Boomerang: Bitcoin Cold Storage with Built-In Coercion Resistance

This system introduces a unique duress mechanism that allows users to discreetly signal distress during coercive situations without tipping off the attacker, thereby marrying advanced security measures with user safety protocols. During the setup, users are required to create and memorize a "consent set" comprising five countries, which is pivotal for the duress checks executed at crucial moments like withdrawals.

The protocol operates through encrypted communications and a strategic partnership with Search and Rescue (SAR) entities to ensure timely and efficient response in emergencies. When a user signals duress by selecting countries outside their consent set during a check, the system clandestinely transmits a payload containing encrypted data, including static information like name and address, along with dynamic data such as real-time phone location to SAR. This enables SAR to locate and commence rescue operations swiftly. The foundational elements of this mechanism include the consent set of countries, country mapping based on a predefined list, and duress checks involving user selection from randomly generated country lists. These components are designed to offer robust security features while maintaining plausible deniability for the user under duress.

Boomerang's introduction serves to address the vulnerability of significant bitcoin holders to physical force or "wrench attacks" by making the withdrawal process unpredictable and securely signaling duress, thereby deterring potential attackers. It shifts from the conventional quick and reliable fund transfer systems to a more secure yet complex setup, making it particularly suitable for big holders in high-risk situations. The setup involves dividing control among a select group using specialized hardware devices for key holding, connecting to neutral watchtowers and SAR services, and providing encrypted personal info for emergency situations.

The withdrawal process, especially during the initial boomerang phase before a specified milestone block (e.g., 2 years), incorporates multiple rounds of checks with an unpredictable total duration due to the privately set ranges of steps by each participant. This uncertainty in timing hampers attackers' ability to plan, offering victims potential rescue time. Post the milestone, the system transitions into a "normal era" with fast, deterministic withdrawals akin to regular cold storage. The duress protection feature allows for a seamless integration of security and user safety by enabling a secret signal system through the choice of countries, effectively triggering SAR intervention without alerting the attacker.

In summary, Boomerang presents itself as a formidable bitcoin safe, ideal for individuals or entities with substantial bitcoin holdings that require ultimate protection over convenience. Its sophisticated duress mechanism and randomized time-delay lock, coupled with the hidden alarm feature during the boomerang phase, mark a significant advancement in securing bitcoin against physical threats, thereby catering to a niche market of users prioritizing security in high-risk environments.