> ## Documentation Index
> Fetch the complete documentation index at: https://kleros-mintlify-6ebc7975.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Proof of Humanity

> Developer overview of Proof of Humanity V1 (Mainnet) and V2 (Gnosis), covering humanityId lifecycle, registry contracts, and integration paths.

## Introduction

Proof of Humanity (PoH) is a Sybil-resistant registry of unique human identities. This page covers both V1 (Ethereum Mainnet) and V2 (Gnosis Chain).

Each verified human receives a soulbound humanity ID (`humanityId`) that persists across wallet changes. PoH V2 uses Kleros Court for dispute resolution when profiles are challenged. Unlike V1, where each registration was bound to a specific wallet address, V2 decouples identity from address. One human maps to one humanity ID, which maps to one wallet address at any time. If a user loses wallet access, they can remove the lost address and re-register with a new one using the same `humanityId`.

<Card title="Smart Contracts" icon="file-contract" href="/developers/products/poh/smart-contracts">
  Core interfaces, data structures, and contract addresses
</Card>

***

## V1 (Ethereum Mainnet)

PoH V1 runs on Ethereum Mainnet and **V1 integration remains available**. A Fork Module allows V1 registrations to be recognized by V2. The EPNS/Push Protocol integration that was active in V1 has been discontinued, and is replaced in V2 by Atlas + SendGrid.

For V1 contract addresses, see [Deployment Addresses](/reference/contracts/deployment-addresses-v1).

***

## V2 (Gnosis Chain)

The sections below document PoH V2 technical details.

Technical notes for integrators:

* **PNK airdrop**: the first 10,000 verified humans can claim 1,200 PNK, doubled by staking in the Humanity Court. A dashboard tracks registrations and airdrop claims.
* **Ledger limitation**: hardware wallets do not currently support EIP-7702 on Gnosis Chain, which the standard airdrop claim flow requires. A manual claiming guide is available.
* **Email notifications**: every step of the profile flow triggers notifications processed end-to-end by Atlas, including pending revocation, vouching activity, disputed flows, and challenge outcomes.
* **Evidence keys**: the interface writes evidence files with the correct evidence key. Court V1 and the Dispute Resolver include a normalization workaround for older submissions that used the wrong key.
* **Execution pipeline**: profile advancement uses a rewritten auto-advance execute pipeline.
* **Security**: frontend security reviews cover XSS attack vectors, and the app runs on a patched NextJS 15.
* **In progress**: a voucher reward distributor contract and a referral system (technical specifications under review).

<Note>
  Atlas is an internal backend library for Kleros development teams only. It is not intended for community use or integration.
</Note>

***

## Contract Addresses

<Tabs>
  <Tab title="Gnosis Chain (Production)">
    | Contract                  | Address                                      |
    | ------------------------- | -------------------------------------------- |
    | ProofOfHumanity           | `0xA7Fd7A97bF12E112B2263957e115e0c46cE6A38C` |
    | CrossChainProofOfHumanity | Deployed per foreign chain                   |
  </Tab>

  <Tab title="Ethereum Mainnet (V1 Fork Module)">
    | Contract             | Address                                      |
    | -------------------- | -------------------------------------------- |
    | ProofOfHumanity (V1) | `0xC5E9dDebb09Cd64DfaCab4011A0D5cEDaf7c9BDb` |
  </Tab>
</Tabs>

<Note>
  PoH V2 operates on Gnosis Chain as the home chain. Cross-chain state is synchronized to other chains through bridge contracts. V1 registrations remain accessible through a Fork Module.
</Note>

***

## Architecture

PoH V2 consists of three layers:

<Steps>
  <Step title="Identity Registry">
    Core contract managing humanity IDs, registration claims, vouching, and challenge periods. Each humanity ID is a `bytes20` value that uniquely identifies a verified human.
  </Step>

  <Step title="Cross-Chain Synchronization">
    Bridge contracts propagate humanity state across chains, enabling `isHuman()` checks on any supported network.
  </Step>

  <Step title="Dispute Resolution">
    Challenged registrations create disputes in Kleros Court. Jurors evaluate video evidence and vouching validity according to the registration policy.
  </Step>
</Steps>

### Identity Model

```
1 human → 1 humanityId (bytes20) → 1 wallet address

// Wallet recovery flow:
humanity.owner == lostAddress      // Lost access
humanity.owner == address(0)       // Removal requested
humanity.owner == newAddress       // Re-registered with new wallet
```

V1 users have a `humanityId` equal to their original registration address (`bytes20(address)`). V2 users receive a new unique `humanityId` at registration.

***

## Registration Lifecycle

```mermaid theme={null}
graph TD
    A[Submit Profile] --> B[Vouching Phase]
    B --> C{Vouched?}
    C -->|Yes| D[Pending Claim - Challenge Period]
    C -->|No| E[Remains in Vouching]
    D --> F{Challenged?}
    F -->|No| G[Resolved Claim - Registered]
    F -->|Yes| H[Kleros Court Dispute]
    H --> I{Ruling}
    I -->|Valid| G
    I -->|Invalid| J[Registration Rejected]
```

***

## Key Features

<AccordionGroup>
  <Accordion title="Soulbound Humanity IDs">
    Humanity IDs persist across wallet changes. Applications that store data by `humanityId` rather than address preserve user reputation and assets even when the underlying wallet changes.
  </Accordion>

  <Accordion title="Cross-Chain Verification">
    The `isHuman()` function is available on multiple chains through `CrossChainProofOfHumanity` contracts. Synchronization uses bridge infrastructure to propagate registration state.
  </Accordion>

  <Accordion title="V1 Backward Compatibility">
    A Fork Module allows V1 registrations to be recognized by V2. The `isHuman()` call automatically checks both V2 native registrations and V1 registrations.
  </Accordion>

  <Accordion title="Vouching System">
    New registrants need a vouch from an existing verified human. The keeper bot processes vouches and reward withdrawals automatically, reducing manual intervention.
  </Accordion>
</AccordionGroup>

***

## Resources

<CardGroup cols={2}>
  <Card title="GitHub Repository" icon="github" href="https://github.com/kleros/proof-of-humanity-v2-contracts">
    Smart contracts source code
  </Card>

  <Card title="Live Application" icon="globe" href="https://proofofhumanity.id">
    Production PoH interface
  </Card>

  <Card title="Discord" icon="discord" href="https://discord.gg/kleros">
    Developer support
  </Card>
</CardGroup>