Subject: [Hipsec] HIP Base draft - ECHO signed/unsigned issue

From: Petri Jokela <[email-masked]>
Date: Fri, 25 May 2007 14:59:14 +0300

Hello everybody,

During IESG evaluation, the following comment (among others) was given
by Sam:

"In a discussion with secdir, Pekka N said that one of the motivations
behind the unsigned echo and echo response is for middleboxes.  I
don't think this is well defined enough to be interoperable as only
one of these parameters can exist in a packet.  What happens if a
middle box wants to add one of these and cannot do so because it
already exists?"

The document seems to require some modifications.

Currently the definition says that there can be either one signed or one
unsigned echo request. To support (multiple) middle-boxes, this should
be modified so that the packet can contain zero or more unsigned echo
requests, even if there is already one signed echo request in the
packet.  Is there any problems with multiple echo requests in one packet
arriving at the HIP host? It just has to respond to all of them.

Checksum calculations and signatures should be handled correctly using
the current HIP base definitions.

If the following modification is ok, do we need even more description
about the possible middle-box operation (adding / removing parameters)
or is this enough? Modified text:

5.2.18. ECHO_REQUEST_UNSIGNED
...
      Type         63661
      Length       variable
      Opaque data  Opaque data, supposed to be meaningful only to the
                   node that sends ECHO_REQUEST_UNSIGNED and receives a
                   corresponding ECHO_RESPONSE_UNSIGNED.

The ECHO_REQUEST_UNSIGNED and corresponding echo response parameters MAY
be used for any purpose where a node wants to carry some state in a
request packet and get it back in a response packet.  The
ECHO_REQUEST_UNSIGNED is not covered by the HMAC and SIGNATURE.  A HIP
packet can contain one or more ECHO_REQUEST_UNSIGNED parameters.  It is
possible that middle-boxes add ECHO_REQUEST_UNSIGNED parameters in
HIP packets passing by.  The sender has to create the Opaque field so
that it can later identify the corresponding ECHO_RESPONSE_UNSIGNED
parameter.

The ECHO_REQUEST_UNSIGNED parameter MUST be responded with an
ECHO_RESPONSE_UNSIGNED parameter.

5.3.2.  R1 - the HIP Responder Packet
...
      IP ( HIP ( [ R1_COUNTER, ]
                   ...
                 <, ECHO_REQUEST_UNSIGNED >i)

5.3.3.  I2 - the Second HIP Initiator Packet
...
      IP ( HIP ( [R1_COUNTER,]
                  ...
                 <, ECHO_RESPONSE_UNSIGNED>i ) )

BR, Petri

-- 
Petri Jokela                         Phone:  +358 44 299 2413
Research Scientist                   Fax:    +358 9 299 3535
Ericsson Research, NomadicLab        E-mail: [email-masked]
Finland

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---

From: Miika Komu <[email-masked]>
Date: Fri, 25 May 2007 15:26:22 +0300 (EEST)

On Fri, 25 May 2007, Petri Jokela wrote:

Hi,

I think the editorial modification you proposed is fine. I don't see any 
issues in having multiple ECHO parameters within a single message.

-- 
Miika Komu                                       http://www.iki.fi/miika/