د/ايمان زغلول قاسم

استاذ تكنولوجيا التعليم المشارك بكلية التربية بالزلفي

Protocol Construction

Protocol Construction with Real Legos
Before designing 3D digital Legos, we have explored
several ways to use real Lego blocks to construct security
126 IEEE TRANSACTIONS ON LEARNING TECHNOLOGIES, VOL. 4, NO. 2, APRIL-JUNE 2011
TABLE 1
Notations of the Symbols
Fig. 1. Two example security protocols, (a) Woo Lam Protocol and
(b) PKP Protocol, shown in plain text.
protocols. This experiment helps us learn how the concepts
of Legos can be used to represent primitives and protocols,
and assists us in designing effective 3D digital Legos for
security education. The results also confirm our hypothesis
that Legos can be used as an appropriate metaphor in an
education tool to expose the relationships among security
primitives and protocols. Below, we describe our selections
of protocol representation and the designs of protocol
construction.
For constructing various protocols using real Legos, we
have selected a Lego product that satisfies two requirements.
First, we look for products that contain small Lego
pieces so that the final construction results are in an
appropriate size for demonstration and storage. Second, we
need a large number of Lego blocks with similar shapes,
since primitives usually appear multiple times in a protocol.
Under these two requirements, we have selected the “Lego
System Ultimate Building Set” made by LEGO as our tool.
We have explored several ways to construct security
protocols with real Legos. We use colors to differentiate
entities. For example, in Fig. 2, red and yellow, blue and
white, or green and white are used to visualize entities A and
B, respectively. We choose one or several Lego blocks to
represent the primitive types. To utilize the available Lego
pieces efficiently, we select combinations of Lego shapes for
different primitive types carefully through the following
procedure. First, we summarize the frequencies of primitives
in several security protocols that are taught in our introductory
level security course. Then, the number of each Lego
shape is counted. By matching the numbers of available Lego
blocks to the frequencies of primitives, we ensure that our
design can utilize the available Lego blocks efficiently.
Based on the designs of primitives, we have explored
several methods to construct protocols. Fig. 2 shows five
designs for the Needhand-Schroeder-Lowe protocol on the
left and four designs for the Andrew Secure RPC protocol
on the right. Our main choices are between the vertical and
flat designs for the message contents. For example, the top
left red-yellow design in Fig. 2a is a vertical version for
providing a strong transition impression, and the bluewhite
designs in Figs. 2a and 2b are flat versions for
demonstrating message contents. It is interesting to note
that multiple ways can be used to construct a protocol even
with a simple Lego set. Also, this experiment helped the
authors to remember several security protocols easily.
4 AUTOMATIC CONSTRUCTION OF 3D DIGITAL
LEGOS
We design a method to construct specialized 3D digital
Legos, automatically, for teaching security protocols. This
method allows more flexible generation of instructional
demonstrations and hands-on experiments than real Legos.
Compared to the traditional text-based methods (examples
shown in Fig. 1), our Lego-based approach provides more
effective course materials to direct the students’ focus and
attract their interests.
In this section, we present a generic method to construct
3D digital Lego sets for teaching various security protocols.
Our method is developed based on the two-tier protocol
representation that enables our approach to visualize
different security protocols and attacks. The entire generation
process is automated to allow easy creation and sharing
of course materials.
4.1 Basic Lego Design
To better expose the relationships among primitives and
protocols, we use different shapes to represent the
primitive types and different colors to represent the entities.
For each Lego block, only one surface is chosen to carry the
information of message contents and is used to determine
whether or not two blocks can fit together. In this way, a
protocol can be visualized as multiple sending and
receiving blocks.
Specifically, our digital Legos are constructed with the
following procedure. First, we generate a set of geometry
meshes to represent the primitive pieces based on2Ddesigns.
Second, multiple blocks of digital Legos are composed in an
appropriate order to visualize a security protocol.
Since we want to construct the digital Lego blocks
automatically for a given protocol, we use two portions
with fixed shapes and two portions with adjustable shapes
to compose one Lego block. As shown in Fig. 3, the top,
bottom, and body define the general shape of a Lego block
and the content surface is generated according to the
message content. The shapes of the top and bottom portions
match each other to ensure the vertical connection between
any two blocks. They always point downward, since we
assume that the protocols are executed from top to bottom.
The content surface carries the most important information,
so we use a later section to discuss its generation in detail.
The length of a block is also automatically adjusted
according to the content of a message.
Our main purpose for separating the sending and
receiving blocks is to provide flexibility to the demonstration
and experiment tasks. Although a message is shared
between a sender and a receiver, their interpretation of the
same message may be different, especially when attackers
are involved. This also allows us to show different detail
levels of the same message in demonstration and experiment
tasks.

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