EXPLANATION

Imagine you want to release a file a group or person in exchange for BTC.
(Note: you can redo this scheme for any number of groups effectively
creating a parallel auction)

You split the file into 100 chunks, and encrypt them using a hash based off the
original chunk data.

* Each chunk is hashed.
* The hash becomes a Bitcoin private key.
* We derive the public key.
* The address for that pubkey is the chunk's release address.
* We hash the public key to get a secret.
* The chunk is encrypted using the secret with AES256.

Spending from that address means you *must* reveal the public key.
Revealing the public key means you reveal the secret.
And so the chunk can be decrypted.

Now in order to keep the leaker honest, before the initial release he
announces a block height (in the future) at which he will unlock some chunks.
These chunks are chosen based off the block hash at that height.
By preannouncing sufficiently in advance, and giving a reasonable number
of chunks to make public (say 20%), then 20% are chosen randomly using a
provably fair system (the Bitcoin blockchain) and released.

People can now vet the released chunks, pass their own judgement and decide
whether to start bidding on the remaining chunks to unlock them.