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AboutPoC.md

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About proof of capacity

PoC is a mining algorithm using storage media such as HDD. BurstCoin is famous for a currency that implement PoC. I used blake2b for a hash function. It's very fast and very optimized for multi-processor.

Tools

plotting tool bc4py_plotter work on Linux/Windows.

Algorithm

  1. We generate seed and push hash0 to top. 
    +---------+----------------+----------------------+
| hash0   | ver+identifier | nonce                |
| 64bytes |    21 bytes    | little endian 4bytes |
+---------+----------------+----------------------+
    ^
    |     |                                       |
    |     +-------------+ blake2b  +--------------+
    |                        |
    |                        v
    |                   +----------+
    +------------------ |  hash0   |
                        +----------+
  2. We generate hashN and push to top. source of hashN is only the last 1024 generated bytes. 
    +---------+---------+     +---------+----------------+----------------------+
| hashN   | hashN-1 |     | hash0   | ver+identifier | nonce                |
| 64bytes | 64bytes | XXX | 64bytes |    21 bytes    | little endian 4bytes |
+---------+---------+     +---------+----------------+----------------------+
    ^
    |     |                                                    |
    |     +----- max size 1024bytes ------+ blake2b  +---//----+
    |                                          |
    |                                          v
    |                                     +----------+
    +------------------------------------ |  hashN   |
                                          +----------+
  3. Once we have created 8192 hashes, we are now going to make a final hash. 
    +----------+----------+     +----------+----------------+----------------------+
| hash8191 | hash8190 |     | hash0    | ver+identifier | nonce                |
| 64bytes  | 64bytes  | XXX | 64bytes  |       21 bytes | little endian 4bytes |
+----------+----------+     +----------+----------------+----------------------+
 
|                                                                              |
+---------+ blake2b   +--------------------------------------------------------+
               |
               v
          +-----------+
          | finalHash |
          +-----------+
  4. All hashes XOR with the final hash and split to 2 scopes. 
    +-------------------------+     +-------------------------+
|         hash0           |     |       hash8191          |
|         64bytes         | XXX |       64bytes           |
+-------------------------+     +-------------------------+
              |              |             |
             XOR            XOR           XOR
              |              |             |
              v              v             v
+-------------------------+     +-------------------------+
|         hash'0          |     |       hash'8191         |
|         64bytes         | XXX |       64bytes           |
+-------------------------+     +-------------------------+
         |           |       |       |          |
         |           |       |       |          |
         v           v       v       v          v
+-------------------------+     +-------------------------+
|  scope0    |  scope1    |     | scope16382 | scope16383 |
|  32bytes   |  32bytes   | XXX | 32bytes    | 32bytes    |
+-------------------------+     +-------------------------+
  5. We get a scope index by int(previousHash) % 16384 and define ths indexed hash a scopeHash.
  6. We generate a pre-workHash from 3 params. Then, we define first 32 bytes a workHash. 
    +------------+                               +------------+
|  scope0    |                               | scope16383 |
|  32bytes   |  X    X    X     X    X    X  | 32bytes    |
+------------+         |                     +------------+
                       |
                       +-----------+
                                   |
                                   v
+----------------------+ +----------------------+ +----------------------+
| blocktime            | | scopeHash            | | previousHash         |
| little endian 4bytes | | 32bytes              | | 32bytes              |
+----------------------+ +----------------------+ +----------------------+
 
|                                                                        |
+----------------------------+ blake2b  +--------------------------------+
                                  v
                           +----------------------+
                           | pre workHash 64bytes |
                           +---+------------------+
                               v
                           +----------+
                           | workHash |
                           | 32bytes  |
                           +----------+

References