Study-Materials CSE 6th Cryptography-Network-Security S.-Dalai

KIIT POLYTECHNIC
LECTURE NOTES
ON
CRYPTOGRAPHY & NETWORK SECURITY
Compiled by
Swagatika Dalai
Lecturer, Department of Computer Science & Engineering,
KIIT Polytechnic, Bhubaneswar
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CONTENTS
S.NO CHAPTER NAME PAGE NO

1 Possible Attacks on Computers 1-7
2 Cryptography Concepts 8-16
3 Symmetric & Asymmetric Key 17-30

Algorithms
4 Digital Certificate & Public Key 31-37

Infrastructure
5 Internet Security Protocols 38-42
6 User Authentication 43-49
7 Network Security & VPN 50-60
8 References 61
Cryptography & Network Security Swagatika Dalai

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CHAPTER-1
POSSIBLE ATTACKS ON COMPUTERS
INTRODUCTION:
➢ Computer data often travels from one computer to another, leaving the safety of its
protected physical surroundings.
➢ Once the data is out of hand, people with bad intention could modify or forge your data,
either for enjoyment or for their own benefit.
➢ Cryptography can reformat and transform our data, making it safer on its trip between
computers.
➢ The technology is based on the secret codes, modern mathematics that protects our data
in powerful ways.
➢ Computer Security - generic name for the collection of tools designed to protect data
and to prevent hackers.
➢ Network Security - measures to protect data during their transmission.
➢ Internet Security - measures to protect data during their transmission over a collection
of interconnected networks.
NEED FOR SECURITY:
Computer security basically is the protection of computer systems and information from harm,
theft, and unauthorized use. It is the process of preventing and detecting unauthorized use of
your computer system. Cyber security is defined as protecting computer systems, which
communicate over the computer networks.
Computer security is important because it keeps your information protected. It's

also important for your computer's overall health; proper computer security helps prevent viruses
and malware, which allows programs to run quicker and smoother.
SECURITY ATTACKS, SERVICES AND MECHANISMS:

To assess the security needs of an organization effectively, the manager responsible for security
needs some systematic way of defining the requirements for security and characterization of
approaches to satisfy those requirements. One approach is to consider three aspects of
information security:
➢ Security attack – Any action that compromises the security of information owned by an
organization.
➢ Security mechanism – A mechanism that is designed to detect, prevent or recover from a
security attack.
➢ Security service – A service that enhances the security of the data processing systems and
Cryptography & Network Security 1 Swagatika Dalai

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the information transfers of an organization. The services are intended to counter security
attacks and they make use of one or more security mechanisms to provide the service.
➢ Security mechanisms have been defined by ITU-T (X 800). They used to implement
security services. Some of the security mechanisms defined by ITU-T (X 800) are shown
in the figure.
Encipherment: This refers to the transformation of the message or data with the help of
mathematical algorithms. The main aim of this mechanism is to provide confidentiality.
The two techniques that are used for encipherment are cryptography and steganography.
Data integrity: This refers to the method of ensuring the integrity of data. For this, the
sender computes a check value by applying some process over the data being sent, and
then appends this value to the data. On receiving the data, the receiver again computes the
check value by applying the same process over the received data. If the newly computed
check value is same as the received one, then it means that the integrity of data is
preserved.
Digital signature: This refers to the method of electronic signing of data by the sender
and electronic verification of the signature by the receiver. It provides information about
the author, date and time of the signature, so that the receiver can prove the sender's
identity.
Authentication exchange: This refers to the exchange of some information between two
communicating parties to prove their identity to each other.
Traffic padding: This refers to the insertion of extra bits into the stream of data traffic to
prevent traffic analysis attempts by attackers.

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Routing control: This refers to the selection of a physically secured route for data
transfer. It also allows changing of route if there is any possibility of eavesdropping on a
certain route.
Notarization: This refers to the selection of a trusted third party for ensuring secure
communication between two communicating parties.
Access control: It refers to the methods used to ensure that a user has the right to access
the data or resource.
PRINCIPLES OF SECURITY/ SECURITY SERVICES:
The classification of security services are as follows:

Confidentiality:
➢ The principle of confidentiality specifies that only the sender and the intended
recipient(s) should be able to access the contents of a message.
➢ Confidentiality gets compromised if an unauthorized person is able to access a
message.
➢ Unauthorized party could be a person, a program or a computer.
➢ Example: Suppose a confidential email message sent by user A to user B, which is
accessed by user C without the permission or knowledge of A and B. This type of
attack is called interception.
➢ Interception causes loss of message confidentiality.
Authentication
➢ Authentication mechanism helps to establish proof of identities.
➢ The authentication process ensures that the origin of a electronic message or
document is correctly identified. This concept is shown in figure.
➢ Fabrication is possible in absence of proper authentication mechanisms.

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Integrity
➢ When the contents of a message are changed after the sender sends it, but before it
reaches the intended recipient, we say that the integrity of the message is lost. It is
shown in figure.
➢ For example, consider that user A sends message to user B. User C tampers with a
message originally sent by user A, which is actually meant for user B. User C
change its contents and send the changed message to user B. User B has no way of
knowing that the contents of the message changed after user A had sent it. User A
also does not know about this change. This type of attack is called modification.
➢ Modification causes of loss of message integrity.
Non repudiation
Requires that neither the sender nor the receiver of a message be able to deny the
transmission.
Access control:
Access control determines and controls who can access what. It regulates which user has access
to the resource, under what circumstances.
Availability:
➢ The principle of availability is that resources should be available to authorized
parties at all times.
➢ For example, due to the intentional actions of an unauthorized user C, an authorized
user A may not be able to contact a server B. This would defeat the principle of
availability. Such an attack is called interruption.
➢ Interruption causes loss of availability.

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TYPES OF SECURITY ATTACK:

There are two types of attacks.
1. Active attacks
2. Passive attacks
Active attacks
An active attack is an attempt to alter system resources or affect their operation.
I.e., these attacks involve in some modification to the original message in some manner or the
creation of a false stream.
These attacks can be classified in to four categories:
Masquerade:
One entity pretends to be a different entity.
It is generally done by using stolen IDs and passwords or through bypassing authentication
mechanism.

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Replay:
This attack involves capturing a copy of the message sent by the original sender and
retransmitting it later to bring an unauthorized result.
Modification of messages:
➢ Some portion of message is altered or the messages are delayed or recorded, to produce
an unauthorized effect.
➢ For example, a message meaning "Allow John Smith to read confidential file accounts" is
modified to mean "Allow Fred Brown to read confidential file accounts."
Denial of service:
➢ A denial-of-service (DoS) is a form of cyberattack that prevents legitimate users from

accessing a computer or network.
➢ In a DoS attack, rapid and continuous online requests are sent to a target server in order
to overload the server’s bandwidth.
➢ Prevents the normal use or management of communication facilities.
➢ Another form of service denial is the disruption of an entire network, either by disabling
the network or overloading it with messages so as to degrade performance.

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Passive Attacks:
➢ Passive attacks are those where the attacker indulges in eavesdropping or monitoring of
data transmission.
➢ Passive attacks do not involve any modifications to the contents of an original message.
There are two types of passive attacks.
1. Release of message contents and
2. Traffic analysis.
Release of message contents:
➢ The release of message contents is a type of attack that analyzes and read the message
delivered between senders to receiver.
➢ A telephone conversation, an electronic mail message, or a transferred file may contain
sensitive or confidential information.
➢ We would like to prevent an opponent from getting the contents of these transmissions.
Traffic analysis.
➢ The attacker simply listens to the network communication to perform traffic analysis to
determine the location of key nodes, the routing structure, and even application behavior
patterns.
➢ In this type of attack, an intruder observes the frequency and length of msg. being
exchanged between communicating nodes.
➢ Attacker can then use this information for guessing the nature of communication that was
taking place.
Passive attacks are very difficult to detect because they do not involve any alteration of the data.
Typically, the messages are sent and received in normal fashion. Neither the sender nor receiver is
aware that a third party has read the messages or observed the traffic pattern. However, message
encryption is a simple solution to prevent passive attacks. Thus, the emphasis in dealing with passive
attacks is on prevention rather than detection.

