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ABSTRACT

Tripwire is an intrusion detection system. It is a software tool that checks to see

what has changed on your system. The program monitors the key attributes of files

that should not change, including the size, binary signature, expected change of

size, and other related important datas. Tripwire is an open source program created

to monitor changes in a key subset of files identified by the user and report on any

changes in any of those files. When changes are detected the system Administrator

can determine whether those changes occurred due to normal, permitted activity, or

whether they were caused by a break-in. If the former, the administrator can update

the system baseline to the new files. If the latter, then repair and recovery activity

begins. Tripwires principle is simple enough. The system administrator identifies

key files and causes Tripwire to record checksum for those files. Administrator also

puts a cron job to scan those files at intervals (daily or more frequently), comparing

to the original checksum. Any changes, addition, or deletion are reported, so the

proper action can be taken.

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CONTENTS

1. INTRODUCTION.6

2. TRIPWIRE FOR SERVERS ..13

3. TRIPWIRE MANAGER 16

4. TRIPWIRE FOR NETWORK DEVICES 18

5. OPERATION OF TRIPWIRE.21

6. EXPERIENCES..26

7. ADVANTAGES31

8. CONCLUSION.....32

9. REFERENCES.33

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INTRODUCTION

Tripwire is a reliable intrusion detection system. It is a software tool that checks to

see what has changed in your system. It mainly monitors the key attribute of your

files, by key attribute we mean the binary signature, size and other related data.

Security and operational stability must go hand in hand, if the user does not have

control over the various operations taking place then naturally the security of the

system is also compromised. Tripwire has a powerful feature which pinpoints the

changes that has taken place, notifies the administrator of these changes,

determines the nature of the changes and provide you with information you need for

deciding how to manage the change.

Tripwire Integrity management solutions monitor changes to vital

system and configuration files. Any changes that occur are compared to a snapshot

of the established good baseline. The software detects the changes, notifies the

staff and enables rapid recovery and remedy for changes. All Tripwire installation

can be centrally managed. Tripwire softwares cross platform functionality enables

you to manage thousands of devices across your infrastructure.

Security not only means protecting your system against various

attacks but also means taking quick and decisive actions when your system is

attacked. First of all we must find out whether our system is attacked or not, earlier

system logs were certainly handy. You can see evidences of password guessing

and other suspicious activities. Logs are ideal for tracing steps of the cracker as he

tries to penetrate into the system. But who has the time and the patience to examine

the logs on a daily basis?

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Penetration usually involves a change of some kind, like a new

port has been opened or a new service. The most common change you can see is

that a file has changed. If you can identify the key subsets of these files and monitor

them on a daily basis, then we will be able to detect whether any intrusion took

place. Tripwire is an open source program created to monitor the changes in a key

subset of files identified by the user and report on any changes in any of those files.

When changes made are detected, the system administrator is informed. Tripwire s

principle is very simple, the system administrator identifies key files and causes

tripwire to record checksum for those files. He also puts in place a cron job, whose

job is to scan those files at regular intervals (daily or more frequently), comparing to

the original checksum. Any changes, addition or deletion, are reported to the

administrator. The administrator will be able to determine whether the changes were

permitted or unauthorized changes. If it was the earlier case the n the database will

be updated so that in future the same violation wouldnt be repeated. In the latter

case then proper recovery action would be taken immediately.

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Motivation

A cautionary tale

Ellen runs a network of 50 networked Unix computers representing

nearly a dozen vendors from PCs running Xenix to a Cray running Unicos. Thismorning, when she logged in to her workstation, Ellen was a bit surprised when the

lastlog message indicated that root had logged into the system at 3 am. Ellen

thought she was the only one with the root password. Needless to say, this was not

something Ellen was happy to see. A bit more investigation revealed that someone

certainly not Ellen had logged on as "root," not only on her machine but also on

several other machines in her company. Unfortunately, the intruder deleted all the

accounting and audit files just before logging out of each machine. Ellen suspects that

the intruder (or intruders) ran the compiler and editor on several of the machines.

