sss.md

Stratum mode self-select

One major concern of pool mining has been that of pool centralization. A malicious pool operator, controlling a pool with a significant portion of the total network hash-rate (e.g. 51% or more), has the ability to perform various attacks. This is made possible due to the fact miners have no visibility into what block template they are actually mining on. This leads to another concern - censorship of transactions. Again, as miners have no visibility of the block template they are mining, they also have no visibility of the transactions included in the block template. This enables a malicious pool be selective as to which transactions get included (or not) into a block.

To address these concerns, I've implemented an optional mode for this pool, which enables miners to select their own block template to mine on.

Along with this pool, the popular miner XMRig has this mode implemented. There is also a very simple demonstration miner in the monero-powpy project which can be used to augment this document for implementers.

Specification

What follows are the stratum message and flow changes required to enable pool miners to mine on miner created block templates.

(1) The miner logs into the pool with an additional mode parameter:

{
    "method": "login",
    "params": {
        "login": "wallet address",
        "pass": "password",
        "agent": "user-agent/0.1",
        "mode": "self-select" /* new field */
    },
    "jsonrpc": "2.0",
    "id":1
}

(2) The pool responds with a result job which includes the pool wallet address and an extra nonce:

{
    "result": {
        "job": {
            "pool_wallet": "pool wallet address", /* new field */
            "extra_nonce": "extra nonce hex", /* new field */
            "target": "target hex",
            "job_id": "job id"
        },
        "id": "client id",
        "status": "OK"
    },
    "jsonrpc": "2.0",
    "id":1
}

(3) The miner can now call a local, or remote, Monero daemons RPC method get_block_template with parameters extra_nonce: "<extra nonce hex>" (implemented in pull request #5728) and wallet_address: "<pool wallet address>", using the result values from step #2 above.

The miner now informs the pool of the resulting block template it will use for the job:

{
    "method":"block_template", /* new method */
    "params": {
        "id": "client id",
        "job_id": "job id",
        "blob": "block template hex",
        "height": N,
        "difficulty": N,
        "prev_hash": "prev hash hex"
    },
    "jsonrpc": "2.0",
    "id":1
}

(4) The pool validates and caches the supplied block template and responds with a status:

{
    "result": {
        "status": "OK",
        "error", null
    },
    "jsonrpc": "2.0",
    "id":1
}

The degree of validation required is at the discretion of the pool implementer. This pool simply ensures the supplied block template can be parsed as a Monero block and that the destination coinbase reward pays out to the pool wallet.

(5) The miner submits results. No changes here:

{
    "method":"submit",
    "params": {
        "id": "client id",
        "job_id": "job id",
        "nonce": "deadbeef",
        "result": "hash hex"
    },
    "jsonrpc": "2.0",
    "id":1
}

(6) The pool responds to job submissions. No changes here:

{
    "result": {
        "status": "OK",
        "error", null
    },
    "jsonrpc": "2.0",
    "id":1
}

(7) The pool asks the miner to start a new job:

{
    "method": "job",
    "params": {
        "pool_wallet": "pool wallet address", /* new field */
        "extra_nonce": "extra nonce hex", /* new field */
        "target": "target hex",
        "job_id": "job id"
    },
    "jsonrpc": "2.0",
    "id":1
}

The miner now repeats from step #3.