Chapter 3

Preventive Security Approaches

3.1 Two Main Approaches

Safeguard is defined as any mechanism or procedure to

mitigate the effect of a threat before it can occur

Countermeasure is defined as any mechanism or procedure to

mitigate the effect of a threat that has already occurred

3.1.1 Safeguards

Integrated into Design introduce safeguard in its earliest stage

Avoids Disastrous Threats life critical operations requires early safeguard

Possible Waste of Resource additional resources must be justified

Difficult to Measure Success uncertainty exists for the practical issues

3.1.2 Countermeasures

Based on acted on EMERGENCY, teams will be formed to respond to the emergency.

Advantages:Possibly Avoids Waste of ResourcesEasier To Measure Success

Drawbacks:Allows Threats to Occur

3.2 Security MechanismsAuditing and Intrusion Detection Identification, Authentication and PasswordsEncryptionKey Management ProtocolsMandatory and Discretionary Access ControlPrivilegeSecurity KernelsConfiguration Management, Formal Methods and

Enhanced Life Cycle Activities

Classifications

Preventive: Auditing, Intrusion Detection, Identification and Authentication and Encryption

Logistic: Passwords, Key Management Protocol, Mandatory and Discretionary Access Control, Privilege and Security Kernels (chapter 4)

Others: Configuration Management, Formal Methods and Enhanced Life Cycle Activities

3.2.1 Auditing

Concept: The method involves the use of automated

mechanisms and associated procedure that cause a record of computer system activity to be automatically created and stored in a protected, computerized log.

The log provides a means of identifying the time, source and other important characteristics of a given attack

3.2.1.1 Auditing Requirements

Mechanisms and Procedures automatic obtaining computer activity and

placing it in a protected log manual logging is not acceptable for on-line

auditing

Recording of Relevant Activity activities about potential malicious attacks must

be included ideally all types of activities are included

Minimal Effect on Functionality the auditing procedure should not introduce harmful

or undesirable effects to the normal functionality of system

Audit Record Format A well-defined format of audit records are required

for data interpretation such as IEEE POSIX

Records in Protected Log records are use to reconstruct the attack hence

protection is very crucial. If protection cannot be introduced, effort should be made to avoid illegal modifications of audit record

3.2.1.2 Operational Description Three-step procedure is requiredStep 1: Determine what must be audited

e.g. file, mode and time

Step 2: Insert Audit Calls e.g. insert audit calls in the open routine

open(file,mode)

{ audit(time)

if mode = 0 “read” audit(file, read)

if mode = 1 “write” audit(file, write)

if mode = 2 “both” audit(file, read/write)

}

Step 3: Create protect Log Routines ensure all log is in the protected area normally append mode is used to avoid

overwritten secured compartment with secondary storage is

another possibility, e.g. magnetic tape printing of hardcopy is another way

user

Open(a,b)

Underlying openroutine sequence

Completion of openroutine sequence

Protectedaudit log

Auditingroutine

Call to auditing routine

Invocation ofcommand

System callinterface

Auditing Operation View

3.2.1.3 Alternate Auditing Approaches

Off-line Monitors drawback of auditing is that if the intruder is

successful in attacking a given system, the auditing scheme could be attacked

to avoid this off-line monitors of traffic is used the traffic monitor connected to off-line

computer which will not be affected limitation for access monitor only

Architectural Auditing Mechanisms by introducing additional auditing hardware e.g. dedicated computer system component to

provide for auditing of security-critical network traffic and operation

3.2.1.4 Attacks Countered by Auditing

Attacks are prevented because the attacker knows that auditing is present

attacks are countered by reconstructing the details of the attack using audit records

Hence innocent will be more careful and intruders are more cautious

3.2.2 Intrusion Detection

An automated support approach and set of associated manual procedure that are used to process and interpret the information in the audit log and to detect the potential presence of intruder is called intrusion detection.

3.2.2.1 Intrusion Detection Architecture

Assumption: a log of all security-relevant activity in a given setting or application is available for inspection.

