# Drand Random 與 Sui Move 的結合

這次我們要用 Drand 產生 安全性的隨機數
並在 Sui 智能合約上 驗證簽章

Drand :
https://drand.love/developer/

Sui Move Example(drand_lib.move):
https://github.com/MystenLabs/sui/blob/main/sui_programmability/examples/games/sources/drand_lib.move

## Drand Lib 智能合約

首先我們先參考 Sui Move 提供的 drand_lib.move檔
我這邊把它翻成中文

// Copyright (c) Mysten Labs, Inc.
// SPDX-License-Identifier: Apache-2.0

/// 用於處理 drand 輸出的輔助模組。
/// 目前適用於鏈 52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971 (quicknet)。
///
/// 請參閱如何在 drand_based_lottery.move 和 drand_based_scratch_card.move 中使用此範例。
///
/// 如果您想在預設網路上使用此模組，該網路有30s的周期，您需要更改公鑰，
/// 創世時間並將先前的簽章包含在 verify_drand_signature 中。請參閱 https://drand.love/developer/ 或
/// 此文件的先前版本：https://github.com/MystenLabs/sui/blob/92df778310679626f00bc4226d7f7a281322cfdd/sui_programmability/examples/games/sources/drand_lib.move
module sui_drand_demo::drand_lib {
    
    use std::hash::sha2_256;
    use sui::bls12381;

    /// Error codes
    const EInvalidRndLength: u64 = 0;
    const EInvalidProof: u64 = 1;

    /// The genesis time of chain 52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971.
    const GENESIS: u64 = 1692803367;
    /// The public key of chain 52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971.
    const DRAND_PK: vector<u8> =
        x"83cf0f2896adee7eb8b5f01fcad3912212c437e0073e911fb90022d3e760183c8c4b450b6a0a6c3ac6a5776a2d1064510d1fec758c921cc22b0e17e63aaf4bcb5ed66304de9cf809bd274ca73bab4af5a6e9c76a4bc09e76eae8991ef5ece45a";

    /// The time in seconds between randomness beacon rounds.
    const PERIOD: u64 = 3;

    /// 透過驗證稍後時間的 drand 簽章來檢查給定的紀元時間是否已經過去。
    /// 回合必須至少為 (epoch_time - GENESIS)/PERIOD + 1)。
    public fun verify_time_has_passed(epoch_time: u64, sig: vector<u8>, round: u64) {
        assert!(epoch_time <= GENESIS + PERIOD * (round - 1), EInvalidProof);
        verify_drand_signature(sig, round);
    }

    /// 驗證 drand 簽章
    public fun verify_drand_signature(sig: vector<u8>, mut round: u64) {
        // Convert round to a byte array in big-endian order.
        let mut round_bytes: vector<u8> = vector[0, 0, 0, 0, 0, 0, 0, 0];
        let mut i = 7;

        // 請注意，此循環永遠不會複製 round_bytes 的最後一個位元組，儘管預計它不會非零。
        while (i > 0) {
            let curr_byte = round % 0x100;
            let curr_element = vector::borrow_mut(&mut round_bytes, i);
            *curr_element = (curr_byte as u8);
            round = round >> 8;
            i = i - 1;
        };

        // 計算 sha256(prev_sig, round_bytes)。
        let digest = sha2_256(round_bytes);
        // 驗證哈希上的簽章。
        let drand_pk = DRAND_PK;
        assert!(bls12381::bls12381_min_sig_verify(&sig, &drand_pk, &digest), EInvalidProof);
    }

    /// 對 drand 的簽章做 sha2_256 雜湊加密，並取到一個vector<u8>
    public fun derive_randomness(drand_sig: vector<u8>): vector<u8> {
        sha2_256(drand_sig)
    }