Being concerned about security, Ellen is worried that the intruder may have thus

changed one or more system files, thus enabling future unauthorized access as well

as compromising sensitive information. How can she tell which files have been altered

without restoring each system from backups? Poor Ellen is faced with one of the most

tedious and frustrating jobs a system administrator can have determining which, if

any, files and programs have been altered without authorization. File modifications

may occur in a number of ways: an intruder, an authorized user violating local policy

or controls, or even the rare piece of malicious code altering system executables as

others are run. It might even be the case that some system hardware or software is

silently corrupting vital system data.

In each of these situations, the problem is not so much knowing that

things might have been changed; rather, the problem is verifying exactly which files

out of tens of thousands of files in dozens of gigabytes of disk on dozens of different

architectures might have been changed. Not only is it necessary to examine every

one of these files, but it is also necessary to examine directory information as well.

Ellen will need to check for deleted or added files, too. With so many different systems

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and files, how is Ellen going to manage the situation? This scenario could prove

tedious and labor intensive for even the most well-prepared system administrator (yes,

even Ellen). Consider the problems with simple check listing schemes:

The resulting challenges

Some established techniques for monitoring file systems for potentially dangerous

changes include maintaining checklists, comparison copies, checksum records, or a

long history of backup tapes for this kind of contingency [4, 2]. However, these

methods are costly to maintain, prone to error, and susceptible to easy spoofing by a

malicious intruder. For instance, the UNIX utility find(1) is often used to generate a

checklist of system files, perhaps in conjunction with ls(1). This list is then saved and

compared using diff(1) to determine which files have been added or deleted, and to

find which files have conflicting modification times, ownership, or sizes. An added level

of security could be added by augmenting these lists with information from sum(8) or

cksum(8), as is done by the crc check program included with COPS [3]. However,

numerous shortcomings in these simple check listing schemes prevent them from

being completely trustworthy and useful. First, the list of files and associated

checksums may be tedious to maintain because of its size and lack of locality (files

are located all over the disk). Second, using timestamps, checksums, and file sizesdoes not necessarily ensure the integrity of each file (e.g., once intruders gain root

privileges, they may alter timestamps and even the checklists at will). Furthermore,

changes to a file may be made without changing its length or checksum generated by

the sum(8) program. And this entire approach presumes that ls(1), sum(8), and the

other programs have not been compromised! In the case of a serious attack, a

conscientious administrator must not assume that these files have remained

unchanged without strong proof. But what proof can be offered that is sufficient for this

situation?

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The resulting wishlist

A successful integrity checking scheme requires a high level of automation both in

generating the output list and in generating the input list of files. If the system is

difficult to use, it may not be used often enough or worse, used improperly. The

automation scheme should include a simple way to describe portions of the filesystem

to be traversed. Additionally, in cases where files are likely to be added, changed, or

deleted, it must be easy to update the checklist database. For instance, files such as

/etc/motd may change weekly, or even daily. It should certainly not be necessary to

regenerate the entire database every time this single file changes to maintain

database accuracy. Ideally, our integrity checking program could be run regularly from

cron(8) to enable detection of file changes in a timely manner. It should also be

possible to run the program manually to check a smaller set of files for changes. As

the administrator is likely to compare the differences between the base checklist and

the current file list frequently, it is important that the program be easy to invoke and

use. A useful integrity checker must generate output that is easy to scan. A checker

generating three hundred lines of output for the system administrator to analyze daily

would be self-defeating this is probably far too much to ask of even Ellen, our

amazingly dedicated system administrator! Thus, the program must allow the

specification of filesystem exceptions that can change without being reported, andhence reduce noise. For example, changes in system log file sizes are expected, but

a change in inode number, ownership, or file modes is cause for alarm. However, a

change in any value stored in the inodes (except for the access timestamp) for system

binaries in /bin should be reported. Properly specified, the integrity checker should

operate unobtrusively, notifying Ellen when a file changes outside the specified

bounds. Finally, assuming that Ellen wants to run the integrity checker on every

machine in her network, the integrity checker should allow the reuse and sharing of

configuration files wherever possible. For example, if Ellen has twenty identical

workstations, they should be able to share a common configuration file, even allowing

machine-specific oddities for operator error.

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BASIC PURPOSE OF TRIPWIRE

Almost the same principle is used in computers. If any

change is met upon while comparing the old values to the new ones, or if any data is

being manipulated on the spot, the logs are checked for intrusion and then detected,

after which all the changes can be undone.

