Data Encryption and Decryption

CONTENTS

1. ABSTRACT

2. INTRODUCTION

3. DESIGN PRINCIPLES & EXPLANATION

3.1. MODULES

3.2. MODULE DESCRIPTIOIN

4. PROJECT DICTIONARY

4.1. DATAFLOW DIAGRAMS

5. FORMS & REPORTS

5.1. I/O SAMPLES

6. BIBILIOGRAPHY

1. ABSTRACT

In the present system the network helps a particular

organization to share the data by using external devices. The

external devices are used to carry the data. The existing system

cannot provide security, which allows an unauthorized user to access

the secret files. It also cannot share a single costly printer. Many

interrupts may occur with in the system. In this project the

networking allows a company to share files or data without using

some external devices to carry the data. Similarly a company can

share the single costly printer. Though it is advantageous we have

numerous disadvantages, somebody writes the program and can

make the costly printer to misprint the data. Similarly some

unauthorized user may get access over the network and may perform

any illegal functions like deleting some of the sensitive information

like employee salary details while they are in transactions.

Security is the term that comes into the picture when some important

or sensitive information must be protect from an unauthorized

access. Hence there must be some way to protect the data from

them and even if he hack the information, he should not be able to

understand what the actual information in the file is? , which is the

main intension of the project. The project is designed to protect the

sensitive information while it is in transaction in the network. There

are many chances that an unauthorized person can have an access

over the network in some way and can access this sensitive

information. The project uses the strong secured algorithm-DATA

ENCRYPTION STANDARDS that enables and guarantees the

security of the information in the network.

2. INTRODUCTION

The project “Data Encryption and Decryption” is totally enhanced

with the features that enable us to feel the real-time environment.

Today’s world is mostly employing the latest networking techniques

instead of using stand-alone PC’s. Encryption or information

scrambling, technology is an important security tool. Properly applied

it can provide a secure communication channel even when the

underlying system and network infrastructure is not secure. This is

particularly important when data passes through shared systems or

network segments where multiple people may have access to the

information. In these situations, sensitive data and especially

passwords should be encrypted in order to protect it from unintended

disclosure or modification. Encryption is a procedure that involves a

mathematical transformation of information into scrambled

gobbledygook, called “cipher text”. The computational process (an

algorithm) uses a key, actually just a big number associated with a

password or pass phrase to compute or convert plain text into cipher

text with numbers or strings of characters. The resulting encrypted

text is decipherable only by the holder of the corresponding key. This

deciphering process is also called decryption. There are many

different and incompatible encryption techniques available, and not

all the software we need to use implements a common approach.

One very important feature of a good encryption scheme is the ability

to specify a key or password of some kind, and have the encryption

method alter itself such that each key or password produces a

different encrypted output, which requires a unique ‘key’ or

‘password’ to decrypt.

This can either be a symmetrical key (both encrypt and decrypt use

the same key) or Asymmetrical (encryption and decryption key are

different). The encryption key, the public key, is significantly different

from the decryption key, the private key such that attempting to

derive the private key from the public key involves many hours of

computing time making it impractical at best.

Decryption of data is also the other module which is implemented at

the receiver. When the encrypted data or a file is reached at the

receiver then that data has to be decrypted so that the information

can be viewed by the client/user.

SCOPE:

With the rapid development of multimedia data management

technologies over the internet there is need to concern about the

network, security and privacy of information. In multimedia

document, dissimation and sharing of data is becoming a common

practice for internet based application and enterprises.

As the networking forms are the open source for all the users, so

security of forms is a critical issue. At the present situations we are

using cryptography technique for providing security. Cryptography

constitutes of encryption and decryption processes.

PROJECT OVERVIEW:

CRYPTOGRAPHY:

Cryptography is the science of writing in secret code and is

an ancient art; the first documented use of cryptography in writing

dates back to circa 1900 B.C cryptography came soon after the

widespread development of computer communications. In data and

telecommunications, cryptography is necessary when communicating

over any untrusted medium, which includes just about any network,

particularly the Internet.

Within the context of any application-to-application communication,

there are some specific security requirements, including:

Authentication: The process of proving one's identity. (The

primary forms of host-to-host authentication on the Internet

today are name-based or address-based, both of which are

notoriously weak.)

Privacy/confidentiality: Ensuring that no one can read the

message except the intended receiver.

Integrity: Assuring the receiver that the received message has

not been altered in any way from the original.

Non-repudiation: A mechanism to prove that the sender

really sent this message.

Cryptography, then, not only protects data from theft or alteration,

but can also be used for user authentication. There are, in general,

three types of cryptographic schemes typically used to accomplish

these goals: secret key (or symmetric) cryptography, public-key (or

asymmetric) cryptography, and hash functions. In all cases, the initial

unencrypted data is referred to as plaintext. It is encrypted into

cipher text, which will in turn (usually) be decrypted into usable

plaintext.

TYPES OF CRYPTOGRAPHIC ALGORITHMS:

There are several ways of classifying cryptographic algorithms. They

will be categorized based on the number of keys that are employed

for encryption and decryption, and further defined by their

application and use. The three types of algorithms are:

Secret Key Cryptography (SKC): Uses a single key for both

encryption and decryption.

Public Key Cryptography (PKC): Uses one key for encryption

and another for decryption.

Hash Functions: Uses a mathematical transformation to

irreversibly “encryption”.

Secret Key Cryptography:

With secret key cryptography, a single key is used for both

encryption and decryption. The sender uses the key to encrypt the

plaintext and sends the cipher text to the receiver. The receiver

applies the same key to decrypt the message and recover the

plaintext. Because a single key is used for both functions, secret key

cryptography is also called symmetric encryption.

With this form of cryptography, it is obvious that the key must be

known to both the sender and the receiver; that, in fact, is the secret.

