Implementation Guide

Here are the steps needed to add RSK merged mining capabilities to mining pool software.

What do you need to do

Add the RSK merged mining information in Bitcoin block as a commitment, the complete steps are as follows:

1. Get the work from RSK node

Use the mnr_getWork method from the RSK node's JSON-RPC API. This method returns the information of the current block for merged mining, the boundary condition to be met ("target"), and some other data.

2. Put the information for merged mining in the Bitcoin block

Format

OP_RETURN + Length + RSKBLOCK: + RskBlockInfo

• OP_RETURN: is0x6a
• Length is 0x29 and represents the length of the information included after the OP_RETURN opcode
• RSKBLOCK: is the ASCII string for0x52534b424c4f434b3a
• RskBlockInfo is the block information in binary format.

For example, if RskBlockInfo is e5aad3b6b9dc71a3eb98a069bd29ca32211aee8b03fd462f4ffbbe97cc75a174 the merged mining information is 6a2952534b424c4f434b3ae5aad3b6b9dc71a3eb98a069bd29ca32211aee8b03fd462f4ffbbe97cc75a174

Position

Include as the last output of Bitcoin coinbase transaction.

Restrictions

• The number of bytes immediately after RskBlockInfo, up to the end of the coinbase transaction must be lower than or equal to 128 bytes.
• The trailing raw bytes must not contain the binary string RSKBLOCK:
• The probability of the RSK tag to appear by chance is negligible, but pool servers must not rule out the possibility of a rogue Bitcoin address included in the coinbase transaction having this pattern, and being used as an attack to break the validity of merged mining header.
• The RSKBLOCK: tag may appear by chance or maliciously in the ExtraNonce2 data field that is provided by miners as part of the Stratum protocol. This is not a problem as long as the poolserver adds the RSKBLOCK: tag after the ExtraNonce2 chunk.

3. Notify Miners on a faster pace

RSK's average block time is 30 seconds, which is faster than Bitcoin's 10 minutes. This fact triggers the following implementation changes:

• Retrieve work from RSK node every 2 seconds, so as to be always mining on the last RSK work.
• Sent to miners a mining.notify message, from stratum protocol, every time new RSK work is received.

4. Mine until work is enough to meet the target received in the work info

5. Submit Solution to RSK node

Use the mnr_submitBitcoinBlockPartialMerkle method from RSK node's JSON-RPC API. That method has optimum performance, and is preferred among other available methods. Other submission methods and information about the pros and cons between them can be found in the Mining JSON-RPC API documentation.

Influence on Bitcoin

As a result of RSK's implementation of merged mining, the Bitcoin network does not get filled up with merged mining information. Only a minimal amount of information is stored: An extra output on the coinbase transaction.

Furthermore, no changes are required on Bitcoin node to support merged mining with RSK.