PA018 –
Advanced Topics in IT Security
Vašek Matyáš
Email: matyas@fi.muni.cz
Office hours: Mon 15:05-55 & Tue 9:05-55 (B415)
Marking Your Performance
• 40% - written exam (closed book).
• 30% - term project:
– Topic of your choice, approved by the lecturer!
– Worth about 30 hours of work (excl. doc. editing).
– Final report (9-10 pages) submitted by May 22nd.
• 30% - assignments (approx. 5) through the term:
– Deadline in 10-14 days.
– Distributed and collected electronically.
The Final Mark
A for 90% or higher, then
B for 80% or higher, then
C for 70% or higher, then
D for 60% or higher, then
E for 50% or higher, then
F(ail) for less than 50%.
Colloquy or credit – at least 50%.
Marking & Language
• The course and assignments are given in
English.
• Questions (course, assignment, etc.) should be
in English.
• Assignments are to be handed in also in
English, as should be the project
presentation!!!
• Final exam and the term project are accepted
in both Czech and English.
Structure of the course
• First half-term of lectures and readings
– Readings – seminal papers in the field
– …and work on the term project!!!
– Rather demanding work, compensating for the
end of the term
• 3-4 guest lectures (fingerprints and liveness,
HSMs, malware and firewalls / networks)
• May (after Easter)
– your term project presentations
• Part (5 of 30 points) of your mark
• With feedback to reflect in the final report
Typical Security Requirements I.
• Authentication: originator’s identity
assured.
• Integrity: information received as
originated.
• Confidentiality: information available
only to authorized parties.
Typical Security Requirements II.
• Availability: data & resources available when
needed.
• Non-repudiation: party cannot deny
communication (origin, receipt, delivery, etc.).
• Access Control: resources controlled by
authorized parties.
• …could list a few more…
Alice
Conventional Names for Players
Bob
Eve
Security-Related
Transmission
Message
Protected
Information Information Channel
Security-Related
Transmission
Message
Protected
Information
Principal
Opponent
Trusted Third Party
(arbiter, distributor of secret information)
Principal
Adapted From: Network and
Internetwork Security (Stallings)
Network Communications Security
Model
What are keys?
• Large bitstrings
– random numbers
...000100101010
01010100010100
10010101001001
00010111110101
01110101011100
10101100101000
10101001010010
10101011111101
10100110010001
00111010101010
110...
• Asymmetric Cryptography
– Private Key
(Confidentiality)
– Public Key (Integrity)
• Symmetric Cryptography
– Same Key for Alice and
Bob
What is hashing?
• “Data Fingerprints”
– short & unique image of
data
... It will be a blustery day in
Scotland with gales and showery
rain in the north-east. Elsewhere
in Scotland the showers will be
more scattered at first with a few
sunny spells, but outbreaks of
rain will spread from the southwest
this afternoon. Northern
Ireland, Wales and England will
also have a showery day. The
showers are likely to merge to
give longer spells of rain at
times, although in the south and
west there is a better chance of
some sunny intervals this....
• EC:43:6F:B3:68:CE:20:E7
• 01:A0:7D:2B:76:52:67:05
... It will be a blustery day for
Scotland with gales and showery
rain in the north-east. Elsewhere
in Scotland the showers will be
more scattered at first with a few
sunny spells, but outbreaks of
• Hashing functions
• one-way, collision-free
• SHA-2 series (256bit and more)
• „retiring“ SHA-1 (160b),
• „retired“ MD5 (128b)
Encryption
Algorithm
Decryption
Algorithm
Shared Key
Plaintext Ciphertext Plaintext
Adapted From: Network and
Internetwork Security (Stallings)
Simplified Model of Conventional
Encryption
Encryption
Algorithm
Decryption
Algorithm
B’s Public Key
Plaintext Ciphertext Plaintext
User A
B’s Private Key
User B
Adapted From: Network and
Internetwork Security (Stallings)
Simplified Model of Public-Key
Encryption
Verification
Algorithm
Signature
Algorithm
B’s Public Key
Signed Message Message
User A
B’s Private Key
User B
Adapted From: Network and
Internetwork Security (Stallings)
Simplified Model of Public-Key
Signatures
Authentication
Integrity
Non repudiation of origin
Alice
Signing
What are Digital Signatures?
Dear Bob,
Yada yada
yada….
