Information systems slide technical aspects of e commerce part 2

Operating System HD Controller Hard Drive Motherboard Presentation Session Transport Network Datalink Application: Programs that directly access the presentation layer belong at least

Technical Aspects of

E-Commerce Part 2 of 2

Mort Anvari

Web Server

FW

PC PC

PC

PC

Mail Server

SQL Server

File Server

Operating System

HD Controller Hard Drive

Motherboard

Presentation Session Transport Network

Datalink

Application: Programs that

directly access the presentation layer belong

at least in part to the application layer.

Web Server CGI Script

Software Hardware

What is it?

- The physical components of a computing

system

- If it can be held in your hand it’s hardware

- If it can’t it’s software

Operating System

HD Controller Hard Drive

Motherboard

Presentation Session Transport Network

Datalink

Application: Programs that

directly access the presentation layer belong

at least in part to the application layer.

Web Server CGI Script

Software Hardware Current Topic

- CISC (Complex Instruction Set Comp.)

Can do complex operations Can do many functions

i.e 486, Pentium, PowerPC

- RISC (Reduced Instruction Set Comp.)

Can do a few simple operations Faster than CISC

i.e SPARC, HP9000

Hard Drives

- Highly Redundant Drive Enclosure

External to server Can lose multiple drives Very fast

Very expensive

Backup Systems

- DAT (Digital Audio Tape)

Fast, efficient and reliable

Tape sizes from 2-24GB

Backwards compatible

- DLT (Digital Linear Tape)

Very fast, reliability problems

Tapes can hold up to 70GB

New technology

Network Interfaces

- LAN (Local Area Network)

Small in geographic size

Fast and cheap

Owned

- WAN (Wide Area Network)

Connects distant LANs

Slow and expensive

Rented

Random Access Memory

- Regular

Garden variety memory

- Parity

Checks for memory errors

Stops machine on error

- ECC (Error Checking and Correcting)

Checks for memory errors

Corrects errors

- Only allows traffic to pass that meets a set of

criteria based on company policy

- Like the gate house in a jail

- It’s software

Web Server

FW

PC PC

PC

PC

Mail Server

SQL Server

File Server

Operating System

HD Controller Hard Drive

Motherboard

Presentation Session Transport Network

Datalink

Application: Programs that

directly access the presentation layer belong

at least in part to the application layer.

Software Hardware Current Topic

Firewall Software

What is it?

- A series of devices called nodes

interconnected by communication pathways

- Nodes can be computers or devices that help the network function

- Networks can be connected or contain sub

networks

- It’s made up of hardware and software

Web Server

FW

PC PC

PC

PC

Mail Server

SQL Server

File Server

Operating System

HD Controller Hard Drive

Motherboard

Presentation Session Transport Network

Datalink

Application: Programs that

directly access the presentation layer belong

at least in part to the application layer.

Software Hardware Current Topic

Power Point

Web Client Mail

Client

- The OSI Model

- An Example Transmission

The OSI Model

- Framework describing network

protocols

- 7 Layers

- 1 Layer = 1 Aspect of Networking

- Layers only aware of neighbors

- Layers provide flexibility and

functionality

The OSI Model

The OS and the Network Card work together to make a

complete stack.

