stun

commit c8e17fa947a17fbedfada5b52639d340e8843579
parent 0ca549361445f8f982eb4bdb18f90b1c3ff8c669
Author: sin <sin@2f30.org>
Date:   Thu, 31 Mar 2016 19:01:27 +0100

rework design comment

Diffstat:
M
stun.c
 | 
30
+++++++++++++++++-------------

1 file changed, 17 insertions(+), 13 deletions(-)
diff --git a/stun.c b/stun.c
@@ -2,12 +2,19 @@
  * Design overview:
  *
  * stun implements a point to point encrypted tunnel.  It supports
- * both layer 2 (TAP) and layer 3 (TUN) tunnels.  At the moment, the
- * only supported transport is TCP.
+ * layer 2 (TAP) and layer 3 (TUN) tunnels.  TCP is the only supported
+ * transport.
  *
- * stun can be started either as a server or a client.  There can only be
- * a single client connected to the server at any time.  When a client connects
- * there is a mutual challenge-response phase as shown below:
+ * All communication is encrypted using a pre-shared symmetric key.
+ * aes-256-gcm was chosen because it is fast and does authentication.
+ * The key is derived with PBKDF2.
+ *
+ * stun is a client-server design.  There can only be a single client
+ * connected to the server at any time.  Routing between clients is handled
+ * by the networking stack on the server side.
+ *
+ * When a client connects there is a mutual challenge-response phase
+ * as shown below:
  *
  * t0: server challenges client
  * t1: client responds to server's challenge
@@ -16,16 +23,13 @@
  *
  * The challenge-response algorithm is as follows:
  *
- * The challenge is a randomly generated 64-bit integer encrypted with a
- * pre-shared symmetric key and sent to the receiver.
+ * The challenge is a randomly generated 64-bit integer encrypted
+ * with the pre-shared key and sent to the receiver.
  * The receiver decrypts it, adds 1, encrypts it and sends it back to
- * the sender.  The sender verifies that the correct response was received.
- *
- * All communication is encrypted using a pre-shared symmetric key.  The cipher
- * used is aes-256-gcm and the key is derived with PBKDF2.
+ * the sender.  The sender verifies the response.
+ * This algorithm is the same as what Kerberos uses for authentication.
  *
- * All tunneled traffic is encapsulated inside the TCP payload.
- * The packet format is shown below:
+ * The stun packet format is shown below:
  *
  * [TAG] [IV] [PAYLOAD LENGTH] [PAYLOAD]
  *