@npio/internals/captcha/index.ts

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export const sha256 = async function (data: string) {
  let buffer = new TextEncoder().encode(data);
  let hashBuffer = await crypto.subtle.digest("SHA-256", buffer.buffer);
  // hashBuffer = await crypto.subtle.digest("SHA-256", hashBuffer);
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  return hashArray.map((c) => c.toString(16).padStart(2, "0")).join("");
};

/*
const verifyDifficultyBtc = async (difficulty: number) => {
  const zeroes = Array(difficulty + 1).join("0");
  return (hash: string) => hash.slice(0, difficulty) === zeroes;
};
*/

const verifyDifficulty = async function (difficulty: number) {
  let minHash = "";
  const maxHex = Array(64 + 1).join("f");

  if (globalThis.BigInt!) {
    const max = BigInt("0x" + maxHex);
    const minSize = max - max / BigInt(difficulty);
    minHash = minSize.toString(16);
  } else {
    const { BigNumber } = await import("bignumber.js");
    BigNumber.config({ DECIMAL_PLACES: 0 });

    const max = new BigNumber(maxHex, 16);
    const minSize = max.minus(max.div(difficulty));
    minHash = minSize.toString(16);
  }

  console.log({
    minHash,
    len: minHash.length,
  });

  return (hash: string) => hash >= minHash;
};

type Input = { data: string; difficulty: number };
type Pow = { hash: string; nonce: number };

export const createPow = async function ({
  data,
  difficulty = 0,
}: Input): Promise<Pow> {
  let hash;
  let nonce = 0;

  const verify = await verifyDifficulty(difficulty);

  do {
    nonce = nonce + 1;
    hash = await sha256(data + nonce);
  } while (!verify(hash));

  return { hash, nonce };
};

export const verifyPow = async function (
  { data, difficulty = 0 }: Input,
  { hash, nonce }: Pow,
) {
  console.log("hash length", hash.length);

  const verify = await verifyDifficulty(difficulty);
  if (!verify(hash)) {
    console.log("difficulty wrong");
    return false;
  }

  if (hash !== (await sha256(data + nonce))) {
    console.log("hash wrong");
    return false;
  }

  return true;
};