CS计算机代考程序代写 scheme database chain Java distributed system case study FTP algorithm Figure 15.1 A distributed multimedia system

Figure 15.1 A distributed multimedia system

Distributed Systems:

Security

Revised and Updated by: Rajkumar Buyya

Chapter 2 Revision: Security Model
Most concepts are

drawn from Chapter 11

Some Cyber Security Facts

15 Alarming Cyber Security Facts and Stats

 1. 95% of breached records came from only three

industries in 2016
– Government, retail, and technology (high level of personal identifying

information contained in their records)

 2. There is a hacker attack every 39 seconds

 3. 43% of cyber attacks target small business
– 64% of companies have experienced web-based attacks. 62%

experienced phishing & social engineering attacks. 59% of companies

experienced malicious code and botnets and 51% experienced denial

of service attacks.

2

4 Industries Likely to Get Hacked

Some Cyber Security Facts

15 Alarming Cyber Security Facts and Stats

 4. The average cost of a data breach in 2020

exceeded $150 million
– As more business infrastructure gets connected, Juniper Research

data suggests that cybercrime will cost businesses over $2 trillion total

in 2019.

– June 2019: The Australian National University has been hit by a

massive data hack, with unauthorised access to significant amounts of

personal details dating back 19 years.

 5. Since 2013 there are 3,809,448 records stolen

from breaches every day
– 158,727 per hour, 2,645 per minute and 44 every second of every day

reports Cybersecurity Ventures.

3

https://www.juniperresearch.com/home

Cybercrime Diary, Vol. 3, No. 3: Who’s Hacked? Latest Data Breaches And Cyberattacks

Some Cyber Security Facts

15 Alarming Cyber Security Facts and Stats

 6. Over 75% of healthcare industry has been

infected with malware over last year

 7. Large-scale DDoS attacks increase in size by

500%

 8. Approximately $6 trillion is expected to be

spent globally on cybersecurity by 2021

4

Some Cyber Security Facts

15 Alarming Cyber Security Facts and Stats

 9. Unfilled cybersecurity jobs worldwide will

reach 3.5 million by 2021
– More than 300,000 cybersecurity jobs in the U.S. are unfilled, and

postings are up 74% over the past five years.

 10. By 2020 there will be roughly 200 billion

connected devices
– The risk is real with

IoT and its growing.

– Smart Healthcare

– Smart City

– Smart Transport

5

https://thehill.com/opinion/cybersecurity/365802-cyber-jobs-are-available-but-americans-dont-realize-they-are-qualified

Some Cyber Security Facts

15 Alarming Cyber Security Facts and Stats

 11. 95% of cybersecurity breaches are due to

human error
– Cyber-criminals and hackers will infiltrate your company through your

weakest link, which is almost never in the IT department.

 12. Only 38% of global organizations claim they

are prepared to handle a sophisticated cyber

attack
– What’s worse? An estimated 54 percent of companies say they have

experienced one or more attacks in the last 12 months.

 13. Total cost for cybercrime committed globally

has added up to over $1 trillion dollars in 2018
– As long as you’re connected to the Internet, you can become a victim

of cyber attacks.
6

Why Educating Your Employees on Cyber Intelligence And Security Will Reduce Risk

‘Zoom bombers’ invade virtual classrooms’:
Unauthorized Participants and Disruptions

7

Zoom Challenges

8

https://www.sumologic.com/blog/zoom-security-challenges/

9

Learning objectives

 Security model
– Types of threat

 Basic techniques
– Cryptographic techniques

 Secrecy

 Authentication

 Certificates and credentials

 Access control

– Audit trails

 Symmetric and asymmetric encryption concepts

 Digital signatures

 Approaches to secure system design

 Pragmatics and case studies (Kerberos and Secure Socket
Layer)

10

Why Security is so important in DS?

 Security Goal: Restrict access to information/resources to

just to those entities that are authorized to access.

 There is a pervasive need for measures to guarantee the

privacy, integrity, and availability of resources in DS.

 Security attacks take various forms: Eavesdropping,

masquerading, tampering, and denial of service.

 Designers of secure distributed systems must cope with the

exposed interfaces and insecure network in an environment

where attackers are likely to have knowledge of the

algorithms used to deploy computing resources.

 Cryptography provides the basis for the authentication of

messages as well as their secrecy and integrity.

11

How is security in real world?

 In the physical world, organisations adopt “security policies”
that provide for the sharing of resources within specified
limits.
– Company may permit entry to its building for its employees and for accredited

visitors.

