Dead-Man’s Switch

Basics

From this blog by Enigma on decentralising such a switch (14-2-2019):

"The ominously named “Dead-Man’s Switch” is a trigger for an event that occurs when an operator becomes incapacitated. Originally, the term described a physical switch that when released, caused a machine to stop running. Now the term also refers to software that asks a user to periodically “check-in”, and releases some information if the user fails to perform this check-in within a certain amount of time.

A basic structure for a DMS:

A user has a secret
The user stores the secret with a third party
The user proves she is alive (“checks-in”) with some predetermined regularity with the third party.
The user ceases to “check-in”.
The trusted third party publishes the secret."

Uses

From the same above mentioned blog.

"We can immediately see how a “dead-man switch”(DMS) could provide insurance against violence or intimidation for journalists (think of Edward Snowden’s disclosures). It could, as a custody or inheritance solution be a cheaper and swifter alternative to lawyers or wills. For example, if you wish to share a private key with your immediate family after you die. Other types of information could also be encrypted and shared later: a password to unlock a phone, email or social media accounts. Existing systems for these scenarios can be both costly and highly fallible.

The attraction of a decentralized solution is obvious: censorship resistant, and secured by everyone invested in that network (not just a few servers run by a small company that are subject to governmental influence, legal obligations, and other powerful forces). Aside from a potential solution, cryptocurrency also presents a compelling use-case: the increased use of private keys to secure funds requires redundancy and security. The recent Quadriga CX situation illustrates the urgency here (a custody solution for a major exchange has requirements beyond what we describe here — but clearly the status quo is unacceptable!)."

Existing decentralized DMS implementations

From the same above mentioned blog:

"Kill Cord is an Ethereum-based dApp that leverages aspects of p2p networks and smart contracts to provide additional confidence in a DMS system.

Kimono has many features in common with a DMS, but might be more accurately described as a “time capsule”. Kimono allows a user to encrypt a message with a secret, and then split that secret into N-many shares, and distribute those shares among peers in a network. Using a technique known as a “time-lock”, a countdown timer is set by the user, and can be easily checked by all parties. When the countdown completes, a reward attached to the smart contract incentivizes the secret-holders (called “revealers” by Kimono) to reveal their shares."

Enigma also proposes their own DMS:

"A dead-man’s switch on Enigma would have a secret contract, which is used to store the secret information. A contract on Ethereum would function as the proof of life/check-in, and would have incentivize “time-keepers” to monitor that the user continues to check-in. The “secret contract” can replace both the publisher and the revealers in the previous two models. Time-Keepers, unlike revealers, do not have the option to collude off-chain as they never have access to the decryption secret. Additionally, the secret contract enables straightforward private recipients."