This is based on identifying the normal and defining the abnormal

The approach is called profiling Algorithm is then created to compare what is

observed in the audit trail with defined user or system profiles and to detect the difference as abnormal

TargetSystemActivity

AuditingMechanism Audit

Log

IntrusionDetection

Mechansim

SystemActivity

Data

Intrusion Detection Architecture

3.2.2.2 Intrusion Detection Concepts

A given individual typically logs onto a system and logs off at roughly the same times and use same CPU time daily - this can be build into a profilee.g. <time_of_login, average_CPU_usage,

time_of_logout>

A record of four days are:<08:00,23, 17:00>

<07:50, 24, 17:10>

<07:56, 23, 16:45>

<08:13, 27, 17:03>

However, if the following behavior is recorded on the some day<03:25, 10, 06:34>

This record will raise suspicionTo build an automated detection algorithm, a

threshold profile is used, e.g.<1.0, 10, 1.0> <variation of one hour log in, 10 hours

CPU usage and one hour logoff>

The size of the threshold will determine the window of the profile and will be set accordingly

3.2.2.3 IDES Model

The Intrusion Detection System (IDES) was introduced by Dorothy Denning from SRI International

The model is composed of five explicit components: Subjects and Objects audit records profiles anomaly records activity rules

Subjects and ObjectsSubjects are the active initiators of

operations that are audited on the system, e.g. processes controlled by OS

Objects are information repositories on which system performs operations, e.g. files and directories

For UNIX, subjects are UNIX processes and objects are files, directories and other entities

Audit Record

In IDES, audit records are assumed to be structures with 6 components, i.e.<subject, object, action, error, resource, time> Subjects is the initiator of action Objects is the record error describes any true exception conditions resources provides statistics on any resource usage time provides a time stamp of when the action

occurs

Example:<joe, myfile, execute, no. CPU(00:02), 2:00>

and

<joe, important_file, read, no, CPU(00:01), 5:00>

<lee, important_file, read, no, CPU(00:01), 5:01>

<scr, important_file, read, no, CPU(00:01), 5:02>

<kin, important_file, read, no, CPU(00:01), 5:03>

This leads to security administrator to investigate why the important_file is read abnormally

6 components can be expanded to suit other applications

ProfileProfile is used to characterize expected

normal activity on a computer systemLogin Activity: time, earliest and frequencyExecutive Parameters: use of CPU, memory

and other resourcesFile access: profiles on frequency of reads

or writes to certain files, number of failed requests and other file access parameters

Format:<subject, object, action, e_pattern, r_pattern,

t_pattern>

Example:<joe, myfile, execute, no, CPU(00:01-00:04), 2:00-

22:00> This would denote Joe executes myfile, no error

are expected, CPU usage should be 1 and 4 seconds and time of execution should be between 2:00 am to 10:00 pm

comparison of profiles can be setup automatically

Anomaly Record

Anomaly records are alarms that are created whenever audited behavior does not match the profiles

In IDES model, 3-tuples are used<event, time, profile> Event specifies the activity that triggered alarm Time specifies when the problem was observed Profile specifies the mismatched structure

Example:Any users tries to log into the system after 2 am

or whenever someone fails to gain access several times in a row

Anomaly records are constructed with the two specific types of behaviors: behavior is suspicious for any user on the

system behavior is suspicious for some specific user on

the system

In the former cases, generic anomaly records and profiles are used to established that someone is causing strange behavior on the system to occur, e.g. many failure attempt of log in

In the latter case, anomaly records and profiles establish that a specific user is acting strangely e.g. access file frequency is more than normal

Activity Rules

Actively rules are programs that describe what action should take place when an alarm is set

Example: terminal screen will blink someone’s phone will ring electronic mail will be sent to an administrator and so

on

if alarm (0) then activity (0)

if alarm (1) then activity (1) …

if alarm (n) then activity (n)

3.2.2.4 Example: ComputerWatch

ComputerWatch is an audit trail analysis tool reported by Cheri Dowell & Paul Ramstedt of AT& T

