encryptor.js

'use strict';

const assert = require('assert');
const crypto = require('crypto');
const util = require('./util');

class Encryptor {
  constructor() {
    this.algorithm = '';
  }

  /**
   * 设置加密算法
   * @param {String} algorithm 算法
   */
  setAlgorithm(algorithm) {
    assert(!util.isEmpty(algorithm), `Algorithm cannot be set empty: ${algorithm}`);
    this.algorithm = algorithm;
  }

  /**
   * 设置偏移量
   * @param {String} password 秘钥
   * @param {String} salt 盐
   * @param {String} iterations 偏移量
   */
  KDF (password, salt, iterations) {
    const pwd = Buffer.from(password, 'utf-8');
    let key = Buffer.concat([pwd, salt]);
    for (let i = 0; i < iterations; i++) {
      key = crypto.createHash('md5').update(key).digest();
    }
    return key;
  }

  /**
   * 获取秘钥和盐
   * @param {String} password 秘钥
   * @param {String} salt 盐
   * @param {String} iterations 偏移量
   */
  getKeyIV(password, salt, iterations) {
    const key = this.KDF(password, salt, iterations);
    const keybuf = Buffer.from(key, 'binary').slice(0, 8);
    const ivbuf = Buffer.from(key, 'binary').slice(8, 16);
    return [ keybuf, ivbuf ];
  }

  /**
   * 加密
   * @param {String} payload 需要加密的文本
   * @param {String} password 秘钥
   * @param {String} salt 盐
   * @param {String} iterations 偏移量
   */
  encrypt(payload, password, salt, iterations) {
    const kiv = this.getKeyIV(password, salt, iterations);
    const cipher = crypto.createCipheriv('des', kiv[0], kiv[1]);

    const encrypted = [];
    encrypted.push(cipher.update(payload, 'utf-8', 'hex'));
    encrypted.push(cipher.final('hex'));

    const out = Buffer.from(encrypted.join(''), 'hex');
    const result =  Buffer.alloc(out.length + salt.length);

    salt.copy(result, 0, 0, salt.length);
    out.copy(result, salt.length, 0, out.length);

    return result.toString('base64');
  }

  /**
   * 解密
   * @param {String} payload 需要解密的文本
   * @param {String} password 秘钥
   * @param {String} iterations 偏移量
   */
  decrypt(payload, password, iterations) {
    const encryptedMessage = Buffer.from(payload, 'base64');
    const decrypted = [];
    const saltStart = 0;
    const saltSizeBytes = 8;

    const saltSize = saltSizeBytes < encryptedMessage.length ? saltSizeBytes : encryptedMessage.length;
    const encMesKernelStart = saltSizeBytes < encryptedMessage.length ? saltSizeBytes : encryptedMessage.length;
    const encMesKernelSize = saltSizeBytes < encryptedMessage.length ? (encryptedMessage.length - saltSizeBytes) : 0;

    const salt = Buffer.alloc(saltSize);
    const encryptedMessageKernel = Buffer.alloc(encMesKernelSize);

    encryptedMessage.copy(salt, 0, saltStart, saltSize);
    encryptedMessage.copy(encryptedMessageKernel, 0, encMesKernelStart, encryptedMessage.length);

    const kiv = this.getKeyIV(password, salt, iterations);
    const decipher = crypto.createDecipheriv('des', kiv[0], kiv[1]);

    decrypted.push(decipher.update(encryptedMessageKernel));
    decrypted.push(decipher.final());

    return decrypted.join('');
  }
}

module.exports = Encryptor;