Alice
Alice’s
Private Key
Certificate
Bob
Generic security goals Protection
against…
• access to information by unauthorized parties
• modification of data by unauthorized parties
• unaccountable modification/deletion/creation…
of data by unauthorized parties
• withholding data or resources from authorized
parties
• false denial of a party’s involvement in a given
action
• …
Security is not just prevention
1. Prevention (protection)
2. Detection
3. Reaction
Information dominance
1. Aim: Reaching own information
dominance: having the right information
at the right place in the right time.
2. Aim (offensive): Limit the other party in
reaching full information dominance.
One after another…
1. Risk analysis
2. Specification of security policy and
security architecture
3. Design and implementation of security
mechanisms
4. Support, maintenance, control, reevaluation
(back to 1…)
Security policy
• VERY IMPORTANT for improving the (IT)
security in any company
• Company business goals  IT goals  IT
security goals
• Helps with
– Setting priorities (for IT, security departments)
• Long-term goals vs. short-term goals
• Improvement of services (vs.) company survival(!)
– Getting management support and assuming direct
responsibilities
Trusted (system, component…)
• Such one that behaves in a way we expect it to
behave
• Can be trusted to only such a functionality that
adheres to the relevant security policy
• Trust
– Belief that (a system…) satisfies given (security)
requirements and specifications
– Chance that (a system…) can breach the (security)
policy without leaving any trace of evidence 
Accident and attack
• Murphy’s Law
– bad things can happen by accident,
– and we should expect that they will happen,
preparing for a malfunction
• Satan’s Law
– very bad things can happen at someone’s will
– and we should do our best to consider all possible
ways of pursuing that will, preparing for an attack
• B. Schneier – see Crypto-Gram (ref. later)
Threat exploits vulnerability…
• Vulnerability – A weakness in system
security procedures, system design,
implementation, internal controls, etc., that
could be exploited to violate system security
policy.
• Threat – Any circumstance or event with the
potential to cause harm to a system in the
form of destruction, disclosure, modification
of data, denial of service…
Risk helps us judge threat…
• Risk – The probability that a particular
threat will exploit a particular vulnerability
of the system.
• Risk analysis – The process of identifying
security risks, determining their magnitude,
and identifying areas needing safeguards.
Risk analysis is a part of risk management.
Attack – the threat comes true…
• Attack – The act of trying to bypass security
controls on a system. An attack may be
active, e.g. resulting in the alteration of data;
or passive, e.g. resulting in the release of data.
Note: The fact that an attack is made does not
necessarily mean that it will succeed. The
degree of success depends on the
vulnerability of the system or activity and the
effectiveness of existing countermeasures.
Authenticate & Authorize
• Authentication
1. To verify the identity of a user, device, or
other entity in a computer system, often as a
prerequisite to allowing access to resources in
a system.
2. To verify the integrity of data that have been
stored, transmitted, or otherwise exposed to
possible unauthorized modification.
• Authorization – The granting of access rights to
a user, program, or process.
Identification vs. Authentication
Determination of a
person’s identity. (1:N)
“Positive authentication”
Hard to achieve
– Small user groups.
– Low accuracy.
– Exception: iris scan.
Verification of a person’s
identity claim. (1:1)
Easier than identification.
User group size – accuracy!
Means of authentication Access to a service
• something you know
(password, PIN)
• something you have (key,
smartcard)
• something you are -
biometrics
• or combination of the above
• Access by a person (process)
that knows a secret.
• Access by a person
possessing a “key”.
• Access by a person with this
characteristic.
Something you know
+ Easy transport
+ Not a physical object
+ Easy & Fast control
+ Easy maintenance
+ (Low cost)
– Easy to copy after
discovery
– Can be discovered without
user’s knowledge
– Limited by human
memory
– Can be forgotten
Something you have
+ Hard to copy
+ Loss easy to discover
+ The object itself can
process information
– Need of reader
– User is not recognized
without the object
– The object must be
complicated so that it is
hard to copy
– Can break down, this
often not detected easily
Something you are
+ Is part of a person
+ Cannot be lost
– Accuracy
– Protests/resistance of
users
– Hard to measure
– Limited number of
object to use 
Combine!
• Multifactor authentication
– Something you know
– Something you have
– Something you are
• ATM/Banking card – card + PIN
• Spoken passphrase – passprase + speaker recogn.