– A security policy for documents may specify groups of employees who can
access classes of documents or it may be defined for individual documents
and users.

 Security policies are enforced with security mechanisms.
– Access to building may be controlled by a reception clerk, who issues

badges to accredited visitors, and enforced by security guard or by electronic
door locks.

 In electronic world, the distinction between security policy
and mechanisms is equally important.

12

Principal (user) Principal (server)

Chapter 2 Revision: Objects and principals

Access rights

Network

invocation

result
Client

Server

Object

 Object (or resource)
– Mailbox, system file, part of a commercial web site

 Principal
– User or process that has authority (rights) to perform actions

– Identity of principal is important

*

13

Chapter 2 Revision: The enemy

Communication channel

Process p Process q

The enemy
m’

Copy of m

m

 Attacks
– On applications that handle financial transactions or other information

whose secrecy or integrity is crucial

 Enemy (or adversary)

 Threats
– To processes, to communication channels, denial of service

*

14

Chapter 2 Revision: Secure channels

 Properties
 Each process is sure of the identity of the other

 Data is private and protected against tampering

 Protection against repetition and reordering of data

 Employs cryptography
 Secrecy based on cryptographic concealment

 Authentication based on proof of ownership of secrets

Cryptographic concealment is based on:

Confusion and diffusion

Ownership of secrets:

Conventional shared crypto keys

Public/private key pair

*

Principal A

Secure channelProcess p Process q

Principal BThe enemy
Cryptography

15

Threats and Attacks

 Security Threats – Three broad Classes:
– Leakage: Acquisition of information by unauthorised recipients

– Tampering: Unauthorised alteration of information

– Vandalism: Interference with the proper operation of systems

 Method of Attacks are listed below:

 Eavesdropping – A form of leakage
– obtaining private or secret information or copies of messages without authority.

 Masquerading – A form of impersonating
– assuming the identity of another user/principal – i.e, sending or receiving messages using the identity

of another principal without their authority.

 Message tampering
– altering the content of messages in transit

 man in the middle attack (tampers with the secure channel mechanism)

 Replaying
– storing secure messages and sending them at a later date

 Denial of service – Vandalism
– flooding a channel or other resource, denying access to others

16

Threats not defeated by secure channels
or other cryptographic techniques

 Denial of service (DoS) attacks
– Deliberately excessive use of resources to the extent that they are

not available to legitimate users

 E.g. the Internet ‘IP spoofing’ attack, February 2000

 Trojan horses and other viruses
– Viruses can only enter computers when program code is imported.

– But users often require new programs, for example:

 New software installation

 Mobile code downloaded dynamically by existing software (e.g. Java

applets)

 Accidental execution of programs transmitted surreptitiously

– Defences: code authentication (signed code), code validation (type

checking, proof), sandboxing.

17

The February 2000 IP Spoofing DDoS attack
(creation of IP packets with a false source IP address)

Echo request | source = x.x.x.x | destination = n.n.n.i

Echo reply | source = n.n.n.i | destination = x.x.x.x

Untrue!
Compromised host on each local network

sends repeatedly (for all i):

resulting in:

Internet

Campus intranets
Firewall

amazon.com

yahoo.com

IP = x.x.x.x

IP = y.y.y.y

IP = n.n.n.i

https://en.wikipedia.org/wiki/Packet_%28information_technology%29
https://en.wikipedia.org/wiki/IP_address

18

Securing Electronic Transactions

 Email
– Traditionally no support for security.

– But it is important to Keep messages secret.

– Modern mail clients incorporate cryptography.

 Purchase of goods and services

 Banking transactions

 Micro-transactions
– Currently access to Web pages is not charged, but the development of

Web as a highly quality publishing medium surely needs it.

– The price of such services may amount to only a fraction of cent and

the payment overhead must be low (for this to be feasible).

– How to manage “fraudulent vendors” – who obtain payment with no

intension of supplying good.

19

Sensible security policies for Internet vendors and buyers leads
to various requirements

 Authenticate the vendor to the buyer

 Keep buyer’s credit card details secure

 Ensure that content is delivered to the buyer

 Authenticate the identity of account holder before

giving them access to their account

20

Designing Secure Systems

 Immense strides have been made in recent years in the
development of cryptographic techniques and their
applications, yet design of secure systems remains an
inherently difficult task.
– Aim: exclude all possible attacks and loop holes.

– This looks like programmer aiming to exclude all bugs from his/her program.