The biggest difficulty with this approach is the distribution of the key.

Secret key cryptography schemes are generally categorized as being

either stream ciphers or block ciphers.

Stream ciphers operate on a single bit at a time and implement some

form of feedback mechanism so that the key is constantly changing.

A block cipher is so-called because the scheme encrypts one block of

data at a time using the same key on each block. In general, the

same plaintext block will always encrypt to the same cipher text

when using the same key in a block cipher whereas the same

plaintext will encrypt to different cipher text in a stream cipher.

Stream ciphers come in several flavors but two are worth mentioning

here. Self-synchronizing stream ciphers calculate each bit in the key

stream as a function of the previous n bits in the key stream. It is

termed "self synchronizing" because the decryption process can stay

synchronized with the encryption process merely by knowing how far

into the n-bit key stream it is. One problem is error propagation; a

garbled bit in transmission will result in n garbled bits at the receiving

side. Synchronous stream ciphers generate the key stream is

independent of the message stream but by using the same key

stream generation function at sender and receiver. While stream

ciphers do not propagate transmission errors, they are, by their

nature, periodic so that the key stream will eventually repeat.

ENCRYPTION:

Encryption refers to algorithmic schemes that encode plain text

into non-readable form or cipher text, providing privacy. The

receiver of the encrypted text uses a “key” to decrypt the

message, returning it to its original plain text form. The key is the

trigger mechanism to the algorithm.

Until the advent of the Internet, encryption was rarely used by the

public, but was largely a military tool. Today, with online marketing,

banking, healthcare and other services, even the average

householder is aware of encryption.

Web browsers will encrypt text automatically when connected to a

secure server, evidenced by an address beginning with https. The

server decrypts the text upon its arrival, but as the information

travels between computers, interception of the transmission will

not be fruitful to anyone “listening in.” They would only see

unreadable data. There are many types of encryption and not all of

it is reliable. The same computer power that yields strong

encryption can be used to break weak encryption schemes.

Though browsers automatically encrypt information when

connected to a secure website, many people choose to use

encryption in their email correspondence as well. This can and

decrypts text. In asymmetric encryption schemes, such as RSA and

Diffie-Hellman, the scheme creates a “key pair” for the user: a

public key and a private key. The public key can be published

online for senders to use to encrypt text that will be sent to the

owner of the public key. Once encrypted, the cipher text cannot be

decrypted except by the one who holds the private key of that key

pair. This algorithm is based around the two keys working in

conjunction with each other. Asymmetric encryption is considered

one step more secure than symmetric encryption, because the

decryption key can be kept private.

Strong encryption makes data private, but not necessarily secure.

To be secure, the recipient of the data -- often a server -- must be

positively identified as being the approved party. This is usually

accomplished online using digital signatures or certificates.

As more people realize the open nature of the Internet, email and

instant messaging, encryption will undoubtedly become more

popular. Without encryption, information passed on the Internet is

not only available for virtually anyone to snag and read, but is often

stored for years on servers that can change hands or become

compromised in any number of ways. For all of these reasons

encryption is a goal worth pursuing.

Encryption and Decryption

ENCRYPTION:

Encryption is used in the creation of certificates and digital

signatures, in secure storage of secrets in the keychain, and in secure

transport of information. For the purposes of this book, encryption is

defined as the transformation of data into a form in which it cannot

be made sense of without the use of some key. Such transformed

data is referred to as cipher text. Use of a key to reverse this

process and return the data to its original (or plaintext) form is

called decryption.

Encryption can be anything from a simple process of substituting one

character for another—in which case the key is the substitution rule—

to a complex mathematical algorithm. For purposes of security, the

more difficult it is to decrypt the cipher text, the better. On the other

hand, if the algorithm is too complex, takes too long to do, or

requires keys that are too large to store easily, it becomes

impractical for use in a personal computer. Therefore, some balance

must be reached between strength of the encryption (that is, how

difficult it is for someone to discover the algorithm and the key) and

ease of use.

For practical purposes, the encryption need only be strong enough to

protect the data for the amount of time the data might be useful to a

person with malicious intent. For example, if you need to keep your

bid on a contract secret only until after the contract has been

awarded, an encryption method that can be broken in a few weeks

will suffice. If you are protecting your credit card number, you

probably want an encryption method that cannot be broken for many

years.

There are two main types of encryption in use in computer security,

referred to as symmetric key encryption and asymmetric key

encryption. A closely related process to encryption, in which the data

is transformed using a key and a mathematical algorithm that cannot

be reversed, is called cryptographic hashing.

The remainder of this section discusses encryption keys, key

exchange mechanisms and cryptographic hash functions.

Symmetric Keys:

Symmetric key cryptography is the classic use of keys that are

familiar with: the same key is used to encrypt and decrypt the data.

The classic, and most easily breakable, version of this is the Caesar

cipher, in which each letter in a message is replaced by a letter that

is a fixed number of positions away in the alphabet. In this case, the

key used to encrypt and decrypt the message is simply the number

of positions in the alphabet to shift the letters. Modern symmetric key

algorithms are much more sophisticated and much harder to break.

However, they share the property of using the same key for

encryption and decryption.

There are many different algorithms used for symmetric key

cryptography, offering anything from minimal to nearly unbreakable

security. Some of these algorithms offer strong security, easy

implementation in code, and rapid encryption and decryption. Such

algorithms are very useful for such purposes as encrypting files

stored on a computer to protect them in case an unauthorized

individual uses the computer. They are somewhat less useful for

sending messages from one computer to another, because both ends

of the communication channel must possess the key and must keep it

secure. Distribution and secure storage of such keys can be difficult

and can open security vulnerabilities.