Tripwire is a free and open-source1 software tool. It

functions as a host-based intrusion detection system. It does not concern itself directly

with detecting intrusion attempts in real time at the periphery of a computing system

(as in network intrusion detection systems), but rather looks for and reports on the

resultant changes of state in the computing system under observationIntruders usually leave traces of their activities (changes in the system state). Tripwire

looks for these by monitoring key attributes of files that should not changeincluding

binary signatures, size, expected changes in size, etc.and reporting its findings.

While useful for detecting intrusions after the event, it

can also serve many other purposes, such as integrity assurance, change

management, policy compliance, and more.

A Host-based Intrusion Detection System (HIDS),

as a special category of an Intrusion-Detection System, focuses its monitoring and

analysis on the internals of a computing system rather than on its external interfaces

(as a Network Intrusion Detection System (NIDS) would do)

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TRIPWIRE RELATED TOPICS

Open source describes practices in production and

development that promote access to the end product's source materialstypically,

their source code. Some consider it as a philosophy, and others consider it as a

pragmatic methodology. Before open source became widely adopted, developers and

producers used a variety of phrases to describe the concept; the term open source

gained popularity with the rise of the Internet and its enabling of diverse production

models, communication paths, and interactive communities. Subsequently, open

source software became the most prominent face of open source practices.

The open source model can allow for the concurrent use of different agendas and

approaches in production, in contrast with more centralized models of development

such as those typically used in commercial software companies. "Open source" as

applied to culture defines a culture in which fixations are made generally available.

Participants in such a culture are able to modify those products and redistribute them

back into the community.

Pragmatism, as a school of philosophy, is a collection of

many different ways of thinking. Given the diversity among thinkers and the variety

among schools of thought that have adopted this term over the years, the term

pragmatism has become all but meaningless in the absence of further qualification.

Most of the thinkers who describe themselves as pragmatists point to some

connection with practical consequences or real effects as vital components of both

meaning and truth. The precise character of these links to pragmata is, however, as

diverse as the thinkers who do the pointing.

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TRIPWIRE FOR SERVERS

Tripwire for Servers is a software that is exclusively used by

servers. This software can be installed on any server that needs to be monitored for

any changes. Typical servers include mail servers, web servers, firewalls,

transaction server, development server etc, Any server where it is imperative to

identity if and when a file system change has occurred should b monitored with

tripwire for servers. For the tripwire for servers software to work two important things

should be present the policy file and the database.

The tripwire for Servers software conducts subsequent file checks,

automatically comparing the state of the system with the baseline database. Any

inconsistencies are reported to the Tripwire Manager and to the host system log file.

Reports can also be emailed to an administrator. If a violation is an authorized

change, a user can update the database so changes no longer show up as

violations.

FLEXIBLE POLICYLANGUAGE

The power behind Tripwire technology lies in its highly

configurable policy language. The policy file is how a user directs Tripwire for

Servers to monitor specific files or directories. The flexible policy tool can be

customized to fit the needs of each and every server. With the release of version

4.0, policy file creation has become even easier. From Tripwire Manager 4.0, a

graphical policy editor allows users to select the files and directories, along with the

scanning options that need to be monitored in each integrity check. Included in the

products are default policy files for each supported operating system to make it easy

for the user to set up which files should be monitored. In the latest version, wildcard

application is also supported which enables users to add objects to the policy file by

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specifying the file type. In 4.0, objects listed in the policy file but not present on the

users machine will no longer be categorized as violations. By only showing

violations caused by added, deleted or changed files, report noise is greatly

reduced. Tripwire policy languages also allow you to group objects around easy-to-

understand rule names and then prioritize them.

The snapshot and the policy file are cryptographically signed with

168-bit Triple DES encryption algorithm that detects any unauthorized tampering.

The default policy file also monitors the tripwire binary files, in short, it uses tripwire

itself to monitor the tripwire.

In the latest version 4.0 in addition to reporting the administrator

which file has changed, when the change occurred and where the change took

place it also to some extend determines who made these changes. Tripwire for

Servers track the identity of who made the change by correlating the information

from the operating systems event and audit log with the integrity information that is

detected by Tripwire for Servers. It uses this information to provide the identity of

who made a certain change. Since we rely on the operating system to gather this

information, the product only captures the who information from the operating

system that track this. Linux and FreeBSD do not track this information. This feature

is called Event Log Correlation.

