NETWORK Authors Hari Thiruvengada Varun Lalchandani SECURITY

NETWORK

Authors

Hari Thiruvengada

Varun Lalchandani

SECURITY...

Contents

• Introduction.

• Encryption and Protocols.

• Kerberos.

• Network Security Issues and Protocols.

• Intrusion Detection

• Web Security.

• Digital Identification Techniques.

• Cryptography and web Security.

• Firewalls.

• References.

Security and its breaches…

Security • a system is secure if it is

– Security goals are achieved.

– Components behaves as expected on it.

Breaches• Interruption - System asset lost , unavailable or unusable.

• Interception - Unauthorized party gains access to asset.

• Modification - Tampering with the asset.

• Fabrication - counterfeit objects on computing system.

Security Goals and Vulnerabilities

Security Goals• Confidentiality - assets of a computing system

accessible only by authorized user.Read only type of access like viewing, printing helps in privacy.

• Integrity - modification only by authorized parties.

Precise, accurate, consistent assets.

• Availability - assets are accessible to authorized parties.Timely response, fair allocation, fault tolerance, usability, controlled concurrency. (Denial of service attacks.)

The people involved…

• Amateurs - fresh players of the game , disgruntled over a -ve work situation.

• Crackers - breaking into unauthorized territory without malicious intent.

• Hackers - breaking into unauthorized territory with malicious intent.

• Career Criminals - people in the game for money and have predefined targets.

Basic Encryption and Decryption

• Encryption - process of encoding a message so that its meaning is not obvious.

• Decryption - process of decoding the encrypted message.

• Cryptography - Hidden writing, which conceals meaningful text.

• Cryptanalyst - studies encryption and finds hidden messages.

• Cryptanalysis – attempt to break a single message.– Recognize patterns in encrypted messages to break into subproblems

by straightforward decryption algorithm.– Find weakness in encryption algorithms.

Contd…

Encryption with Keys

EncryptionEncryption DecryptionDecryptionPlain Text Cipher Text Original Text

Encryption Key (Ke)

(Asymmetric Cryptosystem)

Decryption Key (Kd)

Encryption with Keys


Key

(Symmetric Cryptosystem)


Encryption

Encryption• Substitutions - one letter x-changed for other.

– Monoalphabetic Ciphers.• Caesar Cipher

Example: Plaintext:ABCDEFGHIJKLMNOPQRSTUVWXYZ

Cipher :DEFGHIJKLMNOPQRSTUVWXYZABC

– Polyalphabetic Ciphers.

• Frequency distribution reflects the underlying letters. Table for Odd Positions

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A D G J M P S V Y B E H K N Q T W Z C F I L O R U XA D G J M P S V Y B E H K N Q T W Z C F I L O R U X

Table for Even Positions

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z N S X C H M R W B G L Q V A F K P U Z E J O T Y D IN S X C H M R W B G L Q V A F K P U Z E J O T Y D I

Contd…

Example:

F1(x) = (3 * x)mod 26.

F2(x) = ((5 * x) +13) mod 26.

Encryption for :

TREAT YIMPO SSIBL E

would be

FUMNF DYVTF CZYSH H

Contd…• Transposition - letters of message rearranged.

– GOAL - Diffusion

Example:

C1 C2 C3 C4 C5

C6 C7 C8 C9 C10

C11 C12 etc.

The resulting cipher text will be

C1 C2 C3 C4 C5

C6 C7 C8 C9 C10

C11 C12 etc.

Encryption Protocols…

ArbiterAA

BB

Arbitrated Protocol

Adjudicated Protocol

Self-Enforcing Protocol

AA

AA

BB

BB Adjudicator

You are cheating

A acted fairly

Symmetric Key X-change W/out Server

• Small no. of messages.

• Less risk of intrusion.

• Each user have a copy of symmetric secret encryption key K.

• For greater security one can generate a fresh key called KNEW.

• Send E(KNEW,K).

