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
pre present
syste stem
the
network
helps lps
a
particu icular
orga organi niza zati tion on to shar share e the the data data by usin using g exte extern rnal al devi device ces. s. The The extern external al device devices s are used to carry carry the data. The existing existing system system cannot provide security, which allows an unauthorized user to access the secret files. It also cannot share a single costly printer. Many inte interr rrup uptts may may occur ccur wit with in the the syst system em.. In this this proj proje ect the 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 numero numerous us disadva disadvanta ntages ges,, somebo somebody dy writes writes the progra program m and can make make the the co cost stly ly prin printe terr to misp mispri rint nt the the data data.. Simi Simila larl rly y so some me unau unauth thor oriz ized ed user user may may get get ac acce cess ss ov over er the the netw networ ork k and and may may perf perfor orm m any any illeg illegal al func functi tion ons s like like dele deleti ting ng so some me of the the se sens nsit itiv ive e informat mation ion
like
employe loyee e
salar lary
details ils
while ile
they
are
in
transactions. Secu Se curi rity ty is the term term that that co come mes s into into the the pict pictur ure e whe when some ome impo import rtan antt
or
sens se nsit itiv ive e
info inforrmati mation on
must must
be
prot protec ectt
from 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 prot protec ectt the the se sens nsit itiv ive e info inform rmat atio ion n whil while e it is in tran transa sact ctio ion n in the 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 algorithmDATA ENCRYPTION STANDARDS that enables and guarantees the security of the information in the network.
2. INTRODUCTION
The project project “Data “Data Encrypt Encryption ion and Decryp Decryptio tion” n” is totally totally enhanc enhanced ed with the features that enable us to feel the real-time environment. Today’s world is mostly employing the latest networking techniques inst instea ead d
of
usin using g
stan standd-al alon one e
PC’s PC’s..
Encr Encryp ypti tion on
or
info inform rmat atio ion n
scrambling, technology is an important security tool. Properly applied it ca can n prov provid ide e a se secur cure e co commu mmuni nicat catio ion n chann channel el even even when when the 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 info inform rmat atio ion. n. In thes these e situ situat atio ions, ns, se sens nsit itive ive data data and and es espe pecia cially lly passwords should be encrypted in order to protect it from unintended disclosure or modification. Encryption is a procedure that involves a math mathe emati matica call
tran transf sfo ormat rmatio ion n
of
info inform rmat atio ion n
int into
scra scramb mble led d
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 deci deciph pher erin ing g proc proces ess s is also also ca call lled ed decr decryp ypti tion on.. Ther There e are are many 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 meth method od alte alterr itse itself lf such such that that ea each ch key key or passw passwor ord d prod produc uces es a diff differ eren entt
encr encryp ypte ted d
‘password’ to decrypt.
outp ou tput ut,,
whic which h
requ requir ires es a
uniq unique ue ‘key ‘key’’
or
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
SEND MONEY TONIGHT
line.
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 Taking
has
the
not
example
-
above,
the
take
your
-
take
a
really
take key
(a
operation
changed. is
message
an
as
(plaintext)
algorithm
number
between
follows:
(Caesar) 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
takes
the
message algorithm
(cipher
text)
(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
Strength
carry
out
both
encryption
of
and
decryption.
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, access, and administrat administrator or access. A normal 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 “authe “authenti nticat cation ion”. ”. Confide Confidenti ntialit ality y means means sender sender and intend intended ed 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 discov discovera erable ble by others others if sent sent throug through h or to insecu insecure re networ network k segments or systems. Encr Encryp yptt by using using rece receivi iving ng publi public c key, key, se send nder er priv privat ate e key, key, and and decr decrypt ypt by using using rece receivi iving ng priva private te key, key, se sende nderr publi public c key. key. Here Here encryp encryptt means means “confi “confiden dentia tialit lity y + authen authentic ticati ation” on” decryp decryptt means 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 outp ou tput ut.. The The S-DES S-DES decr decryp ypti tion on algo algori rith thm m take takes s an 8-bit 8-bit bloc block k 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
encry ncrypt ptio ion n
alg algorit orithm hm
invo nvolve lves
five five
func functi tion ons: s:
an
init initia iall
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. 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 sub keys keys (K1) (K1).. The The ou outp tput ut of the the shift shift oper operat atio ion n also also feed feeds s into into another shift and another instance of P8 to produce the second sub key (K2). We can concisely concisely express the encryption encryption algorithm as a composition 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 desi design gnat ate ed
as
(k1, (k1,k2 k2,k ,k3, 3,k4 k4,k ,k5, 5,k6 k6,k ,k7, 7,k8 k8,k ,k9, 9,k1 k10) 0)..
Then hen
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:
IP-1 4 1 3 5 7 2 8 6
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.
E/P 4 1232 3 4 1 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.
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: P4 2
4
3
1
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 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 preoutput. 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 56bit 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:
M 1
M 2
M 3
M 4
M 5
M 6
M 7
M 8
M 9
M 10
M 11
M 12
M 13
M 14
M 15
M 16
M 17
M 18
M 19
M 20
M 21
M 22
M 23
M 24
M 25
M 26
M 27
M 28
M 29
M 30
M 31
M 32
M 33
M 34
M 35
M 36
M 37
M 38
M 39
M 40
M 41
M 42
M 43
M 44
M 45
M 46
M 47
M 48
M 49
M 50
M 51
M 52
M 53
M 54
M 55
M 56
M 57
M 58
M 59
M 60
M 61
M 62
M 63
M 64
Where M i is a binary digit. Then the permutation X = IP (M ) is as follows:
M 58
M 50
M 42
M 34
M 26
M 18
M 10
M 2
M 60
M 52
M 44
M 36
M 28
M 20
M 12
M 4
M 62
M 54
M 46
M 38
M 30
M 22
M 14
M 6
M 64
M 56
M 48
M 40
M 32
M 24
M 16
M 8
M 57
M 49
M 41
M 33
M 25
M 17
M 9
M 1
M 59
M 51
M 43
M 35
M 27
M 19
M 11
M 3
M 61
M 53
M 45
M 37
M 29
M 21
M 13
M 5
M 63
M 55
M 47
M 39
M 31
M 23
M 15
M 7
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 K i 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
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
is
(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 S i 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.
