How to solve cygwin's problem of setting ssh in Windows8.1

Cygwin sets ssh in Windows 8.1 to solve the problem. In order to directly use the Linux environment and hadoop development on Windows, cygwin is installed and ssh password-less login is set. However, if the ssh-keygen file is copied to authorised_keys, the following error occurs during logon: Permissions 0660 for '/home /***/. ssh/id_rsa 'are too open. it is required that your private key files are NOT accessible by others. it means that the permission of the key file is too loose, so I want to narrow down the permission, but no matter how chmod does not receive the rw permission of group and other. After some searches, I found that it was a problem I encountered in my work on AIX N years ago, that is, the file group does not exist or the group in cygwin is displayed as None. The solution is to assign the Group first, and then assign the chgrp Users to a common user group, and then change the permissions.