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CHAPTER-2
CRYPTOGRAPHY CONCEPTS
CRYPTOGRAPHY TECHNIQUES
From the beginning any era, human being has two natural needs:
To communicate and share information and
To communicate selectively.
These two needs gave rise to the art of coding the messages in such a way that only the intended
people could have access to the information. Unauthorized people could not extract any
information.
The word “cryptography‟ is the combination of two Greek words, “Krypto” meaning hidden or
secret and “graphene” meaning writing.
Cryptography: It is the art of achieving security by encoding messages to make them non-
readable format.
It is a method of protecting information and communications through the use of codes, so that
only those for whom the information is intended can read and process it.
Cryptanalysis:
➢ It is the technique of decoding messages from a non-readable format back to a readable

format.
➢ It is done without knowing how they were initially converted from readable format to
non-readable format. Also called code breaking.

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Cryptology: Cryptology is a combination of Cryptography and Cryptanalysis.

Plain Text: Clear text, or plain text, signifies a message that can be understood by the sender,
the recipient, and also by anyone else who gets access to that message.
Cipher text:-When a plain text message is codifies using any suitable scheme, the resulting
message is called as cipher text.
There are two types of techniques used to covert plain text to cipher text.
• Substitution Techniques
• Transposition Techniques
Substitution-cipher technique:
In the substitution-cipher technique, the each characters of a plain-text message are
replaced byother characters, numbers or symbols.
There are several techniques. They are:

➢ Caesar Cipher
➢ Modified version of Caesar Cipher
➢ Monoalphabetic Cipher
➢ Polyalphabetic Cipher
➢ Homophonic Substitution Cipher
➢ Polygram Substitution Cipher
➢ Playfair Cipher
➢ Hill Cipher
Caesar Cipher
➢ Proposed by Julius Caesar.
➢ Mechanism to make a plaintext message into ciphertext message.
➢ It replacing each letter of the alphabet with the letter standing 3 places
further downthe alphabet.
➢ Example: Replace each A with D, B with E, etc.
ABCDEFGHIJKLMNOPQRSTUVYZ
DEFGHIJKLMNOPQRSTUVWXYZC
PT: KIIT
CT: NLLW
Modified version of Caesar Cipher

The Caesar cipher is very simple and very easy to break. To make it complicated the
modified version of Caesar cipher comes into play.
Let us assume that the cipher-text alphabets corresponding to the original plain-text alphabets
may not necessarily be three places down the order, but instead, can be any places down the
order.
As we know, the English language contains 26 alphabets. Thus, an alphabet A can be
replaced by any other alphabet in the English alphabet set, (i.e. B through Z). Of course, it
does not make sense to replace an alphabet by itself (i.e. replacing A with A).
Thus, for each alphabet, we have 25 possibilities of replacement. Hence, to break a message in
the modified version of Caesar cipher, our earlier algorithm would not work.

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Mono-alphabetic Cipher
➢ A monoalphabetic cipher is a substitution cipher where a symbol in the plaintext
has a one-to-one relationship with a symbol in the ciphertext.
➢ It means that a symbol in the plaintext is always replaced with the same
symbol in theciphertext, irrespective of its position in the plaintext.
➢ It uses random substitution.
➢ This means that in a given plain-text message, each A can be replaced by any other
alphabet (B through Z), each B can also be replaced by any other random alphabet (A
or C through Z), and so on. The crucial difference being, there is no relation between
the replacement of B and replacement of A. That is, if we have decided to replace each
A with D, we need not necessarily replace each B with E—we can replace each B with
any other character!
Polyalphabetic Substitution Cipher

➢ Leon Battista invented the polyalphabetic substitution cipher in 1568.
➢ This cipher uses multiple one-character keys. Each of the keys encrypts one plain-
text character. The first key encrypts the first plain-text character; the second key
encrypts the second plain-text character, and so on.
➢ After all the keys are used, they are recycled. Thus, if we have 30 one-letter
keys, every 30th character in the plain text would be replaced with the same key.
Homophonic Substitution Cipher
➢ This substitution cipher is very similar to mono-alphabetic cipher.
➢ However, the difference between the two techniques is in homophonic
substitution cipher, one plain-text alphabet can map to more than one cipher-text
alphabet.
➢ For instance, A can be replaced by <D, H, P, R>; B can be replaced by <E, I, Q, S>
etc.
Polygram Substitution Cipher
➢ Polygram substitution cipher technique replaces one block of plain text with another
block of cipher text—it does not work on a character-by-character basis.
➢ For instance, HELLO could be replaced by YUQQW, but HELL could be replaced by a
totally different cipher text block TEUI,as shown in Fig.
➢ This is true in spite of the first four characters of the two blocks of text (HELL) being the
same. This shows that in the polygram substitution cipher, the replacement of plain text
happens block by block, rather than character by character.

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Playfair Cipher:
➢ The Playfair cipher scheme was invented in 1854 by Charles Wheatstone but was named
after Lord Playfair who promoted the use of the cipher. In playfair cipher unlike
traditional cipher we encrypt a pair of alphabets(digraphs) instead of a single alphabet.
➢ It was used for tactical purposes by British forces in the Second Boer War and in World
War I and for the same purpose by the Australians during World War II. This was
because Playfair is reasonably fast to use and requires no special equipment.
The Playfair encryption scheme uses two main processes.
> Creation and population of matrix
> Encryption process
Step 1: Creation and Population of Matrix
• The Playfair cipher makes use of a 5
x 5 matrix (table), which is used to
store a keyword or phrase that
becomes the key for encryption and
decryption.
• The way this is entered into the 5 x 5
matrix is based on some simple rules:
1. Enter the keyword in the matrix row-wise: left-to-right, and then top-to-bottom.
2. Drop duplicate letters.
3. Fill the remaining spaces in the matrix with the rest of the English alphabets (A-Z)
that werenot a part of our keyword. While doing so, combine I and J in the same cell of
the table.
In other words, if I or J is a part of the keyword, disregard both I and J while filling the
remainingslots.
EXAMPLE OF ENCRYPTION AND DECRYPTION IN PLAYFAIR:

For example, suppose that our keyword=PLAYFAIR EXAMPLE
Then, the 5 x 5 matrix containing our keyword will look
as shownLet us say, our Plaintext= “MY NAME IS
ATUL”
Encryption process – it consists of following steps:
1. Before initiating the encryption, break the plain text in

pair of 2letters.
For ex. if our message is MY NAME IS ATUL, it becomes MY NA ME IS AT UL.
2. If both the alphabets are same or 1 letter is remaining, add X after the first alphabet.
3. After the initial process, take the pairs for encryption.
4. If the alphabets of the pair appear in same row of the matrix, then substitute them
with their immediate right letter. If the alphabets of the plain text is itself the
rightmost, then wrap itup with the left letter of the row it happens.