 Security is about avoiding disasters and minimizing mishaps.
When designing for security it is necessary to assume the
worst.

 The design of security system is an exercise in balancing
costs against threats:
– A cost (computational and network usage) is incurred for their use.

– Inappropriately specified security measures may exclude legitimate users from
performing necessary actions.

21

Worst case assumptions and design guidelines

 Interfaces are exposed
– DSs made up of processes with open interfaces

 Networks are insecure
– Messages sources can be falsified.

 Limit the lifetime and scope of each secret
– Passwords and keys validity – needs to be time restricted.

 Algorithms and code are available to hackers

 Attackers may have access to large resources

 Minimise the trusted base.

22

Overview of Security Techniques

 Digital cryptography provides the basis for most

computer security mechanisms, but it is important to

note that computer security and cryptography are

distinct subjects.
– Cryptography is an art of encoding information in a format that only

intended recipient can access.

– Cryptography can be used to provide a proof of authenticity of

information in a manner analogous to the use of signature in

conventional transactions.

 We will focus more on security of distributed

systems and applications rather than cryptography

algorithms.

23

Cryptography: Introduction

 Cryptography: encryption and decryption

 Encryption is the process of encoding a message in
such a way as to hide its contents.

 Modern cryptography includes several secure
algorithms for encrypting and decrypting messages.
They are based on keys.

 A cryptography key is a parameter used in an
encryption algorithm in such a way that the
encryption cannot be reversed without a knowledge
of the key.

24

Classes of Cryptography Algorithms

 There are two main classes:
– Shared Secret Keys:

 The sender and recipient share a knowledge of the key and it must not be revealed
to anyone.

– Public/Private Key Pair:

 The sender of a message uses a recipient’s public key to encrypt the message.

 The recipient uses a corresponding private key to decrypt the message.

 Uses of Cryptography:
– Secrecy and integrity (to stop eavesdropping and tampering) + also use

redundant information (checksums) for maintaining integrity.

– Authentication

– Digital Signatures

25

Security notations –
Familiar names and notations in security literature

KA Alice’s secret key

KB Bob’s secret key

KAB Secret key shared between Alice and Bob

KApriv Alice’s private key (known only to Alice)

KApub Alice’s public key (published by Alice for all to read)

{M}
K

Message M encrypted with key K

[M]K Message M signed with key K

Alice First participant

Bob Second participant

Carol Participant in three- and four-party protocols

Dave Participant in four-party protocols

Eve Eavesdropper

Mallory Malicious attacker

Sara A server

26

Alice wishes to send some information secretly.

Alice and Bob share a secret key KAB.

1. Alice uses KAB and an agreed encryption

function E(KAB, M) to encrypt and send any

number of messages {Mi}KAB to Bob.

2. Bob reads the encrypted messages using the

corresponding decryption function D(KAB, M).

Alice and Bob can go on using KAB as long as it is safe to

assume that KAB has not been compromised.

Scenario 1:
Secret communication with a shared secret key

Issues:

Key distribution: How can Alice send a shared key KAB to Bob securely?

Freshness of communication: How does Bob know that any {Mi} isn’t a copy of

an earlier encrypted message from Alice that was captured by Mallory and

replayed later? Problem: if the message is a request to pay some money to

someone. Mallory might trick Bob into paying twice?

27

Bob is a file server; Sara is an authentication service. Sara shares secret key KA
with Alice and secret key KB with Bob.

1. Alice sends an (unencrypted) message to Sara stating her identity and

requesting a ticket for access to Bob.

2. Sara sends a response to Alice. {{Ticket}KB, KAB}KA. It is encrypted in KA
and consists of a ticket (to be sent to Bob with each request for file access)

encrypted in KB and a new secret key KAB.

3. Alice uses KA to decrypt the response.

4. Alice sends Bob a request R to access a file: {Ticket}KB, Alice, R.

5. The ticket is actually {KAB, Alice}KB. Bob uses KB to decrypt it, checks

that Alice’s name matches and then uses KAB to encrypt responses to Alice.

Scenario 2: Authenticated communication with a server
(Server knows secret keys of all parties)

 This is a simplified version of the Needham and Schroeder (and Kerberos) protocol.

 Timing and replay issues – addressed in N-S and Kerberos.

 Not suitable for e-commerce because authentication service doesn’t scale…

Scenario 2: Illustration

28

Alice

Bob

Sara

1

2: {{Ticket}KB, KAB}KA

KA

KB

Sara knows KA and KB
Can create KAB

The ticket is actually {KAB, Alice}KB.