Symmetric Key X-change With Server

DISTRIBUTION CENTER(DC)

Renee Pablo

1.Give me a key

(P, R, Ip )

2.Here is the key and E(Ip ,R,KPR,,E((KPR ,P), KR)), KP)

3. DC gave me key for Private Communication

E((KPR ,P), KR )

2. E((KPR ,P), KR )

Asymmetric Key X-change W/out Server

1. EP(DR (K))

Renee sends new key

2. S (n,K)

Pablo sends encrypted random number

3. S (n+1,K)

Renee returns successor of Random Number

ReneePablo

Asymmetric Key X-change With Server

DISTRIBUTION CENTER(DC)

Renee Pablo

1.Give me a Renee’s key (P,R)

2.Here is the Renee’s

Key (DD(ER,R))

3. I’ am Pablo, let’s Talk. ER(P, IP)

6. Renee here , What’s up ? EP(R, IR )

7. Reply with ER(M, IR)

5. Here’s Pablo’s

Key (DD(EP ,P))

4. Please give me Pablo’s public key (R ,P)

Authentication in Distributed Systems

• Kerberos

UserUserUU

Kerberos Kerberos ServerServer

Ticket Granting Ticket Granting ServerServer

1. U’s Identity

Session keySG

Ticket TG

2. Encrypted under Password

Session key SG

2. Encrypted underKS-TGS Key

Initiating a Kerberos Session

Contd..

Obtaining a ticket to access a file

UserUserUU

Ticket Granting Ticket Granting ServerServer

1. Request to AccessFile F

2.Encrypted under TGS - F Key + SF

Ticket to File Serverto access File F + SF

How Kerberos withstand Attacks?

• No passwords communicated on Network.

• Cryptographic protection.

• Limited period of validity.

• Mutual authentication.

Why Kerberos is not the perfect Answer?

• Kerberos requires the availability of continuous trusted

“Ticket Granting Server ”.

• Trusted relationship required between TGS and every server.

• Requires timely transactions.

• Subverted workstation can save and later replay user

passwords.

• Password guessing works.

• Does not scale well.

NETWORK SECURITY ISSUES

• Sharing.

• Complexity of system.

• Unknown Perimeter.

• Many points of attack.

• Anonymity.

• Unknown path.

Threats

• Wiretapping.

• Impersonation.

• Message Confidentiality Violations.

• Message Integrity Violations.

• Hacking.

• Code Integrity Violation.

• Denial of Service.

Wire tapping

AA

BB

CC

Packet Sniffer

Inductance

Microwave link

Network Security Protocols

• Link Encryption.

Message encryptedMessage encrypted Message in plain text.Message in plain text.

sendersender ReceiverReceiver

Intermediate RouterIntermediate Router

ProtocolProtocol

LayersLayers

Contd...

• End to End Encryption.

Message encryptedMessage encrypted Message in plain text.Message in plain text.

sendersender ReceiverReceiver

Intermediate RouterIntermediate Router

ProtocolProtocol

LayersLayers

Comparisons

1.Message X-posed in sending host / intermediate routers.2.Applied by sending host.3.Invisible to user process.4.Host maintains encryption.5.can be done in H/w.6.All / No message encrypted.7.One key per host pair.

1.Message encrypted in sending host / intermediate routers.2.Applied by sending process.3.User selects algorithm.4.User selects encryption.5.S/w implementation.6.User chooses to Encrypt / Not.7.One key per user pair.

Link Encryption End to End Encryption

Intrusion Detection• Intrusion - set of actions attempts to compromise

integrity,confidentiality or availability of resources.

• IDS based on Data source-host based : audit data from single host.-multi host based : audit data from multiple host.-network based : network traffic data along with audit

data from one or many host.

• IDS based on Model of Intrusion.-Misuse detection system: look for the exploitations of

known weak points.

-Anomaly Detection System: detect changes in the pattern of utilization or behavior of system.