    // 將 rnd 的前 16 個位元組轉換為 u128 數字並輸出其與輸入 n 的模。
    // 由於 n 為 u64，假設 rnd 是均勻隨機的，則輸出最多有 2^{-64} 偏差。
    public fun safe_selection(n: u64, rnd: &vector<u8>): u64 {
        assert!(vector::length(rnd) >= 16, EInvalidRndLength);
        let mut m: u128 = 0;
        let mut i = 0;
        while (i < 16) {
            m = m << 8;
            let curr_byte = *vector::borrow(rnd, i);
            m = m + (curr_byte as u128);
            i = i + 1;
        };
        let n_128 = (n as u128);
        let module_128  = m % n_128;
        let res = (module_128 as u64);
        res
    }
}

我們可以看到最上方有 drand 的3個常數
GENESIS ( 自 Unix 紀元以來該組開始產生隨機性的時間，以秒為單位)
DRAND_PK ( drand 某個hashkey的分散式公鑰 )
PERIOD ( 多久時間會產生下一輪，以秒為單位 )

drand_lib.move內主要用的hashkey為

52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971

我們可以使用下面這個 api 來查看這個 hashkey 的基本資訊

https://api.drand.sh/52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971/info

{
  "public_key": "83cf0f2896adee7eb8b5f01fcad3912212c437e0073e911fb90022d3e760183c8c4b450b6a0a6c3ac6a5776a2d1064510d1fec758c921cc22b0e17e63aaf4bcb5ed66304de9cf809bd274ca73bab4af5a6e9c76a4bc09e76eae8991ef5ece45a",
  "period": 3,
  "genesis_time": 1692803367,
  "hash": "52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971",
  "groupHash": "f477d5c89f21a17c863a7f937c6a6d15859414d2be09cd448d4279af331c5d3e",
  "schemeID": "bls-unchained-g1-rfc9380",
  "metadata": {
    "beaconID": "quicknet"
  }
}

這次我們主要會用到 3個 方法
verify_drand_signature (驗證 drand 簽章)
derive_randomness (對 drand 的簽章做 sha2_256 雜湊加密)
safe_selection (安全選擇)

## 使用 Drand Lib 方法 簡易智能合約

下方為一個簡易的 使用 Drand 智能合約範例

module sui_drand_demo::sui_drand_demo {

    use sui_drand_demo::drand_lib::{derive_randomness, verify_drand_signature, safe_selection};

    // 獲獎者物件 - Shared Object
    public struct Winner has key, store{
        id: UID,
        winner_index: vector<u64>
    }

    // 初始化
    fun init (ctx: &mut TxContext){
        // 把獲獎者物件變成Shared Object
        transfer::share_object(
            Winner {
                id: object::new(ctx),
                winner_index: vector::empty()
            }
        );
    }

    // 設定 winner
    public entry fun set_winner (
        winner: &mut Winner, // Winner Shared Object
        max_number: u64, // 最大值
        current_round: u64, // drand current round
        drand_sig: vector<u8> // drand signature
    ){
        // 驗證 drand 簽章
        verify_drand_signature(drand_sig, current_round);

        // 取得 drand randomness
        let digest = derive_randomness(drand_sig);
        // 取得 安全性的 隨機數
        let random_index = safe_selection(max_number, &digest);
        // 塞入 winnder_index vector
        winner.winner_index.push_back(random_index);
    }

    // 清除 winner shared object 內的 winner
    public entry fun clear_winner (
        winner: &mut Winner // Winner Shared Object
    ){
        winner.winner_index = vector::empty();
    }
}

## 前端串接

如果還沒建立Dapp的話，可以先參考我的這篇教學
[快速建立 Sui Move Dapp 並實現贊助交易](https://hackmd.io/iqcfxMR0SwmmEKXhnXe-VA?view)

Drand JS Install :
https://drand.love/developer/clients/#js

Drand JS Example :
https://github.com/drand/drand-client#usage

主要要先安裝他的依賴包

npm install drand-client

創建一個新的 DrandRandom.tsx

import { TransactionBlock } from '@mysten/sui.js/transactions';
import {
  fetchBeacon,
  HttpChainClient,
  HttpCachingChain,
} from 'drand-client'

