Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Security in
Communication Networks
Lehrstuhl für Informatik 4
RWTH Aachen
Prof. Dr. Otto Spaniol
Dr. rer. nat. Dirk Thißen
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
• Fortnightly
• Exercise is given on Monday, 16:45 – 18:15 • Frontal exercise
• Exact dates depend upon the lecture dates • Exercise sheets are provided on the web
page two weeks before an exercise date
Exercises
Planned exercise dates: 23.4. 7.5. 4.6. 25.6. 9.7.
Organization
Lecture
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Organization
Prof. Dr. Otto Spaniol, Dr. Dirk Thißen Lehrstuhl für Informatik 4, RWTH Aachen Ahornstraße 55, 52074 Aachen
Phone: 0241 / 80 – 21400/21450
eMail: {spaniol, thissen}@informatik.rwth-aachen.de
Contact Information for questions regarding lecture/exercises
http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/sikon/sikonSS07/index.html
Slide Copies
At the end of summer term
Written Exam
• Copies to the lecture slides as well as exercise sheets are placed on the web page to the lecture:
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Literature
• Kaufman, Charlie; Perlman, Radia; Speciner, Mike: Network Security – Private
Communication in a Public World. Prentice-Hall, 2002
• Schneier, Bruce: Applied Cryptography - Protocols, Algorithms, and Source Code in C. John Wiley & Sons, 1996
• Mao, Wenbo: Modern Cryptography. Prentice Hall, 2004
• Spaniol, Otto; Güneş, Mesut: Skript zur Vorlesung “Sicherheit in Kommunikationsnetzen”. Mainz-Verlag, 2000
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Evolution of the Internet
• “Necessity is the mother of invention, and computer networks are the mother of modern cryptography“ - R. L. Rivest
• The Story of the Internet:
During the latter half of the 1980's ARPANET moved from the research domain into a transcontinental reality
In November 1988 the "Internet worm" brought the ARPANET to its knees
Since then an almost continuous stream of security-related incidents has affected thousands of computer systems and networks throughout the world (see for more information http://www.cert.org)
By 2005, the Internet had grown from 60,000 host computer systems to over 350 million
Many companies and private users now rely on the Internet for their daily business and private communication (sharing financial, business, or personal information)
Attacks: illegal gain of information, unrecognized change of information, disturbance of the functionality (Confidentiality, Integrity, Availability)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Attacks on Computer
• Stand-alone computer system (UNIX operating system):
Only legitimate user with physical access to the computer system is able to log in by providing name and password
Attacker must have physical access and the login information • Networked computer (UNIX operating system):
System makes available some basic network services:
• telnetd: remote terminal access service, provided at port 23 • sendmail: electronic mail service, provided at port 25
• httpd: WWW, provided at port 80
• nsfd: network file service, provided at port 2049 Attacker does not need physical access
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Attacks on Computer
• Only an attacker who is able to physically access or connect to a computer system can attack it
→By adding more network connections, more vulnerabilities are added automatically
• A networked computer system runs software that is inherently more complex and error prone
→An attacker must know and be able to exploit just one single bug (administrator or security expert must know and fix each bug)
Security Goal: protect networked computers by separating a company network from the Internet (e.g. by a Firewall)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Attacks on Communication Processes
Passive Attack:
• Passive wiretapping attack: the attacker is able to interpret the data and to extract information
• Traffic analysis attack: attacker can observe who communicates with whom (e.g. two companies begin to exchange a large number of messages and combines them)
• Available programs: etherfind, tcpdump, ... Active Attack:
• Modify, extend, delete, and replay data units • Influence or modify routing tables
• Denial of service attack (flood a server)
Netw ork
Router
attacker
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Security in Communication Processes
Confidentiality
• Message contents should be kept confidential; i.e., only the communication partners may see it
• Sender and/or receiver of messages should remain anonymous, and third parties (including the network operators) should be unable to observe their communication • Neither potential communication partners nor third parties (including the network
operators) should be able to locate mobile stations
Integrity
• Forging message contents (including sender’s address) should be detected
• The recipient of a message should be able to prove that a particular message has been sent, and if that the addressee has received the message
• Nobody can cheat the network operators in terms of usage fees. On the other hand, the network operators can only charge fees for correctly delivered services
Availability
• The communication network enables communication between all parties who wish to communicate and who are allowed to do so
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Security Techniques
• Known techniques for
Confidentiality: Data encryption, anonymity techniques
Integrity: Data encryption, digital signatures, access control and authentication Availability: Fault-tolerant systems, access control, firewall, intrusion detection • Important term: Cryptography
Secrecy
• Steganography: Hide message, e.g. in a picture
• Encryption: enc_algorithm: (plaintext, key) → ciphertext Authentication
• Identification, entity authentication: Who is currently on the other end of this connection?
• Message authentication: Who created this message?