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5. If the alphabets of the pair appear in same column of the matrix, then substitute
them with their immediate below alphabets. If the letter of the plain text is itself
below, then wrap it up with the top letter of the column it happens.
6. If the alphabets of the pair are not in same row or column then define a rectangle
with theoriginal pair and substitute them with other corners of the rectangle.
Example
1) Message is: MY NAME IS ATUL It

becomes MY NA ME IS AT UL.
Hill Cipher
The Hill cipher works on multiple letters at the same time.
Lester Hill invented this in 1929. The Hill cipher uses the matrix theory of mathematics.
Working:
• Treat each letter with a number like A=0, B=1, C=2…… Z=25.
• Let us say, our original message is “TAJ”
• As per the rule, T=19 A=0 J=9
• Convert it into matrix form as:

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Now multiply the plain text matrix with any number as keys. The multiplying matrix
should beof n x n where n is the number of rows of original matrix
Now compute mod 26 on resultant matrix i.e. take the remainder after dividing by 26.
Now translating numbers into alphabets, we get:

19=T 25= Z 21=V
Therefore our cipher text is TZV
To decrypt hill cipher, follow the steps:
1.) Take cipher text matrix and multiply it by inverse of original
key matrix2.) Again perform mod by 26.
Thus we get our original text.
Transposition techniques:
Transposition technique is an encryption method which is achieved by
performing permutation over the plain text.
Rail-Fence Technique
This technique is a type of Transposition technique which involves writing the plain text as a
sequence of diagonals and then reading row-by-row to produce cipher text.
It uses a simple algorithm,
1. Writing down the plaintext message into a sequence of diagonals.

2. Read the plain text in step-1 as a sequence of rows.
Example:
Plain Text: meet me Tomorrow

Now, we will write this plain text sequence wise in a diagonal form as you can see below:
Cipher Text: m e m t m r o e t e o o r w

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Simple Columnar Transposition Technique:

A. Basic Technique
It is a slight variation to the Rail-fence technique, let’s see its algorithm:
1. In a rectangle of pre-defined size, write the plain-text message row by row.
2. Read the plain message in random order in a column-wise fashion. It can be any order
such as 2, 1, 3 etc.
3. Thus Cipher-text is obtained.
Let’s see an example:

Original message: "INCLUDEHELP IS AWESOME".
Now we apply the above algorithm and create the rectangle of 4 columns (we decide to make a
rectangle with four column it can be any number.)
Now let’s decide on an order for the column as 4, 1, 3 and 2 and now we will read the text in
column-wise.
Cipher-text: LHIEEIUESSCEPWMNDLAO
B. Columnar Technique with multiple rounds
In this method, we again change the chipper text we received from a Basic technique that is in
round 1 and again follows the same procedure for the cipher-text from round 1.
Algorithm:
1. In a rectangle of pre-defined size, write the plain-text message row by row.
2. Read the plain message in random order in a column-wise fashion. It can be any order
such as 2, 1, 3 etc.
3. Thus, Cipher-text of round 1 is obtained.
4. Repeat from step 1 to 3.
Example:
Original message: "INCLUDEHELP IS AWESOME".
Now we apply the above algorithm and create the rectangle of 4 column (we decide to make a
rectangle with four column it can be any number.)

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Now let’s decide on an order for the column as 4, 1, 3 and 2 and now we will read the text in
column-wise.
Cipher-text of round 1: LHIEEIUESSCEPWMNDLAO
Round 2:
Now, we decide to go with a previous order that is 4,1,3,2.

Cipher-text: EEENLESPICUMHISW
These multi-round columnar techniques are harder to crack as compared to methods seen earlier.
Vernam Cipher (one time pad):
The Vernam Cipher has a specific subset one-time pad, which uses input ciphertext as a random
set of non-repeating character. The thing to notice here is that, once an input cipher text gets used
it will never be used again hence one-time pad and length of cipher-text is the size that of
message text.
Algorithm:
1. Plain text character will be represented by the numbers as A=0, B=1, C=2,... Z=25.
2. Add each corresponding number of a plain text message to the input cipher text alphabet
numbers.
3. If the sum is greater than or equal to 26, subtract 26 from it.
4. Translate each number back to corresponding letters and we got our cipher text.
Example: Our message is "INCLUDEHELP" and input cipher text is "ATQXRZWOBYV"

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One time pad should be discarded after every single use and this technique is proved highly
secure and suitable for small messages but illogical if used for long messages.
Encryption and Decryption:-
Encryption:-The process of encoding plain text messages into cipher text messages is called as
encryption.
Decryption:-The reverse process of transforming cipher text messages back to plain text
messages is called as decryption.
Symmetric and Asymmetric Key Cryptography:
Symmetric key Cryptography:-
Symmetric key cryptography (or symmetric encryption) is a type of encryption scheme in which
the same key is used both to encrypt and decrypt messages.
Asymmetric key Cryptography:-
Asymmetric encryption uses the public key for the encryption, and a private key is used for
decryption.
Or
Asymmetric cryptography, also known as public-key cryptography, is a process that uses a pair
of related keys -- one public key and one private key .

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CHAPTER-3
SYMMETRIC AND ASYMMETRIC KEY ALGORITHMS
Algorithm Types and modes:
Algorithm types:
➢ It defines what size of plain text should be encrypted in each step of algorithm.
➢ It is of two types:
o Stream Ciphers
o Block Ciphers
Stream Ciphers
➢ Bit-by-bit encryption/decryption.
➢ In this scheme, the plaintext is processed one
bit at a time i.e. one bit of plaintext is taken,
and a series of operations is performed on it to
generate one bit of cipher text.
➢ Technically, stream ciphers are block ciphers
with a block size of one bit.
➢ Example: Suppose the original message (plain
text) is Pay 100 in ASCII (i.e. text format).
➢ When we convert these ASCII characters to their
binary values, let us assume that it translates to
01011100. Let us also Assume that we apply the
XOR logic as the encryption algorithm.
➢ As a result of applying one bit of key for every respective bit of the original message,
suppose thecipher text is generated as 11001001 in binary (ZTU91 A% in text).
Block Cipher
➢ Block-by-block encryption / decryption.
➢ In this scheme, the plain binary text is processed in blocks (groups) of bits at a time; i.e. a block of
plaintext bits is selected, a series of operations is performed on this block to generate a block of
cipher text bits.
➢ The number of bits in a block is fixed. For example, the schemes DES and AES have block sizes
of 64 and 128, respectively.
The basic scheme of a block cipher is given as follows:
Block Cipher Example:
Suppose we have a plain text “FOUR_AND
_FOUR” that needs to be encrypted. By
using this technique FOUR could be
encrypted first followed by _AND_ and
FOUR.

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Algorithm Modes:
➢ It is a combination of series of basic algorithm steps on block cipher and
some sort of feedback from the previous steps.
➢ It is divided into four modes:
Electronic Code book (ECB) Mode:
➢ ECB is a simplest and

straightforward method of
converting a block of plaintext
into cipher text.
➢ Here, plain-text message is
divided into blocks of 64 bits
each.
➢ Each such block is then
encrypted independently of the
other blocks.
➢ For all blocks in a message, the
same key is used for encryption.
➢ This encryption process is shown figure.
➢ At the receiver’s end, the
incoming data is divided into
64-bit blocks.
➢ By using the same key as was
used for encryption, each block
is decrypted to produce the
corresponding plain-text block.
➢ This decryption process is shown figure.

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Cipher Block Chaining (CBC) Mode:
In CBC mode, a feedback mechanism is used. Chaining adds a feedback mechanism to a

block cipher.
In Cipher Block Chaining (CBC), the results of the encryption of the previous block are
fed back into the encryption of the current block.
That is, each block is used to modify the encryption of the next block.
Thus, each block of cipher text is dependent on the corresponding current input plain-text
block, as well as all the previous plain-text blocks.
Operation:
The steps are as follows:
➢ Load the n-bit Initialization Vector (IV). IV is a random generated block of text in a
register.
➢ XOR the n-bit plain text block with data value in IV register.
➢ Encrypt the result of XOR operation with the key K. Result is it produce the cipher
text block.
➢ Feed cipher text block into the IVregister and continue the operation till all plaintext
blocks are processed.
Cipher Feedback (CFB) Mode:
➢ Not all applications can work with blocks of data. Security is also required in
applications that are character-oriented.
➢ For instance, an operator can be typing keystrokes at a terminal, which needs to be
immediately transmitted across the communications link in a secure manner, i.e., by
using encryption.
➢ In such situations, stream cipher must be used. The Cipher Feedback (CFB) mode is
useful in such cases.
➢ In this mode, data is encrypted in units that are smaller (e.g., they could be of size 8 bits,
i.e. the size of a character typed by an operator) than a defined block size (which is
usually 64 bits).

