:: Set Variable ::
set key="C:\Path\to\key"

:: Remove Inheritance ::
cmd /c icacls %key% /c /t /inheritance:d

:: Set Ownership to Owner ::
cmd /c icacls %key% /c /t /grant %username%:F

:: Remove All Users, except for Owner ::
cmd /c icacls %key%  /c /t /remove Administrator BUILTIN\Administrators BUILTIN Everyone System Users

CLI:

  :: Set Variable ::
  set key="C:\Path\to\key"

  :: Remove Inheritance ::
  cmd /c icacls %key% /c /t /inheritance:d

  :: Set Ownership to Owner ::
  cmd /c icacls %key% /c /t /grant %username%:F

  :: Remove All Users, except for Owner ::
  cmd /c icacls %key%  /c /t /remove Administrator BUILTIN\Administrators BUILTIN Everyone System Users

  :: Verify ::
  cmd /c icacls %key%

   # Set Variables

     # Key  
       key="/path/to/key"

     # User:
       user="$(echo $USER)"

   # Set Ownership
     # This assumes user's name is also user's group name
       chown $user:$user $key

   # Set Access Rights
     chmod 0600 $key

CLI

  # Set Variables

    # Key  
      key="/path/to/key"

    # User:
      user="$(echo $USER)"

  # Set Ownership
    # This assumes user's name is also user's group name
      chown $user:$user $key

  # Set Access Rights
    chmod 0600 $key

  # Verify
  ls -l $key