[Proposal] Guardian Address + GASPv1

These proposals are designed to allow bitcoin wallets to lock in response to an activation event, thereby preventing unauthorized spending of UTXOs under duress. This is achieved through a standardized on-chain signal that triggers a security lockdown across multiple wallets without necessitating any on-chain linkage among them, facilitated by a single external control address known as the Guardian Address. The mechanism allows for the separation of key material between the user's spending wallet and the Guardian Address. This discrete identity can signal lock state changes via a transaction that embeds data in an OP_RETURN, enabling emergency responders, user-level software, and wallet applications to recognize a distress signal without compromising the privacy of user spending addresses or balances.

The motivation behind these proposals stems from the growing prevalence of physical attacks on bitcoin users, with an increasing number of incidents involving robbery and coercion. Traditional security measures such as decoy wallets have proven inadequate, primarily because attackers may either be aware of their purpose or still achieve their goal of stealing bitcoin even if deceived by a lower balance. The lack of a safe mechanism for responding under physical duress without risking loss of funds, coupled with the use of both self-hosted and centralized services by participants in the Bitcoin ecosystem, underscores the need for a self-sovereign "kill switch". This proposal seeks to provide such a mechanism, allowing for wallet lockdown through separate devices or operations, preserving privacy, enabling defensive reactions from wallet software, and offering protection across multiple wallet configurations with a single on-chain emergency trigger.

The BIPs are structured to ensure clarity and focus: BIP A deals with the Guardian Address Signal Protocol, offering a lightweight protocol for lock/unlock signals that requires no consensus changes and maintains privacy; while BIP B focuses on the practical aspects of wallet implementation, including integration guidelines for developers, state machines, polling mechanisms, and considerations for attack scenarios. Feedback is sought on both the overall approach and the technical specifics to refine these drafts before formal submission. The proposals are accompanied by links to GitHub for further review of the protocol here, the implementation standards here, a demo wallet implementation here, and a Guardian CLI tool here, along with demo wallet screenshots showcasing testnet transactions.

This initiative represents an important stride towards enhancing the security of bitcoin transactions, addressing the urgent need for improved protective measures amidst the rising threats facing cryptocurrency users.