I propose that miners which support this extension send a "X-Mining-Extensions: noncemask" header when requesting work. If the server supports the extension, it should respond with the same header. For other extensions, "X-Mining-Extensions" should be a space-delimited list of elements which can have parameters after an "=" character.

When this extension is active, the server should send an additional field in the JSON-RPC reply: "noncemask" is a hexadecimal-encoded mask of the nonce bits a miner is allowed to change in the header.

For example, if the server sends then the miner should change only the last 29 bits of the nonce.

This allows the server to give the same work to multiple miners with different nonce ranges for each to scan. Combined with X-Roll-Ntime, this can greatly improve efficiency of the work-generating component.

In addition, miners may send a "X-Mining-Hashrate" header set to their average hashrate (in hashes per second) which the upstream server might use to choose a proper sized noncemask.

Thoughts?

Edit: noncemask has been superceded by noncerange