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66

Time is relative. Cryptography lives in the ethereal world of abstract computing machines: there are machines that can do operations. Bigger machines can do operations faster. There is no clock that you can enforce; physical time has no meaning. In other words, if an attacker wants to get your file earlier, he just has to buy a faster computer. Now one can ...


55

If you do not want to involve a third party, you (the party encrypting the file) could simply release the key to decrypt the file on the target date. I have seen this done for video game releases. Customers are allowed to download an encrypted copy of the game in advance. Then, when the release time comes, the game company simply releases the key. That way, ...


43

Carefully place a spaceship broadcasting the decryption key in orbit around a black hole. The pull of gravity will delay the message until the appropriate time. Or you could just do like normal people and place the key broadcasting spaceship an appropriate number of light years away from the intended audience.


16

Use secret sharing to split a private encryption key into N parts, parameterized to allow reconstruction of the key with K or more parts, where K <= N. Best done using CRM, as described on the following page: http://en.wikipedia.org/wiki/Secret_sharing Then send each part to independent services that agree to publish at a given date in the future. Up ...


7

I believe that in order to properly design your system, you need to define what "time" means in your context, and why you chose a specific time. Assuming that your message is to be decrypted on the 29th of August 1997 at 02:14 AM, what is difference between the moment before and the moment after the deadline? Why specifically this date? You may be able to ...


4

If the only trusted party is yourself, and you can't guarantee being available when the message contents are to be made public, then what you can do instead is to build a device (physical or virtual) that will automatically make the key public at the required time, and then hide the device. An easy way would be to buy a virtual server from Amazon or any of ...


2

I'm not fully sure if this paper about time-lock encryption has been inspired by this discussion but it would be the most formal solution to the question "How to build time-lock encryption?", which is a reformulation of "How to protect data so that it can only be decrypted after a specific date?" But now let's get into the details on how this works. One ...


2

Your protocol is not safe by any means! Example for MitM: A sends random nonce G1 to B C intercepts and sends nonce G1c to B B sends back hash_k(G1c) and random nonce G2 C intercepts and sends hash_k(G1) and nonce G2c to A A verifies hash_k(G1) (is OK), then sends back hash_k(G1 | G2c) C intercepts and sends back hash_k(G1c | G2) B verifies and a ...


1

A hypothetical approach is given in the paper cited in the question (which is very interesting BTW, despite the occasional clumsy grammar) which is to use a software containing an encrypted payload, triggering off of some outside value like a news story, and have people around the world run it until such time as the payload is executed. This fails to meet ...


1

Encrypt the file with a very long key, split it up into parts, and give each part to a trusted person along with instructions not to surrender said part until the given date. You may add some redundancy by giving each part out to more people, in case one of them were to be hit by a bus. Of course, a network of computers could do this just as humans can. In ...


1

No. Stick to known protocols such as TLS, Kerberos, SSH & IPSec for key exchanges. Try researching Diffie-Hellman key exchanges and ECDH (Elliptical Curve Diffie-Hellman, the new method of key exchanges like your example).


1

CAN is designed to be relatively simple and is often implemented between microcontrollers with very little processing power (that are busy doing stuff where timings are important), and is used to relay messages in real time. Adding some encryption and DoS protection would introduce too much complexity and given that it's just two wires shared by all ...



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