Make download available after purchase of a physical good I am running a UC Shop with Drupal which sells CDs and LPs and most of the time everything works like it should do. 

Now I want to improve the service for our customers. For this reason, I want to give them the chance to download a zip-file with mp3s of every CD or LP they bought. 

After we received the payment (so we set the order status to "payment received") the customers should get an encrypted link via mail or alternatively have a download button in their profile or so. It's no problem to make that possible only for authenticated users.

Any suggestions?
Sounds like a possible job for the Commerce File module


  This module is an extension of Drupal Commerce that provides the ability to sell file access.
  
  
  Ability to limit access to the file with limit settings
  Default limits: duration, download count, IP address count
  Limit default values can be inherited at the product level such that the product always uses the current default value
  After purchase of a file, limits are statically recorded to the line item so that they do not reflect any changes to the product's file limits.
  A user's limits reflect changes to an order, even after order is completed.
  


You can add a file field to your product entity type, and use the above module + rules to manage access to the file references by granting access licences. The licences are as liberal or as strict as you want to make them, so should be useful for your situation.

I've been using this module for a while and it works great