Although secure techniques for exchanging or creating symmetric

keys can overcome this problem to some extent practical solution for

use in computer communications came about with the invention of

practical algorithms for asymmetric key cryptography.

Symmetric-key cryptography:

In symmetric-key cryptography, we encode our plain text by

mangling it with a secret key. Decryption requires knowledge of the

same key, and reverses the mangling.

Cipher text = encrypt (plaintext, key)

Plaintext = decrypt (cipher text, key)

Symmetric key cryptography is useful if you want to encrypt files on

your computer, and you intend to decrypt them yourself. In security,

we assume the encryption algorithms that we have chosen to use are

publicly known; only the key is secret to the participants.

Slogan: "obscurity is no security".

Introduction to Encryption:

Make any enquiry about computer security, and you will almost

immediately fall over the terms cryptography and encryption also

decryption, but what exactly is meant by this? The dictionary defines

cryptography as hidden writing.  

But what is it used for?

Cryptography is used whenever someone wants to send a secret

message to someone else, in a situation where anyone might be able

to get hold of the message and read it.  It was often used by generals

to send orders to their armies.  

How does it work?

One of the best examples of early cryptography is the Caesar cipher.

It works like this. We should then have two lines of letters

ABCDEFGHIJKLMNOPQRSTUVWXYZ

ABCDEFGHIJKLMNOPQRSTUVWXYZ

Now write the message.  SEND MONEY TONIGHT

That should look like this:

ABCDEFGHIJKLMNOPQRSTUVWXYZ

YZABCDEFGHIJKLMNOPQRSTUVWX

now every time you see a letter of your message in the top line, write

down instead the letter on the bottom line.

SEND MONEY TONIGHT becomes

QCLB KMLCW RMLGEFR

what you have done is performed a cryptographic transformation

your message.

To do it you have used an algorithm and a key, in this case the value

2 because we moved A two places forwards on the bottom line.

All we have to do now is make sure that the person receiving our

message knows the key and the algorithm.  As long as they know it’s

the Caesar cipher and the key is 2 they can put their lower line two

places to the right, and by taking each letter of the message and

writing down the letter immediately above it, they can re-create the

original message.

The symmetric cipher:

Until we started using computers, these ciphers, with very much

better algorithms and much more complex keys were the order of the

day. However, the basic approach to this way of creating secret

messages has not really changed.  

Taking the example above, the operation is as follows:

- take your message (plaintext)

- take an algorithm (Caesar)

- take a key (a number between 1 and 25)

- transform the message according to the algorithm using the key

Now you have an encrypted message (cipher text). The recipient

then:

- takes the encrypted message (cipher text)

- takes the algorithm (Caesar)

- takes the same key (the same number as chosen above)

- transforms the encrypted message according to the algorithm

using the key.

Now they have the original message back (plaintext).  This is called a

symmetric cipher because you use the same algorithm and the same

key to carry out both encryption and decryption.  

Strength of encryption:

The quality of the algorithm and key combination were the factors

that made the strength of the system.  However, until there was

some automation you could not use really complex methods because

it simply took too long to encrypt and decrypt messages.

The encryption and decryption technique can be used to store

sensitive data in the databases. For example if user passwords are

encrypted and stored in the databases, then it’s highly secured

against unauthorized intrusions. Even though if the system is

compromised, the intruder has to know the original algorithm and the

key to retrieve the data.

NETWORK SECURITY:

Security means to protect the sensitive information while it is in

transaction in the network. If there is no security, then there are

many chances that an unauthorized person can have access over the

network in some way and can access this sensitive information. For

example:

Sys1 Sys2

Third

person

In the above diagram shows that sys1 and sys2 are transmit the data

simultaneously. Here third person will comes into the picture, sys1

transmit the data to the third person correctly and third person will

transmit the data to the sys2 is wrong. So in this sys2 will send the

data to the sys1 is wrong information. In the above diagram there is

no security. In this case we protect the security the data will send to

the systems in correct manner.

Network security is a complicated subject, historically only tackled by

well-trained and experienced experts. However as more and more

people need to understand the basics of security in a networked

world. This document was written with the basic computer user and

information systems manager in mind, explaining the concepts

needed to read through the hype in the marketplace and understand

risks and how to deal with them.

Risk Management: The game of security

It’s very important to understand that in security, one simply cannot

say, “What’s the best firewall?” There are two extremes: absolute

security and absolute access. The closest we can get to an absolutely

secure machine is one unplugged from the network, power supply,

locked in a sage, and thrown at the bottom of the ocean.

Unfortunately, it isn’t terribly useful in this state.

Types and Sources of Network Threats

Background information of networking that we can actually get into

the security aspects of all of this. First of all, we’ll get into the types

of threats there are against networked computers, and then some

things that can be done to protect you against various threats.

Denial-of-Service:

These attacks are probably the nastiest, and most difficult to address.

These are the nastiest, because they’re very easy to launch, difficult

to track, and it isn’t easy to refuse the requests of the attacker,

without also refusing legitimate requests for service.

Unauthorized Access:

It is a very high-level term that can refer to a number of different

sorts of attacks. The goal of these attacks is to access some resource

that your machine should not provide the attacker.

Executing Commands Illicitly:

It’s obviously undesirable for an unknown and untrusted person to be

able to execute commands on your server machines. There are two

main classifications of the security of this problem: normal user

access, and administrator access. A normal user can do a number of

things on a system that an attacker should not be able to do.

Confidentiality Breaches:

In the network threats there are must be know the “confidentiality”

and “authentication”. Confidentiality means sender and intended

receiver should only know the data. This means that the sender and

receiver know what the actual data is, third person will not know

theParticular data. That data will be in secured.

Authentication means that providing a way to authenticate yourself

to a computer system without sending your password “in the clear” is

an important security goal. Passwords send without encryption may

be discoverable by others if sent through or to insecure network

segments or systems.

