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Computer Security: Friend, Foe or Failure Dr. Ishbel Duncan School of Computer Science March 13th 20


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Title: Computer Security: Friend, Foe or Failure Dr. Ishbel Duncan School of Computer Science March 13th 20

Computer Security Friend, Foe or Failure?Dr.
Ishbel DuncanSchool of Computer ScienceMarch
13th 2009

Some recent figures
  • The American FBI Internet Crime Complaint Center
    received 207,000 complaints in 2007 relating to
    240M of e-crimes.
  • Japanese cybercrime is at record levels tripling
    between 2004 and 2008. Threats and illegal
    access increased by 90 and 20 between 2007 and
    2008 but fraud has decreased slightly.
  • 33 increase in card fraud forecast for 2009
  • 40 of UK children dont know the people they are
    chatting to online. Half admitted to downloading
    music illegally using P2P software and 20 said
    their systems were infected by viruses after
    downloading. Half share their home systems with
    other members of the family.

UK bank cards
  • UK consumers lost 302M to card fraud in the
    first half of
  • In 2007 it was 535M.
  • Spending on credit cards was 124Bn in 2007 and
    126Bn in
  • Debit card spending rose from 224Bn to 245Bn.
  • Debit cards accounted for 75 of all transactions
    and the
  • number of debit cards in circulation overtook
    credit cards in
  • 2008. There are 75M debit cards in circulation
    and 71M credit
  • cards.
  • Online banking fraud rose 185 in the first half
    of 2008 mainly
  • because of phishing attacks.
  • 1 in 8 UK online firms lose more than 5 of
    income to fraud.

Military Hacker
  • Gary McKinnon of London allegedly hacked into
    NASA, the
  • Pentagon and 12 other military networks between
  • 2001 and March 2002.
  • In one attack on an army computer at Fort Myer,
    Virginia he
  • obtained administrator privileges which allowed
    him to delete
  • 1300 user accounts and copy files containing
    usernames and
  • encrypted passwords. He managed to shut down the
  • Internet on 2000 military computers for three
  • The US Government said it spent 1M cleaning up
  • systems.
  • McKinnon was indicted in November 2002 but is
  • extradition and the hearing is in July 2009 in
    London. His bail
  • agreement prevents him from using any computer

Online Theft
  • Online theft is currently estimated to cost
    1Trillion a year.
  • and rising..
  • But card fraud identikits have fallen in price
    from 15 to 2.
  • More than half the worlds GDP is estimated to
    flow through
  • the internet every day through the SWIFT network.
  • At the World Economics Forum in Davos in January,
    it was
  • stated that the internet was vulnerable but as
    it was now part
  • of societys central nervous system, attacks
    could threaten the
  • whole economy.
  • A virtual group had redirected the details of 25M
    credit cards
  • to the Ukraine.

  • The safest country for computer virus infections
    is Australia.
  • Only 1 in 574 emails contain a virus there
    compared to
  • 1 in 213 here in the UK
  • 1 in 415 for the USA
  • 1 in 451 for Japan.
  • India is the most virus ridden with 1 in 197.
  • Spam emails this year spiked on Valentines Day,
    with 9 of all
  • email.
  • Phishing this year has taken advantage of the
    economic crisis
  • with 1 in 190 emails a phish attack in February
    (up from 396).
  • France is the most spammed country with 75 of
    all emails
  • being spam. The UK get spam in 67 of all email.

Cyber Warfare
  • Cybercrime is one thing, cyber warfare is
  • Estonia came under a denial of service attack
    from Russia in
  • 2007 and 2008 which disabled banking and
  • Cyber Warfare is now a real threat to all
    countries but do we
  • want governments to regulate the internet to
    prevent misuse?
  • Legal problems
  • where an attack takes place is usually different
    from the country of the perpetrator.
  • many satellites or servers may be used to target
    a victim bringing in more victims or

A Short Security History
  • Herodotus chronicles how Demaratus of Greece sent
    tablets covered
  • in wax to the Spartans to warn of a Persian
    invasion and, separately,
  • of Histaiaeus who shaved the head of a servant.
  • The Chinese wrote on fine silk and wrapped it in
    a small ball of wax.
  • Al-Kindi wrote on deciphering cryptographic
    messages in the 9th
  • Century by noting letter frequencies.
  • Chaucer encrypted plaintext (normal language)
    with symbols.
  • By the 15th Century, encryption was common among

The Spartan Scytale
  • The Spartans used a scytale in the 5th Century BC
    a rod of
  • wood with a strip of text wound around it.

