw personal data on-chain
* All identifiers are hashed before storage
* Linking is privacy-preserving and designed to resist reverse lookup
* Verifier services do not retain user identifiers after attestation

Numpay operates on a zero-knowledge principle: the system only verifies that a user controls a verified identifier, not what that identifier is.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://numpay.gitbook.io/numpay/data-privacy-and-security/data-handling-and-identifier-protection.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.