{Ticket}KB, Alice, R.

3

4

5
{Response Msg} KAB

29

Limitation of Needham and Schroeder Protocols

 It depends upon prior knowledge by the

authentication server Sara of Alice’s and Bob’s keys.

This is feasible in a single organisation where Sara

run a physically secure computer and is managed by

a trusted principal.
– Not suitable in E-commerce or other wide area applications.

 Usefulness of challenges: They introduced the

concept of a cryptographic challenge. That means in

step 2 of our scenario, where Sara issues a ticket to

Allice encypted in Alice’s secret key, KA .

30

Bob has a public/private key pair & establishes KAB as

follows:

1. Alice obtains a certificate that was signed by a trusted authority

stating Bob’s public key KBpub

2. Alice creates a new shared key KAB , encrypts it using KBpub using a

public-key algorithm and sends the result to Bob.

3. Bob uses the corresponding private key KBpriv to decrypt it.

(If they want to be sure that the message hasn’t been tampered with, Alice can add an

agreed value to it and Bob can check it.)

Scenario 3:
Authenticated communication with public keys

 Mallory might intercept Alice’s initial request to a key

distribution service for Bob’s public-key certificate and send a

response containing his own public key. He can then

intercept all the subsequent messages.

31

Alice wants to publish a document M in such a way that anyone can

verify that it is from her.

1. Alice computes a fixed-length digest of the document Digest(M).

2. Alice encrypts the digest in her private key, appends it to M and

makes the resulting signed document (M, {Digest(M)}KApriv)

available to the intended users.

3. Bob obtains the signed document, extracts M and computes

Digest(M).

4. Bob uses Alice’s public key to decrypt {Digest(M)}KApriv and

compares it with his computed digest. If they match, Alice’s

signature is verified.

Scenario 4:
Digital signatures with a secure digest function

A Certificate with Digital signatures

32

Transcript

Student: Rajkumar Buyya

1. COMP90015: Distributed Systems: 95 marks

2….

Computed message digest:

{491103ea18660f4c4d9f3c32af5d28f5}KUniMelbpriv

IBM (employer) uses UniMelb’s public key to decrypt {Digest(M)} KUniMelbpriv
and compares it with his computed digest of Transcript content. If they

match, UniMelb’s signature is verified. Then IBM trusts and hires you☺

Algo MD5 128 bit from: https://www.freeformatter.com/message-digest.html

The MD5 hashing algorithm is a one-way cryptographic function that accepts

a message of any length as input and returns as output a fixed-length digest

value to be used for authenticating the original message.

https://www.freeformatter.com/message-digest.html
https://searchsqlserver.techtarget.com/definition/hashing
https://whatis.techtarget.com/definition/algorithm
https://whatis.techtarget.com/definition/function
https://searchsecurity.techtarget.com/definition/digest-authentication
https://searchsecurity.techtarget.com/definition/authentication

33

Cryptographic Algorithms

 Symmetric (secret key)
E(K, M) = {M}K D(K, E(K, M)) = M

Same key for E and D

M must be hard (infeasible) to compute if K is not known.

Usual form of attack is brute-force: try all possible key values for a known pair
M, {M}K. Resisted by making K sufficiently large ~ 128 bits

 Asymmetric (public key)
Separate encryption and decryption keys: Ke, Kd

D(Kd. E(Ke, M)) = M

depends on the use of a trap-door function to make the keys. E has high
computational cost. Very large keys > 512 bits

 Hybrid protocols – used in SSL (now called TLS)
Uses asymmetric crypto to transmit the symmetric key that is then used to

encrypt a session.

Message M, key K, published encryption functions E, D

34

Public Key Infrastructure (PKI)

 PKI allows you to know that a

given public key belongs to a

given user

 PKI builds on asymmetric

encryption:

– Each entity has two keys: public

and private

– Data encrypted with one key can

only be decrypted with other.

– The private key is known only to

the entity

 The public key is given to the

world encapsulated in a X.509

certificate

35

Public Key Infrastructure (PKI) Overview

 X.509 Certificates

 Certificate Authorities (CAs)

 Certificate Policies
– Namespaces

 Requesting a certificate
– Certificate Request

– Registration Authority

36

Certificates

1. Certificate type: Account number

2. Name: Alice

3. Account: 6262626

4. Certifying authority: Bob’s Bank

5. Signature: {Digest(field 2 + field 3)}KBpriv

Figure 7.4 Alice’s bank account certificate

Public-key certificate for Bob’s Bank

1. Certificate type: Public key

2. Name: Bob’s Bank

3. Public key: KBpub

4. Certifying authority: Fred – The Bankers Federation

5. Signature: {Digest(field 2 + field 3)}KFpriv

Certificate: a statement signed by an appropriate authority.