The Caesar Cipher
Replace letters with another at a distance of N
Character Manipulation
  • The most basic character manipulation is a
    substitution cipher. Here letters are exchanged
    in the alphabet.
  • The most famous substitution cipher is the Caesar
  • where letters were replaced with one further
    down, or up, the alphabet.
  • e.g. HAL IBM with a shift of 1.
  • Often letters were/ are arranged in groups of 5
    to avoid noting word lengths.
  • kujdg nfpoe co

Mary of Scotland
The Babington Plot The code was a substitution
cipher plus some symbols representing words such
as bearer, my and pray.
Pattern Analysis
  • There are characteristic letter patterns in any
  • We know the most common letters in English are
  • A 8.0 S 6.0
  • E 13.0 T 9.0
  • I 6.5 N 7.0
  • O 8.0 R 6.5
  • The least frequent is?

Digrams and Trigrams
  • Just as there are common letters so also are
    there common
  • pairs or triples of letters (digrams and
  • Transpositions leave the plaintext letters intact
    so if the
  • letter frequencies are similar to normal
    frequencies then we
  • infer that transposition has taken place.
  • Some of the most common are
  • er th en ed an or in gh
  • ent ion and ing ive for tio one

Charles Babbage
Babbage broke the Vigenere cipher which uses a
keyword to determine a different cipher alphabet.
Vigenère Tableau Example
  • Using the key phrase
  • I am I exist, that is certain
  • To send the message
  • Machines cannot think
  • i am i exist that is certain
  • m ac h inesc anno tt hink
  • Row M, column I is u
  • Row A column A is a
  • Row M column C is o uaopm kmkvt unhbl jmed

The Underground Railroad
Escaping Slaves in the American States would
allegedly follow signals in quilts laid out to
World War 2 The Enigma machine
Scherbiuss machine was patented in 1918. It had
3 scramblers to encipher the plaintext plus a
plugboard that swapped 6 letters. Rejewski of
Poland spent 8 years deciphering Enigma and his
work was passed on to Bletchley Park where it was
A story Key Exchange
  • In pre-revolutionary Ruritania, the postal
    service was not to be
  • trusted. Boxes would be opened and contents
    removed. Only
  • those that could not be opened were delivered.
    Stout boxes
  • and padlocks were available but each padlock had
    a single unique
  • key that could open the lock.
  • How can Prince Rupert send a priceless necklace
    to his beloved
  • Princess Irena if there is no other way of
    transporting his gift
  • other than via the postal service?
  • In other words, how can we send a secret message
    that only
  • the sender and receiver can read.

Rupert sends his gift inside a padlocked
box. Irena returns the box with her padlock on
the box. Rupert removes his padlock and sends
back the box to Irena with only her padlock
History remembers those who publish first
  • One major stumbling block of any cryptographic
    system is the
  • exchange of keys. Any public way of interchange
    may be overheard.
  • Whitfield Diffie, Martin Hellman and Ralph Merkle
    of Stanford
  • are remembered as the fathers of public key
  • publishing and patenting their idea in 1976.
  • There system allows two people to agree keys
    which allow them
  • to communicate an encrypted message without them
    having the
  • same key.
  • However, James Ellis of GCHQ had the same idea 10
    years earlier
  • and Clifford Cocks and Malcolm Williamson
    discovered the key
  • exchange algorithm by 1975. However, their work
    was classified and
  • GCHQ did not contest the American patent.

