Stratum Protocol

The stratum protocol is used by ASIC miners, devices created specifically for performing Bitcoin mining.

Miners use this protocol to reach out to one or more servers (e.g. a mining pool) in order to obtain a template for a new block. The template has gaps where random data can be added until the the miner successfully creates a candidate block that meets the specified difficulty requirements.

Message Format

Stratum uses the JSON-RPC 2.0 message format. That is, JSON-encoded messages, separated by newline (line feed) characters. There are two high-level message formats: requests and responses.

Requests

Requests all contain the following fields:

Responses

Responses all contain the following fields:

Error Array Format

The error array is a JSON array containing the following elements:

Example error: {"result":null,"id":2,"error":[24,"Unauthorized worker",null]}

Beyond those specified by JSON-RPC, the following error codes are used:

Client Methods

mining.subscribe

Upon connecting to a server, clients are expected to send a subscribe request, described as follows.

Example request: {"id": 1, "method": "mining.subscribe", "params": ["Node/1.0.0"]}

In response, the server will send the following data in its result object, which is a JSON array:

Example response: {"result":[[["mining.set_difficulty","731ec5e0649606ff"],["mining.notify","731ec5e0649606ff"]],"e9695791",4],"id":1,"error":null}

mining.authorize

In order to authenticate itself, the client send an authorize message:

Example request: {"id": 1, "method": "mining.authorize", "params": ["username", "p4ssw0rd"]}

Response format:

Example response: {"id": 2, "result": true, "error": null}

mining.submit

Once the client has completed a job (received via mining.notify following an accepted mining.authorize), it returns its result using a submit message. This message is also used to submit shares to a mining pool. The format is as follows:

Example request: {"id": 1, "method": "mining.submit", "params": ["username", "4f", "fe36a31b", "504e86ed", "e9695791"]}

Response format:

Example response: {"id": 2, "result": true, "error": null}

Server Methods

mining.notify

Once a client successfully connects using the mining.subscribe and mining.authorize messages, the server may send a job to the client, informing it of everything it needs to know in order to mine a new block. The notify message is a notification (does not expect a response) and has the following format:

Example request: {"id": null, "method": "mining.notify", "params": ["bf", "4d16b6f85af6e2198f44ae2a6de67f78487ae5611b77c6c0440b921e00000000", "01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff20020862062f503253482f04b8864e5008", "072f736c7573682f000000000100f2052a010000001976a914d23fcdf86f7e756a64a7a9688ef9903327048ed988ac00000000", [], "00000002", "1c2ac4af", "504e86b9", false]}

Merkle Tree Hash Array

The array of merkle tree hashes in the mining.notify request, denote (in order) the hashes that should be iteratively composed with the coinbase transaction has to ultimately generate the merkle root. In the simplest case, where the block will only contain the coinbase transaction, the array is empty and the coinbase transaction hash becomes the merkle root. When there are more transactions, however, the merkle tree hash array contains the leaf nodes of the partial merkle tree, as shown below.

graph TD

root[Merkle Root] --- 0[Hash0]
root[Merkle Root] --- 1[Hash1]
0 --- 00[Hash00]
0 --- 01[Hash01]
00 --- 000[Hash000]
00 --- 001[Hash001]
000 --- coinbase[Coinbase]

style root stroke-width: 3px, stroke-dasharray: 5
style 0 stroke-width: 3px, stroke-dasharray: 5
style 00 stroke-width: 3px, stroke-dasharray: 5
style 000 stroke-width: 3px, stroke-dasharray: 5
style 1 stroke-width: 3px, stroke-bold: 5
style 01 stroke-width: 3px, stroke-bold: 5
style 001 stroke-width: 3px, stroke-bold: 5

In the example above, dashed lines indicate hashes that must be computed, while bold lines indicate hashes are are included in the merkle tree hash array, which in this case would be: ["Hash000", "Hash00", "Hash0"]. So after the coinbase transaction is created, it is hashed into Hash000. Then Hash000 and Hash001 are hashed together to create Hash00, and so on until the Merkle Root is computed.

mining.set_difficulty

When reporting shares to the server, clients are expected to default to a difficulty of 1 (a target of: 0x00000000ffff0000000000000000000000000000000000000000000000000000). At any point, however, the server can change that threshold by sending a set_difficulty message:

Example request: { "id": null, "method": "mining.set_difficulty", "params": [2]}