1587: COMMUNICATION SYSTEMS 11st hour: Mobile Communications
2nd hour :Introduction to Cyber Security
Dr. George Loukas
University of Greenwich, 2015-2016
Handheld mobile phones
1973
2000
2008
1983
mobile service was only provided by one high powered transmitter/receiver
typically supported about 25 channels
had a radius of about 80km
Prior to cellular radio
1st Gen.: Cellular Networks1984
1-G 2-G 3-G 4-G
Cellular Networks Divide the area into cells using
multiple low power transmitters in each cell tiling pattern to provide full
coverage each with own antenna each with own range of
frequencies served by a base station
consisting of transceiver (transmitter – receiver) and control unit
adjacent cells use different frequencies to avoid crosstalk but cells sufficiently distant can use
same frequency band1-G 2-G 3-G 4-G
Cellular Geometries
11.4
All area is covered nicely,
BUT
antennas (at the centres of the squares) are not equidistant
11
Equidistant
BUT
There are gaps (or overlaps) between the circles
Equidistant
No gaps
11
Squares Circles Hexagons
1-G 2-G 3-G 4-G
Cellular Geometries
11
HexagonsFor the same reasons, hexagons are also very common in board and computer games
Equidistant
No gaps
1-G 2-G 3-G 4-G
Frequency Reuse Power of Base Transceiver
controlled Allows communication within
cell on given frequency Limits power escaping to
adjacent cells
Sharing cell frequencies with nearby (but not adjacent) cells without interfering with each other Allows multiple simultaneous
conversations 10 to 50 frequencies per cell
transceiver
1-G 2-G 3-G 4-G
Frequency Reuse PatternsTypical parameters:
Reuse factor N = number of cells in a repetitious pattern (each cell in the pattern uses a unique band of frequencies)
D = minimum distance between centers of cells that use the same band of frequencies
R = radius of a cell DR
1-G 2-G 3-G 4-G
Frequency Reuse Example
Total area covered = 32 x 6.65 = 213 km2 Total area covered = 133 x 1.66 = 221 km2
Consider a geographical area A divided into (a) 32 hexagonal cells of 1.6 km radius or (b) 133 hexagonal cells of 0.8 km radius. The reuse factor is 7 and there are 336 channels in total. Calculate:i) the number of channels per cellii) the maximum number of concurrent calls that can be handled in Aiii) the total area covered
1-G 2-G 3-G 4-G
336 / 7 = 48 channels per cell
(a) ii) Total channel capacity (number of concurrent calls that can be handled) = 48 x 32 = 1,536 channels
(b) ii) Total channel capacity (number of concurrent calls that can be handled) = 48 x 133 = 6,384 channels
(a) iii) 32 cells, each with radius R = 1.6 kmArea A = 3√3R2/2 = 6.65 km2
(b) iii) 32 cells, each with radius R = 0.8 kmArea A = 3√3R2/2 = 1.66 km2
Increasing Capacity add new channels
frequency borrowing congested cells take frequencies from adjacent
cells assign frequencies dynamically
cell splitting use smaller cells in high use areas
1-G 2-G 3-G 4-G
Increasing Capacity: Cell Splitting
Cells can be divided to provide more capacity.
To use a smaller cell, the power level must be reduced to keep the signal within the cell.
As the mobile units move, they pass from cell to cell, which requires transferring of the call from one base transceiver to another. This process is called a handoff.
The smaller the cells, the more frequent the handoffs.
1-G 2-G 3-G 4-G
Increasing Capacity: Cell Sectoring
Each sector is assigned a separate subset of the cell’s channels.
This reduces transmission power and increases battery life
1-G 2-G 3-G 4-G
Single omni-directional antenna
Three directional antennas (120o sectoring)
Six directional antennas (60o sectoring)
Operation of Cellular SystemA base station (BS) at centre of cell. Each BS has one or more antennas, a controller (handling the call process) and a number of transceivers (for communicating on the channels)
Between the mobile unit and the base station:• Control channels exchange information for setting up and
maintaining calls and establishing a relationship between a mobile unit and the nearest BS.
