comp 655: distributed/operating systems summer 2011 dr. chunbo chu week 9: security...

COMP 655:Distributed/Operating

SystemsSummer 2011

Dr. Chunbo ChuWeek 9: Security

04/21/23 1Distributed Systems - COMP 655

04/21/23 Distributed Systems - COMP 655 2

Agenda• Security basics• Encryption• Major functions of a security

system

04/21/23 Distributed Systems - COMP 655 3

Types of security• Confidentiality

– Information disclosed only to authorized parties

• Integrity– Information can be created, changed,

or deleted only in authorized ways

04/21/23 Distributed Systems - COMP 655 4

Types of threats• Interception (confidentiality)• Interruption (integrity)• Modification (integrity)• Fabrication (integrity)

04/21/23 Distributed Systems - COMP 655 5

Major functions of a security system

• Authentication• Authorization• Administration• Journaling• Intrusion detection

04/21/23 Distributed Systems - COMP 655 6

Security basicsGeneral advice when dealing with

security:• Always stay in touch with the basic

question: what is the problem you are trying to solve?

• Compare the cost of security to the cost of loss

These should be covered in a security policy

04/21/23 Distributed Systems - COMP 655 7

Security policy basics• A security policy defines the security

requirements for a system• A security policy identifies

– Types of entities in the systemFor example, “instructor”, “student”,

“gradebook application”

– Types of actions supported by the systemFor example, “view grades”, “assign grades”

– Which types of entities are allowed to perform which types of actions

04/21/23 Distributed Systems - COMP 655 8

More about security policyExamples of security policy statements:• An instructor is allowed to assign and

view grades for all students in sections taught by the instructor

• An instructor is not allowed to assign or view grades for any section that he or she did not teach

• A student is allowed to view all of his or her grades

• A student is not allowed to assign grades

04/21/23 Distributed Systems - COMP 655 9

Yet more security policy• Policy deals with roles, not individuals.

For example, some Franklin students are also instructors

• Policy must be specific to a system– “users may perform only authorized actions” is

NOT useful policy– “instructors and administrators may assign

grades” is much more useful

• Writing a good policy is usually hard– Can any administrator assign a grade?– Or only department chairs and deans with

responsibility for the course?– Can the college president assign a grade?

04/21/23 Distributed Systems - COMP 655 10

Activity: DiNo Security policy• Imagine that DiNo needs to support

confidential notebooks• Discuss the security aspects of DiNo

– What types of entities and operations are important?

• What should the security priorities be?– List at least five policies about who’s allowed to

do what

• NOTE: “all users must be authenticated” does NOT belong in a security policy – it’s about implementation, not requirements

04/21/23 Distributed Systems - COMP 655 11

Kevin Mitnick’s work today• The simple fact is this: People are, and

always have been, the most vulnerable aspect of any organization's security infrastructure …

http://www.mitnicksecurity.com/

Interview on 60 Minutes

04/21/23 Distributed Systems - COMP 655 12

Security – human aspects• “Human engineering” is the most

effective way to gain unauthorized access to systems– Helpfulness can be abused– Garbage can be sifted– Etc

• Basically, it’s a never-ending dialog between builders and crackers If you remember nothing else from tonight …

04/21/23 Distributed Systems - COMP 655 13

Tools for the security provider

• Encryption• Explicit, well-considered policy• QA for code• Security education for developers (for

example, see http://www.sans.org/)• Security education for others with

access to sensitive information• Firewalls• Audits• Monitoring

04/21/23 Distributed Systems - COMP 655 14

More security tools• Research• Former crackers with changed

motives• Good system administration,

including keeping up with patches• Virus checkers (pattern, heuristic)

04/21/23 Distributed Systems - COMP 655 15

Resources• CERT: www.cert.org/• CSRC (NIST): csrc.nist.gov/• Steve Gibson: grc.com/default.htm

• Counterpane: www.counterpane.com/crypto-gram.html

• And 400,000,000 others …

04/21/23 Distributed Systems - COMP 655 16

Activity – implementing your policy

• For each of the five statements in your security policy exercise, identify one or more techniques that could be used to enforce it.