R (32)
)
bits)
E K
(48) ) bits)
48 Bits
+
S
S
1
2
S
S
S
S
S
S
4
5
6
7
8
P
32 Bits
Calculation of F(R, K)
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 (K i). 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 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 Bbox 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
1
1 2
1
1
4 0
3 7
4 1
5 2
1 1
1 5 1
1
4 8 1
4
6
1
1
4 8
3 2 4
5
2
1
8
5 3
1
0
3 1
1
4 8
3
1 0 1 3 1 3 1
9
7 6 1
3
1
6
1
5
9
0 7
0 6
1
2 1
1
1
9
5
3 8
3 2
1
0 1
1
2 9
1 7
3
1
5 0
1 7
5 5
2 1
1
1
0 0
1
6 1
4
0
7 2
1
1
0 1
3 1 0 6
3
1
1
1
6
1
4 7
1
1 2
4 7
1
5 1
1
1 1
0 3
0
0
8
1
0
4 9
1
4
9
8
1
1
4
1
4 1
2 5
8 1
1
3 4
1
2 6 7
2
5
9
4
3
1
6 3
1
3 4
5 6
1
3
0 0
1
7
1 4
9
8 1
0
5 6 9
8
5
1
3
0 5
1
2 6
9 1
0 5
9
1 3 2
1
5 1
5 9
0
2
1
1
1
2
3 8 1 1
4
7
1
4
2
8
2 5
1
1 1
1
1
1
2
4 1
2 5
1 1
5 1
7
1
2 3
1
0 5
4 2
1
S4
0
3
7
1
1
1
3 8
4 1
6
3 1 0 3
1
5
3 0 5 6
1
1 9
0 1
5 1
0
2 6 1
1 1
5
2 S5
1
1
2 1
4 4
1 2
1
8
1 1
S6
0 4
1
9
1
0
0 3
1
1
4
15
4
7 2 1
1 1
2 1
1
9
5
0 2
4 8
4
7
2
14
1
1
1
3 8
5 9
4 4 5 1
1
1
2
3 1
4
0 7
1 1 3 7
2
1
1
2 1
1
1
1
1 7
0 1
3 1
2
4
1
8 5
8
1
1
5 6
3
1
1
0 1
9
0
1
5 1
3 3
4 9 8
6
9
5 1
0 5
6
3 0
1
1
2 0
4 5
4 3
2 1
1
0 4
5 2
7 1
0 9
5 1
1
5
2 2 8
1
4
4 3
5 2
9 5
2 1
1
1
1
5
0
1
4
4 1 3
1 0
2
1
1
1
4 7
5 4
1
5 3
0 8
1
9 1
9
5
1
9
8
3
1
1
6
5
1
1
9 2
6
2
2 8 5
7
1
2
1
1
2 1 3 1
7
2
S7
6
4
0
1
6
3 1 0
7
1 0
3
4
1
1
1
4 0
3 4
4 1
1
0 7
7
5
1
1
3
1 8
1
1 1
1
6
6
3 0
1 8
1 3
3
1
3 1
1
2 3
0
4
9 7 5 1 2
5
1
6 1
2
0 1
8 6
5
1 6
1
4
1
1
1
1
1 1
3 8
2 1
1
3
2
8
3 7
1
1
1
6 8
0
5
9 2
4 1
4 7
0 9
5 5
0 1
1
2
3 12
5
4
0
4 6
1
1
5 3
1 7
3 1
1
1
8 1
7
5 1
3 4
0 1 9
1
1
2
1 1
7 4
2 1
4 8
1 4
(a)
0
1
1
4
0 1
2
2 0
9
3
1
6
4 1
6
5
1
1
1
3
5
2
5
0
1
7
0
1
2 9
2
1
1 1
1
4 3
5
8
0 9
3 0
5 3
5
6
1 1
Input Key
(b) Permuted Choice One (PC-1)
57
49
41
33
25
17
9
1 10 19 63 7 14 21
58 2 11 55 62 6 13
50 59 3 47 54 61 5
42 51 16 39 46 53 28
34 43 52 31 38 45 20
26 35 44 23 30 37 12
18 27 36 15 22 29 4
(c) Permuted Choice Two (PC-2)
14 15 26 41 51 34
7 6 8 52 45 53
11 21 16 31 33 46
24 10 7 37 48 42
1 23 27 47 44 50
5 19 20 55 49 36
3 12 13 30 39 29
28 4 2 40 56 32
(d) Schedule of Left Shifts
1 1
2 1
3 2
4 2
5 2
6 2
7 2
8 2
9 1
10 11 12 13 14 15 16 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) Intercept ion
(d) Modifica tion
(e) Fabrication
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. 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
develops
Sarson
notation
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) DFD:
Decrypt
5. FORMS & REPORTS 5.1. I/O SAMPLES
6. BIBILIOGRAPHY 1. CRYPTOGRAPHY AND NETWORK SECURITY -
William Stallins
2. SOFTWARE ENGINEERING -
Roger Pressman