Encrypt by using receiving public key, sender private key, and

decrypt by using receiving private key, sender public key. Here

encrypt means “confidentiality + authentication” decrypt means

“authentication + confidentiality”.

Before starting every project it’s planning is done. Planning a project

is a very important task and should be taken up with great care as

the efficiency of whole project largely depends upon its planning.

S_DES (Simplified Data Encryption standard):

The S-DES encryption algorithm takes an 8-bit block of plaintext and

a 10-bit key as input and produces an 8-bit block of cipher text as

output. The S-DES decryption algorithm takes an 8-bit block of cipher

text and the same 10-bit key used to produce that cipher text as

input and produces the original 8-bit block of plaintext.

The encryption algorithm involves five functions: an initial

permutation (IP); a complex function labeled fk, which involves both

permutation and substitution operations and depends on a key input;

a simple permutation function that switches (SW) the two halves of

the data; the function fk again; and finally a permutation function

that is the inverse of the initial permutation.

The function fk takes as input not only the data passing through the

encryption algorithm, but also an 8-bit key. The algorithm could have

been designed to work with a 16-bit key, consisting of two 8-bit sub

keys, one used for each occurrence of fk. Alternatively, a single 8-bit

key could have been used, with the same key used twice in the

algorithm. A compromise is to use a 10-bit key from which two 8-bit

sub keys are generated, as depicted in the figure. In this case, the

key is first subjected to a permutation (P10). Then a shift operation is

performed. The output of the shift operation then passes through a

permutation function that produces an 8-bit output (P8) for the first

sub keys (K1). The output of the shift operation also feeds into

another shift and another instance of P8 to produce the second sub

key (K2).

We can concisely express the encryption algorithm as a composition

of functions:

(IP)-1 * fk2 * SW * fk1 * IP

which can also be written as

Cipher text= (IP)-1(fk2 (SW (fk1 (IP (plain text)))))

Where K1=P8 (shift (P10 (key)))

K2 =P8 (shift (shift (P10 (key))))

Decryption is also shown in the figure and is essentially the reverse of

encryption:

Plain text= (IP)-1(fk1 (SW (fk2 (IP (cipher text)))))

S-DES Key Generation:

S-DES depends on the use of a 10-bit key shared between sender and

receiver. From this key, two 8-bit sub keys are produced for use in

particular stages of the encryption and decryption algorithm.

First, permute the key in the following fashion. Let the 10-key be

designated as (k1,k2,k3,k4,k5,k6,k7,k8,k9,k10). Then the

permutation P10is defined as

P10(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)=(k3,k5,k2,k7,k4,k10,k1,k9,k8,k6

)

P10 can be concisely defined by the following display:

This table is read from left to right; each position in the table gives

the identity of the input bit that produces the produces the output bit

in that position. So the first output bit is bit 3 of the input; the second

output bit is bit 5 of the input, and so on.

Next we apply P8, which picks out and permutes 8 of the 10 bits

according to the following rule:

The result is sub key 1 (K1). We then go back to the pair of 5-bit

strings produced by the two LS-1 function perform a circular left shift

of 2 bit positions on each string.

S-DES Encryption:

Encryption involves the sequential applications of five

functions. We examine each of these.

Initial and Final Permutations:

The input to the algorithm is an 8-bit block of plain text, which we

first permute using the IP function:

IP

2 6 3 1 4 8 5 7

This retains all 8 bits of the plaintext but mixes them up. At the end

of the algorithm, the inverse permutation is used:

It is easy to show by example that

the second permutation is indeed

the reverse of the first; that is,

(IP)-1(IP(X)) =X.

The Function fk:

The most complex company of S-DES is the function fk, which

consists of a combination of permutation and substitution functions.

The functions can be expressed as follows. Let L and R be the

leftmost 4 bits and rightmost 4 bits of the 8-bit input to fk, and let F

be a mapping from 4-bit string to 4-bit string. Then we let

fk (L, R) = (L XOR F(R, SK), R)

where SK is a sub key and XOR is the bit-by-bit exclusive-OR

function.

IP-1

4 1 3 5 7 2 8 6

Expansion/Permutation:

And it uses two so-called s-boxes, S0 and S1. Here is S0

And here is S0:

And here is S1:

The first 4 bits are fed into the S-box S0 to produce a 2-bit output,

and the remaining 4 bits are fed into S1 to produce another 2-bit

output.

E/P

4 1 2 3 2 3 4 1

The S-boxes operates as follows. The first and fourth input bits are

treated as a two bit number that specify a row of the S-box, and the

second and third input bits specify a column of the S-box. The entry

in that row and column, in base 2, is the 2-bit output.

Next, the 4 bits produced by S0 and S1 undergo a further

permutation as Follows:

The output of the P4 is the output of the function F.

The Switch Function:

The function fk only alters the leftmost 4 bits of the input. The switch

function (SW) interchanges the left and right 4 bits so that the second

instance of fk operates on a different 4 bits. In this second instance,

the E/P, S0, S1, and P4 functions are the same. The key input is K2.

S-DES Decryption:

As with any, decryption uses the same algorithm as encryption,

except that the application of the sub keys is reserved.

DATA ENCRYPTION STANDARD

The most widely used encryption scheme is based on Data Encryption

Standard (DES) adapted in 1977 by the National Bureau of Standards,

now National Institute of Standards and Technology (NIST), as Federal

P4

2 4 3 1

Information processing standard 46 (FIPS PUB 46). The algorithm

itself is referred to as the Data Encryption Algorithm (DEA). For DES,

data are encrypted in 64-bit blocks using a 56-bit key. The algorithm

transforms 64-bit input in a series of steps into a 64-bit output. The

same steps, with the same key, are used to reverse the encryption.