Each Tripwire for Servers report details when the database was

last updated, providing a quick benchmark of if or when detailing if the data files

have been replaced. In order to replace these files, an attacker requires root or

administrator level privileges and must know where Tripwire for Servers has been

installed. On a properly secured system, gaining this level of access takes time and

leaves physical evidence behind for Tripwire for Servers to detect prior to the

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system being compromised. Methods for reducing the risk of an intruder being able

to replace a Tripwire for Servers installation include:

y Hiding the application by renaming configuration, data, and binary files and

installing to a hidden location.

y Installing Tripwire for Servers to a read-only partition such as a CD-ROM.

TRIPWIRE MANAGER

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Tripwire Manger is a fully functional, cross platform management

console that allows system and security professionals to easily manage all

installations of Tripwire for Servers software across an enterprise network. Tripwire

Manager eliminates the need to manually monitor multiple discrete network platforms

and point solutions. Instead, IT professionals have a comprehensive view of data

integrity status from a single centralized console. Tripwire Manager also enables you

to view and analyze reports from installations of Tripwire for Servers. With Tripwire

Manager you can retrieve an integrity system, which is made up of the configuration,

database, policy, local and site key, from a single golden machine which can then

be distributed to as many servers that need to be compared against this snapshot. In

version 4.0 of the Tripwire Manager you can create and modify policy files by using

graphical policy editor. This GUI will scan the remote file system of a Tripwire for

Servers installation and provide you with an easy mechanism for editing or creating a

policy file without having to know the policy file syntax. Tripwire Manager can

manage the functions of Tripwire for Servers on up to 2500 machines.

Adding or removing recognition of Tripwire for Servers is easy to

do from within the Tripwire Manager console. All you need to know is host name, IP

address and a port number. The Tripwire for Servers database can be updated by

using the database update mode within Tripwire Manager. All communication

between Tripwire Manager and installation of Tripwire for Servers takes place using

Secured Socket Layer (SSL) technology with 168-bit Triple DES encryption. To

protect against unauthorized modification, important files on each Tripwire for

Servers installation are stored in a binary-encoded and signed form. Database,

policy, configuration, and report files generated by the integrity assessment are

protected by using El Gamal asymmetric cryptography with a 1024-bit signature.

There are mainly two types of Tripwire Manager

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y Active Tripwire Manager

y Passive Tripwire Manager

A user can have more than one Tripwire Manager managing the

same set of Tripwire for Servers machines. However, only one can be in active mode

and have complete management control of Tripwire for Servers machines. This

active Tripwire Manager gives a user the ability to update the database, schedule

integrity checks, update and distribute policy and configuration files and view integrity

reports. The other Tripwire Manager are in a passive mode. The passive mode only

allows these Tripwire Manager to view the status of the machines and integrity

reports. Once the active Tripwire Manager shuts down, the next time the passive

Tripwire Manager pings the Tripwire for Servers machine it connects as an active

Tripwire Manager. If more than two passive Tripwire Managers, the one that

connects first to the Tripwire for Servers machine after the active Manager has hut

down becomes the active Manager.

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TRIPWIRE FOR NETWORK DEVICES

Router, switch, and firewall configurations are critical to overall

network operation. Unwanted changes to configuration files can result in downtime

and security issues and waste hours of staff time searching for the cause. Tripwire

for Network Devices monitors the integrity of routers, switches and firewalls-network

devices that communicate network traffic within and between networks. It helps

network administrator answer the question, Has the state of my network devices

changed from a known, trusted state? If so, how?. Problem s with one network

device can seriously disable an organizations entire network. Network downtime can

result in lost revenue and lost customer confidence. Manual processes to secure

your network devices are available and important. Tripwire for Network Devices

augments and helps guarantee that the security of your network devices remains in

tact. With Tripwire for Network Devices, downtime is minimized. Network

administrators can use Tripwire for Network Devices to quickly investigate and

isolate changes and restore changed configuration files within minutes of an alert.

