Computer Security Review for Final Exam, Study notes of Computer Networks

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Computer Security

CS 426

Review for Final ExamReview

for Final Exam

CS

Fall 2010/Lecture 40

Basic Concepts

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C

onfidentiality

-^

Integrity

-^

Availability

•^

Authenticity

Integrity (in communications)

•^

Non

-repudiation

Non repudiation

-^

Privacy (general concept, need to defined for differentcontexts)contexts)– K-Anonymity? CS

Fall 2010/Lecture 40

OTP & Stream Ciphers

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One

Time Pad (OTP)

•^

One

-Time Pad (OTP)

• Provides perfect secrecy– Two-time pad is insecure

Two time pad is insecure

•^

Stream cipher– Simulate OTP by using PRNG

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• Weaknesses: malleable, need to be very careful to avoid

becoming two-time pad

•^

PRNG: should satisfy the next-bit test. CS

Fall 2010/Lecture 40

Block Ciphers

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Block ciphers

-^

Block

ciphers

• Use a larger block size to defeat frequency analysis– Aim at providing Pseudo Random Permutation (PRP)

Aim at providing Pseudo Random Permutation (PRP)

•^

DES: 56-bit key size, 64-bit block size, consideredinsecure now b/c bruteforce attack

-^

Brute-force: exhaustive key search, dictionary attack

-^

A

ES: block size, key sizes, no known weaknesses

,^

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•^

Encryption modes: ECB, CBC, CTR– How they work?

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• ECB insecure because of deterministic encryption– CBC and CTR randomized, secure, CTR builds stream cipher

from block cipherfrom block cipher

CS

Fall 2010/Lecture 40

Public Key Cryptography

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PK Encryption: two keys can check whether two keys

-^

PK

Encryption: two keys, can check whether two keys are a pair, but cannot compute private key from pubic key

-^

How RSA works: pub key: (n=pq e) pri key (d)

-^

How RSA works: pub key: (n=pq,e), pri key (d)

-^

RSA security: depends on factoring, how long should themodulus n=pq bemodulus n pq be.

-^

RSA security: direct usage violates IND, use OAEP (howit works)

•^

Usage of RSA & secret-key encryption

-^

Diffie

-Hellman key agreement (subject to active attacks)

Diffie Hellman key agreement (subject to active attacks)

-^

How El Gamal encryption works? CS

Fall 2010/Lecture 40

Digital Signatures & KeyDistrib tionsDistributions

Non

repudiation (why MAC doesn’t work)

•^

Non

-repudiation (why MAC doesn’t work)

•^

How RSA signatures work?H

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H

ow to sign hashes of messages?

-^

Why want the hash function to be collision resistant?I^

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TTP

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In key distribution, what does the TTP need to do in thesymmetric key setting?

Scalability of the approach

• Scalability of the approach. -^

Public key distribution– Weaknesses of directory & public announcements

Weaknesses of directory & public announcements

• Usage of public key certificates. How they work?– Nature of trust in Root CA. Compare with symmetric case. CS

Fall 2010/Lecture 40

Operating System Security

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G

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G

oal 1: multiple users sharing one computer

-^

Goal 2: secure operation in networkedenvironment

-^

CPU modes: kernel mode vs. user mode

-^

System calls

-^

Privileged processes vs privileged code

-^

Privileged processes vs. privileged code

CS

Fall 2010/Lecture 40

User Authentication

Types of authentication: know have are

-^

Types

of authentication: know, have, are

•^

Threats to passwords

Online guessing offline dictionary spoofing shoulder surfing

• Online guessing, offline dictionary, spoofing, shoulder surfing,

social engineering

•^

UNIX storage of passwords

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• Addition of /etc/shadow in addition to /etc/passwd– Usage of salts -^

Other defenses– Disabling account after multiple failed attempts– Mechanisms to avoid weak passwords

-^

Trusted pathL

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P

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•^

L

amport’s One-time Passwords scheme

CS

Fall 2010/Lecture 40

Software Vulnerabilities

Buffer overflow

-^

Buffer

overflow

• Overflow ret address to shell code, return to libc, off by one,

function pointers, heap overflow

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Effectiveness of different defenses– Type safe languages, safe library functions, non-executable

stack, StackGuard (using canary), Address space layoutrandomization, Instruction set randomization

•^

Integer overflow

-^

Integer overflow

-^

No question on types of malwares and their details

-^

No question on types of malwares and their details. CS

Fall 2010/Lecture 40

Market Failure of SoftwareSec ritSecurity

Wh t i

k t f il

-^

Wh

at is market failure?

-^

Why incentives are not aligned to make securehardware?– No measurement of security, needs to ship product

early, no liability, patching costs little,testing/debugging expensive, buggy software forcesusers to ungradeusers to ungrade

-^

What would help?

CS

Fall 2010/Lecture 40

Trusted Systems

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T

t d

ti

b

-^

T

rusted computing base

-^

TCSEC: D, C1, C2, B1, B2, B3, A1– B requires MAC, A requires formal verification (no

other details required)

• Limited to OS– Combine functionality and assurance in a single linear

l scale

-^

Common Criteria– TOE, PP, ST, EAL– Windows EAL4+

CS

Fall 2010/Lecture 40

Biba, Clark-Wilson, and ChineseWallWall

Integrity levels different from security levels in BLP

-^

Integrity

levels different from security levels in BLP

•^

Five policies in Biba (what they are)T

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bj

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•^

T

wo meanings of integrity levels on objects

-^

Difference between confidentiality and integrity

Integrity has to trust subjects

• Integrity has to trust subjects -^

Clark & Wilson

Two high level mechanisms: Well formed transactions and

• Two high-level mechanisms: Well-formed transactions and

separation of duty

• Concepts: UDI, CDI, IVP, TP -^

Chinese wall: avoid COI CS

Fall 2010/Lecture 40

RBAC

RBAC

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-^

RBAC

models

• Features in the four models– How to determine session permissions, and which

roles can be activated.S

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• Semantics of role hierarchies– Mutual exclusion constraints -^

RBAC manages how to assign permissions toprincipals, unlike DAC and MAC, which primarilyfocus on how to authorize subjects

CS

Fall 2010/Lecture 40

Network Security

y

ARP

fi

-^

ARP

spoofing

-^

TCP sequence prediction attacks– Session hijacking

-^

DOS attacks– SYN flooding, Smurf, reflection, DDoS, pulsing

CS

Fall 2010/Lecture 40