Crypto Basics
 Encryption and Decryption.
Meet Alice and Bob
  • Alice and Bob wish to converse secretly. Alice
    has message M
  • which she encrypts with a function E.
  • C E(M)
  • She sends this to Bob who decrypts the message
    with function D.
  • D(C) D( E(M)) M
  • However, Eve wishes to listen in and can deduce
    the form of the
  • functions E and D or the message M. Bob and
    Alice now have to
  • use a more robust mechanism to pass their

Symmetric Encryption
  • Symmetric algorithms use one key, a secret key
  • A and B share the key and as long as it is
    private it offers
  • authentication. But A and B have to agree on the
    key in
  • advance.
  • What happens if C is invited to share a secret
    with A and B.
  • We may need two more keys for A-C and B-C
  • For an N-user system we would require n(n-1)/2
    keys for
  • each pair of users.

  • A cryptosystem is one in which rules are applied
    to encrypt and decrypt text. These algorithms
    often use a key, denoted by K, as a mechanism to
    adapt the plaintext.
  • The ciphertext is the plain text adapted by the
    algorithm and using the key value.
  • C E(K,P)
  • E is the Encryption Algorithm, or more precisely
    the set of
  • Algorithms, and K is the Key which selects
    precisely one
  • algorithm.
  • (Think of Yale keys there are many but only one
    fits your door lock)

Alice and Bob again
  • Alice and Bob could know each others key (or
    share a key).
  • Eve would then be able to mount a ciphertext only
    attack as she knows C but not P. If she had
    previous knowledge of plaintext she may still be
    able to deduce the messages, or she may use
    probabilities and distribution characteristics of
    the language.

Asymmetric Encryption
  • In public key or asymmetric encryption, each user
    has two keys
  • a public and a private key. The public key is
    published freely
  • because it is only one half of an inverse pair.
  • Using keys for decryption and encryption we have
  • P D(KD, E(KE,P))
  • Now we have P D(Kprivate, E(Kpublic,P))
  • The public key encryption is decrypted via the
    private key.
  • P D(Kpublic, E(Kprivate,P))
  • The private key encryption is decrypted via the
    public key.
  • Multiple users can send messages privately to
    each other using
  • public keys.

Encryption with Keys.
Diffie-Hellman (1976)
  • Diffie and Hellman published the first paper on
    public key
  • cryptography. There are three conditions
  • It must be computationally easy to encode/ decode
    with the a key.
  • It must be computationally infeasible to derive
    the private key from the public key.
  • It must be computationally infeasible to
    determine the private key from a plaintext
  • Mathematically we require to find k such that
  • n gk mod p
  • Where p is prime and g 0,1, or p-1

Asymmetric Encryption Example
  • Alice and Bob have chosen
  • p 53 g 17
  • p is the prime modulus, g is the mantissa.
  • Their private keys are kalice 5 kbob 7
  • Their public keys are kalice 175 mod 53 40
  • kbob 177 mod 53 6
  • Bob sends Alice a message by computing a shared
  • S Bob, Alice K Alice kBob mod p 407 mod 53
  • Alice decrypts using her private key
  • S Alice, Bob K Bon kAlice mod p 65 mod 53

  • The Rivest-Shamar-Adelman (1978) cryptosystem is
    a public
  • key system and has been a de facto standard for
    many years.
  • n pq, where p and q are prime numbers. The
    totient F(n) is the
  • number of numbers with n.
  • Example
  • p 7, q 11, n 77, F(n) 60.
  • e, the encryption key, is relatively prime to
  • d, the decryption key, is e-1 mod ((p-1)(q-1))
  • Encrypt as c me mod n
  • Decrypt as m cd mod n

RSA Example
  • Alice chooses public key as 17, private as 53.
  • Bob sends Hello World which is encoded as
    07 04 11 11 14 26 22 14 17 11 03
  • Bobs ciphertext is 0717 mod 77 28
  • 0417 mod 77 16 etc
  • 28 16 44 44 42 38 22 42 19 44 75

  • The use of a public key system provides non
    repudiation of the
  • the source of the message and the message itself
    as only the
  • private and public key pair can encode and decode
    the system.
  • The security of RSA depends on the factoring
    problem and is
  • an obvious means of attack knowledge of one pair
  • exponents or use of a common modulus will allow
  • Messages should be padded with random values when
  • encryption exponents are used.

