# Can I use a blockchain to lock access to some information before a certain amount of time has passed, without relying on third-parties?

Picture the following (the example is very similar to the real scenario):

• I have a physical item in possession in which I want to lock myself (don't ask [1]) from accessing it until a n number of hours have passed.
• I put the item in a box with a combination lock [2].
• I change the combination, and somehow temporarily save it without looking at the new one (in my case I took a picture with my cellphone and didn't look at it).
• However, I want to completely lose access to the new combination (i.e.: the picture) until a certain number of hours have passed.
• In this particular case, I solved it using a third-party website that sends e-mails on a future date, so I attached the picture of my cellphone (w/o looking) and configured it to send it to me after n hours.

So far there's no cryptography involved above. See below an simpler example which may make more sense:

• I have a file in which its contents I want to lock myself from accessing them until n hours have passed.
• I encrypt the file with a random unknown password, so that I cannot access its contents anymore.
• However, after n hours I am somehow able to figure out the password and decrypt the file, thus accessing its contents.

I searched around (before resorting to asking a question), and in fact cryptographic algorithms are not time aware, so there's no way to get the "self-time-capsule" behavior I need without relying on a third party.

However, it came to me that the Bitcoin blockchain (or any other blockchain) is basically a decentralized third party. So, would there exist any way to get the behavior I need by using the Bitcoin protocol, for example?

Feel free to suggest other solutions, it's quite possible I'm going all over the top here.

Oh, just for giggles: the timed e-mail service I used didn't work at all, I got no e-mail back. Well, that's the problem with trusting a third-party. Guess I'll begin picking the lock anyways...

[1] You can think of it as money, say 100 bucks I really can't/shound't spend it before n hours have passed.

[2] Assume the lock is not pickable or the time it would take to pick it or brute-force is way higher than n, so not worth it.

• This question has papers referenced which do what you want (at about 10min granularity) and this answer refers to a predecessor of these papers (?). Also have a look at this question. – SEJPM Jun 17 '18 at 13:09
• This question really originates from lack of making a simple search . I've reached the SEJPM's questions and many others here pertaining to the same topic. Just google "time capsule criptography" and start from there. You'll find that some people thought of what you're interested in. – Souza Jun 30 '18 at 15:44