Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Security Services in Information Systems
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Antecedents and Motivation
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
What is this part of the course about?
In this part of the course we will discuss the following topics
– security needs– security services– security mechanisms and protocols
for data stored in computers and transmitted across computer networks
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
What we will/won’t cover?
• We will cover– security threats– security protocols in use with emphasis on Authentication– Certificates and PKI– Introduction to Wireless Security
• We will not cover– cryptography (just an overview will be given)– computer networks– operating systems– computers in general– how to hack
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
What security is about in general?
• Security is about protection of assets– D. Gollmann, Computer Security, Wiley
• Prevention– take measures that prevent your assets from being damaged
• Detection– take measures so that you can detect when, how, and by
whom an asset has been damaged
• Reaction– take measures so that you can recover your assets
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Real world example
• Prevention– locks at doors, window bars, secure the walls
around the property, hire a guard
• Detection– missing items, burglar alarms, closed circuit TV
• Reaction– attack on burglar, call the police, replace stolen
items, make an insurance claim
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Services, Mechanisms, Attacks
• 3 aspects of information security:– security attacks (and threats)
• actions that compromise security
– security services• services counter to attacks
– security mechanisms• used by services• E.g. secrecy is a service, encipherment is a mechanism
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
NETWORK SECURITY FUNDAMENTALS
•Security Attacks and Security Services
•A Model of Network Security
•Access Policies
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
SECURITY ATTACKSSECURITY ATTACKS
&&SECURITY SERVICESSECURITY SERVICES
•Unauthorised Access
•Unauthorised Disclosure of Information
•Unauthorised Modification of Information
•Unauthorised Denial of Service
Security Threads
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Attacker resources and methods vary greatly
Resource Teenager Academic Org. Crime Gov’t
Time Limited Moderate Large Large
Budget ($) <$1000 $10K-$100K $100K+ Unknown
Creativity Varies High Varies Varies
Detectability High High Low Low
Target Challenge Publicity Money Varies
Number Many Moderate Few Unknown
Organized No No Yes Yes
Spread info? Yes Yes Varies No
Source: Cryptography Research, Inc. 1999, “Crypto Due Diligence”
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Source: Blaze/Diffie/Rivest/Schneier/Shimoura/Thompson/Wiener: www.bsa.org/policy/encryption
Minimal key lengths for symmetric ciphers
Typeof attacker
Budget Tool Time and costper key recovered
Length needed forprotection in late 1995
40 bits 56 bits
Pedestrian Hacker
SmallBusiness
CorporateDepartment
Big Company
IntelligenceAgency
tiny
$400
$10.000
$300K
$10M
$300M
scavengedcomputer time
FPGA
FPGA
FPGA
ASIC
FPGA
ASIC
ASIC
1 week
5 hours($0.08)12 min($0.08)24 sec($0.08)18 sec
($0.001) 7 sec
($0.08)0.005 sec($0.001)
0.0002 sec($0.001)
infeasible
38 years($5,000)556 days($5,000)19 days($5,000)3 hours($38)
13 hours($5,000)
6 min($38)
12 sec($38)
45
50
55
60
70
75
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
SECURITY ATTACKSSECURITY ATTACKS
&&SECURITY SERVICESSECURITY SERVICES
Passive Attacks
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
SECURITY ATTACKSSECURITY ATTACKS
&&SECURITY SERVICESSECURITY SERVICES
Active Attacks
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
SECURITY ATTACKSSECURITY ATTACKS
&&SECURITY SERVICESSECURITY SERVICES
Attacks
Accidental Intentional•Software Errors
•Hardware Errors
•Poor Management of Resources
Passive Active•Release of Message content•Traffic Analysis
•Data Mod.•Data Delay•Data Blocking•Data Copy•Data Replay•Data Destruction
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Security Mechanisms
• Basically cryptographic techniques/technologies – that serve to security services – to prevent/detect/recover attacks
• Encipherment– use of mathematical algorithms to transform data
into a form that is not readily intelligible• keys are involved
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
• Message Digest– similar to encipherment, but one-way (recovery not
possible)– generally no keys are used
• Digital Signatures– Data appended to, or a cryptographic transformation of, a
data unit to prove the source and the integrity of the data
• Authentication Exchange– ensure the identity of an entity by exchanging some
information
Security Mechanisms
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
• Notarization– use of a trusted third party to assure certain properties of a
data exchange
• Timestamping– inclusion of correct date and time within messages
• Non-cryptographic mechanisms– traffic padding (for traffic analysis)
– intrusion detection
– firewalls
Security Mechanisms
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Security Services
• Confidentiality - protect info value • Authentication - protect info origin (sender)
• Identification - ensure identity of users
• Integrity - protect info accuracy • Non-repudiation - protect from deniability • Access control - access to info/resources • Availability - ensure info delivery
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Relationships
Integrity
Authentication
Non-repudiation
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Two references
• ITU-T X.800 Security Architecture for OSI– gives a systematic way of defining and providing
security requirements
• RFC 2828– over 200 pages glossary on Internet Security
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Security Systems by layers
Computer Arithmetic : Addition, Squaring, multiplication, inversion and exponentiationComputer Arithmetic : Addition, Squaring, multiplication, inversion and exponentiation
Public Key Crypto Algorithms: RSA, ECCSymmetric Crypto Algorithms: AES, DES, RC4, etc.