• Traffic channels carry voice or data connection between users.
Each BS is connected to a Mobile Telecommunications Switching Office (MTSO)
1-G 2-G 3-G 4-G
Call Stages
Monitor for strongest signal
Request connection
Paging
Call accepted
Ongoing Call
Handoff
MTSO
1-G 2-G 3-G 4-G
Design FactorsWhen designing a mobile phone network, we need to take into account:
Geography - Propagation effects (difficult to predict. Often using Okumura/Hata model for path loss)
desired maximum transmit power level at BS and mobile units typical height of mobile unit antennas available height of the BS antenna
Map of base stations around Greenwichfrom http://www.sitefinder.ofcom.org.uk
1-G 2-G 3-G 4-G
2nd Gen.: Digital Networks1991
1-G 2-G 3-G 4-G
2nd Gen Vs. 1st Gen
Digital channels encryption error detection and correction
1-G 2-G 3-G 4-G
Higher data rate
Greater capacity Better security
Shared channel access TDMA (Time division multiple access) FDMA (Frequency division …) CDMA (Code division …)
Thanks to:
Two types of 2G
Uses FDMA, TDMA
Many more subscribers.Covers the whole world, soroaming not an issue
But more interferenceand cells limited to 120 km
Introduced SMS messages
1-G 2-G 3-G 4-G
Uses CDMA
Great capacityVery large cell sizesEven low signal is enough for good qualityDropped calls less likely
But monopoly of a single company bars new entrants in market
Few subscribers
Short Message ServiceIntroduced as part of the GSM standardFirst SMS was sent in the UK over the
Vodafone GSM network (1992).Now, 200,000 SMS are sent every
second
Limited to ~160 charactersLarger SMS messages can be sent, but
need to be split and recombined when received
Includes control information (e.g. destination number, timestamp, data coding scheme …)
Best-effort delivery
Short Message Service Centre (SMSC): store-and-forward
SMS sent to
SMSC
SMS forwarded
if recipient
reachable.
Otherwise,
retry or drop
1-G 2-G 3-G 4-G
3rd and 4th Generation2002, 2010
1-G 2-G 3-G 4-G
Wireless Network Generations 1G 2G 2.5G 3G 4G
Design began 1970 1980 1985 1990 2000Implemented 1984 1991 1999 2002 2010
Provides Analogue voice
Digital voice Higher capacity
packetised data
Higher capacity,
broadband
Completely IP based
Data Rate 1.9 kbps 14.4 kbps 384 kbps 2 Mbps 200 MbpsMultiplexing FDMA TDMA,
FDMA, CDMA
TDMA, FDMA, CDMA
CDMA OFDMA
Core network PSTN PSTN PSTN, packet network
Packet network IP backbone
4-G3-G2-G1-G
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Shipping lost to u-boats (in tons)
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NCZW VUSX PNYM INHZ XMQX SFWX WLKJ AHSH NMCO CCAK UQPM KCSM HKSE INJU SBLK IOSX CKUB HMLL XCSJ USRR DVKO HULX WCCB GVLI YXEO AHXR HKKF VDRE WEZL XOBA FGYU JQUK GRTV UKAM EURB VEKS UHHV OYHA BCJW MAKL FKLM YFVN RIZR VVRT KOFD ANJM OLBG FFLE OPRG TFLV RHOW OPBE KVWM UQFM PWPA RMFH AGKX IIBG
FORCED TO SUBMERGE DURING ATTACK, DEPTH CHARGES.LAST ENEMY LOCATION 08:30, NAVAL GRID AJ 9863, 220 DEGREES, 8 NAUTICAL MILESI AM FOLLOWING THE ENEMYBAROMETER 1014 MILLIBAR TENDENCY FALLING, NORTH NORTH EAST 4, VISIBILITY 10.
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Shipping lost to u-boats (in tons)
500 BCSkytale 9th century
Al-Kindi1918
(enigma machine)
1976(Public-Key
cryptography)
CRYPTOGRAPHY
Cryptography
Single-key cryptographyAlso known as symmetric cryptography.
