Operating System Security: Threats, Encryption, and Authentication - Prof. M. Ali, Study notes of Operating Systems

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Chapter 15: SecurityChapter 15: Security

15.^

Chapter 15: Security^ Chapter 15: Security

„^ The Security Problem „^ Program Threats „^ System and Network Threats „^ Cryptography as a Security Tool „^ User Authentication „^ Implementing Security Defenses „^ Firewalling to Protect Systems and Networks „^ Computer-Security Classifications „^ An Example: Windows XP

15.^

The Security Problem^ The Security Problem

„^ Security must consider external environment of the system, andprotect the system resources „^ Intruders (crackers) attempt to breach security „^ Threat^ is potential security violation „^ Attack^ is attempt to breach security „^ Attack can be accidental or malicious „^ Easier to protect against accidental than malicious misuse

15.^

Security Violations^ Security Violations

„^ Categories^ z^ Breach of confidentiality^ z^ Breach of integrity^ z^ Breach of availability^ z^ Theft of service^ z^ Denial of service „^ Methods^ z^ Masquerading (breach authentication)^ z^ Replay attack^ ^ Message modification^ z^ Man-in-the-middle attack^ z^ Session hijacking

15.^

Security Measure Levels^ Security Measure Levels

„^ Security must occur at four levels to be effective:^ z^ Physical^ z^ Human^ ^ Avoid

social engineering, phishing, dumpster diving

z^ Operating System z^ Network „ Security is as week as the weakest chain

15.^

Program Threats^ Program Threats

„^ Trojan Horse^ z^ Code segment that misuses its environment^ z^ Exploits mechanisms for allowing programs written by users to beexecuted by other users^ z^ Spyware, pop-up browser windows, covert channels „^ Trap Door^ z^ Specific user identifier or password that circumvents normal securityprocedures^ z^ Could be included in a compiler „^ Logic Bomb^ z^ Program that initiates a security incident under certain circumstances „^ Stack and Buffer Overflow^ z^ Exploits a bug in a program (overflow either the stack or memorybuffers)

15.^

Layout of Typical Stack Frame^ Layout of Typical Stack Frame

15.^

Modified Shell Code^ Modified Shell Code

#include <stdio.h> int main(int argc, char *argv[]) {^ execvp(‘‘\bin\sh’’,‘‘\bin \sh’’, NULL);^ return 0; }

15.^

Program Threats (Cont.)^ Program Threats (Cont.)

„^ Viruses^ z^ Code fragment embedded in legitimate program^ z^ Very specific to CPU architecture, operating system,applications^ z^ Usually borne via email or as a macro^ ^ Visual Basic Macro to reformat hard drive

Sub AutoOpen() Dim^ oFS^ Set^ oFS =CreateObject(’’Scripting.FileSystemObject’’)^ vs^ =^ Shell(’’c:command.com

/k^ format

c:’’,vbHide) End Sub

15.^

Program Threats (Cont.)^ Program Threats (Cont.)

„^ Virus dropper

inserts virus onto the system

„^ Many categories of viruses, literally many thousands of viruses^ z^ File^ z^ Boot^ z^ Macro^ z^ Source code^ z^ Polymorphic^ z^ Encrypted^ z^ Stealth^ z^ Tunneling^ z^ Multipartite^ z^ Armored

15.^

System and Network Threats^ System and Network Threats „ Worms – use^ spawn

mechanism; standalone program

„^ Internet worm^ z^ Exploited UNIX networking features (remote access) and bugsin^ finger

and^ sendmail

programs

z^ Grappling hook

program uploaded main worm program

„^ Port scanning^ z^ Automated attempt to connect to a range of ports on one or arange of IP addresses „^ Denial of Service^ z^ Overload the targeted computer preventing it from doing anyuseful work^ z^ Distributed denial-of-service (

DDOS ) come from multiple sites

at once

15.^

The Morris Internet Worm^ The Morris Internet Worm

15.^

Secure Communication over Insecure Medium^ Secure Communication over Insecure MediumOperating System Concepts

15.^

Silberschatz, Galvin and Gagne ©

Encryption^ Encryption

„^ Encryption algorithm consists of^ z^ Set of

K^ keys z Set of M^ Messages z Set of C^ ciphertexts (encrypted messages) z A function^ E^ :^ K^ →^ ( M

→ C ). That is, for each

k^ ∈^ K ,^ E ( k ) is a function for generating ciphertexts from messages.^ ^ Both^ E^ and

E ( k ) for any^ k^ should be efficiently computable functions. z^ A function^ D

:^ K^ →^ ( C^ →^ M ). That is, for each

k^ ∈^ K ,^ D ( k ) is a function for

generating messages from ciphertexts.^ ^ Both^ D^ and

D ( k ) for any^ k^ should be efficiently computable functions. „^ An encryption algorithm must provide this essential property: Given a ciphertext

c^ ∈^ C ,

a computer can compute

m^ such that^ E (

k )( m ) =^ c^ only if it possesses

D ( k ).

z^ Thus, a computer holding

D ( k ) can decrypt ciphertexts to the plaintexts used to produce them, but a computer not holding

D ( k ) cannot decrypt ciphertexts.

z^ Since ciphertexts are generally exposed (for example, sent on the network), it isimportant that it be infeasible to derive

D ( k ) from the ciphertexts