This tool is compatible with most UNIX-based audit trails such as V/MLS audit trail tool

Raw AuditTrail

Audit Trail inDatabase Format

Rule Base

Database Schemas

ReportGeneration

Build-InQueries

CustomQueries

SummaryReport of Activity

User View

AuditTrailTranslation

ComputerWatch Data Flows and Modules

3.2.2.5 Attacks Countered by Intrusion Detection

Benefits: it deters possible attacks whenever an attacker

believes that the chances of getting caught outweigh the payoff of a proposed attack succeeding

use audit trails to determine who initiated the attack and once initiated what damage occurred

it provides evidence of attack

Drawbacks: it may be based on an incorrect profile, I.e

profile is not adequately describe the normal behavior

sophisticated user might behave abnormally to build up a profile that might be useful in subsequent attacks

strange behavior may not be part of attack, e.g. illegal login with good explanation

an attack leaves no identifiable clues that an intrusion detection system will be pick up

3.2.3 Identification and Authenticatin

Identification are techniques for distinguishing those active entities that are responsible for initiating specific actions on a computer system.

Authentication are techniques for ensuring that the identification has been done properly.

Example: the users types in the username and then the system demands a password

3.2.3.1 Concepts

Identification is defined as consisting of those procedures and mechanisms that allows agents external to some computer system to notify that system of their identity. Example: login:Joe

Authentication is defined as consisting of those procedures and mechanisms that allow a computer to ensure the stated identity is correct Example: Password: 123456

3.2.3.2 Approaches

Three major types of approaches exists: something possessed something embodied something known

AgentComputers

system

Identification

Authentication

•Something Possessed•Something Embodied•Something Known

Something Possessed

One way to ensure that the identity has been reported correctly is to check for something that only the identified agent could possibly possesses.

The most common approach is using smart card

The protocol exchange will identify the userAdvantage: the user is difficult to spoof the

function, i.e unbreakable

Steps to identify the agent/user Step 1: a computer system administrator sets up

a smart card for some user by entering a function that is chosen for only that user onto the card. The user is given an identification number that protects the card from being used by an intruder if it is lost

Step 2: The card is given to the user and the user should not lose or loan it. Normally a personal identification number (PIN) is used in conjunction with the card

Step 3: Whenever the user must be authenticated, the system provides a value to the user

Step 4: The users evaluates the function on the smart card for the input and enters it back into the system either by typing or using a card reader

Step 5: The system determines the value of the function on the input and compares it to the user’s result

Step 6: if results match, the user is authenticated

Something Embodied

This approach involves checking in an invoking user for some characteristic that is inherently part of that agent.

Example: voice, fingerprints, rentinal patterns and signature

Advantage: cannot be spoofed easily because the user/agent has distinct features

Disadvantage: expensive hardware

Something Known

Involves a something known scheme.Commonest example: passwordAdvantage:

it increase the amount of information an attacker must obtain to spoof the login

One time pad approach can be integrated to challenge-response scheme

This can also been introduced with smart card devices

Alternate Approaches

Alternate approach: associative Sequence of reasoning or concept association:

login: joe

provide association:

bardados: vacation

football: gaints

cloak: dagger

woman: lee

Another alternative approach: challenge sequence of questions and answers

login: joe

provide responses:

date of birth? 12-03-61

dog’s name? Scrappy

grandfather’s profession? Barber

spouse’s maiden name? matuska

coat size? 40r

3.2.3.3 Example: Polonius

User ID

User PIN

(2)

User Passport Channel Authentication Service Server Provider

User ID Counter(1)

ChallengeGenerator

(4)

(5)(3)

AssessResult(6)

Result(7)