The DES enjoys widespread use. It has also been the subject of much

controversy concerning how secure the DES is.

In the late 1960’s, IBM setup a research project in computer

cryptography led by Horst Feistel. The project concluded in 1971 with

the development of algorithm with the designation LUCIFER, which

was sold to Lloyd’s of London for use in a cash-dispensing system,

also developed by IBM. LUCIFER is a Feistel block cipher that operates

on blocks of 64 bits, using a key size of 128 bits.

In 1973, the National Bureau of Standards (NBS) issued a request for

proposals for a national cipher standard. IBM submitted the results of

its Tuchman-Meyer project. This was by far the best algorithm

proposed and was adopted in 1977 as the Data Encryption Standard.

Before its adoption as a standard, the proposed DES was subjected to

intense criticism, which has not subsided to this day. Two areas drew

the critics’ fire. First, the key length in IBM’s original LUCIFER

algorithm was 128 bits, but that of the proposed system was only 56

bits, an enormous reduction in key size of 72 bits. Critics feared that

this key length was too short to withstand Brute Force attacks. The

second area of concern was that the design criteria for the internal

structure of DES, the S-boxes, were classified. Thus users could not

be sure that the internal structure of DES was free of any hidden

weak points that would enable NSA decipher messages without

benefit of the key. Subsequent events, particularly the recent work

on differential cryptanalysis, seem to indicate that DES has a very

strong internal structure. Furthermore, according to IBM participants,

the only changes that were made to the proposal were changes to

the S-boxes, suggested by NSA that removed vulnerabilities identified

the course of the evaluation process.

DES ENCRYPTION

The overall scheme for DES encryption is illustrated in Figure below.

As with any encryption scheme, there are two inputs to the

encryption function: the plain text to be encrypted and the key. In

this case, the plain text must be 64 bits in length and the key is 56

bits in length.

Looking at the left hand side of the figure, we can see the processing

of the plain text proceeds in three phases. First, the 64-bit plain text

passes through an initial permutation (IP) that rearranges the bits to

produce the permuted input. This is followed by a phase consisting of

16 rounds of the same function, which involves both permutation and

substitution functions. The output of the last (sixteen) round consists

of 64 bits that are a function of the input plain text and the key. The

left and right halves of the output are swapped to produce the pre-

output. Finally, the pre-output is passed through a permutation (IP-1)

that is the inverse of the initial permutation function, to produce the

64-bit cipher text. With the exception of the initial and final

permutations, DES has the exact structure of Feistel cipher, as shown

in the figure.

The right-hand portion of fig above shows the way in which the 56-bit

key is used. Initially, the key is passed through a permutation

function. Then, for each of the 16 rounds, a sub key (K i) is produced

by the combination of a left circular shift and a permutation. The

permutation function is the same for each round, but a different sub

key is produced because of the repeated iteration of the key bit.

Initial Permutation:

Tables as shown in tables below define the initial permutation and its

inverse. The tables are to be interpreted as follows. The input to a

table consists of 64 bits numbered from 1 to 64. The 64 entries in the

permutation table contain a permutation of the numbers from 1 to

64. Each entry in the permutation table indicates the position of a

numbered input bit in the output, which also consists of 64 bits.

To see that these two permutation functions are needed in the

inverse of each other, consider the following 64-bit input M:

M1 M2 M3 M4 M5 M6 M7 M8

M9 M10 M11 M12 M13 M14 M15 M16

M17 M18 M19 M20 M21 M22 M23 M24

M25 M26 M27 M28 M29 M30 M31 M32

M33 M34 M35 M36 M37 M38 M39 M40

M41 M42 M43 M44 M45 M46 M47 M48

M49 M50 M51 M52 M53 M54 M55 M56

M57 M58 M59 M60 M61 M62 M63 M64

Where Mi is a binary digit. Then the permutation X = IP (M) is as

follows:

M58 M50 M42 M34 M26 M18 M10 M2

M60 M52 M44 M36 M28 M20 M12 M4

M62 M54 M46 M38 M30 M22 M14 M6

M64 M56 M48 M40 M32 M24 M16 M8

M57 M49 M41 M33 M25 M17 M9 M1

M59 M51 M43 M35 M27 M19 M11 M3

M61 M53 M45 M37 M29 M21 M13 M5

M63 M55 M47 M39 M31 M23 M15 M7

If we then take the inverse permutation Y= IP-1 (IP (M)), it can be seen

that the original ordering of the bits is restored.

Details of Single Round:

Figure: show the internal structure of a single round. Again, begin by

focusing on the left hand side of the diagram. A left and right half of

each 64-bit intermediate value is treated as separate 32-bit

quantities, labeled L (left) and R (right). The overall processing at

each round can be summarized in the following formulas:

Li = Ri-1

Ri = Li-1 XOR F (Ri-1, Ki)

The round key Ki is 48 bits. The R input is 32 bits. This R input is first

expanded to 48 bits by using a table that defines a permutation plus

an expansion that involves duplication of 16 of the R bits. Resulting

48 bits are XOR ed with Ki. This 48-bit result passes through a

substitution function that produces a 32-bit output, which is

permuted as defined by table.

