readme: better details on psk

README.md

@@ -10,6 +10,14 @@ interface to subscribe to events.
 
 *WARNING: This is not ready for prime time!*
 
+The dishwasher has a local HTTPS port open (and the dryer
+seems to have unencrypted HTTP).  Attempting to connect to
+the HTTPS port with `curl` results in a cryptic protocol error
+due to the non-standard cipher selection, `ECDHE-PSK-CHACHA20-POLY1305`.
+PSK also requires that both sides agree on a symetric key,
+so it is necessary to figure out what that key is before any
+further progress can be made.
+
 
 ## Finding the PSK
 
@@ -19,14 +27,18 @@ You will need to set the dishwasher to "`Local network only`"
 in the setup application so that your phone will connect
 directly to it, rather than going through the cloud services.
 
-You'll also need to find the PSK for your devices with a rooted
-Android phone and the `find-psk.frida` script for Frida.
+You'll also need a rooted Android phone running `frida-server`
+and the `find-psk.frida` script.  This will hook the callback
+from the OpenSSL library `hcp::client_psk_callback` that is called
+when OpenSSL has made a connection and now needs to establish
+the PSK.
 
 ```
 frida --no-pause -f com.bshg.homeconnect.android.release -U -l find-psk.frida
 ```
 
-It should print a message like:
+It should start the Home Connect application and eventually
+print a message like:
 
 ```
 psk callback hint 'HCCOM_Local_App'
@@ -36,7 +48,7 @@ psk 32 0x6ee63fb2f0
 00000010  73 f9 2e 01 fc d8 26 80 49 89 4c 19 d7 2e cd cb  s.....&.I.L.....
 ```
 
-Which gives you the 32-byte PSK value.
+Which gives you the 32-byte PSK value to copy into the `hcpy` program.
 
 ## SSL logging
 
@@ -63,3 +75,6 @@ RX: {'sID': 2354590730, 'msgID': 3182729968, 'resource': '/ci/services', 'versio
 RX: {'sID': 2354590730, 'msgID': 3182729969, 'resource': '/iz/info', 'version': 1, 'action': 'RESPONSE', 'data': [{'deviceID': '....', 'eNumber': 'SX65EX56CN/11', 'brand': 'SIEMENS', 'vib': 'SX65EX56CN', 'mac': '....', 'haVersion': '1.4', 'swVersion': '3.2.10.20200911163726', 'hwVersion': '2.0.0.2', 'deviceType': 'Dishwasher', 'deviceInfo': '', 'customerIndex': '11', 'serialNumber': '....', 'fdString': '0201', 'shipSki': '....'}]}
 ```
 
+There are other things that can be hooked in the application
+to get the mappings of the `uid` to actual menu settings and
+XML files of the configuratio parameters.  TODO: document this.