A binary message is encrypted and decrypted using the same secret key.The simplest type of binary encryption/decryption is to XOR each bit of the message with the secret key.
XOR =XOR =XOR =
logicalXOR
Message 1010100101010011010110 Key 0110011001010100110001
Encrypted message 1100111100000111100111
XOR
Cryptographic exerciseXOR =XOR =XOR =
logicalXOR
The hacker is looking for the solutions to the mock test. She knows the approximate format of the URL because that’s what George uses most of the time: http://staffweb.cms.gre.ac.uk/~lg47/lectures/COMP1587/COMP1587-MockTest2015-XXXX.docx She found the XXXX part but encrypted: 00010000 00010100 00000110 00001100 The encryption function is XOR. What is the XXXX part if the key is 01110101?
01110011 0111100101110101 01110101 01110101 01110101XOR00010000 00010100 00000110 00001100
01100101
e01100001
a s ya = 01100001 f = 01100110 k = 01101011 p = 01110000 u = 01110101 z = 01111010b = 01100010 g = 01100111 l = 01101100 q = 01110001 v = 01110110
ASCII TABLE OF CHARACTERS
c = 01100011 h = 01101000 m = 01101101
r = 01110010 w = 01110111
d = 01100100 i = 01101001 n = 01101110 s = 01110011 x = 01111000e = 01100101 j = 01101010 o = 01101111 t = 01110100 y = 01111001
Confidentiality
CONFIDENTIALITY
IntegrityJan. 2010: Spanish PM’s website defaced
June 2010: Stuxnet
CONFIDENTIALITY INTEGRITY
A computer program that altered the motor speeds of an Iranian nuclear facility’s centrifuges.
A common method is to use Cross-site Scripting (XSS)
<script>document.body.background="http://your_image.jpg";</script>
Availability2004: US businessman hires hackers to launch Denial of Service attacks against competitors. $2 million in losses.
2002: UK teenager disables Port of Houston web systems accidentally, while trying to take cyber-revenge over a girl.
2000: Canadian teenager knocks offline Amazon, yahoo, CNN, eBay ….
2008: Georgia accuses Russia of coordinated availability attacks, coinciding with military operations in South Ossetia.
2007: Estonian parliament, newspapers and banks are knocked offline by Russian hacktivists over a political issue
CONFIDENTIALITY INTEGRITY AVAILABILITY
Since then, the group Anonymous have launched several availability attacks for political purposes
A Denial of Service attack (DoS) is any intended attempt to prevent legitimate users from reaching a specific network resource.G. Loukas and G. Oke. Protection Against Denial of Service Attacks: A Survey. Comp. Journal, 53(7): 1020-1037, 2010
Example DoS: Reflector attack• Send packets to
several computers pretending to be the target
• When they reply, they all send ACK packets to the target
G. Loukas and G. Oke. Protection Against Denial of Service Attacks: A Survey. Comp. Journal, 53(7): 1020-1037, 2010
A Denial of Service attack (DoS) is any intended attempt to prevent legitimate users from reaching a specific network resource.
CONFIDENTIALITY INTEGRITY AVAILABILITY
Common countermeasures
CONFIDENTIALITY INTEGRITY
Detect unauthorised access
Detect and remove malicious software
Block/filter connections to critical systems
Protect real users by attracting attacks to fake users
Set strict rules for users to reduce security breaches
Cyber-physical attacks
Underlying causes of security failures Monopolies present juicy targets. A single vulnerability affects
millions of people
Deficit of computer security experts in the market
Strong at Windows, Linux and network technologiesAbility to think adversariallyAbility to adapt/learn constantlyWriting well-structured and clear reportsWorking in teams
Job adverts
online
Malware analysisJoanna Rutkowska, Invisible Things Lab
White hat hacker, Google“Security Princess” Parisa Tabriz
Director of Technology StrategyJames Lyne, Sophos
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