Block Cipher Modes of Operation

How to use a block cipher?

• Block Ciphers encrypt fixed size blocks
• e.g. DES encrypts 64bit blocks
• We need some way to encrypt a message of arbitary length
• e.g. a message of 1000 bytes
• NIST defines several ways to do it
• called modes of operation

Encrypting a Large Message

1. Electronic Code Book (ECB)
2. Cipher Block Chaining (CBC)
3. Output Feedback Mode (OFB)
4. Cipher Feedback Mode (CFB)
5. Counter Mode (CTR)

Difference between Packet Switching and Circuit Switching

Difference between Packet Switching and Circuit Switching is as shown below :

Packet Switching	Circuit Switching
Packet travel on different path.	Packet travel on same path.
Packet Switching uses connection less service.	Circuit Switching uses connection oriented service.
Large message or data is divided into small packets(segments).	Large message or data travel as it is.
More path available.	Only one path is used for.
Less time require.	More time require.
Maximum bandwidth is utilized.	During the call,third party can't access this bandwidth.
Require sequence number.	No need of sequence number.
More path available.	Only one path is used for.
More path available.	Only one path is used for.

How is data transferred through network? (Switching Technology)

Data is being transferred through net. It have two types :

Circuit Switching : Dedicated circuit per call(Ex. telephone net).
Packet Switching : Data sent through net in discrete “chunks”.

Circuit Switching :

There are three phases in circuit switching :

1. Establish
2. Transfer
3. Disconnect

The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was originally sent. In modern circuit-switched networks, electronic signals pass through several switches before a connection is established. During a call, no other network traffic can use those switches. The resources remain dedicated to the circuit during the entire data transfer and the entire message follows the same path. Circuit switching can be analogue or digital.

Packet Switching :

In packet-based networks, the message gets broken into small data packets. These packets are sent out from the computer and they travel around the network seeking out the most efficient route to travel as circuits become available. This does not necessarily mean that they seek out the shortest route. Each packet may go a different route from the others. Each packet is sent with a ‘header address’. This tells it where its final destination is, so it knows where to go. The header address also describes the sequence for reassembly at the destination computer so that the packets are put back into the correct order. One packet also contains details of how many packets should be arriving so that the recipient computer knows if one packet has failed to turn up. If a packet fails to arrive, the recipient computer sends a message back to the computer which originally sent the data, asking for the missing packet to be resent.

Communication Devices

There are two types of Communication Devices. They are :

1. Synchronous communication uses a clock signal separate from the data signal communication can only happen during the ‘tick’ of the timing cycle.
2. Asynchronous communication does not use a clock signal- rather, it employs a start and stop bit to begin and end the irregular transmission of data.

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DSDV Protocol TCL Script

# A 100-node example for ad-hoc simulation with AODV

# Define options

set val(chan)           Channel/WirelessChannel    ;# channel type

set val(prop)           Propagation/TwoRayGround   ;# radio-propagation model

set val(netif)          Phy/WirelessPhy            ;# network interface type

set val(mac)            Mac/802_11                 ;# MAC type

set val(ifq)            CMUPriQueue    ;# interface queue type

set val(ll)             LL                         ;# link layer type

set val(ant)            Antenna/OmniAntenna        ;# antenna model

set val(ifqlen)         50                         ;# max packet in ifq

set val(nn)            3                        ;# number of mobilenodes

set val(rp)             DSDV                       ;# routing protocol

set val(x)              500                        ;# X dimension of topography

set val(y)              400                        ;# Y dimension of topography

set val(stop)           150                        ;# time of simulation end

#-------Event scheduler object creation--------#

set ns              [new Simulator]

#Creating trace file and nam file

set tracefd       [open dsr.tr w]

set windowVsTime2 [open win.tr w]

set namtrace      [open dsr.nam w]  

$ns trace-all $tracefd

$ns namtrace-all-wireless $namtrace $val(x) $val(y)

# set up topography object

set topo       [new Topography]

$topo load_flatgrid $val(x) $val(y)

create-god $val(nn)

# configure the nodes

        $ns node-config -adhocRouting $val(rp) \

                   -llType $val(ll) \

                   -macType $val(mac) \

                   -ifqType $val(ifq) \

                   -ifqLen $val(ifqlen) \

                   -antType $val(ant) \

                   -propType $val(prop) \

                   -phyType $val(netif) \

                   -channelType $val(chan) \

                   -topoInstance $topo \

                   -agentTrace ON \

                   

-routerTrace ON \

                   -macTrace OFF \

                   -movementTrace ON

                  

      for {set i 0} {$i < $val(nn) } { incr i } {

            set node_($i) [$ns node]    

      }

# Provide initial location of mobilenodes

$node_(0) set X_ 5.0

$node_(0) set Y_ 5.0

$node_(0) set Z_ 0.0

$node_(1) set X_ 490.0

$node_(1) set Y_ 285.0

$node_(1) set Z_ 0.0

$node_(2) set X_ 150.0

$node_(2) set Y_ 240.0

$node_(2) set Z_ 0.0

# Generation of movements

$ns at 10.0 "$node_(0) setdest 250.0 250.0 3.0"

$ns at 15.0 "$node_(1) setdest 45.0 285.0 5.0"

$ns at 110.0 "$node_(0) setdest 480.0 300.0 5.0"

# Set a TCP connection between node_(0) and node_(1)

set tcp [new Agent/TCP/Newreno]