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Steps of operation are:

➢ Assuming that we are dealing with j bits at a time (as we have seen usually, but not
always, j = 8).
➢ we shall study CFB in a step-by-step fashion.
➢ Step 1 Like CBC, a 64-bit Initialization Vector (IV) is used in the case of CFB mode.
The IV is kept in a shift register. It is encrypted in the first step to produce a
corresponding 64 bit cipher text.
➢ Step 2 Now, the leftmost (i.e. the most significant) j bits of the encrypted IV are
XORed with the first j bits of the plain text.
➢ Step 3 Now, the bits of IV (i.e. the contents of the shift register containing IV) are
shifted left by j positions. Thus, the rightmost j positions of the shift register now
contain unpredictable data. These rightmost j positions are now filled with C.
➢ Step 4 Now, steps 1 through
3 continue until all the plain-
text units are encrypted.
That is, the following steps are repeated:
o IV is encrypted.
o The leftmost j bits
resulting from this
encryption process are
XORed with the next j
bits of the plain text.
o The resulting cipher-text
portion (i.e., the next j
bits of cipher text) is
sent to the receiver.
o The shift register
containing the IV is left-
shifted by j bits.
o The j bits of the cipher
text are inserted from
right into the shift
register containing the
IV.
Output Feedback (OFB) Mode:

➢ The OFB mode is similar to CFB, but the only difference is that in CFB, the cipher text is
fed into the next stage of encryption process.
➢ But in case of OFB the output of IV encryption process is fed into the next stage of
encryption process.
➢ In this mode, if there are errors in individual bits, they remain errors in individual bits and
do not corrupt the whole message.
➢ That is, bit errors do not get propagated.

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Encryption & Decryption:

Encryption or Encoding or Encode:
➢ The process of converting or transforming plain text or original text into cipher
text is called as encoding.
➢ This new form of the message is totally different from the initial message.
➢ It occurs at the sender’s side.
➢ The sender uses an encryption algorithm and a key to transform the original
message into an encrypted message i.e., cipher text.
➢ Encryption is also called enciphering or encipherment.
Decryption or Decoding or Decode:

➢ The process of converting cipher text into plain text is called as decoding.
➢ It occurs at the receiver’s end.
➢ The receiver uses decryption algorithms and a key to transform the cipher text back
to original plaintext message.
➢ The decryption is also called deciphering or decipherment.
➢ Decryption is the reverse process of encryption.

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An Overview of Symmetric Key Cryptography

Symmetric key cryptography (or symmetric encryption) is a type of encryption scheme in which
the same key is used both to encrypt and decrypt messages. Such a method of encoding
information has been largely used in the past decades to facilitate secret communication between
governments and militaries.
Data Encryption Standard:
The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National
Institute of Standards and Technology (NIST). DES is an implementation of a Feistel Cipher. It
uses 16 round Feistel structure. The block size is 64-bit.
The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National
Institute of Standards and Technology (NIST).
How DES Works?
DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size
is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the
64 bits of the key are not used by the encryption algorithm (function as check bits only). General
Structure of DES is depicted in the following illustration −

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Since DES is based on the Feistel Cipher, all that is required to specify DES is −
Round function
Key schedule
Any additional processing − Initial and final permutation
Initial and Final Permutation
The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of
each other. They have no cryptography significance in DES. The initial and final permutations
are shown as follows −
Round Function
The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the
rightmost 32 bits to produce a 32-bit output.
Expansion Permutation Box − Since right input is 32-bit and round key is a 48-bit, we first
need to expand right input to 48 bits. Permutation logic is graphically depicted in the following
illustration −

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The graphically depicted permutation logic is generally described as table in DES specification
illustrated as shown −
XOR (Whitener). − After the expansion permutation, DES does XOR operation on the
expanded right section and the round key. The round key is used only in this operation.
Substitution Boxes. − The S-boxes carry out the real mixing (confusion). DES uses 8 S-boxes,
each with a 6-bit input and a 4-bit output. Refer the following illustration −
The S-box rule is illustrated below −
There are a total of eight S-box tables. The output of all eight s-boxes is then combined in to 32
bit section.

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Straight Permutation − The 32 bit output of S-boxes is then subjected to the straight
permutation with rule shown in the following illustration:
Key Generation
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of
key generation is depicted in the following illustration −
The logic for Parity drops, shifting, and Compression P-box is given in the DES description.

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DES Analysis
The DES satisfies both the desired properties of block cipher. These two properties make cipher
very strong.
Avalanche effect − A small change in plaintext results in the very great change in the ciphertext.
Completeness − Each bit of cipher text depends on many bits of plaintext.
During the last few years, cryptanalysis has found some weaknesses in DES when key selected
are weak keys. These keys shall be avoided.
DES has proved to be a very well designed block cipher. There have been no significant
cryptanalytic attacks on DES other than exhaustive key search.
Asymmetric-key Enclpherment:
The asymmetric-key encipherment also called public-key encipherment or public-key
cryptography, was introduced by Diffie and Hellman in 1976 to overcome the problem
found in symmetric key cryptography.
It uses two different keys for encryption and decryption.
These two keys are referred to as the public key (used for encryption) and the private key
(used for decryption).
Each authorized user has a pair of public and private keys. The public key of each user is
known to everyone, whereas the private key is known to its owner only.
A public-key encryption scheme has six ingredients as shown in figure.
➢ Plaintext: This is the readable message or data that is fed into the algorithm as input.
➢ Encryption algorithm: The encryption algorithm performs various
transformations on the plaintext. This encrypts plain text using public key of
receiver.
➢ Public and Private keys: This is a pair of keys used for encryption; the other is
used for decryption. In figure, encryption is done using public key and decryption
using private key.
➢ Cipher-text: This is the coded message produced as output. It depends on the plaintext
and the key.
➢ Decryption algorithm: This algorithm accepts the cipher text and the matching
key and produces the original plaintext. In figure, decryption algorithm uses
private key.
➢ Now, suppose that a user ·A wants to transfer some information to· user B
securely. The user A encrypts the data by using the public key of B and sends the

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encrypted message to B.
➢ On receiving the encrypted message, B decrypts it by using his/ her private key.
Since decryption process requires a private key of user B, which is only known to
B, the information is transferred securely. The above figure states the whole
process.
➢ RSA is a well-known example of asymmetric-key algorithm.
➢ The main advantage of public-key cryptography is that the sender and the receiver
need not have to share the secret key. All communication involves only public
keys.
➢ Thus, the private key is never transmitted or shared. Anyone can send a
confidential message using a public key, but the message can only be decrypted
with a private key, which is kept by the intended recipient.
Differentiate between symmetric-key and asymmetric-key cryptography:
Symmetric-key Asymmetric-key
1. It uses a single key for both encryption and 1. It uses .two different keys-public key for encryption and
decryption of data. private key for decryption.
2. Both the communicating parties share the 2. Both the communicating parties should have at least one
same algorithm and the key. of the matched pair of keys.
3.The processes of encryption and decryption 3. The· encryption and decryption processes are slower as
are very fast. compared to symmetric-key cryptography.
4. Key distribution is a big problem. 4. Key distribution is not a problem.
5.The size of encrypted text is usually same or 5. The size of encrypted text is usually more than the size
less than the original text. of the original text.
6. It can be used for confidentiality of data as well as for
6.It can only be used for confidentiality, that is, integrity and non-repudiation checks (i.e.for digital
only for encryption and decryption of data. signatures).
THE RSA ALGORITHM:
This algorithm proposed by Ron Rivest, Adi Shamir, Len Adleman (RSA) in 1978 at
MIT. It is based on asymmetric key cryptography.
1. Choose two large prime numbers P and Q.

