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94 lines
3.5 KiB
Markdown
94 lines
3.5 KiB
Markdown
NIP-13
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======
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Proof of Work
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-------------
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`draft` `optional` `author:jb55` `author:cameri`
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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.
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`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.
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Mining
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------
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To generate PoW for a `NIP-01` note, a `nonce` tag is used:
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```json
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{"content": "It's just me mining my own business", "tags": [["nonce", "1", "20"]]}
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```
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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.
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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.
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Example mined note
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------------------
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```json
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{
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"id": "000006d8c378af1779d2feebc7603a125d99eca0ccf1085959b307f64e5dd358",
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"pubkey": "a48380f4cfcc1ad5378294fcac36439770f9c878dd880ffa94bb74ea54a6f243",
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"created_at": 1651794653,
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"kind": 1,
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"tags": [
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[
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"nonce",
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"776797",
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"20"
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]
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],
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"content": "It's just me mining my own business",
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"sig": "284622fc0a3f4f1303455d5175f7ba962a3300d136085b9566801bc2e0699de0c7e31e44c81fb40ad9049173742e904713c3594a1da0fc5d2382a25c11aba977"
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}
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```
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Validating
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----------
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Here is some reference C code for calculating the difficulty (aka number of leading zero bits) in a nostr note id:
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```c
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int zero_bits(unsigned char b)
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{
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int n = 0;
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if (b == 0)
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return 8;
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while (b >>= 1)
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n++;
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return 7-n;
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}
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/* find the number of leading zero bits in a hash */
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int count_leading_zero_bits(unsigned char *hash)
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{
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int bits, total, i;
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for (i = 0, total = 0; i < 32; i++) {
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bits = zero_bits(hash[i]);
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total += bits;
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if (bits != 8)
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break;
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}
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return total;
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}
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```
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Querying relays for PoW notes
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-----------------------------
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Since relays allow searching on prefixes, you can use this as a way to filter notes of a certain difficulty:
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```
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$ echo '["REQ", "subid", {"ids": ["000000000"]}]' | websocat wss://some-relay.com | jq -c '.[2]'
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{"id":"000000000121637feeb68a06c8fa7abd25774bdedfa9b6ef648386fb3b70c387", ...}
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```
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Delegated Proof of Work
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-----------------------
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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.
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