Time-Lock Encryption | Hacker News Reader

Time-Lock Encryption

gwern.net

37 pointsrzk4 comments

This is a very interesting compilation of various approaches to the cryptographic time-lock problem. The Bitcoin idea is particularly enticing, even if impractical, since the idea of using the Bitcoin blockchain as a relatively tamper proof "timer" feels like something that could be made to work in practice.

One gap though is that the opening example is the idea of creating an insurance file that is publicly decryptable at a certain date if a particular real-world condition exists, like the file's author being kidnapped or whatever. But to make that work in practice you need not just time-lock encryption, but resetable time-lock encryption where it's possible to delay the release of the time-lock if that condition has not been met. I can see why the examples don't tackle that since even the basic problem seems unsolved, much less a tunable version of it, but it's a very interesting thought exercise.

The “resetable” aspect seems to be a crucial part of true “time-lock” encryption… rather than what feels like a “proof of work” mode where an amount of computation stands in as a proxy for “time elapsed”. But regardless of how good a proxy it is, “time-elapsed” is not really what we want - we don’t want a lock that takes “at least n seconds of effort to open”, we want a lock that will not open before a timestamp.

It feels like a true time-lock solution should be impossible to unlock before a particular date, but trivial afterwards, rather than assuming the opener started work on it at the moment it was released and has been burning cycles at some maximal rate since then.

I don’t think the universe contains unfakeable timestamps, which seem to be a requirement for that true solution - it feels like it’s not compatible with relativity, so maybe proxies are the best we can do on a fundamental level.

If you are interested in a time-lock implementation you can use today, here is one I made some 5 years ago and still using: https://github.com/rayanamal/timelock

- Can time-lock (encrypt) in negligible time (almost instantaneosly)

- Non-parallelizable sequential algorithm

- Decrypts in constant CPU cycles (meaning CPU with 2x faster clock will decrypt 2x faster)

It can only time-lock numeric data though. It's enough for me, I'm using it to encrypt PINs and root passwords for the Screen Time restriction setups of my various devices (iPhone, Linux PC). It allows me to have unbypassable restrictions while also not having to trust a friend/relative. This concept is known as a commitment device: https://en.wikipedia.org/wiki/Commitment_device

I have created nanotimestamps.org , which feels similar to this except it's not for time lock encryption , but time verification. Um... Nanotimestamps.org/appseed has a nanotimestamp video as well , I am too lazy to really work on nanotimestamp org lol

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