Tripwire for Network Device includes six primary functions :

y Automatic notification of changes to your routers, switches and firewalls

y Automatic restoration of critical network devices

y Audit trail from log files and change reports ideal for internal/external network

audits.

y Baseline archiving and configuration file Hot Back-up solution

y Heterogeneous support for todays most commonly used network devices

y Sets a framework for autonomic recovery

Tripwire for Network Devices does not provide real time

monitoring. It checks your network devices for change according to schedule you set.

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Device passwords stored by the software are protected by robust 1024-bit Blowfish

cryptography. The software has four user authorization levels:

y Monitors are allowed only to monitor the application. They cannot make

changes to Tripwire for Network Devices or to the devices that the software

monitors.

y Users can make changes to Tripwire for Network Devices, such as add routers,

switches. Groups, tasks, etc., but they cannot make changes to the devices it

monitors.

y Power users can make changes to the software and to the devices it monitors.

y Administrator can perform all actions, plus delete violations and log messages

as well as add, delete, or modify user accounts.

Tripwire for Network Devices maintains a log of all significant

actions, including adding and deleting nodes, rules, tasks, and user accounts. All log

entries include a time and date, and identify the user who initiated the process. The

log entries cannot be modified by anyone other than the administrator and can becopied and pasted into a text file so you can create a library of log activities that are

ideal for network audits.

Device password are stored by the software are protected by

robust 1024-bit Blowfish cryptography. Tripwire for Network Devices has been tested

and can monitor thousands of network devices.

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OPERATION OF TRIPWIRE

At installation time - and whenever any of the monitored objects

change legitimately - a HIDS must initialize its checksum-database by scanning the

relevant objects. Persons in charge of computer security need to control this process

tightly in order to prevent intruders making un-authorized changes to the database(s).

Such initialization thus generally takes a long time and involves cryptographically

locking each monitored object and the checksum databases or worse. Because of

this, manufacturers of HIDS usually construct the object-database in such a way that

makes frequent updates to the checksum database unnecessary.

Computer systems generally have many dynamic (frequently

changing) objects which intruders want to modify - and which a HIDS thus should

monitor - but their dynamic nature makes them unsuitable for the checksum

technique. To overcome this problem, HIDS employ various other detection

techniques: monitoring changing file-attributes, log-files that decreased in size since

last checked, and a raft of other means to detect unusual events.

Once a system administrator has constructed a suitable object-

database - ideally with help and advice from the HIDS installation tools - and initialized

the checksum-database, the HIDS has all it requires to scan the monitored objects

regularly and to report on anything that may appear to have gone wrong. Reports can

take the form of logs, e-mails or similar.

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PROTECTING THE HIDS

A HIDS will usually go to great lengths to prevent the object-database, checksum-

database and its reports from any form of tampering. After all, if intruders succeed in

modifying any of the objects the HIDS monitors, nothing can stop such intruders from

modifying the HIDS itself - unless security administrators take appropriate

precautions. Many worms and viruses will try to disable anti-virus tools, for example.

Sadly, lot of them succeeds in doing so. Apart from crypto-techniques, HIDS might

allow administrators to store the databases on a CD-ROM or on other read-only

memory devices (another factor militating for infrequent updates...) or storing them in

some off-system memory. Similarly, a HIDS will often send its logs off-system

immediately - in some instances via one-way communications channels, such as a

serial port which only has "Transmit" connected for example.

One could argue that the trusted platform module comprises a type of HIDS.

Although its scope differs in many ways from that of a HIDS, fundamentally it

provides a means to identify whether anything/anyone has tampered with a portion of

a computer. Architecturally this provides the ultimate (at least at this point in time)host-based intrusion detection, as depends on hardware external to the CPU itself,

thus making it that much harder for an intruder to corrupt its object and checksum

databases.

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FLOW CHART SHOWING THE WORKING OF TRIPWIRE

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1. Install Tripwire and customize the policy file

Install the Tripwire software into the system and then specify the

files to be checked by writing the policy files. Using the version 4.0 writing the policyfile is made very easy.

2. Initialize the Tripwire database

The database is initialized with the important key attribute in the

file to be checked. Build database of critical system files to monitor based on the

contents of the new, signed Tripwire policy file.