StepsStep 1: User enters a user identification sequence to

the hostStep 2: host uses a database to provide challenge

sequencing information to a challenge generatorStep 3: a challenge is issue to the userStep 4: user enters PIN to passportStep 5: Passport computes a responses using secret keyStep 6: A response is sent to hostStep 7: host use secret key to compute the responseStep 8: Authentication results are passed to host

service provider

3.2.3.4 User sessionsIn normal login, users are identified and

authenticated by a system in the login session after that the user is authentic to use the system by invoking a series of commands

If during the login session, some attack occurs and the user’s identity has changed, the initial identification and authentication will no longer be valid as a result of some spoof that steals the passwords

Thus, in some systems explicit authentication may be required during a user session if certain critical commands are invoked

Example is the superuser commands in UNIX system

To strengthen this weakness, a secondary authentication is introduced in addition to the primary authentication used normally.

3.2.3.5 Trusted Path

A trusted path is a direct communication path between a user and a routine or program that results from some procedure or mechanism that suitably authenticates the routine or program in a manner that cannot be spoofed.

This approach is complicated if one’s means for accessing a system is more than just a dumb terminal.

3.2.3.6 Attacks Countered by Identification and Authentication

Two categories exist: attacks that require an external intruder gaining

unauthorized access to a system attacks that can be traced back to an individual that was

identified and authenticated by the system

Problem only exists if the scheme is not planned or implemented properly

Integrated with auditing will strengthen the approach

3.2.4 Encryption

Encryption Encryption will modify data into irregular form for

security storage and transmission. The reconstruction is achieved by using a set of relevant Keys.

Two cryptosystems are currently being used, i.e. symmetric (DES/FEAL) and asymmetric (RSA, ECC). Symmetric cyptosystem requires only one common key for encryption and decryption whereas asymmetric system requires two keys, i.e. private/user key and public/system key.

Common Encryption Techniques

Three algorithms will be introduced DES (Data Encryption Standard) RSA (Rivet, Shamir, Adleman) ECC (Elliptic Curve Cryptography)

DES

DES the most well-known symmetric system being

used by banking sector and computer security. the technique was originated from IBM and

certified by National Bureau of Standards in 1977.

an official unclassified data encryption method. widely been used by Banking sectors

64 Bit Plaintext

Initial Permutation

32 Bit L0 32 Bit R0

F(R0,K1)+

32 Bit L1 32 Bit R1

32 Bit L15 32 Bit R15

F(R15,K16)+

32 Bit L16 32 Bit R16

Final Permutation

64 Bit Ciphertext

Encryption ProcessDES System

64 Bit Key

Permutation Choice 1

56 Bit Key

28 Bit C0 28 Bit D0

Left Shift Right Shift

C1 D1

BuildingBlock

PermutedChoice 2

K1(48 bits)

C16 D16

PermutedChoice 2

Key Schedule

Li-1

32 bitsRi-1 32 bits

ExpansionPermutation 48 bits

S-BoxSubstitution

choice 32 bits

P-box Permutation

Li

32 bitsRi

32 bits

56 bits KeyPermuted Choice

48 bits

Function f

DES Substitution Boxes Operation

Operation Tables of DES (IP, IP-1, E and P)

RSA

developed by 3 researchers at MIT in 1977based on two prime numbers (p & q) to generate

the keysmost popular is RSA 129 where p x q gives a 129

bit numberhighly security and has once been proposed to

replace DES in banking application report cipher analyzed by a group of 600 specialist

in May 1994 through internetFast Montgomery’s approach available

RSA Steps

Select two large prime p& qGenerate n = pqGenerate f(n) = (p-1)(q-1)Select e (encryption/public key) and d

(decryption/secret) as ed = 1 (mod(f(n))

Encrption by C =(Me, mod n) where M is the message

Decrypt by M =(Cd, mod n)

ECC

ECC a new elliptic curve cryptosystem method for

public key applications developed by Neil Koblitz (Washington

University) and Victor Miller (IBM, Yorktown Heights) in 1985

using points in the elliptic curve as the elements for encryption

will become IEEE standard in 2000 (P1613)