2. Calculate N = P x Q.
3. Select the public key (i.e. the encryption key) E such that it is not a factor of ( P - 1) and
( Q - 1 ).
4. Select the private key (i.e., the decryption key) D such that the
following equation is true: (D x E) mod (P - 1) x (Q - 1) = 1
5. For encryption, calculate the cipher text CT from the plain text PT as follows:
CT = PTE mod N.
6. Send CT as the cipher text to the receiver.

7. For decryption, calculate the plain text PT from the cipher text CT as follows:
PT = CTD mod N

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Examples of RSA
Let us take an example of this process to understand the concepts.
1. Choose two large prime numbers P and Q. Let P = 7, Q = 17.

2. Calculate N = P x Q.
We have N = 7 x 17= 119.
3. Select the public key (i.e., the encryption key) E such that it is not a factor
of (P - 1) X (Q - 1). Let us find (7 - 1) x (17 - 1) = 6 x 16 = 96.
The factors of 96 are 2, 2, 2, 2, 2 and 3 (because 96 = 2 x 2
x 2 x 2 x 2 X 3). Thus, we have to choose E such that it is
not the factors of E is 2 and 3.
Let us choose E as 5 (it could have been any other number that does not its factors as 2
and 3).
4. Select the private key (i.e., the decryption key) D such that the
following equation is true: (D x E) mod (P - 1) x (Q -1) = 1.
Let us substitute the values of E, P and Q
in the equation. We have: (D x 5) mod (7 -
1) x (17 - 1) = 1
That is: (D x 5) mod (6) x (16) = 1
That is: (D x 5) mod (96) = 1
After some calculations, let us take D = 77. Then the following is true: (77 x 5)
mod (96) = 385 mod 96 = 1.
5. For encryption, calculate the cipher text CT from the plain
text PT as follows: CT= PTE mod N.
Let us assume that we want to encrypt plaintext=10. Then we have:

CT = 105 mod 119 = 100000 mod 119 = 40.

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6. Send CT as the cipher-text to the receiver. Send 40 as the cipher text to the receiver.
7. For decryption, calculate the plaintext PT from the cipher-
text CT as follows: PT = CTD mod N.
That is: PT = 4077 mod 119 = 10.
This was the original plaintext of step 5
Digital signature:
➢ It is an authentication mechanism that allows the sender to attach an electronic
code with the message. This electronic code acts as the signature of the sender and
hence, is named digital signature.
➢ It is done to ensure its authenticity and integrity.
➢ Digital signature uses the public-key cryptography technique. The sender uses his
or her private key and a signing algorithm to create a digital signature and the
signed document can be made public. The receiver, uses the public key of the
sender and a verifying algorithm to verify the digital signature.
➢ A normal message authentication scheme protects the two communicating parties
against attacks from a third party (intruder). However, a secure digital signature
scheme protects the two parties against each other also.
➢ Suppose A wants to send a signed message (message with A's digital signature) to
B through a network. For this, A encrypts the message using his or her private
key, which results in a signed message. The signed message is then sent through
the network to B.
➢ Now, B attempts to decrypt the received message using A's public key in order to
verify that the received message has really come from A.
➢ If the message gets decrypted, B can believe that the message is from A. However,
if the message or the digital signature has been modified during transmission, it
cannot be decrypted using A's public key. From this, B can conclude that either
the message transmission has tampered with, or that the message has not been
generated by A.
Message integrity:
➢ Digital signatures also provide message integrity.
➢ If a message has a digital signature, then any change in the message after the
signature is attached will invalidate the signature.
➢ That is, it is not possible to get the same signature if the message is changed.
Moreover, there is no efficient way to modify a message and its signature such that
a new message with a valid signature is produced.
Non-repudiation:
➢ Digital signatures also ensure non-repudiation.
➢ For example, if A has sent a signed message to B, then in future A cannot deny
about the sending ofthe message. B can keep a copy of the message along with A's
signature.
➢ In case A denies, B can use A’s public key to generate the original message. If
the newly created message is the same as that initially sent by A, it is proved that
the message has been sent by A only.
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➢ In the same way, B can never create a forged message bearing A's digital
signature, because only Acan create his or her digital signatures with the help of
that private key.
Message confidentiality:
➢ Digital signatures do not provide message confidentiality, because anyone knowing
the sender's public key can decrypt the message.
Digital signature process:

The digital signature process is shown in Figure. Suppose user A wants to send a signed
message to B through a network. To achieve this communication, these steps are
followed:
➢ A uses his private key (EA), applied to a signing algorithm, to sign the message (M).
➢ The message (M) along with A's digital signature (S) is sent to B.
➢ On receiving the message (M) and the signature (S), B uses A's public key (DA),
applied to the verifying algorithm, to verify the authenticity of the message. If the
message is authentic, B accepts the message, otherwise it is rejected.

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CHAPTER-4
DIGITAL CERTIFICATE & PUBLIC KEY INFRASTRUCTURE
Digital Certificate:
➢ A digital certificate is simply a small computer file. For example, my digital
certificate would actually be a computer file with a file name such as name .cer.
➢ The digital certificate is actually quite similar to a passport. As we know every
passport has a unique passport number, similarly every digital certificate has a
unique serial number. Also gives information of the issuer’s name, serial number,
public key, validity period, etc.
➢ Digital Certificate is issued by a trusted agency called as CA (Certification
Authority).
➢ Another third party called as RA (Registration Authority) acts as a intermediate
entity between CA and end user.
➢ Satisfies the principle of Authentication, non-repudiation.
Certification Authority (CA)
➢ CA has to be someone, who everybody trusts. Consequently, the governments in
variouscountries decide who can and who cannot be a CA.
➢ Usually, a CA is a reputed organization, such as a post office, financial
institution, software company, etc. Two of the world’s most famous CAs are
VeriSign and Entrust. Safescrypt Limited is the first Indian CA.
➢ Thus, a CA has the authority to issue digital certificates to individuals and
organizations, who want to use those certificates in asymmetric-key cryptographic
applications.
Technical Details of a Digital Certificate:
A standard called X.509 defines the structure of a digital certificate. The International
Telecommunication Union (ITU) designs this standard. At that time, it was a part of
another standard called X.500. The current version of the standard is Version 3, called
X.509V3.

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Contents of Digital Certificate:
Version: Version of X.509 protocol. Version can be 1,2 or 3

Certificate Serial No.: Contains unique integer which is generated by CA
Signature Algorithm Identifier: Identifies the algorithm used by CA to sign the certificate.
Issuer Name: Identifies the Distinguished Name that created & signed the certificate Validity:
(not before/not after) Contains two date-time values. This value generally specifies the date &
time up to seconds or milliseconds.
Subject name: Distinguished Name of the end user (user or organization)
Subject Public key info.: This field can never be blank. Contains public key & algorithm
related.
Issuer Unique Identifier: Helps identify a CA uniquely if two or more CAs have used the same
Issuer Name over time.
Subject Unique Identifier: Helps identify a subject uniquely if two or more subjects have used
the same Subject Name over time.
Digital-Certificate Creation:
1. Parties Involved
➢ end user (may be a single user or organization),
➢ issuer (CA),
➢ third party is also (optionally) called a Registration Authority (RA), involved in the
certificate creation and management.
The RA commonly provides the following services
➢ Accepting and verifying
registrationinformation about new users.
➢ Generating keys on behalf of the end users.
➢ Accepting and authorizing requests for
keybackups and recovery.
➢ Accepting and authorizing the requests
forcertificate revocation.
➢ RA is mainly set up for facilitating the
interaction between the end users and the
CA
➢ The RA cannot issue digital certificates.
➢ The CA must handle this. Additionally,
after a certificate is issued, the CA is
responsible for all the certificate
management aspects, such as tracking its
status, issuing revocation notices if
the certificate needs to be invalidated for some reason, etc.
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2. Certificate Creation Steps
Step 1: Key Generation:
➢ The action begins with the subject (i.e. the

user/organization) who wants to obtain a
certificate.
➢ There are two different approaches for this
purpose:
➢ Firstly, the subject can create a private key
and public key pair using some software.
• The subject must keep the private
key which is generated, keep it
secret. The subject then sends the
public key along with other
information to the RA.
➢ Secondly, the RA can generate a key pair on-behalf the subject.