General Users passwords
  • Consider what is at risk if you password is
  • Consider how much you trust the systems that see
  • passwords.
  • Which is better write down a few important
    passwords or
  • reuse passwords or make them weak?
  • Use a phrase or a song rather than single word.
  • If the password is 6 characters, 99.95 of
    variants will be non words use one of them!

  • Feb 2009
  • 28,000 log in details stolen from a well known
    website were
  • posted online. It was noted that
  • 14 of users used sequential passwords such as
    123456 or QWERTY
  • 16 used their first name as a password
  • 5 used the names of popular celebrities.
  • 4 used password
  • 3 chose idontcare, whatever, yes and no
  • Are these users naïve?

  • Voice recognizers, handprint detectors,
    thumbprint analysis,
  • retinal scanners are coming into more use for
    other than
  • military security or government systems.
  • Biometrics are biological authenticators based on
  • characteristics. These cannot be lost, but may
    be stolen!
  • Authentication is not always easy fingerprints
    may be
  • damaged by scarring, voice recognition systems
    must be trained to the users voice/ accent.
  • Current biometric systems are expensive, bulky
    and slow.
  • Users are still unsure about the privacy issues
    and some
  • consider the systems intrusive.

Biometric Systems
  • Fingerprint recognition Voice recognition
  • Iris Scanners Face Recognition
  • Keystrokes Signatures
  • Combination systems use two or more of the above.
    Most systems are used in supervised areas, e.g.
  • Systems use sampling and thresholds for pattern
  • This requires training the systems and a lot of
    statistical data.
  • Performance
  • False acceptance rate (fraud rate), False
    rejection rate (insult rate) are major issues.

Todays problems
  • Computers have come a long way in 25 years from
    being research
  • instruments to everyday tools for schools,
    libraries, telephones,
  • transport etc.
  • Most people have over 6 computers in their home
    mobiles, tv,
  • video, CD players/ recorders, microwave, cookers,
    a Wii plus the
  • computer itself.
  • Walking in the street we may have cameras
    watching us and all
  • our movements recorded and analysed by computer.
  • We assume that computers are safe and reliable.
  • But they can also be our enemy.

Key Principles
  • Principle of Easiest Penetration
  • An intruder must be expected to attempt any
    available means of penetration and the one that
    succeeds may not be the obvious one.
  • Principle of Adequate Protection
  • Computer Items must be protected until they lose
    their value and they must be protected to a
    degree consistent with their value.
  • Principle of the Weakest Link
  • Security is as strong as the weakest link.
  • Principle of Effectiveness
  • Controls must be used, be appropriate and be
    applied properly

Security Failures
  • The vast majority of attacks are done by Bots or
  • These are automatic, and to some extent
    autonomous, small
  • programs which trawl the internet. They can be
  • Spam
  • Viruses Worms
  • Rootkits
  • DDOS attacks
  • Phishing attacks
  • Bots
  • Another technique is Social engineering
  • We need to secure networks, operating systems,
  • and files.

  • Large numbers of computers have been brought
  • Non-owner control (?) to launch attacks, spam,
    DoS or some
  • fraudulent activity.
  • The BBC (25 Jan 2007) Of the 600 million
  • currently on the internet, between 100 and 150
    million were
  • already part of these botnets.
  • Yahoo suffered one botnet using up 15 of search

Whose Failure?
  • Security is not just technical, it also requires
    educating users.
  • If users fail to follow advice then it is not
    surprising attacks
  • and failures happen. But, can the user be blamed
    for not
  • following advice when most computer users are non
  • and believe they are safe because they buy
  • Users are led to believe that if they pay for
    cover they are
  • safe. But measures against security are allegedly
  • proportional to the perceived threat. Every
    breach will make us
  • protect even more.
  • All companies have losses, perhaps we should
    expect failure in
  • our protection systems?