// 獲獎者 Shared Object ID
const winner_shared_object_id = "0x47a5401cf3e63981383ceb49984ac0f7ed04788acc4b76f5051c905adefc0d84";
// 智能合約 Package ID
const contract_package_id = "0xc964346ca241df9e9b9f5a7995cc4ad470a0cc46747bde87a542cd36a9867bd7";
// 智能合約 module 名稱
const contract_module_name = "sui_drand_demo";
// 智能合約 呼叫方法 名稱
const contract_set_winner_method = "set_winner";
const contract_clear_winner_method = "clear_winner";
const winner_count = 5;
const lottery_count = 100;

/**
 * 設定獲獎者資訊
 */
export async function getWinnerInfoTransactionBlock() {

  // 產生一個新的交易區塊
  const txb = new TransactionBlock();

  // hash key
  const chainHash = '52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971'
  // 公鑰
  const publicKey = "83cf0f2896adee7eb8b5f01fcad3912212c437e0073e911fb90022d3e760183c8c4b450b6a0a6c3ac6a5776a2d1064510d1fec758c921cc22b0e17e63aaf4bcb5ed66304de9cf809bd274ca73bab4af5a6e9c76a4bc09e76eae8991ef5ece45a";

  // 選項
  const options = {
    disableBeaconVerification: false, // `true` disables checking of signatures on beacons - faster but insecure!!!
    noCache: false, // `true` disables caching when retrieving beacons for some providers
    chainVerificationParams: { chainHash, publicKey }  // these are optional, but recommended! They are compared for parity against the `/info` output of a given node
  }

  // 使用這個 chain
  const chain = new HttpCachingChain(`https://api.drand.sh/${chainHash}`, options)
  // 得到 client cli
  const client = new HttpChainClient(chain, options)
  // 取得目前的 RandomnessBeacon
  // 其實就跟使用 https://api.drand.sh/52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971/public/latest 一樣
  /*
   {
      "round": 7283409,
      "randomness": "f6f92b1dc4a2e5231573423aa6e7e026afc59e46bddd087e0126377a038682c1",
      "signature": "b58e76a3dc5cb831d681c5d9e02f7fe95b8b42ec1cb3c6640470d08c1f7bf60b63f443297f12a9c24a53ff488b22cc31"
    }
   */
  const theLatestBeacon = await fetchBeacon(client)

  // 取得目前 round
  const drand_round: number = theLatestBeacon.round;

  // 要抽的獲獎者數量
  let run_count = winner_count;

  // 存入 daran round
  let randomRoundArray: number[] = [];

  while (run_count > 0){

    // 隨機抽選 round
    let random_round = Math.floor(Math.random() * drand_round);

    // 如果重複了，則略過
    if (randomRoundArray.includes(random_round)){
      continue
    }

    randomRoundArray.push(random_round);

    run_count = run_count -1;
  }

  for (let round of randomRoundArray){

    // 取得某個round的RandomnessBeacon 物件
    // https://api.drand.sh/52db9ba70e0cc0f6eaf7803dd07447a1f5477735fd3f661792ba94600c84e971/public/123
    /*
     {
        "round": 123,
        "randomness": "fb8f7bc29bf24db51871ec8c79f3a1e4bd0557bc0dfcee9ed1d924e69d1c60dc",
        "signature": "b75c69d0b72a5d906e854e808ba7e2accb1542ac355ae486d591aa9d43765482e26cd02df835d3546d23c4b13e0dfc92"
     } 
     */
    let randomnessBeacon = await client.get(round);
    // signature 16進制字串 轉換成 vector<u8>
    const byteArray = hex16String2Vector(randomnessBeacon.signature);

    let args = [
      // 第1個為 Winner Shared Object Id
      txb.object(winner_shared_object_id),
      // 第2個為 最大值 ex:100
      txb.pure(lottery_count),
      // 第3個為 drand current round
      txb.pure(randomnessBeacon.round),
      // 第4個為 drand signature
      txb.pure(byteArray)
    ]

