NIP-13 ====== Proof of Work ------------- `draft` `optional` `author:jb55` `author:cameri` This NIP defines a way to generate and interpret Proof of Work for nostr notes. Proof of Work (PoW) is a way to add a proof of computational work to a note. This is a bearer proof that all relays and clients can universally validate with a small amount of code. This proof can be used as a means of spam deterrence. `difficulty` is defined to be the number of leading zero bits in the `NIP-01` id. For example, an id of `000000000e9d97a1ab09fc381030b346cdd7a142ad57e6df0b46dc9bef6c7e2d` has a difficulty of `36` with `36` leading 0 bits. `002f...` is `0000 0000 0010 1111...` in binary, which has 10 leading zeroes. Do not forget to count leading zeroes for hex digits <= `7`. Mining ------ To generate PoW for a `NIP-01` note, a `nonce` tag is used: ```json {"content": "It's just me mining my own business", "tags": [["nonce", "1", "20"]]} ``` When mining, the second entry to the nonce tag is updated, and then the id is recalculated (see [NIP-01](./01.md)). If the id has the desired number of leading zero bits, the note has been mined. It is recommended to update the `created_at` as well during this process. The third entry to the nonce tag `SHOULD` contain the target difficulty. This allows clients to protect against situations where bulk spammers targeting a lower difficulty get lucky and match a higher difficulty. For example, if you require 40 bits to reply to your thread and see a committed target of 30, you can safely reject it even if the note has 40 bits difficulty. Without a committed target difficulty you could not reject it. Committing to a target difficulty is something all honest miners should be ok with, and clients `MAY` reject a note matching a target difficulty if it is missing a difficulty commitment. Example mined note ------------------ ```json { "id": "000006d8c378af1779d2feebc7603a125d99eca0ccf1085959b307f64e5dd358", "pubkey": "a48380f4cfcc1ad5378294fcac36439770f9c878dd880ffa94bb74ea54a6f243", "created_at": 1651794653, "kind": 1, "tags": [ [ "nonce", "776797", "21" ] ], "content": "It's just me mining my own business", "sig": "284622fc0a3f4f1303455d5175f7ba962a3300d136085b9566801bc2e0699de0c7e31e44c81fb40ad9049173742e904713c3594a1da0fc5d2382a25c11aba977" } ``` Validating ---------- Here is some reference C code for calculating the difficulty (aka number of leading zero bits) in a nostr event id: ```c #include #include #include int countLeadingZeroes(const char *hex) { int count = 0; for (int i = 0; i < strlen(hex); i++) { int nibble = (int)strtol((char[]){hex[i], '\0'}, NULL, 16); if (nibble == 0) { count += 4; } else { count += __builtin_clz(nibble) - 28; break; } } return count; } int main(int argc, char *argv[]) { if (argc != 2) { fprintf(stderr, "Usage: %s \n", argv[0]); return 1; } const char *hex_string = argv[1]; int result = countLeadingZeroes(hex_string); printf("Leading zeroes in hex string %s: %d\n", hex_string, result); return 0; } ``` Here is some JavaScript code for doing the same thing: ```javascript // hex should be a hexadecimal string (with no 0x prefix) function countLeadingZeroes(hex) { let count = 0; for (let i = 0; i < hex.length; i++) { const nibble = parseInt(hex[i], 16); if (nibble === 0) { count += 4; } else { count += Math.clz32(nibble) - 28; break; } } return count; } ``` Querying relays for PoW notes ----------------------------- Since relays allow searching on prefixes, you can use this as a way to filter notes of a certain difficulty: ``` $ echo '["REQ", "subid", {"ids": ["000000000"]}]' | websocat wss://some-relay.com | jq -c '.[2]' {"id":"000000000121637feeb68a06c8fa7abd25774bdedfa9b6ef648386fb3b70c387", ...} ``` Delegated Proof of Work ----------------------- Since the `NIP-01` note id does not commit to any signature, PoW can be outsourced to PoW providers, perhaps for a fee. This provides a way for clients to get their messages out to PoW-restricted relays without having to do any work themselves, which is useful for energy-constrained devices like mobile phones.