使用Google Script散列并取消哈希键(Hash and un-hash a key with Google Script)

 我需要散列一个键，并且我发现这个方法由Google Script提供： https : //developers.google.com/apps-script/reference/utilities/utilities#computeHmacSha256Signature%28String,String%29 
 
 但是，我怎样才能用这种方法解密密钥？ 
 
 这是我试图做的事情： 
 
  var my_key = "g1w9625bf43bfd91s6c2095c1w160699a59m72t"
  var hash = Utilities.computeHmacSha256Signature("this", my_key);

  var un_hash = Utilities.base64Decode(hash);
 
 散列函数有效，但un_hash返回我Could not decode string 。 
 
 我感谢任何帮助。 

I need to hash a key and I found this method provided by Google Script: https://developers.google.com/apps-script/reference/utilities/utilities#computeHmacSha256Signature%28String,String%29
 
But how can I un-hash the key computed with that method?
 
Here is what I've tried to do:
 
  var my_key = "g1w9625bf43bfd91s6c2095c1w160699a59m72t"
  var hash = Utilities.computeHmacSha256Signature("this", my_key);

  var un_hash = Utilities.base64Decode(hash);
 
The hash function works, but un_hash returns me Could not decode string.
 
I appreciate any help.

原文：https://stackoverflow.com/questions/39465329