updated protocol design to reflect ROS recommendations

1 files changed, 6 insertions, 3 deletions

diff --git a/ecp/doc/protocol.md b/ecp/doc/protocol.md
index e395e96..a386c21 100644
--- a/ecp/doc/protocol.md
+++ b/ecp/doc/protocol.md
@@ -20,7 +20,7 @@ Short-term keys have "parity" property. Initial key (server's first key upon sta
 
 | Client -> server                              | Server -> client
 | ---                                           | ---
-| Init request packet:<br>  `(I,C',N,Box[INIT_REQ message](C'->S))`     ||
+| Init request packet:<br>  `(I,C',0,N,Box[INIT_REQ message](C'->S))`   ||
 | | Init reply packet:<br>  `(I,N,Box[INIT_REP message](S->C'))`
 | Open request packet:<br>  `(I,C',K,N,Box[OPEN_REQ message](C'->S'))`  ||
 | | Open reply packet:<br>  `(I,C',N,Box[OPEN_REP message](S'->C'))`
@@ -37,6 +37,7 @@ Where:
   - S' is server's short-term public key (32 bytes);
   - S is server's long-term public key (32 bytes);
   - N is nonce (64-bit integer in big endian form);
+  - 0 is zero zero-padding (64 bytes: all zero);
   - K is a cookie (28 bytes) &mdash; see cookie in open request message below;
   - `Box[X](C->S)` is a cryptographic box, encrypting and authenticating X from the public key C to the public key S.
 
@@ -81,7 +82,7 @@ Message format is (MT,MD[,MT,MD,...]) where:
 ###Init request message
 
   - Message type is `INIT_REQ`;
-  - Message data is null.
+  - Message data is 64 bytes: all zero.
  
 ###Init reply message
 
@@ -98,6 +99,7 @@ Message format is (MT,MD[,MT,MD,...]) where:
 
 K &mdash; cookie (present in packet header) is constructed by concatenating nonce and authentication tag from previously received init reply packet/message. 
 Server may reject cookies with nonces that are too distant from current init reply nonce counter, thus preventing replay attack using captured open request packets.
+Purpose of vouch subpacket is to authenticate client towards the server (optional).
 
   - Message type is `OPEN_REQ`;
   - Message data is (CT,VP[,V]) where:
@@ -106,10 +108,11 @@ Server may reject cookies with nonces that are too distant from current init rep
       - b10000010: VLINK connection (TBD);
       - b0xxxxxxx: application specific;
     - VP is vouch present (1 byte): 1 if vouch subpacket is present, 0 otherwise;
-    - V  is vouch subpacket `(C,N,Box[C'](C->S))` where:
+    - V  is vouch subpacket `(C,N,Box[C',S'](C->S))` where:
       - C  is client's long-term public key (32 bytes);
       - N  is nonce (8 bytes) &mdash; 96-bit AEAD nonce is constructed by prepending ASCII "VBOX" to N;
       - C' is client's short-term public key (32 bytes).
+      - S' is server's short-term public key (32 bytes).
 
 ###Open reply message