site: support multiple transforms

[secnet.git] / NOTES

diff --git a/NOTES b/NOTES
index 33c010e47d18100f2edc5b53bd8d63afbfdd4f13..7ead923be70060d708e287b24d63a7dc2093e39a 100644 (file)
--- a/NOTES
+++ b/NOTES
@@ -174,8 +174,9 @@ quite stable so the feature doesn't gain us much.
 
 Definitions:
 
 
 Definitions:
 

-A is the originating gateway machine
-B is the destination gateway machine
+A is the originating gateway machine name
+B is the destination gateway machine name
+A+ and B+ are the names with optional additional data, see below

 PK_A is the public RSA key of A
 PK_B is the public RSA key of B
 PK_A^-1 is the private RSA key of A
 PK_A is the public RSA key of A
 PK_B is the public RSA key of B
 PK_A^-1 is the private RSA key of A


@@ -193,18 +194,45 @@ i? is appropriate index for receiver
 Note that 'i' may be re-used from one session to the next, whereas 'n'
 is always fresh.
 
 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.
+The optional additional data after the sender's name consists of some
+initial subset of the following list of items:
+ * A 32-bit integer with a set of capability flags, representing the
+   abilities of the sender.
+ * More data which is yet to be defined and which must be ignored
+   by receivers.
+The optional additional data after the receiver's name is not
+currently used.  If any is seen, it must be ignored.
+
+Capability flag bits must be in one the following two categories:
+
+1. Early capability flags must be advertised in MSG1 or MSG2, as
+   applicable.  If MSG3 or MSG4 advertise any "early" capability bits,
+   MSG1 or MSG3 (as applicable) must have advertised them too.  Sadly,
+   advertising an early capability flag will produce MSG1s which are
+   not understood by versions of secnet which predate the capability
+   mechanism.
+
+2. Late capability flags are advertised in MSG2 or MSG3, as
+   applicable.  They may also appear in MSG1, but this is not
+   guaranteed.  MSG4 must advertise the same set as MSG2.
+
+No capability flags are currently defined.  Unknown capability flags
+should be treated as late ones.
+

 
 Messages:
 
 
 Messages:
 

-1) A->B: *,iA,msg1,A,B,nA
+1) A->B: *,iA,msg1,A+,B+,nA
+
+i* must be encoded as 0.  (However, it is permitted for a site to use
+zero as its "index" for another site.)

 
 

-2) B->A: iA,iB,msg2,B,A,nB,nA
+2) B->A: iA,iB,msg2,B+,A+,nB,nA

 
 (The order of B and A reverses in alternate messages so that the same
 code can be used to construct them...)
 
 
 (The order of B and A reverses in alternate messages so that the same
 code can be used to construct them...)
 

-3) A->B: {iB,iA,msg3,A,B,nA,nB,g^x mod m}_PK_A^-1
+3) A->B: {iB,iA,msg3,A+,B+,[chosen-transform],nA,nB,g^x mod m}_PK_A^-1

 
 If message 1 was a replay then A will not generate message 3, because
 it doesn't recognise nA.
 
 If message 1 was a replay then A will not generate message 3, because
 it doesn't recognise nA.


@@ -212,7 +240,7 @@ it doesn't recognise nA.
 If message 2 was from an attacker then B will not generate message 4,
 because it doesn't recognise nB.
 
 If message 2 was from an attacker then B will not generate message 4,
 because it doesn't recognise nB.
 

-4) B->A: {iA,iB,msg4,B,A,nB,nA,g^y mod m}_PK_B^-1
+4) B->A: {iA,iB,msg4,B+,A+,nB,nA,g^y mod m}_PK_B^-1

 
 At this point, A and B share a key, k. B must keep retransmitting
 message 4 until it receives a packet encrypted using key k.
 
 At this point, A and B share a key, k. B must keep retransmitting
 message 4 until it receives a packet encrypted using key k.