From: wollman@bimajority.org   
      
   In article <0fc4b088-b15a-8c93-9995-613645f44451@billhorne.com>,   
   Bill Horne   wrote:   
      
   >Why, I wonder, has this particular phone started demanding to go home   
   >to suck juice from it's mama's tap? Why, I wonder, does this happen   
   >after five years of fault-free service while charging from a USB cube?   
   >Could it be that Verizon has decided I've been away from their store   
   >too long?   
      
   This is going to blow your mind: every USB-C plug has an embedded   
   microprocessor, and with it an X.509 digital certificate that it uses   
   to authenticate itself to the device it's plugged into.  USB-PD ("USB   
   Power Delivery") uses this mechanism to allow (among other things) the   
   device being powered to negotiate with the dock, cord, and power   
   supply how much current it can draw.  When you're drawing 95 watts at   
   5 volts, that's a lot of amps over that tiny little connector and   
   cable.   
      
   The authentication mechanism was allegedly introduced to allow devices   
   to warn users about nonstandard, counterfeit, or even dangerous   
   chargers.  Of course it's impractical for the USB Implementers Forum   
   to actually enforce this by revoking counterfeiters' certificates, and   
   many rather darker explanations have been suggested.   
      
   -GAWollman   
      
   --   
   Garrett A. Wollman    | "Act to avoid constraining the future; if you can,   
   wollman@bimajority.org| act to remove constraint from the future.  This is   
   Opinions not shared by| a thing you can do, are able to do, to do together."   
   my employers.         | - Graydon Saunders, _A Succession of Bad Days_ (2015)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)