@polkadot/keyring/pair/decode.js

// Copyright 2017-2022 @polkadot/keyring authors & contributors
// SPDX-License-Identifier: Apache-2.0
import { u8aEq } from '@polkadot/util';
import { jsonDecryptData } from '@polkadot/util-crypto';
import { PKCS8_DIVIDER, PKCS8_HEADER, PUB_LENGTH, SEC_LENGTH, SEED_LENGTH } from "./defaults.js";
const SEED_OFFSET = PKCS8_HEADER.length;
export function decodePair(passphrase, encrypted, _encType) {
  const encType = Array.isArray(_encType) || _encType === undefined ? _encType : [_encType];
  const decrypted = jsonDecryptData(encrypted, passphrase, encType);
  const header = decrypted.subarray(0, PKCS8_HEADER.length);

  if (!u8aEq(header, PKCS8_HEADER)) {
    throw new Error('Invalid Pkcs8 header found in body');
  }

  let secretKey = decrypted.subarray(SEED_OFFSET, SEED_OFFSET + SEC_LENGTH);
  let divOffset = SEED_OFFSET + SEC_LENGTH;
  let divider = decrypted.subarray(divOffset, divOffset + PKCS8_DIVIDER.length); // old-style, we have the seed here

  if (!u8aEq(divider, PKCS8_DIVIDER)) {
    divOffset = SEED_OFFSET + SEED_LENGTH;
    secretKey = decrypted.subarray(SEED_OFFSET, divOffset);
    divider = decrypted.subarray(divOffset, divOffset + PKCS8_DIVIDER.length);

    if (!u8aEq(divider, PKCS8_DIVIDER)) {
      throw new Error('Invalid Pkcs8 divider found in body');
    }
  }

  const pubOffset = divOffset + PKCS8_DIVIDER.length;
  const publicKey = decrypted.subarray(pubOffset, pubOffset + PUB_LENGTH);
  return {
    publicKey,
    secretKey
  };
}