3. Run the integrity check

Compare the newly created Tripwire database with the actual system files,

looking for missing or altered files, according to the integrity check timing specified

by in the policy file for different files that are to be monitored.

4. Examine the Tripwire report file

View the Tripwire report file to note any integrity violations.

5. If unauthorized integrity violations occur, take appropriate security

measures

If monitored files have been altered inappropriately, the system

administrator have to take immediate action, you can either replace the original files

from backup copies reinstall the program, or completely reinstall the operating

system.

6. If the file alterations were valid, verify and update the Tripwire database

file.

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If the changes made to monitor files are intentional, edit Tripwires

database file to ignore those changes in subsequent report.

7. If the policy file fails verification, update the Tripwire policy file

To change the list of files Tripwire monitors or how it treats

integrity violations, update the supplied policy file, regenerate a signed copy, and

update the Tripwire database.

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Experience

Since the initial release, four versions have been released to incorporate bug fixes,

support additional platforms, and add new features. The authors estimate Tripwire isbeing actively used at several thousand sites around the world. Retrievals of the

Tripwire distribution from our FTP server initially exceeded 300 per week. Currently,

seven months after the last official patch release, we see an average of 25 fetches per

week. This does not include the copies being obtained from the many FTP mirror sites

around the net. We have received considerable feedback on Tripwire design and

implementation. We believe that version 1.1 of Tripwire has succeeded in meeting

most of the goals of system administrators needing an integrity checking tool. Most of

the feedback that we received falls into one of the following categories: theory of

integrity checking workability, features needed, operational use of Tripwire.

Securing the database

Because Tripwire reports are only as reliable as its inputs, the design document

stresses the need to ensure the integrity of the baseline database. Namely, we

suggest that the baseline database, immediately after. The copyright on the available

code for MD-2 strictly limits its use to privacy-enhanced mail functions. RSA Data

Security, Inc. has kindly given us permission to include MD-2 in the Tripwire package

without further restriction or royalty. it is is generated, be moved to some secure read-

only media. The most common Tripwire configuration to facilitate this is the use of a

secure server, a specialized server receiving extra scrutiny from administrators. A

remote file system is then used to export the baseline database to clients. However,

several sites have gone to much further lengths to maintain the integrity of Tripwire

databases.At least two sites have considerably modified Tripwire to support alternate channels

for receiving the database and transmitting the report, adding layers for networking

support, encryption, and host authentication. Since then, Tripwire has added full

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support for using open UNIX file descriptors to read the configuration and database

files. This allows system administrators to easily add support for encryption and

compression without having to modify the Tripwire package so drastically. Instead, a

wrapper program (even a shell script) can be used to supply these facilities. It is

interesting to note that mistrust of networked file systems motivate the undertaking of

such modifications to Tripwire.

Concealing Tripwire operation

Several sites have reported going to considerable lengths to conceal the operation of

Tripwire. These system administrators feel strongly that they should not advertise their

security measures or policies. As a result, Tripwire is not being run programs like

cron(8), the conventional means of executing programs on a regular schedule.

Instead, a wide variety of local tools are used. For example, a special daemon is

loaded at system startup, waking only to run Tripwire at a scheduled time. Where cron

is used, indirection is sometimes used to mislead an intruder from immediately seeing

evidence of Tripwire use. In one case, a system administrator uses three levels o

indirection before finally executing Tripwire (e.g., cron runs a script that runs a script

than runs a script that runs Tripwire). We wonder whether these measures to conceal

Tripwire are necessary, or even desirable. One of us (Spafford) has seen anunderground publication warning the need for special vigilance when attempting to

crack system running Tripwire. If this warning is true, then Tripwire may have the

ability to deter crackers.

Tracking Tripwire configurations

Tripwire provides a configuration language intended to aid system administrators in

managing larger sites. We were especially interested in how these tools would be

used by system administrators the Tripwire design document suggests that a core

configuration file could be shared by numerous hosts by using the @@include

directive. From reports we have gathered, this appears to be a less than popul

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method. Instead, system administrators create one configuration file to be shared by

all machines, using the @@ifhost directive to segregate non-common file groups. We

suspect that the overhead of tracking multiple configuration files outweighs the

inconvenience caused by files obfuscated by many @@ifdef statements. These

shared configuration files are apparently still manageable, since the number of entries

in the file is not large. (We suspect that if files had to be individually enumerated,

these configuration files be far larger, and therefore unmanageable.) Tripwire has

proven scalable, with documented cases of sites of almost one thousand machines

running Tripwire, as well as sites of only one machine. That system administrators

have done so using a different mechanism than suggested in the design document is

especially interesting.