Table: Permutation Table for DES

(a)Initial Permutation (IP)

58 50 42 34 26 18 10 2

60 52 44 36 28 20 12 4

62 54 46 38 30 22 14 6

64 56 48 40 32 24 16 8

57 49 41 33 25 17 9 1

59 51 43 35 27 19 11 3

61 53 45 37 29 21 13 5

63 55 47 39 31 23 15 7

(b) Inverse Initial Permutation (IP-1)

40 8 48 16 56 24 64 32

39 7 47 15 55 23 63 31

38 6 46 14 54 22 62 30

37 5 45 13 53 21 61 29

36 4 44 12 52 20 60 28

35 3 43 11 51 19 59 27

34 2 42 10 50 18 58 26

33 1 41 9 49 17 57 25

(c) Expansion Permutation (E)

32 1 2 3 4 5

4 5 6 7 8 9

8 9 10 11 12 13

12 13 14 15 16 17

16 17 18 19 20 21

20 21 22 23 24 25

24 25 26 27 28 29

28 29 30 31 32 1

(d) Permutation function (P)

16 7 20 21 29 12 28 17

1 15 23 26 5 18 31 10

2 8 24 14 32 27 3 9

19 13 30 6 22 11 4 25

The role of the S-boxes in the function F is illustrated in Figure. The

substitution consists of a set of eight S-boxes each of which accepts 6

bits as input and produces 4 bits as output. The first and last bits of

the input to box Si form a 2-bit binary number to select one of four

substitutions defined by the four rows in the table for S i. The middle

four bits select one of the sixteen columns. The decimal value in the

cell selected by the row and column is then converted to its 4-bit

representation to produce the output.

Each row of an S-box defines a general reversible substitution. Figure

may be useful in understanding the mapping. The figure shows the

substitution for row 0 of box S1.

The operation of the S-boxes is worth further comment. Ignore for the

moment the contribution of the key (Ki). If you examine the

expansion table, you see that the 32 bits of input are split into groups

of 4 bits, and then become groups of 6 bits by taking the outer bits

R (32) )bit

s)

E

48 Bits

+

K (48) )b

its)

S1

S8

S2

SS4

S5

S6

S7

P

32 Bits

Calculation of F(R, K)

from the two adjacent groups. For example, if part of the input word

is

….efgh ijkl mnop…

this becomes

…defrghi hijklm imnopq…

The outer two bits of each group select one of four possible

substitutions. Then a 4-bit output value is substituted for the

particular 4-bit input. The 32-bit output from the eight S-boxes is then

permuted, so that on the next round the output from each B-box

immediately affects as many others as possible.

KEY GENERATION:

Returning to fig, we see that a 64-bit key used as input to the

algorithm. The bits of the key are numbered from 1 through 64; every

eight bit is ignored, as indicated by the lack of shading in table. This

is first subjected to a permutation governed by table labeled

Permuted Choice One. The resulting 56-bit key is then treated as two

28-bit quantities, labeled C0 and D0. At each round, Ci-1 and Di-1 are

separately separated to a circular shift, or rotation of 1 or 2 bits, as

governed by Table. These shifted values serve as input to the next

round. They also serve as input to Permuted Choice Two, which

produces a 48-bit output that serves as input to the function F (R i-1,

Ki).

DES DECRYPTION

As with any decryption uses the same algorithm as encryption,

except that the application of the sub keys is reserved.

Table Definition of DES S-Boxes

1

4

4 1

3

1 2 1

5

1

1

8 3 1

0

6 1

2

5 9 0 7

0 1

5

7 4 1

4

2 1

3

1 1

0

6 1

2

1

1

9 5 3 8

4 1 1

4

8 1

3

6 2 1

1

1

5

1

2

9 7 3 1

0

5 0

1

5

1

2

8 2 4 9 1 7 5 1

1

3 1

4

1

0

0 6 1

3

1

5

8 1 1

4

6 1

1

3 4 9 7 2 1

3

1

2

0 5 1

0

3 1

3

4 7 1

5

2 8 1

4

1

2

0 1 1

0

6 9 1

1

5

0 1

4

7 1

1

1

0

4 1

3

1 5 8 1

2

6 9 3 2 1

5

1

3

8 1

0

1 3 1

5

4 2 1

1

6 7 1

2

0 5 1

4

9

1

0

0 9 1

4

6 3 1

5

5 1 1

3

1

2

7 1

1

4 2 8

1

3

7 0 9 3 4 6 1

0

2 8 5 1

4

1

2

1

1

1

5

1

1

3

6 4 9 8 1

5

3 0 1

1

1 2 1

2

5 1

0

1

4

7

1 1

0

1

3

0 6 9 8 7 4 1

5

1

4

3 1

1

5 2 1

2

7 13 14 3 0 6 9 10 1 2 8 5 11 12 4 15

S2

S3

S1

13 8 11 5 6 15 0 3 4 7 2 12 1 10 14 9

10 6 9 0 12 11 7 13 15 1 3 14 5 2 8 4

3 15 0 6 10 1 13 8 9 4 5 11 12 7 2 14

21

2

4 1 7 1

0

1

1

6 8 5 3 1

5

1

3

0 1

4

9

1

4

1

1

2 1

2

4 7 1

3

1 5 0 1

5

1

0

3 9 8 6

4 2 1 1

1

1

0

1

3

7 8 1

5

9 1

2

5 6 3 0 1

4

1

1

8 1

2

7 1 1

4

2 1

3

6 1

5

0 9 1

0

4 5 3

1

2

1 1

0

1

5

9 2 6 8 0 1

3

3 4 1

4

7 5 1

1

1

0

1

5

4 2 7 1

2

9 5 6 1 1

3

1

4

0 1

1

3 8

9 1

4

1

5

5 2 8 1

2

3 7 0 4 1

0

1 1

3

1

1

6

4 3 2 1

2

9 5 1

5

1

0

1

1

1

4

1 7 6 0 8 1

3

4 11 2 14 15 0 8 13 3 12 9 7 5 10 6 1

13 0 11 7 4 9 1 10 14 3 5 12 2 15 8 6

1 4 11 13 12 3 7 14 10 15 6 8 0 5 9 2

6 11 13 8 1 4 10 7 9 5 0 15 14 2 3 12

1

3

2 8 4 6 1

5

1

1

1 1

0

9 3 1

4

5 0 1

2

7

S4

S5

S6

S7

1 1

5

1

3

8 1

0

3 7 4 1

2

5 6 1

1

0 1

4

9 2

7 1

1

4 1 9 1

2

1

4

2 0 6 1

0

1

3

1

5

3 5 8

2 1 1

4

7 4 1

0

8 1

3

1

5

1

2

9 0 3 5 6 1

1

(a) Input Key

(b) Permuted Choice One (PC-1)

