copyright © 2010 pearson education, inc. technology solutions protecting internet communications...

Copyright © 2010 Pearson Education, Inc.

Technology Solutions

Protecting Internet communications (encryption) Symmetric Key Encryption

Public key Encryption

Securing channels of communication (SSL, S-HTTP, VPNs)

Protecting networks (firewalls)

Protecting servers and clients

Slide 5-1


Protecting Internet communications (encryption)

Because e-commerce transactions must flow over the public Internet, and there for involve thousands of routers and servers through which the transaction packets flow, security experts believe the greatest security threats occur at the level of Internet Communications.

This is very different from a private network where a dedicated communication line is established b/w two parties.

A number of tools are available to protect the security of Internet communications, the most basic of which is message encryption.


Encryption Encryption

The process of transforming plain text or data into cipher text that cannot be read by anyone other than the sender and the receiver.

There are two purpose of Encryption To Secure stored information To Secure information transmission

Provides 4 of 6 key dimensions of e-commerce security:

1. Message integrity2. Nonrepudiation3. Authentication4. Confidentiality

Slide 5-3


Encryption Cipher Text

Text that has been encrypted and thus can cannot be read by anyone other than the sender and receiver is called Cipher Text.

Key (Cipher) Any method for transforming plain text to cipher text.

Ancient Egyptian commercial records were encrypted using substitution & transposition Ciphers

Substitution Cipher Every occurrence of a given letter is replaced systematically by another letter. Example: key (cipher)=letter + 2 , so

HELLO (Plain text) = JGNNQ (Cipher Text)

Transposition Cipher The ordering of the letters in each word is changed in some systematic way. Example: key (cipher) = (reverse order) , so

HELLO (Plain text) = OLLEH


Symmetric / Secret/Same Key Encryption

Symmetric encryption scheme has five ingredients:Plaintext (Text that need to be encrypted)

Encryption algorithm (how to process the

plain text)

Secret Key (same key use by sender and receiver)

Ciphertext (Encrypted text)

Decryption algorithm (reverse of Encryption algorithm)


Algorithm (Just Concept) To make a computer do anything, you have to write a

computer program. To write a computer program, you have to tell the computer, step by step, exactly what you want it to do. The computer then "executes" the program, following each step mechanically, to accomplish the end goal.

When you are telling the computer what to do, you also get to choose how it's going to do it. That's where computer algorithms come in. The algorithm is the basic technique used to get the job done. Let's follow an example to help get an understanding of the algorithm concept.

Let's say that you have a friend arriving at the airport, and your friend needs to get from the airport to your house. Here are four different algorithms that you might give your friend for getting to your home:


Algorithm (Just Concept) The taxi algorithm:

Go to the taxi stand. Get in a taxi. Give the driver my address.

The call-me algorithm: When your plane arrives, call my cell phone. Meet me outside baggage claim.

The rent-a-car algorithm: Take the shuttle to the rental car place. Rent a car. Follow the directions to get to my house.

The bus algorithm: Outside baggage claim, catch bus number 70. Transfer to bus 14 on Main Street. Get off on Elm street. Walk two blocks north to my house.

All four of these algorithms accomplish exactly the same goal, but each algorithm does it in completely different way. Each algorithm also has a different cost and a different travel time.

Taking a taxi, for example, is probably the fastest way, but also the most expensive. Taking the bus is definitely less expensive, but a whole lot slower. You choose the algorithm based on the circumstances.



• Sender and receiver use same digital key (which they exchange over some communication media) to encrypt and decrypt message.

• Symmetric key encryption was used extensively throughout World War II and is still a part of Internet encryption.

• Modern encryption systems are digital. The ciphers or keys used to transform plain text into cipher text are digital strings.

• Computers store text or other data as binary strings composed of 0s and 1s.

• Example: plain text (message) = A (binary of A is

01000001) key (cipher) = 0101 0101 (same key use by both) encryption algorithm = Multiply Cipher text = 0100001…………………… decryption algorithm = divide

Again plain text is 01000001 = A


Symmetric / Secret/Same Key Encryption (cocept)

In above example there are only 28 = 256 possibilities. If the intruder knows you are using an eight – bit key,

then he or she could decode the message in few seconds using a modern desktop PC just by using the brute force method of checking each of the 256 possible keys.

That is the reason modern encryption systems use keys with 56, 128, 256, or 512 binary digits.

With encryption keys of 512 digits, there are 2512 possibilities to check out . It is estimated that all the computers in the world would need to work for 10 years before stumbling upon the answer.



Symmetric key encryption algoritms Data Encryption Standard

Developed by NSA (Nation security Agency ) and IBM in the 1950s. DES uses a 56 – bit encryption key. An improved version of DES is 3DES

With Triple DES essentially encrypting the message three times each with a separate key .

Advance Encryption Standard (AES) Today, the most widely used symmetric key encryption algorithm. Which offers key sizes of 128, 192, and 256 bits.

There are also many other symmetric key systems with keys up to 2,048 bits. Which mean 22048 possible combinations required to break the encrypted message.


Just Concept

Average time required for exhaustiveAverage time required for exhaustive key search key search

Key Size (bits)

Number of Alternative Keys

Time required at 106 Decryption/µs

32 232 = 4.3 x 109 2.15 milliseconds

56 256 = 7.2 x 1016 10 hours

128 2128 = 3.4 x 1038 5.4 x 1018 years

168 2168 = 3.7 x 1050 5.9 x 1030 years


Just Concept


Common flaws in Symmetric key Encryption

First: in the digital age computer are so powerful and fast that these ancient means (Substitution and Transposition) of encryption can be broken quickly.

Second: Same key is share by both, and they exchange over some communication medium where it could be stolen and used to decipher messages.

Third: In, commercial use, we are all not part of the same team, you would need a secret key for each of the parties with whom you transacted, for example An key for the bank, Another key for departmental store Another for government One for other and so

In a large population of users , this could result in as n(n-1) keys. In a population of millions of Internet users, thousands of millions of keys

would be needed to accommodate all e – commerce.

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