SON Smart Contracts

Purpose
The purpose of this document is to outline the steps required to use smart contracts for Inter-blockchain communication with blockchains that support smart contracts such as Ethereum, EOS and the likes.
Scope
The functional requirement listed in this document will be limited to the use of smart contracts to enable inter-blockchain communication between Peerplays and other blockchains that support smart contracts. This will outline the required steps to create smart contracts on other blockchains which can then be called by the Peerplays blockchain to perform various operations such as withdrawal of the cryptocurrency back to the user. Also outlined here will be the sequence in which the required steps will be performed including:
any interactions with the user.
validations to ensure complete and accurate information gathering.
Background
The Bitcoin Sidechain functionality has been implemented in the Peerplays blockchain but it doesn't take into account, the change of witnesses. As per the current implementation of Sidechain, a multisig bitcoin wallet will be created on the bitcoin blockchain to hold the bitcoins that have been deposited into the pBTC accounts of the Peerplays users. Every Peerplays witnesses will have a bitcoin transaction signing key for this multisig bitcoin wallet and will be required to sign any withdrawal transaction. When a witness changes, the transaction signing key of the outgoing witness needs to be removed from the multisig bitcoin wallet and the key of the incoming witness needs to be added. The suggested proposal is to make the Sidechain code available as a plugin and assign the responsibility for running the sidechain code to separate nodes called the Sidechain Operating Nodes (SONs). The SONs will be independent of the witnesses and don't need to be changed much often.
Process Overview
Described here is the process to use smart contracts on enable inter-blockchain communication between Peerplays and other blockchains that support smart contracts. For ease of understanding, we will use EOS as an example for the parent chain.
Context
To facilitate the transfer of tokens from other blockchains to Peerplays, smart contracts have to be deployed on both Peerplays and the EOS blockchain. We would also need to check the smart contract tables every 5-10 seconds, scanning for transactions to relay across the network. This can be done by polling functions relay_eos and relay_ppy running on the SONs. relay_eos will check the smart contract tables on the EOS and relay_ppy will check the smart contract tables on PPY. These functions may be called IBC Relays. 
This cannot be implemented until we have Smart Contracts implemented in Peerplays.
Smart Contracts Flow
1.The user will initiate an inter-blockchain transaction orig_trx on the EOS mainnet using peerplays.io contract. The transaction information will be recorded in the origtrx table of the peerplays.io contract on the EOS mainnet side;
2.relay_eos will get the transaction and transaction-related information (block information and Merkle path), then pass it to the relay of Peerplays side (relay_ppy);
3.relay_ppy constructs 'cash' transaction and calls the cash action of the eos.io contract on the Peerplays side. If the call succeeds in the cash function, the corresponding token will be issued to the target user after deducting the fees;
4.relay_ppy will get cash_trx and related information (block information and Merkle path) and pass them to relay_eos. relay_eos will construct the cashconfirm transaction and call the cashconfirm action of the peerplays.io contract on the EOS mainnet side, which will delete the original transaction record in peerplays.io contract. This will complete the inter-blockchain transaction.
5.At step 3, if the call fails, relay_ppy will get an exception in the cash_trx and pass them to relay_eos. relay_eos will construct a cashrefund transaction and call the cashrefund action of the peerplays.io contract on the EOS mainnet side, which will refund the amount to the sender after deducting the fees.
References
​https://github.com/boscore/Documentation/blob/master/IBC/EOSIO_IBC_Priciple_and_Design.md​

Proposals

Bitcoin Sidechain Docs

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