from Hacker News

How can a time traveler encrypt info so it's only decryptable after a given date

by azeemba on 7/28/24, 5:27 PM with 67 comments

  • by card_zero on 7/28/24, 7:07 PM

    There's this star called R Scuti:

    https://en.wikipedia.org/wiki/R_Scuti

    * The light from it is variable,

    * This variation is continuous, not a rare event,

    * It's 4,000 light years away, so the butterfly effect is irrelevant because the light is already on its way,

    * It's chaotic and unpredictable.

    Basically a reliable stream of random data. I guess the only problem is that you need to know what observations of its light levels were, throughout the 80s, if the records even exist.

    Edit: "The AAVSO International Database currently contains over 110,000 observations of this erratic star spanning nearly a century of activity." There you go, that should provide a thousand measurements to base a key on in any given year.

  • by slicktux on 7/28/24, 6:03 PM

    This reminds me of the Joe Grand video titled:

    “ I hacked time to recover $3 million from a Bitcoin software wallet”

    Just put a program in the computer that generates a ‘random’ key based on time of day and second…and it does this every day at pre defined hours…and maybe some way that the time and date can’t be modified. Then, only when that day and time comes will the right key be generated and the files decrypted. Program does not know when that date is it just bases the key generation on time and date.

  • by mrrccc on 7/28/24, 8:20 PM

    The team behind the awesome drand project (https://drand.love) has proposed a timelock encryption scheme based on an existing threshold network (the League of Entropy).

    They even provided a fully operational, web-based, open-source implementation: https://timevault.drand.love

  • by kdkdodiei4 on 7/28/24, 6:34 PM

    Make it only decrypted by brute force, taking into account the history of the algorithms and the computational level. There is no clue, you just have to use the knowledge of the time to try to solve it. You can even create the program and its minimum requirements to make sure they have a direction.

  • by nickdothutton on 7/28/24, 6:26 PM

    Position in a coordinate system of epicentre of earthquakes, perhaps those above a certain threshold depending on how much entropy you needed.

  • by motohagiography on 7/28/24, 7:03 PM

    the comment in the response about using stars going nova between the present and the travelled-from time was probably the best answer, but it requires accepting the paradox of the possibility of time travel while still ruling out faster than light travel- as you could get the key earlier than the set date by travelling light years toward where the stars were sampled from.

    If you are protecting the secret from non-time travelers, you're probably fine, but if you are protecting it from other time travellers, your compute or proof of work has to be more expensive than their time-travel propulsion energy units.

    We have this same problem with device attestation, where if the key exists in the same "universe" (hardware substrate) as the ciphertext, you're effectively fighting time travellers because they can run, re-run, use side channels, insert a breakpoint anywhere along the way. The current solutions are in the domains of physical tamper proofing, "white box" cryptography and other obfuscation schemes, and ultimately fully homomorphic encryption (FHE).

    FHE would be the necessary solution against time travellers in this case because no matter where in time they were, they would have to be present at the instant the compute operation completes- and then you're into a race condition against Planck time to see who can grab the result of the computation first when it finishes. (assuming they can't infer or predict the result earlier than the completion of the FHE computation, that earlier decryption rounds don't reduce the time it takes to brute force the rest of it in a parallel stopped-timeline, and that Planck time still means anything in a universe where time isn't unidirectional and scalar)

    Writing wise, there would have to be a hitch in their time travel scheme where to work it needed randomness and a lack of precision for some important quantum uncertainty reason, and the race to be present for the FHE decryption before the time travellers resolved their precision problem would drive the plot.

    don't be discouraged though, a cursory reading of scientific discovery shows that impossible is mostly a convention, and cryptography historically reduces to a gentleman's agreement.

  • by paulmendoza on 7/28/24, 6:46 PM

    Use an encryption key that is a headline from a newspaper for that day. This assumes the time travel works like the Marvel movies and not like Back to the Future.

  • by K0balt on 7/28/24, 6:34 PM

    In order for the butterfly effect to not disturb the results of any random or pseudorandom key, the key must be derived in such a way that the distance of the key generation event is greater than 1/2 the light-time of the key delivery delay, so that in no case can any information from the key holders reference reach the key source prior to key generation.

    Other than that the key must be based in a purely deterministic algorithm to be immune to butterfly factors, which can always be brute forced by accelerating the civilization to fractional relativistic velocities or bringing it close to an extremely massive object. (Leaving the keygen at rest) Of course other ways to brute force such a key generator are probably more practical, but a relativistic attack is the steel man for the impossibility of reliability.

    Stealth might be the best bet, an undersea bouy that pops up and broadcasts the key at the specified time or something like that. But then again, a fast moving civilisation would get the key “early” from their frame, even for astronomical events.

    I posit that there is no absolutely reliable delay, but stealth is probably the best practical hedge.

  • by foota on 7/28/24, 8:50 PM

    How about this: take as input something random from beyond the time horizon (e.g., brightness from stars 300 light years away). Then (if we assume the input is sufficiently random) they should be fine.

  • by bdjsiqoocwk on 7/29/24, 1:02 PM

    This is really one of those questions where you want X, you started down the path of answering the question but got stuck, and now are asking how to get unstuck when you should be asking for X.

    He's asking "how to decrypt only after a certain date" when in reality he should be asking "how to make information available after a certain date".

  • by PaulKeeble on 7/28/24, 7:00 PM

    The more generic although potentially harder question is without the time traveler element what could you do today to make sure something could not be decrypted before a certain date. This seems potentially useful but also every bit as tricky to answer especially since we don't know what the future entails unlike a time traveller.

  • by kdkdodiei4 on 7/28/24, 6:28 PM

    For me it is easy if you are an old man you can simply know what algorithm was used at each time and at the computational level of each time, therefore you can make the only way to decipher the cave is by brute force and that it is probable and easy to resolved in each era through advances and knowledge.

  • by a1o on 7/28/24, 6:21 PM

    I don't quite get notion of sending something back in time but before the actual date you want the thing to work... But anyway, you really can't make the crypto device a tech level superior of the time or the crypto device itself gives information on the future.

  • by 0cf8612b2e1e on 7/28/24, 6:38 PM

    Not going to result in an equal sharing of information, but if you can drop doodads at different time and locations, make a scavenger hunt for the key.

    First key is stored at the center of Olympus Mons on Mars.

  • by mtremsal on 7/28/24, 6:55 PM

    Isn’t that exactly what drand is meant to provide?

    See drand, the distributed randomness beacon protocol at https://drand.love/

  • by mikewarot on 7/29/24, 2:58 AM

    Lost texts are recovered, and artifacts are found all the time. You could use an old artifact's decrypted text, or location, as a source of a passkey.

  • by geekodour on 7/28/24, 6:17 PM

  • by staplung on 7/28/24, 6:23 PM

    A basket of specified (closing) stock prices on day X.

  • by piinbinary on 7/28/24, 6:03 PM

    Ignoring the butterfly effect issue, I would have said just pick the title of a given newspaper on a given date as the password.

  • by trabs4t on 7/28/24, 7:23 PM

    Transmit the key via radio wave, from a point source located x light years from earth. The key will reach earth after x years.

  • by eknkc on 7/28/24, 6:17 PM

    Would earthquakes be susceptible to butterfly effect? Historic earhquake data might solve the issue.

  • by aquafox on 7/28/24, 6:09 PM

    Why not use a private key based on a bunch of lottery draws that happened just before the date?

  • by _boffin_ on 7/29/24, 4:35 AM

    market close data: tickers, their closing prices, and volumes for a given market or markets. For more, first paragraph of a story for each ticker.