If you build it, they will come.
  • You can build a secure system but if you cant
    enforce a
  • security policy then you cant be 100 secure.
  • This is not unknown in history
  • You can build a fortress but attacks will happen
    if people can
  • climb the walls or break down the small servants
    back door.
  • We dont want to live in isolation so we need to
  • therefore choices must be made between total
    security and
  • openness.
  • Companies are the same they want network and
    file security as
  • long as it doesnt cost too much in money and

Lost Discs
  • HMRC sent two discs containing the entire Child
  • database to the National Audit Office
    unregistered and
  • unencrypted in 2007. The data contained personal
    details of
  • 25 Million people and was reckoned to be worth up
    to 1.5B to
  • criminals.
  • The discs were lost
  • 90,000 staff at HMRC have been given extra
    training and 20,000 MoD laptops have been
  • An ex contractor of the DWP had two discs with
  • claimant details. She forgot to return them but
    was never
  • asked for them (2007).

More Lost Data
  • It was estimated that sensitive data affecting 4M
    people was
  • lost in 2007/8
  • NI numbers of 17,000 people lost on a disc
  • theft of a laptop with encrypted details of
    17,000 Sats markers
  • The Ministry of Justice lost information on
    45,000 people regarding their criminal histories.
  • The FO lose data on 190 people in 5 separate
  • The Dept. of Transport lost 3M records of driving
    test applicants.
  • The HSBC lost a disc with data on 370,000
  • HMRC sent Standard Life a CD through the post
    containing data on 15,00 Standard Life customers.
    It didnt arrive.
  • Documents from the DWP were dumped on a
    roundabout in Devon.

Missing Laptops
  • In 2007, a laptop was stolen from the boot of an
  • car. It was suggested that the computer
    contained data on
  • 400 customers holding high value ISAs at five
  • companies.
  • Also in 2007, a laptop was stolen from a
    Nationwide employees
  • home. It contained 11M customer records.
    Nationwide were
  • Fined 980,000 by the City watchdog.
  • A Royal Navy officer had his laptop stolen from
    his car. It
  • contained information on 600,000 people.
  • Hard drives were reported missing from the MoD
    and the
  • National Offender Management Service.

More Government mishaps
  • The MoD lost an encrypted laptop with 620,000
  • records including bank account and NI numbers as
    well as
  • 45,000 people named as referees or next-of-kin
    for service
  • applicants.
  • An external contractor downloaded information
    onto a memory
  • stick and then lost it. The data concerned 10,000
  • and the names, dates of birth and release dates
    of 84,000
  • prisoners in England and Wales.
  • The MoD confirmed 121 computer memory sticks had
    been lost
  • or stolen since 2005 and 658 laptops since 2004.
  • Only 5 memory sticks contained secret data!

Security Mechanisms Access Control List
  • An Access Control Matrix describes the rights of
    subjects and
  • objects.
  • ACLs work well with data oriented system where
  • are stored with the data or the owner can set up
    the ACL.
  • ACLs are less suited to systems with large user

  • Role based access control (RBAC) is an example of
  • control that applies at the application layer.
    Here we have
  • functional groups or user roles.
  • A user could be a system administrator, a general
    user, a tutor
  • etc. Some roles could be qualified such as a
    tutor on a module.
  • Each role allows the certain privileges or allows
    them to
  • execute some tasks (procedures).

Rings of Protection
  • Rings of protection offer different levels of
    privilege for the
  • users or system programs. (Multics, Unix, Intel
    80286 onwards)
  • Ring 0 kernel, access to disk
  • Ring 1 process manager
  • Ring 3 all other programs.
  • Current privilege can only be changed by a
    process in Ring 0.
  • Outer rings have fewer privileges, I/O forbidden,
  • mapping disallowed.

Bell-LaPadula (Multilevel Security)
  • David Bell and Len LaPadula (1973) responded to
    problems with
  • the US Air Force mainframe security. The goal is
    to identify
  • Allowable communication when maintaining secrecy.
  • Information cannot flow downwards
  • The simple security policy (ss-property) no
    process can read data at a higher level, i.e. no
    read up (NRU)
  • The -property no process can write data to a
    lower level, i.e. no write down (NWD)
  • i.e sensitive data can only be written to the
    same or a higher level.