57 49 41 33 25 17 9

1 58 50 42 34 26 18

10 2 59 51 43 35 27

19 11 3 16 52 44 36

63 55 47 39 31 23 15

7 62 54 46 38 30 22

14 6 61 53 45 37 29

21 13 5 28 20 12 4

(c) Permuted Choice Two (PC-2)

S8

14 7 11 24 1 5 3 28

15 6 21 10 23 19 12 4

26 8 16 7 27 20 13 2

41 52 31 37 47 55 30 40

51 45 33 48 44 49 39 56

34 53 46 42 50 36 29 32

(d) Schedule of Left Shifts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1 1 2 2 2 2 2 2 1 2 2 2 2 2 2 1

INTRODUCTION ABOUT THE PROJECT

The project “DATA ENCRYPTION AND DECRYPTION” is totally

enhanced with the features that enable us to feel the real-time

environment. As the today’s world is mostly employing the latest

networking techniques instead of using stand-alone PC’s. As every

product possessing advantages might also have some disadvantages.

The advantages with the networking are that a company can share

files or data without need to use some external devices to carry the

data. Similarly, a company can share the single costly printer. Likely,

the disadvantages are also numerous. Somebody writes a program

and can make the costly printer to misprint the data. Similarly, some

unauthorized user may get access over the network and may perform

any illegal functions like deleting some of the sensitive information

like employee salary details, while they are in transaction. Our project

has some of the features described as follows:

Firstly, the project makes use of the secured networking concepts

that will make the sensitive information to be encrypted (converted)

in such a manner that will not be understood by the unauthorized

user who gains access over this information. To read the information

one must decrypt the encrypted information in a pre-specified

manner. Only sender and receiver both can have the systematic way

of access to the information.

Secondly, many of the today’s software are being pirated from the

original one. This must be prevented which is also the one of the

main intention of the project. Otherwise some other might pirate the

important software developed by you. A unique identification number

namely the “MAC Address” is used to protect the software from

piracy.

SECURITY:

“Security” is the term that comes into picture when some important

or sensitive information must be protected from an unauthorized

access. Today, the maximum of the world’s population is using

computers to access their required information in some form of the

networked systems. Some are accessing through the world’s famous

Internet and some through the different networks like LAN, WAN etc.

At the same time, there are some unauthorized persons, whom we

call “hackers”, who will just make some miscellaneous things in the

information. Neither the sender nor the receiver is aware of the

hacker and both thinks that the flow is going in the normal way

without any disturbance. Hence there must be some way to protect

the data from them and even if he hacks the information, he should

not be able to understand what’s the actual information in the file,

which is the main intention of the project.

The requirements of “information security” within an organization

have undergone two major changes in the last several decades.

Before the widespread use of data processing equipment, the

security of information felt to be valuable to an organization lock for

storing sensitive documents. An example of the latter is personnel

screening procedures used during the hiring process.

The first and foremost, security for this sensitive information

especially the case for a shared system, such as time-sharing system,

is even more accurate for systems that can be accessed over a public

telephone network, data network, or the Internet. To protect data and

to thwart hackers is known as “computer security”.

Secondly, the change that affected security is the introduction of

distributed systems and the use of networks and communication

facilities for carrying data between terminal user and computer and

between computer and computer. “Network security” measures

are needed to protect data during their transmission.

Before we proceed, there are some considerations how Information

can be threatened to access from an unauthorized person, what we

call as “Security Threats”. Some of them are shown as under:

Information Source

Information Destination

(a) Normal flow

(b) Interruption

(c) Interception

(d) Modification

The figure (a) shown is the normal flow of the information describing

how the actual data is sent from sender to receiver. The following

respective figures are described as below:

Interruption: This is the type of security threat in which the

sender thinks that he has successfully sent his file to the

receiver. The receiver is unaware of the information and he

might think that the sender has not yet sent the file.

Interception: In this, an unauthorized party gains access to

an asset. This is an attack on confidentiality. The unauthorized

party could be a person, a program, or a computer. Examples

include wiretapping to capture data in a network and the illicit

copying of files or programs.

Modification: In this, an unauthorized party not only gains

access to but tampers with an asset. This is an attack on

integrity. Examples include changing values in a data file,

altering a program so that it performs differently, and

modifying the content of messages being transmitted in a

network.

(e) Fabrication

Fabrication: An unauthorized party inserts counterfeit objects

into the system. This is an attack on authenticity. Examples

include the insertion of spurious messages in a network or the

addition of records to a file.

The assets mentioned above may be one of the following:

Hardware

Software

Data and

Communication lines and Networks

Note: - Our project is limited to the assets - Software and Data. We

are not at all concerned with Hardware and Communication lines and

Networks.

A MODEL FOR NETWORK SECURITY

A model for much of what we will be discussing is captured, in very

general terms, in figure. A message is to be transferred from one

party to another across some sort of Internet. The two parties, who

are the principals in this transaction, must cooperate for the

exchange to take place. A logical information channel is established

by defining a route through the Internet from source to destination

and by the cooperative use of communication protocols by the two

principals.

Security aspects come into play when it is necessary or desirable to

protect the information transmission from an opponent who may

present a threat to confidentiality, authenticity, and so on. All the

techniques for providing security have two components:

A security-related transformation on the information to be sent.