Certificates require:

• An agreed standard format

• Agreement on the construction of chains of trust.

• Expiry dates, so that certificates can be revoked.

37

X509 Certificate format

Subject
Distinguished Name, Public Key

Issuer Distinguished Name, Signature

Period of validity Not Before Date, Not After Date

Administrative information Version, Serial Number

Extended Information

It provides a public key to a named entity called the subject.

The binding is in the signature, which is issued by another

entity called issuer (CA, Certificate Authority)

38

Rajkumar Buyya

111, Barry Street

Carlton

BD 01-0X-197X

Male 165cms, 65Kg

Valid: Jun 30, 2030

State of

Victoria

Seal

Certificates

 Similar to passport or driver’s license

Name

Issuer

Public Key

Signature

39

An example of Certificate

Certificate:
Data:

Version: 3 (0x2)
Serial Number: 28 (0x1c)
Signature Algorithm: md5WithRSAEncryption
Issuer: C=US, O=Globus, CN=Globus Certification Authority
Validity

Not Before: Apr 22 19:21:50 2020 GMT
Not After : Apr 22 19:21:50 2030 GMT

Subject: /O=Grid/O=Globus/OU=cis.unimelb.edu.au/CN=Rajkumar Buyya
Subject Public Key Info:

Public Key Algorithm: RSAEncryption
RSA Public Key: (1024 bit)

Modulus (1024 bit):
00:bf:4c:9b:ae:51:e5:ad:ac:54:4f:12:52:3a:69:

b4:e1:54:e7:87:57:b7:d0:61

Exponent: 65537 (0x10001)
Signature Algorithm: md5WithRSAEncryption

59:86:6e:df:dd:94:5d:26:f5:23:c1:89:83:8e:3c:97:fc:d8:

8d:cd:7c:7e:49:68:15:7e:5f:24:23:54:ca:a2:27:f1:35:17:

Validity Start

40

Certificates as credentials

 Certificates can act as credentials

– Evidence for a principal’s right to access a resource

 The two certificates shown in the last slide could act as credentials for Alice

to operate on her bank account

– She would need to add her public key certificate

Public-key certificate for Bob’s Bank

1. Certificate type: Public key

2. Name: Bob’s Bank

3. Public key: KBpub
4. Certifying authority: Fred – The Bankers Federation

5. Signature: {Digest(field 2 + field 3)}KFpriv

1. Certificate type: Account number
2. Name: Alice
3. Account: 6262626
4. Certifying authority: Bob’s Bank
5. Signature: {Digest(field 2 + field 3)}KBpriv

Alice’s bank account certificate

41

Access control

 Protection domain
– A set of pairs

 Two main approaches to implementation:
– Access control list (ACL) associated with each object

 E.g. Unix file access permissions

 For more complex object types and user communities, ACLs can complex

– Capabilities associated with principals

 Like a key – allowing the holder access to certain operations on a

specified resource.

 Format:

drwxr-xr-x gfc22 staff 264 Oct 30 16:57 Acrobat User Data

-rw-r–r– gfc22 unknown 0 Nov 1 09:34 Eudora Folder

-rw-r–r– gfc22 staff 163945 Oct 24 00:16 Preview of xx.pdf

drwxr-xr-x gfc22 staff 264 Oct 31 13:09 iTunes

-rw-r–r– gfc22 staff 325 Oct 22 22:59 list of broken apps.rtf

42

Case study: Kerberos authentication and key distribution service

 Secures communication with servers on a local network

– Developed at MIT in the 1980s to provide security across a large

campus network > 5000 users

– based on Needham – Schroeder protocol

 Standardized and now included in many operating systems

– Internet RFC 1510, OSF DCE

– BSD UNIX, Linux, Windows 2000, XP, Windows 2012, Windows 8

 Kerberos server creates a shared secret key for any required

server and sends it (encrypted) to the user’s computer

 User’s password is the initial secret shared with Kerberos

43

ServerClient

DoOperation

Authentication
database

Login
session setup

Ticket-
granting
service T

Kerberos Key Distribution Centre

Server
session setup

Authen-
tication

service A

Service
function

System architecture of Kerberos

3. Request for
server ticket

4. Server ticket

Step B

5. Service
request

Request encrypted with session key

Reply encrypted with session key

Step C

1. A->S: A, B, NA

2. S->A: {NA , B, KAB,

{KAB, A}KB}KA

3. A->B:

4. B->A:

{KAB, A}KB

{NB}KAB

Needham – Schroeder

protocol

5. A->B: {NB – 1}KAB

Step B once per server session

Step C once per server transaction

Step A once per login session

1. Request for

TGS ticket

2. TGS
ticket

Step A

TGS: Ticket-
granting
service

44

Kerberized NFS

 Kerberos protocol is too costly to apply on each NFS operation

 Kerberos is used in the mount service:
– to authenticate the user’s identity

– User’s UserID and GroupID are stored at the server with the client’s IP address

 For each file request:
– UserID and GroupID are sent encrypted in the shared session key

– The UserID and GroupID must match those stored at the server

– IP addresses must also match

 This approach has some problems
– can’t accommodate multiple users sharing the same client computer

– all remote filestores must be mounted each time a user logs in

45

Case study: The Secure Socket Layer (SSL)

 Key distribution and secure channels for Internet commerce
– Hybrid protocol; depends on public-key cryptography

– Originally developed by Netscape Corporation (1994) and supported by most
browsers and is widely used in Internet commerce.

– Extended and adopted as an Internet standard with the name Transport Level
Security (TLS) – RFC 2246

– Provides the security in all web servers and browsers and in secure versions of
Telnet, FTP and other network applications

 Key Feature
– Negotiable encryption and authentication algorithms. In an open network we

should NOT assume that all parties use the same client software or all
client/server software includes a particular encryption algorithms.

 Design requirements
– Secure communication without prior negotiation or help from 3rd parties

– Free choice of crypto algorithms by client and server

– communication in each direction can be authenticated, encrypted or both

46

Bootstrapped secure communication

 To meet the need for secure communication without previous
negotiation/help from 3rd parties, the secure channel is
established using a hybrid schemes.

 The secure channel is fully configurable.

 The details of TLS protocols are standardized and several
software libraries and toolkits are available to support it
[www.openssl.org]

 TLS consists of two layers:
– TLS Record Protocol Layer: implements a secure channel, encrypting and

authenticating messages transmitted through any connection oriented
protocol. It is realized at session layer.

– Handshake Layer: Containing Handshake protocol and two other related
protocols that establish and maintain a TLS session (i.e., secure channel)
between client and server.

– Both are implemented by software libraries at application level in the client
and the server.

47

TLS protocol stack

TLS

Handshake

protocol

TLS Change

Cipher Spec

TLS Alert

Protocol

Transport layer (usually TCP)

Network layer (usually IP)

TLS Record Protocol

HTTP Telnet

TLS protocols: Other protocols:

negotiates cipher
suite, exchanges
certificates and key
masters

changes the
secure channel
to a new spec

implements the
secure channel

48

Client

A

Server

B

ClientHello

ServerHello

TLS/SSL handshake protocol
(Handshake is performed over an existing connection)

Establish protocol version, session ID,
cipher suite, compression method,
exchange random start values

Certificate

Certificate Request

ServerHelloDone

Optionally send server certificate and

request client certificate

Certificate

Certificate Verify

Send client certificate response if

requested

Change Cipher Spec

Finished

Change Cipher Spec

Finished

Change cipher suite and finish
handshake

Includes key master exchange.
Key master is used by both A and B
to generate:
2 session keys 2 MAC keys

KAB MAB
KBA MBA

Message Authentication Code (MAC)

49

TLS handshake configuration options

Component Description Example

Key exchange
method

the method to be used for
exchange of a session key

RSA with public-key
certificates

Cipher for data
transfer

the block or stream cipher to be
used for data

IDEA (International Data

Encryption Algorithm)

Message digest
function

for creating message
authentication codes (MACs)

SHA (Secure Hash Algorithm)

50

TLS record protocol operation: a pipeline for data transformation

Application data
abcdefghi

abc def ghiRecord protocol units

Fragment/combine

Compressed units

Compress

MAC

Hash

Encrypted

Encrypt

TCP packet

Transmit

51

Summary

 Threats for the security in distributed systems are pervasive.

 It is essential to protect the resources, communication
channels and interfaces of distributed systems and
applications against attacks.

 This is achieved by the use of access control mechanisms
and secure channels.

 Public-key and secret-key cryptography provide the basis for
authentication and for secure communication.

 Kerberos and SSL are widely-used system components that
support secure and authenticated communication.