Desirable Characteristic of ID

• Must run continually.• Must be fault tolerant.• Must resist subversion.• Must impose minimal overhead.• Must be able to adapt changes in the behavior of user

and system.• Must be scalable.• Must provide graceful degradation.• Must allow dynamic reconfiguration.

Limitations of Existing ID

• Central Analyzer is single point of failure.

• Scalability is limited.

• Difficult to add capability or reconfigure.

• Analysis of Network data can be flawed.

Intrusion Types

• Attempted Break-in.

• Masquerade attack.

• Penetration of security control system.

• Leakage.

• Denial of service.

• Malicious use.

ARCHITECTURE TO GENERATE THE STD. FORMAT

LOG FILTERLOG GENERATOR

LOG GENERATOR LOG FILTER

LO

G P

RO

CE

SS

OR

AN

AL

YIS

EN

GIN

E

STANDARD AUDIT TRAIL FORMAT

• Must satisfy two basic properties:Extensibility: Neither the names nor the number of fields of

the log record are fixed.

Portability : The log can be processed on any system.

• SUMMARY OF THE STD. LOG FORMAT #S# start log record. #Fc# change field separator to c.#E# end log record. #Cc# change nonprinting delimiter to c.

#N# next log record. #I# ignore next field.

# default field sep. \ default nonprinting delimiter.

The standard log contains fields.

Each field is associated with an attribute.

SunOS MLS Logs

• A simplified example of a SunOS MLS log record is given as:

header, 120, AUE_UNLINK, Wed Sep 18 11:35:28 1999, +57000ms

process, bishop, root, root, daemon, 1234,

label, confidential, nuclear, crypto

pathname, /, / usr / holly,…/ matt / tmp / junkfile

return, Error 0, 5trailer, 120

• Put into the standard log format , this looks like:#S#event=AUE_UNLINK#date=09181999@113528#usedtime=57000#I##logid=bishop#ruid=root#euid=root#rgid=daeon#procid=1234#I##seclevel=confidential#class=nuclear#class=crypto#I##rootdr=/#cwd=/usr/holly#pathname=../matt/tmp/junkfile#I##errno=0#retval=5#E#

Typical Anomaly Detection System

Audit Data System Profile

statistically

deviant

Update profile

Generates new profile

Attack State

Anomaly ID(Statistical Approach)

• Let S1, S2, S3 … Sn, represent abnormality values of profile

measures M1, M2, M3 … Mn respectively.

• Higher value of Si indicates greater abnormality.

• A combining function of individual S values will be,

a1S12 + a2S2

2 + a3S32 + … + anSn

2 , a i > 0.

Pros and Cons of Anomaly ID.

• Statistical techniques have applicability here.

• Statistical patterns could be used to capture patterns unique to the

user.

Types of Measure.

• Activity Intensity Measure – measures the rate at which activity is progressing. E.g. no. of audit

records processed per minute.

• Audit record distribution measure – measures the all activity types in recent audit records.E.g. I/O

activities.

• Categorical Measure – measures the distribution of particular activity over categories. E.g.

relative frequency of logins,relative usage of compiler, shells,editor etc.

• Ordinal Measure – measure activity whose output is in numeric value. E.g. CPU usage.

Typical Misuse Detection System

Audit Data System ProfileSystem ProfileAttack

stateRulematch

Modify existing rule

Add new ruleTiming Info

Misuse ID• Detection of intrusions by precisely defining them well ahead of

time and watching for their occurrence.• Intrusion signatures are sequence of events and conditions that

lead to a break-in.• Abstract high quality patterns from attack scenarios.• Should be simple enough to keep the matching tractable and

should be compared.• If pattern matches then issue an alarm warning.

Pros and Cons of Misuse ID

• Looks only for known vulnerabilities, comparison is finite.• Little use to detect little known future intrusion patterns.

Continues…

Model based Intrusion DetectionA Pattern Matching approach

• Consider an initial set of 100 measures as potentially relevant to predicting intrusions.

• Resultant is a set of 2100 possible measures.• Appropriate set of measures depend on the types of measures being

detected, so highly intractable to search this large space X - haustively.