• This can happen in cases where either the user is not aware of the
technicalitiesinvolved in the generation of a key pair.
• The RA sends the private key which is generated, to the subject. The
RA keepsthe public key.
Step 2: Registration:
➢ This step is required only if the user generates the key pair in the first step. If the
RA generates the key pair on the user’s behalf, this step will also be a part of the
first step itself.
➢ Assuming that the user has generated the key pair, the user now sends the public
key and the associated registration information (e.g. subject name, as it is desired
to appear in the digital certificate) and all the required evidence about
himself/herself to the RA.
➢ For this, the software provides a wizard in which the user enters all the data then
submits it. This data then travels over the network/Internet to the RA. This format
for the certificate requests has been is called Certificate Signing Request (CSR).
This is one of the Public Key Cryptography Standards (PKCS),
➢ Note that the user must not send the private key to the RA—the user must keep it
securely.
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Step 3: Verification:
After the registration process is complete, the RA has to verify the user’s
credentials. This verification is in two respects, as follows.
1. Firstly, the RA needs to verify the user’s credentials which are provided by the user.
• If the user were actually an organization then the RA would perhaps like
to check the business records, historical documents and credibility proofs.
• If it is an individual user then simpler checks are in call, such as verifying
the postal address, email id, phone number, passport or driving-license
details can be sufficient.
2. Secondly, check is to ensure that the user who is requesting for the certificate,
whether he/she possesses the private key or not corresponding to the public key
that is sent to the RA.
This is very important, because there must be a record that the user possesses the private
key corresponding to the given public key. Otherwise, this can create legal problems. This
check is called the Proof Of Possession (POP) of the private key.
How can the RA perform this check? There are many approaches to this, the chief
ones being as follows.
➢ The RA can demand that the user must digitally sign his/her Certificate Signing
Request (CSR) using his/her private key. If the RA can verify the signature (i.e.
de-sign the CSR) correctly using the public key of the user, the RA can believe
that the user indeed possesses the private key.
➢ Alternatively, the RA can create a random number challenge; encrypt it with the
user’s public key and send the encrypted challenge to the user. If the user can
successfully decrypt the challenge using his/her private key, the RA can assume
that the user possesses the right private key.
➢ Thirdly, the RA can actually generate a dummy certificate for the user, encrypt it
using the user’s public key and send it to the user. The user can decrypt it only if
he/she can decrypt the encrypted certificate, and obtain the plain-text certificate.
Step 4: Certificate Creation:
➢ Assuming that all the steps so far have been successfully done, and then RA
passes on allthe details of the user to the CA.
➢ The CA does its own verification (if required) and creates a digital certificate for the
user.
➢ The creation of certificate as per the X.509 standard.
➢ The CA sends the certificate to the user, and also retains a copy of the certificate
for itsown record.
➢ The CA’s copy of the certificate is maintained in a certificate directory. This is a
centralstorage location maintained by the CA.
Certificate Hierarchies and Self-signed Digital Certificates:

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Certificate hierarchy relieves the root CA from having to manage all the possible digital
certificates.
As a substitute, the root CA can hand over this job to the second-level CAs. This hand
over can happen region-wise. E.g. one second level CA could be responsible for the
Western region, another for the Eastern region, a third one for the Northern region, and a
fourth one for the Southern region, etc.). Each of these second-level CAs could appoint
third-level CAs state-wise within that region. Each third-level CA could hand over its
responsibilities to a fourth-level CA city-wise, and so on.
The root CA signs its own certificate. This certificate of the root CA is called self-signed
certificate.
Cross-Certification
➢ It is quite possible that user A and user B live in different countries.
➢ This would mean that their root CAs may be different. Because generally each
countryappoints its own root CA. In fact, one country can have multiple root CAs
as well.
➢ For instance, the root CAs
in the US are VeriSign,
Thawte, and the US Postal
Service. In such cases, there
is no single root CA, which
can be trusted by all the
concerned parties.
➢ In our example, why should
user A—a Japanese
national, trust user B’s root
CA—a US-based
organization?
➢ Cross-certification allows
CAs and end users from
different PKI domains to
interact called cross
certification.
Certificate Revocation:
Reasons for revocation:
➢ If the private key corresponding to the public key is stolen.
➢ The CA realizes that it had made mistake while issuing the certificate.
➢ The certificate holder leaves a job and the certificate was issued specifically
while thePerson was employed in that job.
➢ It checks: Online revocation status, Off-line revocation status

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Private Key Management:

To protect the private key by means:-
➢ Password protection
➢ Tokens
➢ Biometrics
➢ Smart Cards
➢ Apart from these, the private key used for digital signing must be destroyed. In
contrast,the Private key used for encryption/decryption must be archived.
• In case of certificate expiration, the user needs to update its key.
• The CA should maintain history of certificates & keys to prevent any
legalproblems.
The PKIX (Public Key Infrastructure X.509) model:

(a) Registration:
In this process the end-entity (subject/user) registers to a CA. Usually this is via an RA.
(b) Initialization:
Process to verify that the end-entity is talking to the right CA.
(c) Certification:
In this step, the CA creates a digital certificate for the end-entity and returns it to
the end-entity and keeps a copy for its own records.
(d) Key-Pair Recovery:
Keys used for encryption of some old documents may be required to be
recovering datafor decrypting. Key archival and recovery services can be provided
by a CA.
(e) Key Generation:
PKIX specifies that the end-entity should be able to generate private-and
public-keypairs, or the CA/RA should be able to do this for the end-entity.
(f) Key Update:
This allows issuing new key pair from old one by the automatic renewal of
digitalcertificates. But there is a provision for issuing digital certificate manually.
(g) Cross-certification:
In this, each end-entity that are certified by different CAs can cross-verify each other.
(h) Revocation:
PKIX provides support for the checking of the certificate status in two modes:
online oroffline.
PKIX Architectural Model:
➢ X.509 v3 Certificate & v2 Certificate Revocation List profiles:
Lists the use of various options while describing extensions of a digital certificate.
➢ Operational Protocol:
Defines the underlying protocols that provide the transport mechanism.
➢ Management Protocol:
Enables exchange of information between the various PKI entities and
specifies thestructure & details of PKI messages.
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➢ Policy outlines:
Defines policies for the creation of Certificate Policies & Certificate Practice
Statements.
➢ Timestamp & Data Certification Services:
Both are the trusted third parties that provide services to guarantee the
existence ofcertificate & DCS verifies the correctness of data that it receives.
PKCS (Public Key Cryptography Standards)

Standard Description
PKCS#1: RSA Encryption Standard. Defines rules for calculating digital certificate.
PKCS#2: RSA Encryption Standard for Message Digest.
PKCS#3: Diffie-Hellman Key Agreement Standard.
PKCS#4: NA. Merged with PKCS#1
PKCS#5: Password Based Encryption(PBE). Defines method to encrypt symmetric key.
PKCS#6: Extended Certificate Syntax Standard. Defines syntax for extending
the basicattribute of an X.509 digital certificate.
PKCS#7: Cryptographic Message Syntax Standard.
PKCS#8: Private Key Information Standard.
PKCS#9: Selected Attribute Types. Defines selected attribute for use in PKCS#6
extendedcertificates.
PKCS#10: Certificate Request Syntax Standard
PKCS#11: Cryptographic Token Interface Standard.
PKCS#12: Personal Information Exchange Syntax Standard.
PKCS#13 Elliptic Curve Cryptography Standard.
PKCS#14 Pseudo –Random Number Generation Standard.
PKCS#15 Cryptographic Token Information Syntax standard.
Digital Envelop:
➢ A digital envelope is a secure electronic data

container that is used to protect a message
through encryption and data authentication.
➢ A Digital Envelope is created by symmetric
key algorithm (e.g. AES) and the symmetric
key.
➢ The symmetric key is then encrypted with
an asymmetric key algorithm (e.g. RSA) and
the recipient’s public key.

