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I work as a spy for a top secret and ruthless government organisation with a three letter acronym. I know all their dirty secrets and where the skeletons are literally buried. In order to protect myself from being eliminated when I’m no longer required, I’ve downloaded all the organisation’s data and securely encrypted it. I’ve then distributed that encrypted data to friends and reporters.

Is there a technique whereby the data remains encrypted whilst I’m still alive? Clearly I would have to actively take steps to ensure this, and these steps would end upon my disappearance. So whilst I’m alive I do “stuff” perhaps every month, and the shameful secrets remain impossible to decrypt.

I’m aware of secret sharing and key /certificate revocation but not of their flavours. It seems like the very opposite of revoking a public key though. Would I have to keep sending newly encrypted copies out? Is there a cryptographic way to protect myself like this? I’ve read somewhere that Edward Snowdon has such a protective scheme.

Edit: The things I know would bring down the organisation and my friends being reporters, they would publish it as soon as possible. Hence the notion of them not mathematically being able to decrypt unless I'm eliminated. I do not want to rely on their assurances that they won't break the story at the earliest possible opportunity. This allows the organisation to leave me alone.

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    $\begingroup$ Something along the lines of a cryptographic dead man's switch? Sounds like like crypto.stackexchange.com/q/48179 $\endgroup$
    – puzzlepalace
    Commented Apr 1, 2017 at 21:42
  • $\begingroup$ Similar. Your example ultimately relies on the positive action of a centralised device to send out a decrypt notice or the data itself. It isn't designed to work in an adversarial situation were a single device could be compromised. I was thinking of something mathematically orientated and distributed like secret sharing (but different???) $\endgroup$
    – Paul Uszak
    Commented Apr 1, 2017 at 22:00
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    $\begingroup$ You could use secret-sharing to distribute the task over multiple devices. $\hspace{1.86 in}$ $\endgroup$
    – user991
    Commented Apr 2, 2017 at 2:33

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If your friends and the reporters can decrypt the data without any action from you, then even if you're alive they should be able decrypt. You could trust a certain threshold of them to not collude with each other unless they're certain you're dead, in which case secret sharing the key might work.

If you trust your parties to publish the secret material as soon as they can get it (and not destroy it), something like this might also work: suppose you hide the key in a certain location, encrypt the location such that breaking (brute-forcing) the encryption will take at least $t$ time given a large amount of computational power, and send the encrypted location to all the parties. Before $t$ time is up, you move the key to a new location, and again encrypt the location to all the parties. This way, even if you don't trust the parties to not collude, they will not be able to access it as long as you keep moving the key in time.

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    $\begingroup$ No I don't trust them - they're reporters who'll sell out their grandmothers. $\endgroup$
    – Paul Uszak
    Commented Apr 2, 2017 at 1:51

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