• A Learning Classifier Scheme generates initial set of measures.• Refined using “Rule Evaluation” techniques like mutation and

crossover.• Highly predictable sets of intrusions are combined and then

searched, while lower predictable ones are weeded out.

… Continued

• Combined Belief in I is

P ( I | A1, A2... An) = P (A1, A2... An | I ) x P ( I )

P(A1, A2... An )

• Each Ai depends only on I and is independent of the other measures of Ai , j = i, then

P (A1, A2... An | I ) = P(Ai | I )

P (A1, A2... An | ~I ) = P(Ai | ~I ) , and then

P ( I | A1, A2... An) P( I ) x P(Ai | I )

P ( ~I | A1, A2... An) P(~ I ) x P(Ai |~ I )

n

i=1n

i=1n

i=1n

i=1

Inference

• Determine odds of an intrusion given,– Values of various anomaly measure from the

prior odds of intrusion,

likelihood of each measure being anomalous is presence of INTRUSION !!

A Trivial Bayesian Belief Network modeling Network Intrusion activity

INTRUSION

DISK I/O

Too many users

Fragmentation

Trashing

Newly available program on

the net

Net I/OCPU

Too many CPU Intensive

jobsToo many Disk Intensive

jobs

Conditional Probability

• If we wish to detect P( Intrusion | Event Pattern)

By Baye’s Law,

P( Intrusion | Event Pattern) = P(Event Pattern | Intrusion ) x P(Intrusion)

P(Event Pattern)

P(Event Sequence) = (P( ES | I ) P( ES | ~I)) x P( I ) + P( ES | ~I)

where,

ES - Event Sequence,

I - Intrusion.

Web Security...

• IN A NUTSHELL– A set of procedures, practices, and technology to protect web

severs,web users and the surrounding Organizations.

– Internet is a two way network.

– Used by everybody.

– Potential security flaws exist.

– If subverted can be used by bad guys for malicious operations.

– Unsophisticated users are the major population.

– More expensive and time-consuming.

Why worry about web security ?

• Publicity - successful attack is a public event.

• Commerce - Money is involved as transactions.

• Proprietary Info - used to distributed information to

internal members and external partners. • Network Access - used by people both inside and

outside an organization.

• Others - like server X-tensibility, Browser X-tensibility, disruption of service, complicated support, etc.,

The Web Security Problem...

• Securing information in transit.– Digital Identification Techniques– Cryptography and Web security

• Securing the Web Server.– Host and site security. (Firewalls)

Digital Identification Techniques

• Digital Signatures,– a protocol that produces the same effect as real

signature.

– Only the sender can mark it.

– Easily identifiable by others as one from the sender.

– Used to confirm agreement to a message.

– Similar to biometrics such as image of a person’s face , fingerprints, Hand shape and size, DNA patterns, Voice prints, pattern of blood vessels in Retina, etc.

Contd..

Digital Signatures must be– Authentic : Person B receives the pair [M, S(A,M)]

from A, B can check if it came from A, and also this is firmly attached to M.

– Unforgeable: Person A signs message M with sign S(A, M) , it is impossible for others to produce a pair S[M, S(A,M)].

AuthenticationProtects B

UnforgeableProtects A

BBAA

CC

Impostor ADigital Signature

Symmetric Key Digital Signatureswith Arbiter

– Private key encryption system guarantees authenticity of message as well as its secrecy.

KR

SS MKs M

MKs M

Sender

1. S sends sealed M to Arbiter ArbiterArbiter retrieves Plain text M from S

Recipient 3. Arbiter seals [S’s sealed M, identity of S,and copy of plain text M and sends all to R]

Symmetric Key Digital Signature with Arbiter

Asymmetric Key Digital Signature

SS RRMM

For authenticity,

unforgeability

D:KSDecrypts M

Saves a copy to answer future disputes.

MM

D:KS

E(D(M, KS), KR)

Certification Authorities(CA’s)

– An organization that issues public key certificates(Digital Signature).