$tcp set class_ 2

set sink [new Agent/TCPSink]

$ns attach-agent $node_(0) $tcp

$ns attach-agent $node_(1) $sink

$ns connect $tcp $sink

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ns at 10.0 "$ftp start"

# Printing the window size

proc plotWindow {tcpSource file} {

global ns

set time 0.01

set now [$ns now]

set cwnd [$tcpSource set cwnd_]

puts $file "$now $cwnd"

$ns at [expr $now+$time] "plotWindow $tcpSource $file" }

$ns at 10.1 "plotWindow $tcp $windowVsTime2"

# Define node initial position in nam

for {set i 0} {$i < $val(nn)} { incr i } {

# 30 defines the node size for nam

$ns initial_node_pos $node_($i) 30

}

# Telling nodes when the simulation ends

for {set i 0} {$i < $val(nn) } { incr i } {

    $ns at $val(stop) "$node_($i) reset";

}

# ending nam and the simulation

$ns at $val(stop) "$ns nam-end-wireless $val(stop)"

$ns at $val(stop) "stop"

$ns at 150.01 "puts \"end simulation\" ; $ns halt"

proc stop {} {

    global ns tracefd namtrace

    $ns flush-trace

    close $tracefd

    close $namtrace

exec nam dsr.nam &

exit 0

}

$ns run

Output

AODV Protocol TCL Script

# A 100-node example for ad-hoc simulation with AODV

# Define options

set val(chan)           Channel/WirelessChannel    ;# channel type

set val(prop)           Propagation/TwoRayGround   ;# radio-propagation model

set val(netif)          Phy/WirelessPhy            ;# network interface type

set val(mac)            Mac/802_11                 ;# MAC type

set val(ifq)            Queue/DropTail/PriQueue   ;# interface queue type

set val(ll)             LL                         ;# link layer type

set val(ant)            Antenna/OmniAntenna        ;# antenna model

set val(ifqlen)         50                         ;# max packet in ifq

set val(nn)            3                        ;# number of mobilenodes

set val(rp)             AODV                       ;# routing protocol

set val(x)              500                        ;# X dimension of topography

set val(y)              400                        ;# Y dimension of topography

set val(stop)           150                        ;# time of simulation end

#-------Event scheduler object creation--------#

set ns              [new Simulator]

#Creating trace file and nam file

set tracefd       [open dsr.tr w]

set windowVsTime2 [open win.tr w]

set namtrace      [open dsr.nam w]  

$ns trace-all $tracefd

$ns namtrace-all-wireless $namtrace $val(x) $val(y)

# set up topography object

set topo       [new Topography]

$topo load_flatgrid $val(x) $val(y)

create-god $val(nn)

# configure the nodes

        $ns node-config -adhocRouting $val(rp) \

                   -llType $val(ll) \

                   -macType $val(mac) \

                   -ifqType $val(ifq) \

                   -ifqLen $val(ifqlen) \

                   -antType $val(ant) \

                   -propType $val(prop) \

                   -phyType $val(netif) \

                   -channelType $val(chan) \

                   -topoInstance $topo \

                   -agentTrace ON \

                   -routerTrace ON \

                   -macTrace OFF \

                   -movementTrace ON

                  

      for {set i 0} {$i < $val(nn) } { incr i } {

            set node_($i) [$ns node]    

      }

# Provide initial location of mobilenodes

$node_(0) set X_ 5.0

$node_(0) set Y_ 5.0

$node_(0) set Z_ 0.0

$node_(1) set X_ 490.0

$node_(1) set Y_ 285.0

$node_(1) set Z_ 0.0

$node_(2) set X_ 150.0

$node_(2) set Y_ 240.0

$node_(2) set Z_ 0.0

# Generation of movements

$ns at 10.0 "$node_(0) setdest 250.0 250.0 3.0"

$ns at 15.0 "$node_(1) setdest 45.0 285.0 5.0"

$ns at 110.0 "$node_(0) setdest 480.0 300.0 5.0"

# Set a TCP connection between node_(0) and node_(1)

set tcp [new Agent/TCP/Newreno]

$tcp set class_ 2

set sink [new Agent/TCPSink]

$ns attach-agent $node_(0) $tcp

$ns attach-agent $node_(1) $sink

$ns connect $tcp $sink

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ns at 10.0 "$ftp start"

# Printing the window size

proc plotWindow {tcpSource file} {

global ns

set time 0.01

set now [$ns now]

set cwnd [$tcpSource set cwnd_]

puts $file "$now $cwnd"

$ns at [expr $now+$time] "plotWindow $tcpSource $file" }

$ns at 10.1 "plotWindow $tcp $windowVsTime2"

# Define node initial position in nam

for {set i 0} {$i < $val(nn)} { incr i } {

# 30 defines the node size for nam

$ns initial_node_pos $node_($i) 30

}

# Telling nodes when the simulation ends

for {set i 0} {$i < $val(nn) } { incr i } {

    $ns at $val(stop) "$node_($i) reset";

}

# ending nam and the simulation

$ns at $val(stop) "$ns nam-end-wireless $val(stop)"

$ns at $val(stop) "stop"

$ns at 150.01 "puts \"end simulation\" ; $ns halt"

proc stop {} {

    global ns tracefd namtrace

    $ns flush-trace

    close $tracefd

    close $namtrace

exec nam dsr.nam &

exit 0

}

$ns run

Output