X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?a=blobdiff_plain;f=NOTES;h=6a245ec3bc3bb458ab1df49473b59cac1cd6d4d8;hb=1e80c220a810380ae8b5a155e2bd6937c951c83c;hp=485443b1c13320836b6b1d7c0acd9a25e13dea1b;hpb=794f2398b8fe84bf398bb10d6eeca6fe6737f65f;p=secnet.git

diff --git a/NOTES b/NOTES
index 485443b..6a245ec 100644
--- a/NOTES
+++ b/NOTES
@@ -60,6 +60,17 @@ explicit option. NB packets may be routed if the source OR the
 destination is marked as allowing routing [otherwise packets couldn't
 get back from eg. chiark to a laptop at greenend]).
 
+[the even newer plan]
+
+secnet sites are configured to grant access to particular IP address
+ranges to the holder of a particular public key.  The key can certify
+other keys, which will then be permitted to use a subrange of the IP
+address range of the certifying key.
+
+This means that secnet won't know in advance (i.e. at configuration
+time) how many tunnels it might be required to support, so we have to
+be able to create them (and routes, and so on) on the fly.
+
 ** VPN-level configuration
 
 At a high level we just want to be able to indicate which groups of
@@ -182,6 +193,11 @@ i? is appropriate index for receiver
 Note that 'i' may be re-used from one session to the next, whereas 'n'
 is always fresh.
 
+The protocol version selection stuff is not yet implemented: I'm not
+yet convinced it's a good idea.  Instead, the initiator could try
+using its preferred protocol (which starts with a different magic
+number) and fall back if there's no reply.
+
 Messages:
 
 1) A->B: *,iA,msg1,A,B,protorange-A,nA
@@ -231,26 +247,33 @@ retransmit or confirm reception. It is suggested that this message be
 sent when a key times out, or the tunnel is forcibly terminated for
 some reason.
 
-8) i?,i?,NAK (encoded as zero)
+**** Protocol sub-goal 3: send a packet
+
+8) i?,i?,msg0,(send-packet/msg9,packet)_k
+
+Some messages may take a long time to prepare (software modexp on slow
+machines); this is a "please wait" message to indicate that a message
+is in preparation.
+
+**** Other messages
+
+9) i?,i?,NAK (NAK is encoded as zero)
 
 If the link-layer can't work out what to do with a packet (session has
-gone away, etc.) it can transmit a NAK back to the sender.  The sender
-can then try to verify whether the session is alive by sending ping
-packets, and forget the key if it isn't. Potential denial-of-service
-if the attacker can stop the ping/pong packets getting through (the
-key will be forgotten and another key setup must take place), but if
-they can delete packets then we've lost anyway...
+gone away, etc.) it can transmit a NAK back to the sender.
 
-The attacker can of course forge NAKs since they aren't protected. But
-if they can only forge packets then they won't be able to stop the
-ping/pong working. Trust in NAKs can be rate-limited...
+This can alert the sender to the situation where the sender has a key
+but the receiver doesn't (eg because it has been restarted).  The
+sender, on receiving the NAK, will try to initiate a key exchange.
 
-Alternative idea (which is actually implemented): if you receive a
-packet you can't decode, because there's no key established, then
-initiate key setup...
+Forged (or overly delayed) NAKs can cause wasted resources due to
+spurious key exchange initiation, but there is a limit on this because
+of the key exchange retry timeout.
 
-Keepalives are probably a good idea.
+10) i?,i?,msg8,A,B,nA,nB,msg?
 
-**** Protocol sub-goal 3: send a packet
+This is an obsolete form of NAK packet which is not sent by any even
+vaguely recent version of secnet.  (In fact, there is no evidence in
+the git history of it ever being sent.)
 
-9) i?,i?,msg0,(send-packet/msg9,packet)_k
+This message number is reserved.