Chapter 3 Systems Security 1 - Operating Systems and Networks
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Transcript of Chapter 3 Systems Security 1 - Operating Systems and Networks
© 2011 Cengage Learning. All Rights Reserved. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole or in part.
IT Auditing, Hall, 3e
© 2011 Cengage Learning. All Rights Reserved. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole or in part.
Perform three main tasks:◦ translates high-level languages into the machine-level language
◦ allocates computer resources to user applications
◦manages the tasks of job scheduling and multiprogramming
1Hall, 3e
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Protect against tampering by users
Prevent users from tampering with the programs of other users
Safeguard users’ applications from accidental corruption
Safeguard its own programs from accidental corruption
Protect itself from power failures and other disasters
2Hall, 3e
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Log-On Procedure◦ first line of defense – user IDs and passwords
Access Token◦ contains key information about the user
Access Control List◦ defines access privileges of users
Discretionary Access Control◦ allows user to grant access to another user
3Hall, 3e
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Access Privileges Audit objectives: verify that access
privileges are consistent with separation of incompatible functions and organization policies
Audit procedures: review or verify…◦ policies for separating incompatible functions◦ a sample of user privileges, especially access
to data and programs◦ security clearance checks of privileged
employees◦ formal acknowledgements to maintain
confidentiality of data◦ users’ log-on times
4Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
Password Control Audit objectives: ensure adequacy and
effectiveness of password policies for controlling access to the operating system
Audit procedures: review or verify…◦ passwords required for all users◦ password instructions for new users◦ passwords changed regularly◦ password file for weak passwords◦ encryption of password file◦ password standards◦ account lockout policies
5Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
Malicious & Destructive Programs
Audit objectives: verify effectiveness of procedures to protect against programs such as viruses, worms, back doors, logic bombs, and Trojan horses
Audit procedures: review or verify…◦ training of operations personnel concerning
destructive programs◦ testing of new software prior to being
implemented◦ currency of antiviral software and frequency of
upgrades
6Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
Audit Trail Controls
Audit objectives: used to (1) detect unauthorized access, (2) facilitate event reconstruction, and/or (3) promote accountability
Audit procedures: review or verify…◦ how long audit trails have been in place
◦ archived log files for key indicators
◦ monitoring and reporting of security violations
7Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
The communications component is a unique aspect of computer networks:◦ different than processing (applications) or data
storage (databases)
Network topologies – configurations of:◦ communications lines (twisted-pair wires,
coaxial cable, microwaves, fiber optics)
◦ hardware components (modems, multiplexers, servers, front-end processors)
◦ software (protocols, network control systems)
8Hall, 3e
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Intercepting network messages◦ sniffing: interception of user IDs, passwords,
confidential e-mails, and financial data files
Accessing corporate databases◦ connections to central databases increase the
risk that data will be accessible by employees
Privileged employees ◦ override privileges may allow unauthorized
access to mission-critical data
Reluctance to prosecute◦ fear of negative publicity leads to such
reluctance but encourages criminal behavior
9Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
How serious is the risk?◦ National Consumer League: Internet fraud rose
by 600% between 1997 and 1998
◦ SEC: e-mail complaints alleging fraud rose from 12 per day in 1997 to 200-300 per day in 1999
Major areas of concern:◦ Theft of credit card numbers
◦ Theft of passwords
◦ Consumer privacy--cookies
10Hall, 3e
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IP spoofing: masquerading to gain access to a Web server and/or to perpetrate an unlawful act without revealing one’s identity
Denial of service (DOS) attacks: assaulting a Web server to prevent it from servicing users ◦ particularly devastating to business entities that
cannot receive and process business transactions
Other malicious programs: viruses, worms, logic bombs, and Trojan horses pose a threat to both Internet and Intranet users
11Hall, 3e
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SYN Flood – when the three-way handshake needed to establish an Internet connection occurs, the final acknowledgement is not sent by the DOS attacker, thereby tying-up the receiving server while it waits.
Smurf – the DOS attacker uses numerous intermediary computer to flood the target computer with test messages, “pings”.
Distributed DOS (DDOS) – can take the form of Smurf or SYN attacks, but distinguished by the vast number of “zombie” computers hi-jacked to launch the attacks.
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In a DOS Attack, the sender sends hundreds of messages, receives the SYN/ACK packet, but does not response with an ACK packet. This leaves the receiver with clogged transmission ports, and legitimate messages cannot be received.
13
Sender Receiver
Step 1: SYN messages
Step 2: SYN/ACK
Step 3: ACK packet code
Hall, 3e
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Include:◦Disrupting, destroying, or corrupting transmissions between senders and receivers
◦ Loss of databases and programs stored on network servers
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duplicated, or posted to a publicly accessible website, in whole or in part.
Firewalls provide security by channeling all network connections through a control gateway.
