node js 小程序解密失败 乱码 Illegal Buffer

node js解密代码 微信官方地址

• 官方的解释
  

前端代码

• 使用的是uni
• 一定要尽量保证uni.login和获取用户信息wx.getWeRunData api一起请求,尽量避免在后台储存session_key

uni.getProvider({
						service: 'oauth',
						success: function(res) {
							console.log(res.provider)
							if (~res.provider.indexOf('weixin')) {
								uni.login({
									success(res) {
										if (res.code) {
											code = res.code;

											// #ifdef MP-WEIXIN
											wx.getWeRunData({
												async success(res) {
													res.code = code;
													const step = await getStep(res);//调用后台接口进行解密
													
												}
											})
											// #endif
										} else {
											console.log('登录失败！' + res.errMsg)
										}
									}
								})
							}
						}
					});

后台代码

var crypto = require('crypto')//需要安装插件

function WXBizDataCrypt(appId, sessionKey) {
  this.appId = appId
  this.sessionKey = sessionKey
}

WXBizDataCrypt.prototype.decryptData = function (encryptedData, iv) {
  // base64 decode
  var sessionKey = new Buffer(this.sessionKey, 'base64')
  encryptedData = new Buffer(encryptedData, 'base64')
  iv = new Buffer(iv, 'base64')

  try {
     // 解密
    var decipher = crypto.createDecipheriv('aes-128-cbc', sessionKey, iv)
    // 设置自动 padding 为 true，删除填充补位
    decipher.setAutoPadding(true)
    var decoded = decipher.update(encryptedData, 'binary', 'utf8')
    decoded += decipher.final('utf8')
    
    decoded = JSON.parse(decoded)

  } catch (err) {
    throw new Error('Illegal Buffer')
  }

  if (decoded.watermark.appid !== this.appId) {
    throw new Error('Illegal Buffer')
  }

  return decoded
}

module.exports = WXBizDataCrypt