BLP Secure Flow of Information.
The Chinese Wall
  • Brewer and Nash (1989) defined the Chinese Wall
    to reflect
  • protection requirements for commercial
  • Objects files, low level information pertaining
    to one company
  • Groups All objects pertaining to one company is
    grouped together
  • Conflict Classes all groups of objects for
    competing companies are clustered together
  • A person can access any information as long as
    they have not
  • accessed information from a different company is
    the same
  • conflict class.

Chinese Wall Security Policy for chocolate
companies, airlines and banks.
Chinese Walls for Banks and Chocolate Makers
  • What?
  • Fraud Destructive Attacks
  • Monetary Theft Reputation destruction
  • Denial of Service Identity Theft
  • Brand Theft Intellectual Property Theft
  • Publicity Terrorism
  • Surveillance
  • Who?
  • Hackers System Crackers
  • Organised Crime Career Criminals
  • Malcontents Industrial spies
  • Press Police
  • Intelligence Services Terrorists
  • Info Warriors

Attack Trees (Schneier)
  • The goal is the root and the lower nodes the
    possible routes/ subgoals . Each node can have an
    associated risk assessment. Logical or/and may be

  • A firewall is a special monitor which mediates
    access to a
  • network and hides the structure of the internal
  • Firewalls may be
  • Packet filters // looks at packet headers
  • Stateful inspection filters // maintains state
  • Application proxies //simulates application and
    performs access control
  • Personal firewalls //blocks traffic
  • Types of Attacks DoS, DDoS, Flash Crowds (not
    really an
  • attack but can still bring down a network)

Firewall Problems
  • No protection against attacks based on bugs.
  • No protection against internal attackers.
  • No protection inside once an internal machine is
  • Accidental routes around the firewall dialup
    servers, cross links.
  • Can be too restrictive and interfere with wanted
  • Encryption prevents the firewall blocking
    malicious traffic.
  • A lot of services are done through HTTP so the
    firewall just sees Web traffic.

Information Warfare
  • Information warfare isnt a new post WW2 issue
  • 5000 years ago Chinese emperors guarded secrets
    of silk production,
  • 3500 years ago Mesopotamians guarded secrets of
    pottery glazing,
  • 2000 years ago Julius Caesar wrote messages in
  • However, it is true to say the post Internet
    world has increased
  • problems of secrecy, privacy, trust and
    integrity. The current online
  • population is 1,574,313,184 as of December 31
    2008, 23.7 of the
  • Planet. (http//
  • Advances in computers have also led to advances
    in sensors and
  • ubiquitous computing (Pervasive Computing, Gloss
  • Information technologies will increasingly be
    worn (biosensors), and
  • therefore used to monitor, predict, perhaps
    manage people.

Offensive Information Warfare
  • Computers and telecomm systems support energy
    distribution, emergency services, financial
    services. The critical infrastructure of many
    western countries are now solely dependent on
  • 95 of military communications are routed over
    civilian networks.
  • The number of potential targets and critical
    points for failure is increasing. Operations or
    attacks can be launched by governments, military
    or civilians. Conventional warfare is expensive
    (cost of weaponry, vehicles, manpower, lives) but
    computational power is a lot cheaper. Automated
    scripts for eavesdropping, password cracking etc
    are available online.

The Enemy Within
  • We trust computers -
  • We store a lot of personal information on it
  • We use an internet provider to attach to the
  • Our machine gets viruses
  • Hackers may hack into our systems (our own PC or
  • businesses we log into)
  • We lose information, identity, money..
  • The computer itself is not our enemy but the
    amount of trust
  • we put into it is. It has no loyalty like a dog
    or best friend.
  • We presume privacy and integrity but a computer
    is only as
  • secure as we can make it.

The Future Big Brother?
  • Your computer may be watching you!
  • The government certainly is, via cameras, banking
  • automatic licence plate scanners, RFID chips
  • Can a computer ever be as secure as we want it to
  • Can we stop it from watching us?
  • The latest thing in Computer Science is Cloud
  • Yesterday, an article in the Register
  • indicated a flaw in a search service that could
    attack many
  • users.

A Scottish Aphorism
  • As my granny used to say
  • Ye cannae keep what ye cannae hud in yer hands

  • Simon Singh The Code Book
  • Pfleeger and Pfleeger Security in Computing
  • http//