Network level firewalls ◦ Low cost and low security access control ◦ Do not explicitly authenticate outside users◦ Filter junk or improperly routed messages ◦ Experienced hackers can easily penetrate the
system
Application level firewalls ◦ Customizable network security, but expensive ◦ Sophisticated functions such as logging or user
authentication
17Hall, 3e
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Denial-of-service (DOS) attacks
◦ Security software searches for connections which have been half-open for a period of time.
Encryption
◦Computer program transforms a clear message into a coded (cipher) text form using an algorithm.
19Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
Controlling for three common forms of DOS attacks:◦ Smurf attacks—organizations can program firewalls to
ignore an attacking site, once identified
◦ SYN flood attacks—two tactics to defeat this DOS attack
Get Internet hosts to use firewalls that block invalid IP addresses
Use security software that scan for half-open connections
◦ DDos attacks–many organizations use Intrusion Prevention Systems (IPS) that employ deep packet inspection (DPI) IPS works with a firewall filter that removes malicious packets from the
flow before they can affect servers and networks
DPI searches for protocol non-compliance and employs predefined criteria to decide if a packet can proceed to its destination
(See chapter 12 for more on DOS attacks)
20Hall, 3e
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The conversion of data into a secret code for storage and transmission
The sender uses an encryption algorithm to convert the original cleartext message into a coded ciphertext.
The receiver decodes / decrypts the ciphertext back into cleartext.
Encryption algorithms use keys◦ Typically 56 to 128 bits in length ◦ The more bits in the key the stronger the encryption
method.
Two general approaches to encryption are private key and public key encryption.
21Hall, 3e
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Digital signature – electronic authentication technique to ensure that…◦ transmitted message originated with the authorized
sender
◦ message was not tampered with after the signature was applied
Digital certificate – like an electronic identification card used with a public key encryption system ◦ Verifies the authenticity of the message sender
22Hall, 3e
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Digital Signature
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Message sequence numbering – sequence number used to detect missing messages
Message transaction log – listing of all incoming and outgoing messages to detect the efforts of hackers
Request-response technique – random control messages are sent from the sender to ensure messages are received
Call-back devices – receiver calls the sender back at a pre-authorized phone number before transmission is completed
24Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
Review firewall effectiveness in terms of flexibility, proxy services, filtering, segregation of systems, audit tools, and probing for weaknesses.
Review data encryption security procedures
Verify encryption by testing
Review message transaction logs
Test procedures for preventing unauthorized calls
25Hall, 3e
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duplicated, or posted to a publicly accessible website, in whole or in part.
Line errors are data errors from communications noise.
Two techniques to detect and correct such data errors are:
◦ echo check - the receiver returns the message to the sender
◦ parity checks - an extra bit is added onto each byte of data similar to check digits
26Hall, 3e
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Using a sample of messages from the transaction log:◦ examine them for garbled contents caused by line noise
◦ verify that all corrupted messages were successfully retransmitted
28Hall, 3e
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Electronic data interchange (EDI) uses computer-to-computer communications technologies to automate B2B purchases.
Audit objectives: 1. Transactions are authorized, validated, and in
compliance with the trading partner agreement.
2. No unauthorized organizations can gain access to database
3. Authorized trading partners have access only to approved data.
4. Adequate controls are in place to ensure a complete audit trail.
29Hall, 3e
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Reduction or elimination of data entry
Reduction of errors Reduction of paper Reduction of paper processing and postage
Reduction of inventories (via JIT systems)
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Authorization ◦ automated and absence of human intervention
Access◦ need to access EDI partner’s files
Audit trail◦ paperless and transparent (automatic) transactions
31Hall, 3e
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Authorization◦ use of passwords and value added networks (VAN) to ensure valid partner
Access◦ software to specify what can be accessed and at what level
Audit trail◦ control log records the transaction’s flow through each phase of the transaction processing
32Hall, 3e
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EDI System
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EDI System using Transaction Control Log for Audit Trail
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Tests of Authorization and Validation Controls◦ Review procedures for verifying trading partner
identification codes ◦ Review agreements with VAN◦ Review trading partner files
Tests of Access Controls◦ Verify limited access to vendor and customer files◦ Verify limited access of vendors to database◦ Test EDI controls by simulation
Tests of Audit Trail Controls◦ Verify existence of transaction logs◦ Review a sample of transactions
35Hall, 3e
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PC operating systems PC systems risks & controls
In general: Relatively simple to operate and program Controlled and operated by end users Interactive data processing vs. batch Commercial applications vs. custom Often used to access data on mainframe or
network Allows users to develop their own
applications Operating Systems:
Are located on the PC (decentralized) O/S family dictates applications (e.g.,
Windows)
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Controls Risk assessment Inherent weaknesses Weak access control Inadequate segregation of duties Multilevel password control – multifaceted access
control
Risk of physical loss Laptops, etc. can “walk off”
Risk of data loss Easy for multiple users to access data End user can steal, destroy, manipulate Inadequate backup procedures
Local backups on appropriate medium Dual hard drives on PC External/removable hard drive on PC
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Risk associated with virus infection Policy of obtaining software Policy for use of anti-virus software Verify no unauthorized software on PCs
Risk of improper SDLC procedures Use of commercial software Formal software selection procedures
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Verify controls are in place to protect data, programs, and computers from unauthorized access, manipulation, destruction, and theft
Verify that adequate supervision and operating procedures exist to compensate for lack of segregation between the duties of users, programmers, and operators
Verify that backup procedures are in place to prevent data and program loss due to system failures, errors
Verify that systems selection and acquisition procedures produce applications that are high quality, and protected from unauthorized changes
Verify the system is free from viruses and adequately protected to minimize the risk of becoming infected with a virus or similar object
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Verify that microcomputers and their files are physically controlled
Verify from organizational charts, job descriptions, and observation that the programmers of applications performing financially significant functions do not also operate those systems.