    // 呼叫智能合約 設定獲獎者
    txb.moveCall({
      // target 要帶入 PageckId::moduleName::methodName
      // ex: 0xc964346ca241df9e9b9f5a7995cc4ad470a0cc46747bde87a542cd36a9867bd7::sui_drand_demo::set_winner
      target: `${contract_package_id}::${contract_module_name}::${contract_set_winner_method}`,
      // 參數
      arguments: args,
    });
  }

  return txb;
}

// 取得 清除獲獎者資訊 交易區塊
export async function getClearWinnerInfoTransactionBlock() {
  // 產生一個新的交易區塊
  const txb = new TransactionBlock();

  let args = [
    // Winner Shared Object Id
    txb.object(winner_shared_object_id),
  ]

  // 呼叫智能合約 清除獲獎者資訊
  txb.moveCall({
    // target 要帶入 PageckId::moduleName::methodName
    // ex: 0xd9326566facfff6e8250ce92b71bf91427cc197e052d0c8a162b6cd7cb9c3e83::sui_drand_demo::clear_winner
    target: `${contract_package_id}::${contract_module_name}::${contract_clear_winner_method}`,
    // 參數
    arguments: args,
  });

  return txb;
}

function hex16String2Vector(str: string) {
  // 定義一個空數組來存儲結果
  let byteArray = [];

  // 將十六進制字符串每兩個字符分割並將其轉換為十進制數字，然後添加到數組中
  for (let i = 0; i < str.length; i += 2) {
    byteArray.push(parseInt(str.slice(i, i + 2), 16));
  }

  return byteArray;
}

import { useCurrentAccount, useSignTransactionBlock, useSignAndExecuteTransactionBlock } from "@mysten/dapp-kit";
import { Button, Container, Flex, Heading, Text } from "@radix-ui/themes";
import { OwnedObjects } from "./OwnedObjects";
import { getWinnerInfoTransactionBlock, getClearWinnerInfoTransactionBlock } from "./DrandRandom";

export function WalletStatus() {
  const account = useCurrentAccount();
  const { mutate: signTransactionBlock } = useSignTransactionBlock();
  const { mutate: signAndExecuteTransactionBlock } = useSignAndExecuteTransactionBlock();
  return (
    <Container my="2">
      <Heading mb="2">Wallet Status</Heading>
      {account ? (
        <Flex direction="column">
          <Text>Wallet connected</Text>
          <Text>Address: {account.address}</Text>

          <Button
            onClick={() => {
              getWinnerInfoTransactionBlock().then(txb => {
                signAndExecuteTransactionBlock(
		    {
		        transactionBlock: txb
		    },
		    {
		    onSuccess: (successResult) => {
                        console.log('executed transaction block success', successResult);
		    },
                   onError: (errorResult) => {
                        console.log('executed transaction block error', errorResult);
                   },
		  },
		);
              });
            }}
          >
            Set Winner By Drand Random
          </Button>

          <Button
            onClick={() => {
              getClearWinnerInfoTransactionBlock().then(txb => {
                signAndExecuteTransactionBlock(
		    {
		        transactionBlock: txb
		    },
		    {
		    onSuccess: (successResult) => {
                        console.log('executed transaction block success', successResult);
		    },
                   onError: (errorResult) => {
                        console.log('executed transaction block error', errorResult);
                   },
		  },
		);
              });
            }}
          >
            Clear Winner By Drand Random
          </Button>

        </Flex>
      ) : (
        <Text>Wallet not connected</Text>
      )}
      <OwnedObjects />
    </Container>
  );
}

## 驗證結果

目前 Winner Shared Object 是沒有任何獲獎者的
https://suiscan.xyz/devnet/object/0x47a5401cf3e63981383ceb49984ac0f7ed04788acc4b76f5051c905adefc0d84

執行結果 - 抽5個人


清空獲獎者資訊