Subject: [ippm] Re: owamp protocol

From: stanislav shalunov <[email-masked]>
Date: 01 Jul 2004 12:12:07 -0400

Roman Lapacz <[email-masked]> writes:

> finally, I understand section 5.1 (it took me a while :). I think (maybe
> I'm wrong) there should be exact information in the text that there are
> the same bindings 'username-secret_key' stored on both sides (client ad
> server) before the protocol starts. Maybe this could clarify the
> description of secured session establishing.

Roman,

I see what the difficulty was.

I think I made clarifications to this section by inserting the
attached text.  Let me know if it makes the document easier to
understand for you.

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

This message is designed to be viewed with 0.06479891g of NaCl.

@@ -469,6 +469,13 @@
 Block Chaining (CBC). Encryption MUST be performed using an
 Initialization Vector (IV) of zero and a key value that is the shared
 secret associated with Username.
+(Both the server and the client use the same mappings from user names
+to secret keys; the server, being prepared to conduct sessions with
+more than one client, uses user names to choose the appropriate secret
+key; a client would typically have different secret keys for different
+servers.  The situation is analogous to that of passwords, except that
+secret keys, rather than being the typical low-entropy passwords, are
+suitable for use as AES keys.)
 The shared secret will typically be provided as a passphrase; in this
 case, the MD5 sum [RFC1321] of the passphrase (without possible
 newline character(s) at the end of the passphrase) SHOULD be used as a
@@ -476,6 +483,14 @@
 passphrase also SHOULD NOT contain newlines in the middle).
 
 Session-key and Client-IV are generated randomly by the client.
+Session-key MUST be generated with sufficient entropy not to reduce
+the security of the underlying cipher.  Client-IV merely needs to be
+unique (i.e., it MUST never be repeated for different sessions using
+the same secret key; a simple way to achieve that without the use of
+cumbersome state is to generate the Client-IV strings using a
+cryptographically secure pseudo-random number source: if this is done,
+the first repetition is unlikely to occur before 2^64 sessions with
+the same secret key are conducted).

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