04/21/23 Distributed Systems - COMP 655 17

Comp 655 - Security• Security basics• Encryption• Major functions of a security

system

04/21/23 Distributed Systems - COMP 655 18

Encryption - general

04/21/23 Distributed Systems - COMP 655 19

More terminology• Symmetric cryptosystem

– aka secret-key, shared-key

• Asymmetric cryptosystem– aka public-key

• Computational infeasibility• Hash function• Block cipher• Stream cipher

04/21/23 Distributed Systems - COMP 655 20

Important encryption algorithms

• DES• AES• RSA• MD5• SHA-1

04/21/23 Distributed Systems - COMP 655 21

Data Encryption Standard (DES)

04/21/23 Distributed Systems - COMP 655 22

DES key generation

04/21/23 Distributed Systems - COMP 655 23

Attacks on DES• Analytical

– DES has held up pretty well

• Brute force– Hardware is now fast enough to allow

practical guess-and-check attacks on 56-bit DES

• Triple DES “appears to be safe for the moment”

• To be replaced by Rijndael algorithm

04/21/23 Distributed Systems - COMP 655 24

AES

• NIST selection process, 1997-2000, whose goal was a symmetric block cipher to replace DES for protection of sensitive unclassified information. AES is– unclassified– publicly disclosed encryption– available royalty-free, worldwide– supports block sizes of at least 128 bits– supports key sizes of 128, 192, and 256 bits.

04/21/23 Distributed Systems - COMP 655 25

AES Selection criteria1. Security was the most important factor, including

– resistance to cryptanalysis

– soundness of mathematical basis

– randomness of the algorithm output

– relative security as compared to other candidates.

2. Cost was a second important area – licensing requirements

– speed on various platforms

– memory requirements

04/21/23 Distributed Systems - COMP 655 26

AES Selection Criteria continued

• Algorithm characteristics – Adaptability to larger key sizes– Adaptability to other applications,

including stream cipher, hash– Adaptability to various

implementation environments including software, firmware, hardware

– Overall simplicity

04/21/23 Distributed Systems - COMP 655 27

AES continued

• Winner was Rijndael (“Rhine-doll”)• NIST evaluation tested C and Java

implementations of the candidates• Implementations have also appeared

in Lisp, Pascal, JavaScript, C++, hardware, etc

• See the NIST crypto toolkit web site:http://csrc.nist.gov/CryptoToolkit/

04/21/23 Distributed Systems - COMP 655 28

RSA

• Widely used for public-key cryptosystems

• Relies on computational infeasibility of factoring a product of large primes

• A key set includes– d (decryption key)– e (encryption key)– n (product of large primes)

04/21/23 Distributed Systems - COMP 655 29

RSA continued• Publish n and one key, keep the other

key private• Which key gets published depends on

the problem you’re trying to solve– Publish encryption key for data

protection– Publish decryption key for authentication

• Expensive! (2-3 orders of magnitude slower than DES)

04/21/23 Distributed Systems - COMP 655 30

Cryptographic hash functions

• With encryption, they guard against modification

• (kind of like a checksum or check digit)• A hash computes a fixed-length summary

(or digest) of a string (message) that is hard to reproduce– Given a message m, it’s computationally

infeasible to find another message m’ such that H(m’) = H(m).

– And it’s even harder to find such an m’ that says what you want …

04/21/23 Distributed Systems - COMP 655 31

Using a cryptographic hash:digital signature

04/21/23 Distributed Systems - COMP 655 32

MD5

‘<<<‘ is a “circular shift”:10110001 <<< 3 = 10001101

04/21/23 Distributed Systems - COMP 655 33

SHA-1(from Adam Back’s web site)• SHA1 (Secure Hash Algorithm 1) is a

cryptographic message digest algorithm.• It is considered to be more secure than

MD5– it has longer hash size– Hans Dobbertin discovered a partial weakness

in the MD5 collision function.

• There was a SHA0 but it had some security problems which were fixed in SHA1.

http://www.cypherspace.org/adam/rsa/sha.html

04/21/23 Distributed Systems - COMP 655 34

Comp 655 - Security• Security basics• Encryption• Major functions of a security

system

04/21/23 Distributed Systems - COMP 655 35

Major functions of a security system

• Authentication• Authorization• Administration• Journaling• Intrusion detection

04/21/23 Distributed Systems - COMP 655 36

Authentication is …Checking that you are who you say

you are

04/21/23 Distributed Systems - COMP 655 37

Implementation – authentication in Kerberos

Kerberos• is a network authentication protocol• provides strong authentication for

client/server applications by using secret-key cryptography

• implementations are available commercially and free from MIT

• assumes black-hats are sniffing and spoofing everywhere

04/21/23 Distributed Systems - COMP 655 38

How Kerberos authentication works

TG Ticket Secret keySession key

Service ticket

04/21/23 Distributed Systems - COMP 655 39

Setting up a secure channel with Kerberos

How does Bob know KB,TGS?

