Private tx key generation algorithm

Problems with current algorithm:

It's possible to recover private tx key with only the list of miner wallet addresses. Full sidechain data is not required
It's also possible to tell which wallet mined this block
Different miners generate different tx keys which makes crypto cache bigger and reduces its efficiency

New algorithm which will solve these problems:

m_txkeySecSeed will replace m_txkeySec in sidechain data
get_tx_keys(pub, sec, spend_pub_key, m_prevId) -> get_tx_keys(pub, sec, m_txkeySecSeed, m_prevId)
m_txkeySecSeed is the same as parent sidechain block's m_txkeySecSeed if they're both built on top of the same Monero block (m_prevId)
m_txkeySecSeed = H("tx_key_seed" || parent_data) if parent block is built on top of a different Monero block, where parent_data is serialized parent block with nonce and extra_nonce fields set to 0 (because different nodes can theoretically see parent blocks with the same ID but different nonces - see https://github.com/SChernykh/p2pool/blob/master/src/pool_block.h#L44).

SChernykh / p2pool