• Really smart smartcard – card + PIN + fingerprint
Passwords
• Group passwords common to all users (in a
group) of a system
• Passwords unique to individual users
• Non-unique passwords confirming identity
• One-time passwords
Don’t store passwords in clear text!
• Salting technique
– userID, salt, hash(password, salt)
– Effective password
• Longer
• Not a common word/combination
– Two users with the same password have
different entries in the password database.
Passwords
Human memory vs. security
(short easy-to-guess string vs. long complicated string)
• Dictionary attack
– All combinations of up to 5-8 characters.
– Common words and user-related values.
– Usual success rate 20-40%
Choice of passwords – problems
• Easy to remember for the user and hard to
guess for anyone else
• Requested change (password “circulation”)
• Password selection without user input 
• Same password over more systems
Choice of passwords – suggestions
• Password (choice) quality control!!!
• Special characters, Shift, substitutions
(phonetic, mnemonic)
• Use phrases: Early One Morning With Time
To Kill ( Sting) – EY1ghe2KL
• Enforce your password security policy
through some mechanism!!!
Banks – card & PIN
• Personal Identification Number
– Every combination with same probability
– Not discarding “easy” combinations
– Not only 4, but up to 8 (6) digits
– Markus Kuhn – Cambridge (UK) – ref. later
• Distribution of card, PIN
– Both via different routes (or instances)
– Personal retrieval (of at least one)
– PIN of own choice
Suggested (not required) readings
• M. Kuhn: Probability Theory for Pickpockets –
ec-PIN Guessing
http://www.cl.cam.ac.uk/~mgk25/ec-pin-prob.pdf
• J. Yan et al.: The memorability and security of
passwords – some empirical results, University
of Cambridge Computer Laboratory Technical
Report No. 500
http://www.cl.cam.ac.uk/TechReports/
Tokens
• Keys
• Magnetic cards (3-track strip ~ 250 B)
– Easy to copy
• Shifting tracks of limited use
• Individual characteristics of tracks can be of some use
– PIN manipulation also easy
• Bank cards – with signature, possibly PIN
– Customer Not Present transactions problematic
Smartcards
• Smartcard vs. Chipcard
• Can store (some even work with) a crypto key
• Cash-loading (anonymous vs. loss-recoverable)
• GSM – authentication key; PIN-PUK
• Implementation in bank cards
– Compatibility – users, retailers(!) (VISA – 2007)
– Potentially can be used with biometrics
Authentication calculators
• Challenge-response based
– Response = f(secret key, challenge)
• Time-based (SecurID)
– Server takes care of time-frame shifts
• Transfer – manual vs. automatic
• PIN – standard and emergency
Biometrics
• PIN/password either
matches (at 100%) or not
• Biometrics rarely match at
100% (often taken as a
fake/attack).
• Threshold-based decision
introduces the rates of false
acceptance and rejection
• Verification (of identity) -
1:1 match)
• Identification - 1:N
search for the best match
Biometrics – major issues
• Biometrics are very sensitive
• Biometrics are not secrets
• Copying: neither trivial nor hard
• New attack countermeasures are followed
by newer attacks
Crypto-Gram Newsletter
• Free monthly e-mail newsletter on general
and computer security from Bruce Schneier
(author of Secrets and Lies and Applied
Cryptography, inventor of Blowfish and
Twofish, CTO and founder of Counterpane
Internet Security…).
• http://www.schneier.com/crypto-gram.html
The RISKS Forum
• The RISKS Forum is a moderated digest. Its
USENET equivalent is comp.risks.
• http://www.risks.org
Course reading – week 1
• Why Cryptosystems Fail, R. Anderson
• 1993 paper with results of a survey of the failure
modes of retail banking systems, with criticism of
the threat model commonly used by cryptosystem
designers: most frauds were not caused by
cryptanalysis or other technical attacks, but by
implementation errors and management failures.
• http://www.cl.cam.ac.uk/users/rja14/wcf.html
Topics for term projects
• Study of… a virus, a particular security
solution/system, crypto algorithm…
• Security of … JavaCard 3.0, smartcard X…
• New… firewall, IDS, mobile security app,
malware trend…
• Focus (don’t go for broad topic/area)!
• Mail me, with Subject: PA018 – term project
• Deadline for proposal and approval – Feb 28!!!
Questions, comments,
suggestions…???
Go ahead!