ECC - key generation

Select an elliptic curveGenerate the coordinate pairs which satisfy the

conditions of modulo n and select starting point P

Key generation: select a random integer d (secret key) in the interval

[2, n-2] compute point Q = dP make Q public

ECC Encryption

Encryption select a random integer k in the interval [2, n-2] compute (x1,y1) = kP and (x2,y2) generate a mask Y from secret as f(x2) and

compute C = YM where M is the message send the encrypted ciphertext EM as

concatenated [x1, y1, C]

ECC Decryption

Decryption extract (x1,y1) from ciphertext EM compute (x2,y2) from d(x1,y1) compute mask Y as f(x2) recover message by M = CY

Encryption and Decryption :

Actions perform by Party B

Encryption :

Actions perform by Party A

Decryption Process

1. Looks up A public key : Q =

(xQ,yQ)

= ( ,0)

2. Select a random integer k = 2 in the

interval [2, n -2 ] - the private key

for

the one - time key pair

3. Computes the point (x1,y1) = kP =

2(5, 11) = ( , ) =

((1100),(1100))

- the public key for one - time key

pair

4. Computes the point (x2,y2) = kQ =

2( , ) = (5, 11) =

((1010),(1110))

x2 is the secret value.

5. Generates a mask Y of length 6

with the mask generation function

used, Y will vary. For the purposes

in this example, let Y = 011010.

6. Computes C = Y M = (011010)

(010100) = (001110)

7. Computes the encrypted message

by concatenating (x1,y1) and C,

and transmit (11001100001110) to

A.

1.Ciphertext EM = (11001100001110)

received from B

2. Uses the first 8 bits of the string for

one

- time public key : ((1100),(1100)).

The rest of EM will be stored in C

3. Computes the point (x2,y2) = d

( x1,y1) = 3 (1100,1100) = 3(, ) =

(5, 11)= ( (1010),(1110)). X2 is the

secret value.

4. Using the same mask generation

function as B, A generate from x2 the

mask Y = 011010.

5. Recover the message M by XORing

all

but the first 8 bits of EM with the

mask Y: M : C Y = (001110)

(011010) = (010100)

Attacks Countered by Encryption

Attacks that are designed to disclose information in transit between remote computer systems or between a user and a remote system to an unauthorized entity

attacks that are designed to masquerade information in transit between remote computer systems or between a user and a remote system

attacks that are designed to disclose certain “expendable” types of stored data

3.2.5 Configuration Management

Careful Maintenance of computer recordThreats normally required get access to the

software and introduce Trojan HorsesCareful management can avoid this types of

threats by comparing the difference of different versions to avoid illegal modification to software

3.2.6 Formal Methods

Formal method based on formal specification and verification is normally used for accurate and vigorous computer system development

Tools are available for verifying the validity of the software to avoid any introduction of software threats

3.2.7 Enhanced Life Cycle

Provide an enhance life cycle to the software such as

documentation needs to identify work and unwork portion of

software to avoid threats

Reviews walkthrough and review possible weaknesses in

the code

Traceability mapping ensure all materials are traceable to avoid

malicious developer

Tool Use if automatic tools can be used the manual

intervention can be avoid

Testing introduce tests on different scenarios are

required to ensure all possible threats can be eliminated or minimized

3.3 Selection Principles

Cost Effectiveness to consider the impact of mechanism related to

all costs such as fix and recurring costs

Human Invention human intervention can cause error and the

protection will not be optimal

Failsafe Operation the fail must be safe contained but not open

Design Secrecy design must kept confidential to avoid possible

leak to intruders

Entrapment to allow certain degree of allowance for possible

intruder to attack

Independence of Control and Subject those develop the protection such be eliminated

from controlling the operation to reduce the risk possibilities

Universal Application preventive mechanism must not be associated

with special cases and exceptions, they must be more universal and general

Acceptance and Tolerance by Personnel introduction of preventive mechanism should

not introduce inconvenience to affected personnel otherwise methods will be developed to subverting the protection methods

3.4 Reference

E Amoroso Chapters 15, 16, 17,18, 20