– Certificates are synonymous to cryptographically signed index cards.

– Signed by certification authority’s own private keys, contains name of the person, person’s public key, a serial number, and other info.,

– Example: verisign corp.

Types of CA• Internal CA

– can operate to certify its own employees– used to control access to internal resources

• Outsourced Employee and Customer CA– leases trusted outsiders to certify employees and

potential customers respectively.

• Trusted Third Party CA– no prior relationship can establish and engage in

legal transactions and business.

Different kinds of certificates

• Certification authorities Certificates– contain public key of CAs and name of service

– this can in turn be signed by other certification authorities.

• Server Certificates– contain public key of SSL server,

– name of the organization running the server, Internet hostname, server’s public key.

Contd...

• Personal Certificates– contains individual’s name and public key.

– other information is also allowed.

• Software Publisher Certificates– certificates used to sign the distributed software.

Cryptography and Web Security• Functions,

– Confidentiality, • Encryption is used to scramble the message.

– Authentication, • Digital Signatures are used for verification.

– Integrity,• methods used to verify whether the message has been

modified on transit.

• Digital Signed message codes are used.

– Nonrepudiation• author of a message can’t deny sending a message.

What cryptography can’t do ?

• Protect unencrypted documents.

• Protect against stolen encryption keys.

• Against denial-of-service attacks.

• Against the record of a note that a message was sent.

• Against a traitor or a mistake.

Working Encryption Systems

• Programs– PGP(Pretty Good Privacy).– S/MIME.

• Protocols– SSL(Secure Socket Layer).– PCT(Private Communications Technology).– S-HTTP(Secure HTTP).– Cybercash.

Contd…

– SET(used in web shopping).• “Electronic Wallet” with User.

• Server that runs on Merchant’s web site.

• SET payment server runs in merchant’s bank.

– DNSSEC(Domain Name System Security).– IPSec and IPv6.

• IPsec works with IPv4 and standard version used today works for IPv6 and includes IPsec.

– Kerberos.

Network Layer Security Protocol(IPsec)

• IP Security protocol - a suite of protocols that provides security at the network layer.

• Network layer must provide – Secrecy - hide message from any third party that is "wire tapping" the

network.– Source authentication -IP datagram with a particular IP source address, it

might authenticate the source.• there are two principal protocols:

– the Authentication Header (AH) protocol.

provides source authentication and data integrity but not secrecy.– the Encapsulation Security Payload (ESP) protocol.

provides data integrity and secrecy.

Security Agreement (SA) - the source and network hosts handshake and create a network layer logical connection

Authentication Header Protocol (AH)

• SA is set up • source can send secured datagrams, that include the AH header.• Value of 51 in IP header means a AH Header has been included.

• AH Headers have the following fields, – Next Header field, same as the protocol field for an ordinary datagram.– Security Parameter Index (SPI) field, an arbitrary 32-bit value that, in combination with the destination

IP address and the security protocol, uniquely identifies the SA for the datagram. – Sequence Number field, a 32-bit field containing a sequence number– Authentication Data field, a variable-length field containing signed message digest (i.e., a digital

signature) for this packet.

Encapsulation Security Payload Protocol (ESP)

• SA is set up.

• source can send secured datagrams, that include the AH header.

• a secured datagram is created by surrounding the original IP datagram data with header and trailer fields,

• value 50 is used to indicate that the datagram includes an ESP header and trailer.

• ESP header consists of a 32-bit field for the SPI and 32-bit field for the sequence number, which have exactly the same role as in the AH protocol.

• trailer includes the Next Header field.

What is SSL ?• Exists between raw TCP/IP and Application Layer.• Features added to streams by SSL

– Authentication and Nonrepudiation of Server, using Digital Signatures.– Authentication and Nonrepudiation of Client, using Digital Signatures.– Data confidentiality through Encryption.– Data Integrity through the use of message authentication codes.

• Functions– Separation of duties.– Efficiency. – Certification - based authentication– Protocol Agnostic.

