feat: add decrypt function into ether ext

[Sotatek-HauTran3]

Additional decrypt function into ether-ext
Keystore v4 format support example

• Parse multisig or rolebase key that includes 3 keys into multiple json for each key
• Decrypt the keys
• Took the code from Ethers to bypass the address comparison part.
• Return Wallet instance

[kjeom]

@Sotatek-HauTran3 Could you add some description for this PR?

[blukat29]

I found a way to make it much simpler by using the existing ethers.js decryptKeystoreSync function.
Async versions can be constructed similarly.

It works because decryptKeystoreSync accepts a JSON object without the .address field, where the address check is skipped.

@Sotatek-HauTran3 If this method makes sense to you, can you update the current pull request?

ethers/keystore.ts:

import * as _ from "lodash";
import { decryptKeystoreSync } from "@ethersproject/json-wallets";
import { Bytes } from "@ethersproject/bytes";

// Modified from KeystoreAccount at @ethersproject/json-wallets/src.ts/keystore.ts
interface KeystoreAccountList {
  address: string;
  privateKeys: string[];
}

function decryptKey(crypto: any, password: Bytes | string): string {
  const datav3 = {
    version: 3,
    crypto: crypto,
  }
  const jsonv3 = JSON.stringify(datav3);
  const ka = decryptKeystoreSync(jsonv3, password);
  return ka.privateKey;
}

// Decrypts the Klaytn KIP-3 (https://github.com/klaytn/kips/blob/main/KIPs/kip-3.md) JSON wallet.
//
// KIP-3 v4 wallet comes in one of three shapes:
// - An array of one key = [key]
// - An array of multiple keys = [key, key, key]
// - A nested array of keys = [[key], [], [key, key]]
//
// Regardless of how they are organized, each encrytped key object is decrypted
// then returned in a flattend array of private keys.
function decryptKeystoreV4(json: string, password: Bytes | string): KeystoreAccountList {
  const data = JSON.parse(json);
  let privateKeys: string[] = [];

  if (!_.has(data, "keyring")) {
    throw new Error("invalid JSON wallet v4 (KIP-3)");
  }
  if (!_.isArray(data.keyring)) {
    throw new Error("invalid JSON wallet v4 (KIP-3)");
  }

  _.each(data.keyring, (keyOrKeys: any) => {
    if (!_.isArray(keyOrKeys)) {
      let key: any = keyOrKeys;
      privateKeys.push(decryptKey(key, password));
    } else {
      let keys: any[] = keyOrKeys;
      _.each(keys, (key: any) => {
        privateKeys.push(decryptKey(key, password));
      });
    }
  });

  return {
    address: _.toString(data.address),
    privateKeys: privateKeys,
  };
}

// Decrypts a JSON keystore wallet and returns the account details containing
// the account address and the list of private keys.
// It accepts a Crowdsale wallet, V3 keystore, and KIP-3 V4 keystore wallets.
export function decryptKeystoreListSync(json: string, password: Bytes | string): KeystoreAccountList {
  const data = JSON.parse(json);
  const version = parseInt(data.version);

  // decryptKeystoreV4 handles v4 (KIP-3) wallets.
  if (version == 4) {
    return decryptKeystoreV4(json, password);
  }

  // decryptKeystoreSync handles v3 and Crowdsale wallets.
  const ka = decryptKeystoreSync(json, password);
  return {
    address: ka.address,
    privateKeys: [ka.privateKey],
  };
}

ethers/signer.ts:

import { decryptKeystoreListSync } from "./keystore";

export class Wallet extends EthersWallet {
  // ...
  
  static fromEncryptedJsonSync(json: string, password: string | Bytes): Wallet {
    const { address, privateKeys } = decryptKeystoreListSync(json, password);
    return new Wallet(address, privateKeys[0]);
  }

  static fromEncryptedJsonListSync(json: string, password: string | Bytes): Wallet[] {
    const { address, privateKeys } = decryptKeystoreListSync(json, password);
    return _.map(privateKeys, (privateKey) => new Wallet(address, privateKey));
  }
}
``

[kjeom]

@Sotatek-HauTran3 LGTM.
I think it's better to check the result more detail in the unit test. let's leave it another task.