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CHAPTER-5
INTERNET SECURITY PROTOCOL
Basic concept
In computing, Internet Protocol Security (IPSec) is a secure network protocol suite that
authenticates and encrypts the packets of data to provide secure encrypted communication
between two computers over an Internet Protocol network. It is used in virtual private networks
(VPNs).
Static Web page
Static web pages are also known as flat or stationary web page. They are loaded on the client’s
browser as exactly they are stored on the web server. Such web pages contain only static
information. User can only read the information but can’t do any modification or interact with
the information.
Static web pages are created using only HTML. Static web pages are only used when the
information is no more required to be modified.
Dynamic Web page
Dynamic web page shows different information at different point of time. It is possible to
change a portion of a web page without loading the entire web page. It has been made possible
using Ajax technology.
Server-side dynamic web page
It is created by using server-side scripting. There are server-side scripting parameters that
determine how to assemble a new web page which also includes setting up of more client-side
processing.

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Client-side dynamic web page

It is processed using client side scripting such as JavaScript. And then passed in to Document
Object Model (DOM).
A static web page (sometimes called a flat page or a stationary page) is a web page that is
delivered to the user's web browser exactly as stored,[1] in contrast to dynamic web pages which
are generated by a web application.
Consequently, a static web page displays the same information for all users, from all contexts,
subject to modern capabilities of a web server to negotiate content-type or language of the
document where such versions are available and the server is configured to do so.
Secure Socket Layer

➢ World’s most widely used security mechanism on the Internet.
➢ Secures communication between a client and a server.
➢ Located between the Application and Transport Layers of TCP/IP protocol suite.
SSL Architecture:
SSL is designed to make use of TCP to provide a reliable end-to-end secure service.
SSL is not a single protocol but rather two layers of protocols.
The SSL Record Protocol provides basic security services to various higher-layer protocols.
The HTTP which provides the transfer service for Web client/server interaction, can operate on
top of SSL.

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SSL consists of three higher-layer protocols:

➢ Handshake Protocol
➢ the Change CipherSpec Protocol
➢ Alert Protocol.
SSL consists of one lower-layer protocols:
SSL Record Protocol
SSL Record Protocol Operation:
The SSL Record Protocol provides two services for SSL connection:
Confidentiality: The original data and the MAC are encrypted using secret key cryptography to
provide confidentiality.
Message Integrity: The Hash function is applied on compressed data to compute a MAC. This
provides integrity.
Fragmentation: each upper layer message is fragmented into block of 214 bytes (16384bytes) or
less.
Compression: must be lossless and may not increase the content length by more than 1024 bytes.
Message Authentication Code: it is compute a code over the compressed data. For this purpose a
shared secret key is used.
Next, the compressed message plus the MAC are encrypted using symmetric encryption.
Handshake Protocol:
This protocol allows the server and client to authenticate each other.
Used to negotiate an encryption and MAC algorithm and cryptographic keys to be used to
encrypt data in an SSL record.
In this protocol several msg. are exchanged between client and server.
All of these messages have a fixed format with three fields.
Change CipherSpec protocol:
The cryptographic secret (encrypted data) is generated, once the handshake protocol is over.
It is used to signal that cryptographic secret is ready to use.
This protocol consists of a single message, which consists of a single byte with the value 1.
The sole purpose of this message is to cause the pending state to be copied to into the current
state.
Alert Protocol:
The alert protocol is Used to signal errors or any abnormal condition.
Each message in this protocol consists of two bytes.
The first byte takes the value warning(1) or fatal(2) to convey the severity of the Message.
In case of fatal error, the connection is immediately terminated.
SECURE HYPER TEXT TRANSFER PROTOCOL (SHTTP)
➢ The Secure Hyper Text Transfer Protocol (SHTTP) is a set of security mechanisms
defined for protecting the Internet traffic.
➢ This includes the data-entry forms and Internet-based transactions.
➢ The services offered by SHTTP are quite similar to those of SSL. However, SSL has
become highly successful—SHTTP has not.
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➢ SHTTP works at the application layer, and so it is tightly coupled with HTTP, unlike
SSL.
➢ SHTTP supports both authentication and encryption of HTTP traffic between the client
and the server.
➢ The key difference between SSL and SHTTP is that SHTTP works at the level of
individual messages.
➢ It can encrypt and sign individual messages. On the other hand, SSL does not
differentiate between different messages.
➢ It aims at making the connection between a client and the server, regardless of the
messages that they are exchanging.
➢ Not as popular as SSL
➢ Almost obsolete.
SET (Secure Electronic Transaction):

➢ SET is an open encryption and security specification designed to protect
credit cardtransactions on the internet.
➢ It is developed by VISA and MasterCard for securing credit card
transactions overinsecure networks, specifically, the internet.
➢ SET was not itself a payment system. It provides a set of security protocols and
formatsthat enable users to do credit card payment on an open network in secure
fashion.
➢ Merchant does not get to know the credit card details of the cardholder.
➢ It requires software set up on both client and server.
SET specification:
➢ Uses public key cryptography and digital certificates for validating both
consumers andmerchants.
➢ It provides the four security requirements – confidentiality, data integrity, user
andmerchant authentication, and consumer non-repudiation.
Architecture OR participants of SET:
The SET protocol coordinates the activities of:
1. Card Holder (Consumer) – he is the buyer who is the registered holder of the credit card.
2. Card Issuer(Consumer’s Bank) – bank that issues the credit card to card holder.
3. Merchant – refers to the seller who is connected to an acquirer.
4. Acquirer (Merchant’s Bank) – bank that serves as an agent to link a merchant to
multipleissuers(customer’s banks).
5. Payment Gateway – this is connected to acquirer. It is situated between the SET
systemand the financial network of the credit card system for processing
the credit card payment.
6. Certification Authority (CA) – Issues digital signatures to concerned parties.
Working/ Process of SET

Before using SET, both the cardholder and the merchant must register with the CA.
After theregistration process, the working of SET involves many steps, which are as
follows:
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l. The customer browses the merchant's website to evaluate the products offered by the
merchant. He or she then selects the products to be purchased and adds them to the
shopping cart.
2. The customer then uses a single message to communicate with the merchant and
payment gateway. The message has two parts, namely, purchase order, which is used by
the merchant, and card information, which is used by the merchant's bank (acquirer).
3. The card information is then forwarded to the acquirer authorization.
5. If the purchase is authorized, the issuer sends the authorization to the acquirer.
6. A copy of the authorization is also forwarded to the merchant.
7. The merchant completes the order and informs the customer about it.
8. Merchant captures the transaction from its bank.
9. Finally, the credit card invoice is printed by the issuer and provided to the customer.
Time Stamping Protocol (TSP)

➢ It is a Digital version of a notary service.
➢ It proves that a document existed at a specific date and time.
➢ Time Stamping Authority (TSA) is used.

