Multi-sig Wallets

So sánh:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Ví thông thường (1-of-1):
┌─────────────────────────────────────────┐
│  [Key A] ────────────► Transaction ✓    │
│                                         │
│  Một key = full control                 │
│  Mất key = mất tiền                     │
└─────────────────────────────────────────┘

Multi-sig (2-of-3):
┌─────────────────────────────────────────┐
│  [Key A] ─┐                             │
│           ├───────────► Transaction ✓   │
│  [Key B] ─┘                             │
│  [Key C] (backup)                       │
│                                         │
│  Cần 2/3 keys để ký                     │
│  Mất 1 key vẫn an toàn                  │
└─────────────────────────────────────────┘

Use cases:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

1. Bảo mật cá nhân
   • Không có single point of failure
   • Keys ở nhiều locations
   • Chống hack/theft

2. Tổ chức/DAO
   • Treasury cần nhiều người approve
   • Không ai có full control
   • Transparent governance

3. Gia đình/Thừa kế
   • Backup cho trường hợp qua đời
   • Quản lý tài sản chung
   • Bảo vệ inheritance

4. Business
   • Accounting controls
   • Giảm internal fraud
   • Compliance requirements

M-of-N configurations:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

2-of-2:
• Cần cả 2 keys
• Use: Cặp vợ chồng, 2 partners
• Risk: Mất 1 key = locked forever

2-of-3:
• Cần 2/3 keys
• Use: Cá nhân, small teams
• Popular: Mất 1 key vẫn access được
• Flexibility + Security

3-of-5:
• Cần 3/5 keys
• Use: DAOs, companies
• More decentralized

Ví dụ 2-of-3 setup:
┌─────────────────────────────────────────┐
│ Key 1: Hardware wallet (tại nhà)        │
│ Key 2: Mobile wallet (mang theo)        │
│ Key 3: Paper backup (bank safe)         │
│                                         │
│ → Hàng ngày: Key 1 + Key 2              │
│ → Emergency: Key 2 + Key 3              │
│ → Worst case: Key 1 + Key 3             │
└─────────────────────────────────────────┘

Smart Contract Wallets:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Safe (formerly Gnosis Safe):
• Leading multi-sig solution
• EVM chains (ETH, Polygon, etc.)
• Web interface + mobile
• Dùng bởi DAOs lớn

Squads (Solana):
• Multi-sig cho Solana
• Similar concept
• Program-based

Hardware Multi-sig:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

• Ledger + Trezor combo
• Multiple hardware devices
• Native Bitcoin multi-sig
• Coldcard, Specter, etc.

Bước 1: Truy cập Safe
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
• app.safe.global
• Connect wallet
• Chọn network

Bước 2: Create new Safe
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
• Đặt tên cho Safe
• Chọn threshold (M of N)
• Add owner addresses

Bước 3: Add owners
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
┌─────────────────────────────────────────┐
│ Owner 1: 0x123... (Your main wallet)    │
│ Owner 2: 0x456... (Hardware wallet)     │
│ Owner 3: 0x789... (Backup wallet)       │
│                                         │
│ Threshold: 2 of 3                       │
└─────────────────────────────────────────┘

Bước 4: Deploy
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
• Review settings
• Pay gas fee
• Safe được tạo on-chain

Cách multi-sig transaction hoạt động:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

1. Propose (Owner 1)
   ┌────────────────────────────────────┐
   │ "Send 1 ETH to 0xABC..."           │
   │ Status: 1/2 signatures             │
   └────────────────────────────────────┘

2. Review & Sign (Owner 2)
   ┌────────────────────────────────────┐
   │ Verify: amount, recipient, data    │
   │ Sign if correct                    │
   │ Status: 2/2 signatures ✓           │
   └────────────────────────────────────┘

3. Execute
   ┌────────────────────────────────────┐
   │ Threshold reached                  │
   │ Anyone can execute                 │
   │ Pay gas → Transaction sent         │
   └────────────────────────────────────┘

Timeline:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
[Propose] → [Wait for signs] → [Execute]
   ↓              ↓                ↓
 Owner 1    Other owners      Any owner

Lợi ích:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
✓ No single point of failure
✓ Key compromise ≠ fund loss
✓ Shared control for teams
✓ Audit trail of approvals
✓ Customizable thresholds

Hạn chế:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
✗ Higher gas costs
✗ Slower transactions
✗ More complex UX
✗ Need coordination
✗ Setup requires knowledge

Security:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
□ Keys ở different locations
□ Different device types
□ Test với small amount trước
□ Document owner addresses
□ Have recovery plan

Configuration:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
□ 2-of-3 cho cá nhân
□ 3-of-5 cho organizations
□ Không dùng 2-of-2 (risky)
□ Always have backup key

Operations:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
□ Verify transaction details
□ Use hardware wallets
□ Regular key health checks
□ Update owners khi cần

Native Bitcoin Multi-sig:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Bitcoin hỗ trợ multi-sig native:
• P2SH (Pay to Script Hash)
• P2WSH (SegWit)

Tools:
• Sparrow Wallet
• Specter Desktop
• Coldcard + others
• Caravan (Unchained)

Ví dụ tạo 2-of-3:
┌─────────────────────────────────────────┐
│ Device 1: Coldcard                      │
│ Device 2: Trezor                        │
│ Device 3: Ledger                        │
│                                         │
│ Coordinator: Sparrow Wallet             │
│ → Import public keys                    │
│ → Create multi-sig wallet               │
│ → Sign từ 2 devices bất kỳ              │
└─────────────────────────────────────────┘

Nên dùng khi:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
✓ Số tiền lớn (> $10,000)
✓ Long-term holdings
✓ Shared funds (team, family)
✓ Business treasury
✓ DAO funds

Không cần khi:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
• Số tiền nhỏ
• Frequent trading
• Hot wallet cho daily use
• Testing/development