The OS is responsible for these functions

The Network Card is responsible for these

Application Presentation Session Transport Network Datalink

- Router works at this level

- If destination is on same network

host sends data directly

Network Layer

- If destination is on another network host sends data to right router

- If right router is unknown, data is

sent to the Default Router or Default Gateway

Data Link Layer

- How data should actually be transmitted

- How the bits should be arranged

Data Link Layer

- A bridge splits network into 2

segments

- Makes decisions based on MAC

address in each packet

- Improves performance

- A switch is a bridge that works

with more than 2 segments

The Physical Layer

- Defines the electrical, mechanical and physical aspects of a network

Star Topology Very Manageable and Reasonably Priced

Physical Layer: Topologies

Hub

Computers Network Cable

Physical Layer: Topologies

Point to Point Topology

Used Almost Exclusively in WANs

Physical Layer: Topologies

Send picture to client

Encrypt using SSL Establish

connection

Establish connection Divide picture into tiny packets

Divide picture into tiny packets

Send to proper network

Send to proper network

Format packet and identify client

Format packet and identify client

Transmit packet to client

Transmit packet to client

Authenticate and receive connection

Reassemble packets into picture

Reassemble packets into picture Determine if it’s our packet and network

Determine if it’s our packet and network Check for errors and if it’s ours

Check for errors and if it’s ours Receive packets from server

Receive packets from server

Application Presentation Session Transport Network Datalink Physical

Client

An Example

When the packet is transmitted each layer

has added it’s own “Header” The Datalink layer often adds a “Tail” as well

to provide error checking

A Packet in Transit

D

D N N T T S S P P Data Fragment D

PC Client

PC

PC

Router PC

PC PC

What is it?

- The conversion of data into a form that cannot

be easily understood by unauthorized people

- The opposite is decryption, that is, changing the difficult to read form back into the original

- It’s usually software, but can be hardware

- What does it do for me?

- Symmetric Encryption

- Asymmetric Encryption

- One Way Hash

- Example: An Encrypted E-Mail

What does it do for me?

Confidentiality: The data can only be read

by the intended recipients

Non-Repudiation: The data cannot be

forged If data is “signed” by a person,

the data could only have come from

them No more “I didn’t send that!”

Data Integrity: The data cannot be modified without detection

Symmetric Encryption

- Data is encrypted and decrypted

with the same key

- Fast

- Key must be kept secret

- Key must be sent Out of Band

- DES and IDEA are symmetric

Asymmetric Encryption

- Uses 2 keys

- Data encrypted with one key can

only be decrypted with the other

- Public key is shared with all

- Public key can be sent In Band

- Private key must be kept secret

- RSA is asymmetric

One Way Hash

- A “fingerprint” of data

- Any size data = same size hash

- Tiny changes in data produce

a very different hash

Example: Encrypted E-Mail

Anne wants to send e-mail to Bob The plaintext message compressed to make

it smaller and the ciphertext stronger

Plaintext Compression Small

Plaintext

Example: Encrypted E-Mail

The plaintext message is run through a hash algorithm to generate a

“fingerprint”

Small Plaintext Hash Function Fingerprint

Example: Encrypted E-Mail

The fingerprint is encrypted using

Anne’s private key This makes it into a digital signature It is then appended to the plaintext

Anne’s Private

Key

Small Plaintext

Signature Fingerprint

Example: Encrypted E-Mail

A Random key is generated and the mail is symmetrically encrypted using that

e-Small Plaintext Random Key

Ciphertext Encrypted with Random Key Signature

Example: Encrypted E-Mail

The Random Key is Encrypted using

Bob’s public key The result is called a

“Strong Box” Remember that only Bob can read the contents of the Box

Random Key

A Box for Bob

Example: Encrypted E-Mail

The Box is attached to the ciphertext

and they are sent over e-mail to Bob

Ciphertext

Encrypted

with Random

Key

To Bob Internet

Example: Encrypted E-Mail

Bob decrypts his Strong Box to get the Random Key Only Bob’s private key

can open the Box which was encrypted with his public key

Example: Encrypted E-Mail

Bob decrypts the ciphertext using the

random key which he got from his

Key

Small Plaintext

Signature

Example: Encrypted E-Mail

Bob decrypts Anne’s signature using

her public key Since only Anne could have encrypted it with her private key, Bob knows the message had to come from her

Anne’s Public

Key Signature Fingerprint

Example: Encrypted E-Mail

Bob runs the unencrypted message

through the hash function If this

fingerprint is the same as the one from the signature, the message was not

changed in transit

Small Plaintext

Hash Function

Calculated Fingerprint

Received

 or



Example: Encrypted E-Mail

Finally, the message is uncompressed Bob can read the message knowing for certain that it’s from Anne, it’s what

Anne wrote and only the two of them

could have read it

Plaintext Compression Small

Plaintext