• Transport Layer Security is being tried out.

Secure Web Server

• Implements cryptographic protocols.• Safeguard any personal info received or collected.• Resistant to a determined attack over the I-net.

Bad GuysBad Guys

Bad GuysBad Guys

Bad GuysBad Guys

SERVER ACTIVE AND PROVIDES SERVICES TO AUTHORIZED PERSONEL

SECURE WEB SERVER

ATTACK ATTACK

ATTACK

Web server Security• Host Security

– Security of the computer on which web server is running.

• Problems are due to– Security not viewed as a fundamental part of system setup and design.– Transmitting plain text and reusable password over networks.– Failure to obtain software to monitor bugs.– Failure to use security tools.– Lack of adequate Logging.– Lack of adequate backup procedures.– Lack of adequate System and network monitoring.– Failure to track security developments and take preventive action.

Firewalls

• Process that filters all traffic between a protected or “inside ” network and a less trustworthy or an “outside”

network. • Special form reference monitor.

• That which is not expressly forbidden is permitted.

• That which is expressly forbidden is not permitted.

• Challenge of protecting a network with a firewall is determining the security policy that meets the need of the installation.

Types of Firewalls• Screening Router.

Address192.19.33.0

Address144.27.5.3

Address100.24.4.0

Allow in only A.Allow out only B , C.

AA

BB

CC

Contd …

• Route Screening outside Addresses

ScreeningRouter

Subnet 100.50.25.x

100.50.25.1 100.50.25.2

100.50.25.x100.50.25.3

Contd … • Proxy Gateway

– Two headed piece of software.

– runs pseudo applications.

Local Area Network

Remote Access

WWW Access

Logging

Remote File Fetches

Address

Contd … • Guard

– sophisticated proxy firewall.– Receives PDU’s interprets them passes the through same or different PDU’s.

ScreeningRouter

ProxyFirewall

Address

Comparisons of Firewall types

Screening Router1.Simplest.2.Sees only address and service protocol type.3.Auditing difficult.4.Screens based on connection rules.5.Complex addressing rules can make configuration tricky.

Proxy Gateway1.Somewhat complex.2.Sees full text of communication.3.Can audit activity.4.Screens based on behavior of proxies.5.Simple proxies can substitute for complex addressing rules

Guard1.Most Complex.2.Sees full text of communication.3.Can audit activity.4.Screens based on interpretation of message content.5.Complex guard functionality can limit assurance.

Encrypting Gateway(Virtual Private Network)

• Internal encryption between offices for further protection.

Address

CryptographicServer

100.24.4.5

ProxyGateway

100.24.4.0

192.19.33.0

144.27.5.3

Conclusions

• Risks are involved in Computing.

• Various techniques Encryption, Digital Signatures, Firewalls, etc can be used to provide security.

• Web security is not a “Win” or “Loose” there is just a degree to which it can be realized.

• No Solution is a complete solution !!!

References• Papers

– “Model based Intrusion Detection” - Dorothy E Denning.– “Goal Oriented Auditing and Editing” - M.. Bishop.– “An Introduction to Intrusion Detection” - Aurobindo Sundaram.– “An application of Pattern Matching in Intrusion detection” - Sandeep Kumar and Eugene H Spafford.

• White Papers– “CERT Advisory CA-2000-02 Malicious Tags Embedded in Client Web Requests.”

• Books– “Security in Computing” - Charles P. Pfleeger.– “web Security and Commerce” - Simson Garfinkel and Gene Spafford.

• Websites– http://www.crypto.com/papers/– http://www.awl.com/cseng/titles/0-201-63489-9/url_list.html– http://www.datafellows.com/products/white-papers/– http://www.cerias.purdue.edu/coast/coast-library.html– http://www-net.cs.umass.edu/kurose/security/IPsec.htm– http://www.ietf.org/html.charters/tls-charter.html– http://www.counterpane.com

Questions and Comments ???

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NETWORK Authors Hari Thiruvengada Varun Lalchandani SECURITY