Mini miner

15 points

With the Bitcoin thing going strong, I figured it would be interesting to do some simplified mining.

Connect to the problem endpoint. You'll receive a JSON with two attributes. One is block, which is in essence an object with a nonce value (initially empty) and a data key which contains some arbitrary data. The other attribute is difficulty - we'll get back to it in a moment.

Your goal is find a nonce value that will cause the SHA256 hash of the block object to begin with difficulty zero bits. E.g. a difficulty of 14 means that the SHA256 digest needs to start with at least 14 zero bits.

The hash should be calculated from a JSON-serialized block value without any whitespace. The keys needs to be in alphabetical order.

Let's illustrate this on a really simple case. For a block with an empty data array and a given difficulty of 8 (so the first 8 bits of the SHA256 hash need to be all 0), a nonce value of 45 is one perfectly valid solution:

SHA256('{"data":[],"nonce":45}') -> 00d696db4...cfb19ec2e0141

Keep in mind, difficulty is the number of 0 bits, not bytes.

Getting the problem set

GET /challenges/mini_miner/problem?access_token=...

Problem JSON will be in the following format:

• difficulty: how many bits (high order) need to be 0 in the SHA256 hash
• block:
  • nonce: the nonce you will need to find so that the hash meets the criteria, None
  • data: some dummy data that makes up the block

Submitting a solution

POST /challenges/mini_miner/solve?access_token=...

You'll only need to submit the nonce that causes the JSON-serialized block to yield the proper hash.

Solution JSON structure:

• nonce: the nonce you found

Why this challenge?

Because hashcash is an interesting read. Check out the anti-spam usage.