crosschain-connect 0.1.0

# CrossChain Connect Protocol

## Overview

CrossChain Connect is a universal protocol for connecting multi-chain wallets to decentralized applications. Unlike WalletConnect (EVM-only), it supports Bitcoin, Monero, and EVM chains with a unified approach.

## Message Types

All communication is JSON-based with the following structure:

### ConnectionRequest

```json
{
  "type": "ConnectionRequest",
  "session_id": "550e8400-e29b-41d4-a716-446655440000",
  "timestamp": "2025-01-15T10:30:00Z",
  "dapp_name": "MyDApp",
  "dapp_url": "https://mydapp.com",
  "requested_chains": ["ethereum", "bsc", "bitcoin"]
}
```

### ConnectionResponse

```json
{
  "type": "ConnectionResponse",
  "session_id": "550e8400-e29b-41d4-a716-446655440000",
  "selected_chain": "ethereum",
  "wallet_address": "0x742d35Cc6634C0532925a3b844Bc9e7595f42553"
}
```

### TransactionRequest

```json
{
  "type": "TransactionRequest",
  "session_id": "550e8400-e29b-41d4-a716-446655440000",
  "to": "0x...",
  "value": "1000000000000000000",
  "data": "0x..."
}
```

### SignMessageRequest

```json
{
  "type": "SignMessageRequest",
  "session_id": "550e8400-e29b-41d4-a716-446655440000",
  "message": "Sign this message to verify ownership"
}
```

## Supported Chains

```
EVM Chains:
- ethereum       (Chain ID: 1)
- bsc            (Chain ID: 56)
- polygon        (Chain ID: 137)
- arbitrum       (Chain ID: 42161)
- optimism       (Chain ID: 10)

Non-EVM:
- bitcoin        (Bitcoin Mainnet)
- bitcoin-testnet
- monero         (Monero Mainnet)
- monero-stagenet
- monero-testnet
```

## Connection Flow

1. **dApp** sends ConnectionRequest with requested chains
2. **Wallet** generates session and QR code
3. **User** approves on wallet app
4. **Wallet** sends ConnectionResponse with selected chain & address
5. **dApp** can now request transactions/signatures for that session

## Session Management

- Sessions expire after 15 minutes by default
- Each session has unique ID (UUID v4)
- Session token is cryptographically generated

## Security

### Message Authentication
- HMAC-SHA256 for message integrity
- EIP-191 for Ethereum message signing
- Chain-specific signing for non-EVM

### Private Keys
- Private keys never leave the wallet
- Only signatures transmitted
- Public keys used for verification

## QR Code Format

```
crosschain://connect?session_id=<UUID>&dapp_url=<URL>
```

Example PNG size: 200x200 pixels

## Error Handling

```json
{
  "type": "Error",
  "error": "Invalid chain requested"
}
```

## Implementation Notes

- All timestamps in UTC ISO8601
- Addresses must be validated per-chain
- Amount values are in smallest unit (wei for EVM, satoshi for BTC)
- Nonces prevent replay attacks