Simple configuration files

How Tripwire is used on workstations with minimal disk resources proved surprising.

Although the Tripwire configuration file allows considerable flexibility in specifying files

and directories to monitor, configuration files for these workstations consist of only one

character: / Thusly, Tripwire scans all the local disk partitions under the root

directory, collecting the default MD5 and Snefru signatures. For some sites, this has

proved adequate for all their machines!

Frequency of Tripwire runs

The Tripwire design document recommends running Tripwire in integrity checking on a

regular basis (e.g., daily) to ensure that file system tampering can be detected in a

timely manner. However, there have been two reported cases of sites running Tripwire

far more frequently. In fact, these sites motivated the feature addition to skip certain

signatures by specifying it on the command line. Because they were running Tripwireon their machines hourly and with all signatures enabled, the Tripwire runs were not

completed by the time the next Tripwire run started! (The authors were left wondering

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what these machines did besides spending all the CPU cycles computing file

signatures.)

Validating the integrity checking scheme

We have gathered at least seven cases of sites who have detected intruders by using

Tripwire. In at least two of these cases, the penetration was widespread, with system

programs and libraries replaced with Trojan horses. Potentially less exciting than

these stories, but equally inspiring, are the dozens of stories we have received of sites

using Tripwire as a system administration enforcement tool. System administrators

report having found hundreds of program binaries changed, only to find that another

system administrator had made the changed without following local policy. There has

also been one reported case of a system administrator detecting a failing disk with

Tripwire. All three classes of stories seem to validate the theory behind integrity

checking programs. Although the foundations of integrity checkers have been

discussed in [1, 2, 4], when Tripwire design was started in May 1992, no usuable,

publically available integrity tools existed undoubtedly providing one of the primary

motivations for writing Tripwire.

Evaluating Tripwire portability

Tripwire has proven to be highly portable, successfully running on over 28 UNIX

platforms. Among them are Sun, SGI, HP, Sequents, Pyramids, Crays, Apollos,

NeXTs, BSDI, Lynix, Apple Macintosh, and even Xenix. Configurations for new

operating systems has proven to be sufficiently general to necessitate the inclusion of

only eight example tw.config files.

Frequency of file system changes

According to system administrators, the ability to update Tripwire databases is amongits most important features. Files seem to change for many unforeseen reasons.

Consequently, the database is updated regularly. The addition of the interactive

update facility in Tripwire was among the most enthusiastically received features.

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ADVANTAGES

Tripwire Integrity Management solutions give organizations visibility into service

affecting changes and, in the process, increase security, instill process

accountability, and improve system availability.

yIncrease security

Tripwire software immediately detects and pinpoints unauthorized

change-whether malicious or accidental, initiated externally or internally. Tripwire

provides the only way to know, with certainty, that systems remains uncompromised.

yInstill Accountability

Tripwire identifies and reports the sources of change, enabling IT

to manage by fact. It also captures an audit trail of changes to servers and network

devices.

y Gain Visibility

Tripwire software provides a centralized view of changes acrossthe enterprise infrastructure and support multiple devices from multiple vendors.

yEnsure Availability

Tripwire software reduces troubleshooting time, enabling rapid

discovery and recovery. Immediate detection of change enables the fastest possible

restoration back to a desired, good state.

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CONCLUSION

Tripwire is a reliable intrusion detection system. It is a software

that can be installed in any type of system where damaged files are to be detected.

The main attractive feature of this system is that the software generates a report

about which file have been violated, when the file have been violated and also what

in the files have been changed. To some extend it also helps to detect who made the

changes. New versions of Tripwire are under research and development. The latest

version under research is the Tripwire for Open Source.

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REFERNECE

1. www.tripwire.com

2. www.iec.com3. www.itpaper.com

4. Cryptography and network security William Stallings

5. Operating System SilberSchertz

6. Linux for you magazine

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