It’s the session key he got at his login

04/21/23 Distributed Systems - COMP 655 40

Activity - authentication• When you talk to someone on the

phone, how do you know who it is?– List at least three ways– For each way, how can it be spoofed?

• If you suspect you’re being spoofed, how can you verify the other person’s identity?

• Same two questions for instant messaging

04/21/23 Distributed Systems - COMP 655 41

Major functions of a security system

• Authentication• Authorization• Administration• Journaling• Intrusion detection

04/21/23 Distributed Systems - COMP 655 42

Authorization is …Granting access to resources so that

the ability to create, read, update, or delete things is available only to those who are authorized.

04/21/23 Distributed Systems - COMP 655 43

Authorization - General

How will it decide?What data will it use?How will it enforce its decision?

04/21/23 Distributed Systems - COMP 655 44

ACLs vs Capabilities

04/21/23 Distributed Systems - COMP 655 45

Java Security• Top-priority problem: protect hosts

from damage or eavesdropping by mobile Java code.

• For applets, security is built on a co-ordinated authorization system called a “sandbox”.

04/21/23 Distributed Systems - COMP 655 46

Java Sandbox overview

04/21/23 Distributed Systems - COMP 655 47

SecurityManager

04/21/23 Distributed Systems - COMP 655 48

SecurityManager security = System.getSecurityManager();

if (security != null) { security.checkXXX(argument, . . . ); }

SecurityManager

04/21/23 Distributed Systems - COMP 655 49

Sandbox vs Playground

04/21/23 Distributed Systems - COMP 655 50

Leaning out of the sandbox …

• Object references as capabilities• Stack introspection• Name space management (bait-n-

switch based on class names)

04/21/23 Distributed Systems - COMP 655 51

Object reference as capability

04/21/23 Distributed Systems - COMP 655 52

Stack introspection

1. Method invocation forces a call to enable_privilege

2. enable_privilege examines the stack for a suitable privilege or prohibition

3. If OK, enable_privilege pushes a disable_privilege frame onto the stack

4. When method returns, disable_privilege turns privileges off

04/21/23 Distributed Systems - COMP 655 53

Major functions of a security system

• Authentication• Authorization• Administration• Journaling• Intrusion detection

04/21/23 Distributed Systems - COMP 655 54

Administrative functions• Setting up

– Exchanging secret keys– Publishing public keys– Granting privileges

• Tearing down– Removing privileges– Changing compromised secret keys– Revoking compromised public keys

• Managing trust– Adding or removing a server– Delegating privileges

04/21/23 Distributed Systems - COMP 655 55

Setup: Diffie-Hellman Key Exchange

For gory details: http://www.faqs.org/rfcs/rfc2631.html

Commercial application: Cisco’s IKE

IKE standard: RFC 2409(the patent expired in 1997)

04/21/23 Distributed Systems - COMP 655 56

Setup: exchanging secret keys

setup

04/21/23 Distributed Systems - COMP 655 57

Setup: publishing keys

If you have K+, how can you know that K- is actually possessed by the person or company you think it is?

04/21/23 Distributed Systems - COMP 655 58

Setup: establishing trust in public keys

• Usually, public keys are published in a certificate, consisting of– Public key– String identifying the owner– Digital signature of a certificate

authority

04/21/23 Distributed Systems - COMP 655 59

Example: “secure” web site

04/21/23 Distributed Systems - COMP 655 60

Example: certificates

04/21/23 Distributed Systems - COMP 655 61

Certificates on the path

04/21/23 Distributed Systems - COMP 655 62

Certification practice statement

https://www.verisign.com/repository/CPS2.1/cps2-1.pdf

Why is this such an elaborate document?

The simple fact is this: People are, and always have been, the most vulnerable aspect of any organization's security infrastructure …

and that means lawsuits

04/21/23 Distributed Systems - COMP 655 63

Certificate Revocation Lists

• The certificate was good at one time, but not anymore

• CAs publish their revocation lists, usually daily

• But clients rarely check

04/21/23 Distributed Systems - COMP 655 64

Major functions of a security system

• Authentication• Authorization• Administration• Journaling• Intrusion detection

http://www.informit.com/articles/article.asp?p=174342