Examples include the encryption of the message, which

scrambles the message so that it is unreadable by the

opponent, and the addition of a code based on the contents of

the message, which can be used to verify the identity of the

sender.

Some secret information shared by the two principals and, it is

hoped, unknown to the opponent. An example is an encryption

key used in conjunction with the transformation to scramble the

message before transmission and unscramble it on reception.

A trusted third party may be needed to achieve secure transmission

and is responsible for distributing the secret information to the two

principals while keeping it from any opponent. Or a third party may

be needed to arbitrate disputes between the two principals

concerning the authenticity of a message transmission.

This general model shows that there are four basics tasks in

designing a particular security service:

Design an algorithm for performing the security-related

transformation. The algorithm should be such that an opponent

cannot defeat its purpose.

Generate the secret information to be used with the algorithm

Develop methods for the distribution and sharing of the secret

information.

Specify a protocol to be used by the two principals that makes use of

the security algorithm and the secret information to achieve a

particular security service.

EXISTING SYSTEM:

In the physical system the network helps a particular organization to

share the data by using external devices. The external devices are

used to carry data. The existing system cannot provide security,

which allows an unauthorized user to access the secret files. It also

cannot share a single costly printer. Many interrupts may occur with

in the system.

PRORPOSED SYSTEM:

In this system ‘security’ is the term that comes into picture when

some important or sensitive information must be protected from an

unauthorized access. Hence there must be some way to protect the

data from them and even if he hacks the information, he should not

be able to understand what’s the actual information in the file, which

is the main intension of the project.

3. DESIGN PRINCIPLES & EXPLANATION

3.1. MODULES

The system can be divided into 3 modules:

1. Login

2. Send File

3. View File

3.2. MODULE DESCRIPTIOIN

Login:

In this module the user is requested to enter the user name and

password, if he is a valid user, he enters the home page. The user ID

given is checked with the database table. The user has two options in

the home page to view a file and to send a file to other user.

Send File:

This module details with sending a file by attaching it to a message to

the other user specified. Before attaching a file, the specified file will

be encrypted by using a randomly generated key. We can send

maximum of only 3 files with a message. The major disadvantage of

the module is that it will encrypt only the plain text format files.

View File:

In this module the user is enabled to view the file that has been send

to him by other users. When the user selects a file from all the list of

files, the file is decrypted by using the same key, used while

encrypting. The decrypted file can be saved as an external file into

the secondary storage.

4. PROJECT DICTIONARY

4.1. DATAFLOW DIAGRAMS

A data flow diagram is graphical tool used to describe and analyze

movement of data through a system. These are the central tool and

the basis from which the other components are developed. The

transformation of data from input to output, through processed, may

be described logically and independently of physical components

associated with the system. These are known as the logical data flow

diagrams. The physical data flow diagrams show the actual

implements and movement of data between people, departments

and workstations. A full description of a system actually consists of a

set of data flow diagrams. Using two familiar notations Yourdon,

Gane and Sarson notation develops the data flow diagrams. Each

component in a DFD is labeled with a descriptive name. Process is

further identified with a number that will be used for identification

purpose. The development of DFD’s is done in several levels. Each

process in lower level diagrams can be broken down into a more

detailed DFD in the next level. The lop-level diagram is often called

context diagram. It consists a single process bit, which plays vital role

in studying the current system. The process in the context level

diagram is exploded into other process at the first level DFD.

The idea behind the explosion of a process into more process is that

understanding at one level of detail is exploded into greater detail at

the next level. This is done until further explosion is necessary and

an adequate amount of detail is described for analyst to understand

the process.

Larry Constantine first developed the DFD as a way of expressing

system requirements in a graphical from, this lead to the modular

design

.

A DFD is also known as a “bubble Chart” has the purpose of clarifying

system requirements and identifying major transformations that will

become programs in system design. So it is the starting point of the

design to the lowest level of detail. A DFD consists of a series of

bubbles joined by data flows in the system.

TYPES OF DATA FLOW DIAGRAMS

Current Physical

Current Logical

New Logical

New Physical

CURRENT PHYSICAL:

In Current Physical DFD process label include the name of people or

their positions or the names of computer systems that might provide

some of the overall system-processing label includes an identification

of the technology used to process the data. Similarly data flows and

data stores are often labels with the names of the actual physical

media on which data are stored such as file folders, computer files,

business forms or computer tapes.

CURRENT LOGICAL:

The physical aspects at the system are removed as mush as possible

so that the current system is reduced to its essence to the data and

the processors that transforms them regardless of actual physical

form.

NEW LOGICAL:

This is exactly like a current logical model if the user were completely

happy with he user were completely happy with the functionality of

the current system but had problems with how it was implemented

typically through the new logical model will differ from current logical

model while having additional functions, absolute function removal

and inefficient flows recognized.

NEW PHYSICAL:

The new physical represents only the physical implementation of the

new system.

SAILENT FEATURES OF DFD’s

The DFD shows flow of data, not of control loops and decision

are controlled considerations do not appear on a DFD.

The DFD does not indicate the time factor involved in any

process whether the dataflow take place daily, weekly, monthly

or yearly.

The sequence of events is not brought out on the DFD.

1) Login DFD:

2) View Files DFD:

3) Send File DFD:

4) Decrypt DFD:

5. FORMS & REPORTS

5.1. I/O SAMPLES

6. BIBILIOGRAPHY

1. CRYPTOGRAPHY AND NETWORK SECURITY

- William Stallins

2. SOFTWARE ENGINEERING

- Roger Pressman

3. MICROSOFT VB.NET 2003

- (PRESS)

4. ASP.NET 1.1 PROFESSIONAL

- (WROX PUBLICATIONS)

WEBSITES:

1. www.msdn.microsoft.com

2. www.4guysrolla.com

3. www.asp11.com

4. www.dotnetspider.com