1. Rating
    Rate the paper in the following categories (For each category,
    choose a one numeric rating)

   Technical quality
     3: Some errors which can be easily corrected, as described below.

   Originality
     3: No significantly new ideas, but good analysis of current state

   Editorial quality
     3: Understandable with some effort, several improvements suggested
        below

   Overall grade (overall, how do you rate this paper?)
     3: Good

   Confidence (how confident are you about this review?)
     2: I have some general knowledge of this subject


2. Detailed comments

2a.

The paper describes the current status in the area of generating a
shared session key between hosts in an ad-hoc network. Further, it
suggests to combine two existing solutions in a case when there are
clusters of nodes that are one-hop away from each other (cliques). Nodes
use broadcast based method to generate a shared key inside the cluster
and the cluster head in turn uses another method with other
cluster-heads to build a shared secret for the nodes in the system.

In general, the paper is written in compact way; it gives the feeling
that the author is aware of the existing protocols and problems that
they have. The introduction part is clear in that sense. The background
part is still missing some text to be clear and fully understandable.
Protocols that are used later in the proposed new solution are not very
clearly explained.

2b.

The paper presents a nice way to combine existing protocols for generating
the group key. However, the background information describing the
protocols that are used in the proposed new method, is not clear enough.
More text is required to make especially the BD protocol understandable.
The efficiency of the proposed protocol is also somewhat unclear; a
comparison chart (with the existing protocols) would help.


2c.

The introductory part of the document is clear and gives a good view
of the area that is discussed in the paper. In general, few pictures
would help to understand how the protocols described in the document
work.

Section 2. Background

In 2.1, the role of cluster-heads is a bit unclear. What are the operations
that they perform during the cluster forming and after that.

Last paragraph in 2.2 is a bit orphan when written like
this. Re-ordering of paragraphs and adding some text might help.

In 2.3, the broadcast protocol is very shortly presented. There should
be more text, especially because this is one key part of the proposed
new key generation mechanism.

In 2.4, the first paragraph is not understandable. There is probably
something missing.

The TGDH abbreviation should be opened in the beginning of the
subsection.

In 2.5, the abbreviation AT-GDH should be opened. It might also be better
to first describe the basic operation of the AT-GDH before going into
the part telling where it can be used.

How does AT-GDH work when hosts join or leave the system? Is it
possible to negotiate the key only "partly", i.e. where the host
has left/joined and only distribute the new key to old hosts that
are not at the same subnet where the modifications have happened?

Sections 3 and 4 could possibly be combined into a one section,
describing the environment, its challenges, as well as requirements for
the key establishment. The way they are currently written, leaves

In Section 6:

The section lacks some discussion about how the final keys are distributed
to the end-hosts. Also, there is no discussion about re-keying situations
and how efficient that is.

For the reader it is not necessarily clear what are the possible
advantages of the described system. There should be more text explaining
this.

Section 7: "turned out to be very efficient". Is there more work done on
this issue than the one presented in this paper? If so, it should be
mentioned in section 6. From the text it is not clear how efficient this
is compared to other solutions.


Editorial:

- Cluster-head vs. clusterhead: both exist in the document
- Section 2.5, Last paragraph: "is does not" => "does not"
- Section 5, Par 3: [G89] with dots on top of 8, and on the
   next line it's -> its.
- Section 6, Par 2: it's -> its