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Requirement: Trusted Domains
Source
Trusted Domain
Protection technique
Untrusted Area
Nearly no security technique is perfect: you mostly need to trust somebody: • Protection against every possible attacker is impossible
• Before the design of a protection technique it is necessary to identify trusted domains • A trusted domain comprises systems or parts of systems (e.g. security module)
• No attackers are assumed within a trusted domain (restriction of the attacker) • A trusted domain is always related to a single user or group of users
Destination Trusted Domain
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Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Shared-key Encryption Scheme
Encryption algorithm Secret Channel k enc(k, m) m Key generator Decryption algorithm m or „error“ random secur . par a m. k Trusted Domain k m = message, k = key • One-time pad, DES, IDEA etc.
• Can handle data volumes of several Gigabyte/s, but security is questionable • Key sizes of 56-128 bit
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Shared-key Authentication Scheme
Test algorithm Secret Channel k m, auth(k, m) “ok” or “error” Key generator Auth. algorithm m random secur . par a m. k Trusted Domain k m = message, k = key • Message authentication codes
• Specific constructions, or based on block ciphers or keyed hash functions • Limitation: third party cannot check authenticity
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Cryptographic Hash Functions
• Hash Function H: variable length in
fixed length out (≥128 bit) • One-way:
easy to compute infeasible to invert • Collision resistant
• Practical hash functions: SHA, MD5, etc.
• Cryptographic primitive
H: collision-resistant one-way hash-function fixed H: H(x) “simulates” a random oracle
variable H: Keyed hash functions, family of hash functions
H
≠
easy
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Public-key Encryption Scheme
Encryption algorithm Authenticated Channel pk enc(pk, m) m Key generator Decryption algorithm m or „error“ random secur . par a m. pk Trusted Domain sk Trusted Domain
m = message, sk = secret key, pk = public key • RSA, Diffie-Hellman/El Gamal
• About 10 times slower than symmetric schemes • “Key size” of 512-2048 bit for RSA
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Digital Signature Scheme
Test algorithm Authenticated Channel pk m, sign(sk, H(m)) Key generator Signature algorithm m random secur . par a m. pk Trusted Domain sk Trusted Domain “ok” or „error“
m = message, sk = secret key, pk = public key, H = hash function • Digital Signature: A hash value (collision-resistant) of a message is encrypted with the
secret key of a public-key encryption scheme. • RSA, El Gamal, etc.
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Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Access Control
•In general: authentication refers to the process of verifying the claimed identity of a principal
•User → Computer
Knows (proof of knowledge)
Possesses (proof of possession)
Biometric characteristics (proof by property) •User → System (via network)
Password-Based (Name A, Password B) Address-Based (Name A, Address B) Cryptographic:
Name: A Challenge: X Response: Y=f(X)
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Security in Layered Protocols
Application Transport IP PGP, PEM, ... SSH, SSL, ... AH, ESP Application Transport IP
PGP = Pretty Good Privacy, PEM = Privacy Enhanced Mail, SSH = Secure Shell, SSL= Secure Socket Layer, AH = Authentication Header, ESP = Encapsulating Security Payload • There are always alternative ways to provide a (security) service
Higher layers are more application dependent and technology independent
End-to-end security is easier provided at higher layers; link (point-to-point) security at lower layers
Higher layers are more likely implemented in software; lower layers in hardware Higher layer encryption cannot protect lower layer headers; lower layer encryption
may have to trust intermediate nodes
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Anonymity
Untraceability Unobservable by Outsiders Alice Bob• Multi-party protocol: collectively use of cryptographic protocols
• The sender and/or the recipient of a communication can remain anonymous
• Nobody (not even the network operator) can trace communication relations
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Protection of Networks: Firewall
• A firewall represents a barrier between a privately owned and protected network and another network (e.g. the Internet)
• Purpose: prevent unwanted and unauthorized communication into or out of the protected network
• Assume: Firewall is a trusted domain
Intranet Internet
Accessibility Security Firewall
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Protection of Networks: Intrusion Detection
System (IDS)
• IDS is a “burglar alarm for computers and networks” • Functional components
An analysis engine that finds signs of intrusion
A response component that generates reactions based on the outcome of the analysis engine
• Analysis engine:
Offline: analysis of stored log data
Online: “on the fly analysis” of observed data • Response capabilities after analysis:
Alarm
Deny operation
• Attack Recognition: learning of attack patterns or usual habit of users → Privacy problem
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Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Content
Chapter 2: Security Techniques Background • Secret Key Cryptography
• Public Key Cryptography • Hash Functions
• Authentication
Chapter 3: Security on Network and Transport Layer • e.g. IPsec, SSL, TLS, …
Chapter 4: Security on the Application Layer • e.g. Kerberos, PGP
Chapter 5: Security Concepts for Networks • e.g. Firewalls, Intrusion Detection