Confirm that reports of processed transactions, listings of updated accounts, and control totals are prepared, distributed, and reconciled by appropriate management at regular and timely intervals.
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Determine that multilevel password control or multifaceted access control is used to limit access to data and applications, where applicable.
Verify that the drives are removed and stored in a secure location when not in use, where applicable.
Verify that backup procedures are being followed.
Verify that application source code is physically secured (such as in a locked safe) and that only the compiled version is stored on the microcomputer.
Review systems selection and acquisition controls
Review virus control techniques.
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Internet Technologies
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Packet switching◦ messages are divided into small packets◦ each packet of the message takes a different routes
Virtual private network (VPN)◦ a private network within a public network
Extranets◦ a password controlled network for private users
World Wide Web ◦ an Internet facility that links users locally and globally
Internet addresses◦ e-mail address◦ URL address◦ IP address
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facilitate the physical connection between the network devices.
synchronize the transfer of data between physical devices.
provide a basis for error checking and measuring network performance.
promote compatibility among network devices.
promote network designs that are flexible, expandable, and cost-effective.
44Hall, 3e
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Transfer Control Protocol/Internet Protocol (TCP/IP) - controls how individual packets of data are formatted, transmitted, and received
Hypertext Transfer Protocol (HTTP) - controls web browsers
File Transfer Protocol (FTP) - used to transfer files across the internet
Simple Network Mail Protocol (SNMP) - e-mail
Secure Sockets Layer (SSL) and Secure Electronic Transmission (SET) - encryption schemes
45Hall, 3e
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A federation of computers located close together (on the same floor or in the same building) linked together to share data and hardware
The physical connection of workstations to the LAN is achieved through a network interface card (NIC) which fits into a PC’s expansion slot and contains the circuitry necessary for inter-node communications.
A server is used to store the network operating system, application programs, and data to be shared.
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File Server
LAN
LAN
Node
Node
Node
Node
Printer Server
Files
Printer
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A WAN is a network that is dispersed over a wider geographic area than a LAN. It typically requires the use of:◦ gateways to connect different types of
LANs◦ bridges to connect same-type LANs
WANs may use common carrier facilities, such as telephone lines, or they may use a Value Added Network (VAN).
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LANLAN
Bridge
Gateway
Gateway
LAN
WAN
WAN
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A network of IPUs with a large central computer (the host)
The host computer has direct connections to smaller computers, typically desktop or laptop PCs.
This topology is popular for mainframe computing.
All communications must go through the host computer, except for local computing.
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Local Data Local Data
Local Data
Local Data
Central Data
POS
POS
POS
POS
POS
Topeka St. Louis
Kansas
City
DallasTulsa
Star Network
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A host computer is connected to several levels of subordinate smaller computers in a master-slave relationship.
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Production
Planning System
Production
Scheduling
System
Regional
Sales System
Warehouse
System
Warehouse
System
Production
System
Production
System
Sales
Processing
System
Sales
Processing
System
Sales
Processing
System
Corporate
Level
Regional
Level
Local
Level
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This configuration eliminates the central site. All nodes in this configuration are of equal status (peers).
Responsibility for managing communications is distributed among the nodes.
Common resources that are shared by all nodes can be centralized and managed by a file server that is also a node.
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Ring Topology
Figure 12-10
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The nodes are all connected to a common cable - the bus.
Communications and file transfers between workstations are controlled by a server.
It is generally less costly to install than a ring topology.
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Bus Topology
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This configuration distributes the processing between the user’s (client’s) computer and the central file server.
Both types of computers are part of the network, but each is assigned functions that it best performs.
This approach reduces data communications traffic, thus reducing queues and increasing response time.
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Client-Server Topology
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establish a communications sessionbetween the sender and the receiver
manage the flow of data across the network
detect errors in data caused by line failure or signal degeneration
detect and resolve data collisions between competing nodes
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A random access technique that detects collisions when they occur
This technique is widely used--found on Ethernets. The node wishing to transmit listens to the line to
determine if in use. If it is, it waits a pre-specified time to transmit.
Collisions occur when nodes listen, hear no transmissions, and then simultaneously transmit. Data collides and the nodes are instructed to hang up and try again.
Disadvantage: The line may not be used optimally when multiple nodes are trying to transmit simultaneously.
62Hall, 3e