Public Key Crypto Algorithms: RSA, ECCSymmetric Crypto Algorithms: AES, DES, RC4, etc.
Crypto User Functions: Encrypt/Decrypt, Sign/verify
Crypto User Functions: Encrypt/Decrypt, Sign/verify
Security Services: Confidentiality, Data Integrity, Data Authentication, Non-Repudiation
Security Services: Confidentiality, Data Integrity, Data Authentication, Non-Repudiation
Communication Protocols : SSL, TLS, WTLS, WAP, etc.
Communication Protocols : SSL, TLS, WTLS, WAP, etc.
Applications: Secure e-mail, Digital Money, Smart Cards, Firewalls, etc.
Applications: Secure e-mail, Digital Money, Smart Cards, Firewalls, etc.
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Fundamental Dilemma of Security
• Security unaware users have specific security requirements but no security expertise.– from D. Gollmann– Solution: level of security is given in predefined
classes specified in some common criteria
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Fundamental Tradeoff
• Absolutely secure systems do no exist
• To half your vulnerability you have to double your expenditure
• Cryptography is typically bypassed not penetrated.
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
The Three Laws of Security
• Security unaware users have specific security requirements but no security expertise.– from D. Gollmann– Solution: level of security is given in predefined
classes specified in some common criteria
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Kerckhkoffs’s Principle
While assessing the strength of a cryptosystem, one should always assume that the enemy knows the cryptographicalgorithm used.
The security of the system, therefore, should be based on
* the quality (strength) of the algorithm but not its obscurity* the key space (or key length)
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
A Cryptosystem Classification
• Public key cryptography (RSA, ECC, NTRU)
• Secret key Cryptography (DES, AES, RC4)
• Block ciphers (DES, IDEA, RSA) 64-128 bits
• Stream ciphers (A5, RC4, SEAL) encryption in a bit to
bit basis.
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
A Simplified Model of Conventional Encryption
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Message Digest
• A message digest, also known as a one-way hash function, is a fixed length computionally unique identifier corresponding to a set of data. That is, each unit of data (a file, a buffer, etc.) will map to a particular short block, called a message digest. It is not random: digesting the same unit of data with the same digest algorithm will always produce the same short block.
• A good message digest algorithm possesses the following qualities– The algorithm accepts any input data length.
– The algorithm produces a fixed length output for any input data.
– The digest does not reveal anything about the input that was used to
generate it. – It is computationally infeasible to produce data that has a specific digest.
– It is computationally infeasible to produce two different unit of data that produce the same digest.
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Hash Algorithms
• Reduce variable-length input to fixed-
length (128 or 160bit) output
• Requirements
– Can't deduce input from output
– Can't generate a given output
– Can't find two inputs which produce the
same output
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Hash Algorithms
• Used to
– Produce fixed-length fingerprint of arbitrary-length data
– Produce data checksums to enable detection of modifications
– Distill passwords down to fixed-length encryption keys
• Also called message digests or fingerprints
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Message Authentication Code MAC
• Hash algorithm + key to make hash value dependant on the key
• Most common form is HMAC (hash MAC)
– hash( key, hash( key, data ))
• Key affects both start and end of hashing process
• Naming: hash + key = HMAC-hash
– MD5 HMAC-MD5
– SHA-1 HMAC-SHA (recommended)
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
An Example
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Digital Signature/Verification Schemes
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Digital Signature/Verification Schemes
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Digital Signature/Verification Schemes
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Seven-Layer OSI Model
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
SECURITY ATTACKSSECURITY ATTACKS
&&SECURITY SERVICESSECURITY SERVICES
OSI Security Services•Authentication
•Access Control
•Data Confidentiality
•Traffic Flow Confidentiality
•Data Integrity
•Non-Repudiation of both Origin and Delivery of Data
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
SECURITY ATTACKSSECURITY ATTACKS
&&SECURITY SERVICESSECURITY SERVICES
OSI Security Mechanisms•Encipherment•Digital Signatures•Access Control Mechanisms•Data Integrity Mechanisms•Authentication Exchange Mechanisms•Traffic Padding Mechanisms•Notarisation Mechanisms•Routing Control Mechanisms
Seguridad en Sistemas de Información
verano 2004Francisco Rodríguez Henríquez
Inter-network Protocol (IP)
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