Add Silent Payments support for reusable and private receiving addresses

[nejos97]

Implement Silent Payments to allow users to receive Bitcoin payments without sharing a static address, improving privacy and eliminating address reuse.

Senders derive a unique address per payment using the receiver’s public key.

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Objectives

• Eliminate address reuse
• Improve receiver privacy
• Simplify receiving UX

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Scope

1. Silent Payment Address Generation

• Generate Silent Payment public key (scan key + spend key)

• Display as:

  • QR code
  • Shareable string

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2. Sending Flow

• Detect Silent Payment address format
• Derive unique destination output
• Construct compatible transaction
• Ensure Taproot compatibility

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3. Receiving Flow

• Scan blockchain for matching outputs
• Detect owned outputs via scan key
• Recover spendable UTXOs
• Add to wallet balance

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4. Performance Optimization

• Efficient block scanning strategy

• Indexing or light client integration

• Optional:

  • Use Electrum server extensions
  • Background scanning

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5. Privacy & Security

• Ensure:

  • No address reuse
  • No linkability between payments

• Protect scan key

• Optimize for low metadata leakage

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6. UX/UI

• Single “Receive privately” button

• No need to generate new address each time

• Optional explanation tooltip:

  • “Each payment uses a unique address automatically”

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Acceptance Criteria

• User can generate a Silent Payment identifier
• Sender can send funds using it
• Receiver detects and spends funds correctly
• No visible address reuse
• Works reliably on testnet

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Risks / Considerations

• Still early adoption
• Heavy scanning requirements
• Compatibility with existing infrastructure
• Requires Taproot support

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References

• Silent Payments proposal (BIP352)
• Taproot (BIP341)

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Nice-to-have (Future)

• Silent Payments + PayJoin combo
• Contact-based payments (like “send to username”)
• Push notifications on detection