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CHAPTER-6
USER AUTHENTICATION
Authentication Basics:
Authentication
➢ Proof of identity or we can say that “who is Who”.
➢ It is the process of giving someone identity so that he or she can access that particular
application or data.
➢ For e.g.: giving identity-card to a student of an institute.
➢ Authentication is the first step in any cryptographic solution
o –Because unless we know who is communicating, there is no point in
encryption what is being communicated.
➢ Authentication is any process by which a system verifies the identity of a user who
wishes to access it.
➢ Establish trust before communication takes place.
Passwords:
➢ A password is a string of alphabets, numbers and special characters, which is supposed
to be known only to the entity (usually person) that is being authenticated.
➢ Password Based Authentication
o –Clear Text Passwords is the Simplest Password based Authentication
Mechanism.
➢ How it works?
o –Prompt for user ID and Password
o –User enters user ID and Password
o –User ID and Password Validation i.e user-id and password are validated.
o –Authentication Result: Inform user accordingly.
Password Based Authentication:

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Problems with Clear Text/plain-text Passwords:

i)Database contains Passwords in clear text
• It is advised that password should not be stored in clear text in databases.
• The passwords should be stored in encrypted form in database.
ii)Password travel in clear text/ plain-text from user’s computer to the server
• If the attacker breaks into the communication link, he can easily obtain the
clear textpassword.
Message Digests of the Passwords
•Adding Randomness
To improve the security and to detect a replay attack we need to add a bit of randomness to the
earlier schemes.
Steps
1. Storing Message Digests as derived passwords in the user database.
2. User sends a login request
3. Server creates a random Challenge
4. User Signs the Random Challenge with the Message Digest of the Password
5. Server Verifies the Encrypted Random Challenge from the user
Server returns an appropriate message back to the user

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Authentication Tokens:
• It is an extremely useful alternative to a password
•These small devices are usually of the size of a small key chain.
•Usually an authentication Token has the following features
–Processor
–LCD for displaying outputs
–Battery
–Optionally a small keypad for entering information
–Optionally a real-time clock
Each Authentication Token is pre-programmed with a unique number called as a random

seed or justseed.
Step Involved in Authentication Token:
1. Creation of a Token
–Created by the Authentication servers that are designed to use with authentication tokens.
–A unique value i.e. a seed is automatically placed or pre-programmed inside each token by
the server.
–Server also keeps a copy of the seed against the user ID in the user database.
–Seed can be conceptually considered as a user password.
–Difference is that the user password is known to the user, seed value remains unknown to the
user.
2. Use of the Token
–An Authentication Token automatically generates pseudorandom numbers called one- time
passwords.
–One-time passwords are generated randomly by authentication tokens using seed value.
–When a user wants to be authenticated by any server, the user will get a screen to enter user ID
and the latest one-time password.
–The users enter its ID and gets is latest one-time password from the authentication token.
–The user ID and password travels to the server as a part of the login request
–Server verifies using some mechanism that this one-time password is created using the valid
seed value.
3: Server Returns an Appropriate Message back to the User
Finally, the server sends an appropriate message back to the user, depending on whether the
previous operations yielded success or failure.

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Authentication Token Types:

1. Challenge/Response Tokens
2. Time-based Tokens
1. Challenge/Response Tokens:
Step 1: User Sends a Login Request.
In this technique, the user sends the login request only with his/her user id (and
not the one-timepassword).
Step 2: Server Creates a Random Challenge
If the user id is valid, the server now creates a random challenge (a random number,
generated using a pseudo-random number generation technique), and sends it back to
the user.
Step 3: User Signs the Random Challenge with the Message Digest of the Password
This request is then sent to the server as the login request.
Step 4: Server Verifies the Encrypted Random Challenge Received from the User
The server receives the random challenge, which was encrypted with the seed by the
user’s authentication token. In order to verify that the random challenge, the server must
perform an identical operation.
Step 5: Server Returns an Appropriate Message Back to the User
Finally, the server sends an appropriate message back to the user, depending on whether
the operation is success or failure.
2. Time-based Tokens:
Step 1: Password Generation and Login Request:
The seed value and the system time of token, together perform cryptographic algorithm
to generate a password automatically.
Step 2: Server-side Verification:
The server receives the password. It also performs an independent cryptographic
function on the user’s seed value and the current system time to generate its version of
the password. If the two values match, it considers the user as a valid one.
Step 3: Server Returns an Appropriate Message Back to the User:
Finally, the server sends an appropriate message back to the user, depending on
whether the operation is success or failure.
Certificate Based Authentication:

This is based on the Digital Certificates of the user.
• In PKI, the digital certificates are used for secure digital transactions.
•This can be re-used for user authentication as well.
•This is a stronger mechanism as compared to password based authentication
How does Certificate Based Authentication works?
1. Creation, Storage and Distribution of Digital Certificates.
–Certificates are created by CA ( Certificate Authority), sent to user as well as a copy to the
server.

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2. Login Request
–User sends its ID only.
3. Server Creates a Random Challenge
–User ID validity is checked.
–Sends random challenge in plain text to user.
4. User Signs the Random Challenge
–User signs the random challenge received from Server by using its Private Key
–User’s private key is stored in a file in user computer
–To access its private key file, user has to give a correct password
–User sends the signed random challenge to the server
5. Server returns an appropriate message back to the user
Smart Cards:
➢ A smart card is a security token that has an embedded chip.
➢ Smart cards are typically the same size as a driver's license and can be made out
of metal orplastic.
➢ They connect to a reader either by direct physical contact (also known as chip
and dip) orthrough a short-range wireless connectivity standard such as Near Field
Communication (NFC).
➢ It is Portable.
➢ Used to perform cryptographic mechanisms
Use of Smart Cards:
➢ The use of Smart Cards is related to Certificate Based Authentication
➢ This is because the smart cards allows the generation of public-private key pairs within
the card
➢ They also support the storage of digital certificates within the card.
➢ The private key always remain in the smart card in a secure fashion
➢ The public key and the certificate is exposed outside
➢ Also the smart cards are capable of performing cryptographic functions such as
encryption, decryption,message digest creation and signing within the card
➢ T
hus during the certificate based authentication, the signing of random challenge sent by
the server can be performed inside the card

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Problems and issues in Smart Cards:

➢ Lack of standardization and inter-operability between smart cards vendors
➢ Smart card reader are not yet a part of a desktop computer like hard disk drive or floppy
drives
➢ Non-availability of smart card reader driver software
➢ Non-availability of smart card aware cryptographic service software
➢ cost of smart cards and card reader is high.
Biometric Authentication:
Definition:
Biometrics refers to the automatic identification of a person based on his or her
physiological orbehavioral characteristics.
➢ A
biometric device works on the basis of some human characteristics, such as
fingerprints,voice orthe pattern of lines in the iris of your eye
➢ The user database contains a sample of user’s biometric characteristics
➢ During the authentication, the user is required to provide another sample of the
users’ biometriccharacteristic.
➢ This is matched with the one in the database, and if the two samples are same, the user is
considered tobe a valid one.
➢ The samples produced during every authentication process can vary slightly. (e.g. cuts on
the finger)
➢ An approximate match can be acceptable.
Any Biometric Authentication System defines two configurable parameters:
False Accept Ratio (FAR):
• It is a measurement of the chance that a user who should be rejected is actually
accepted byasystem as good enough.
–False Reject Ratio (FRR):
• It is a measurement of the chance that a user who should be accepted as valid
is actuallyrejected by a system as not good enough
•Thus FAR and FRR are exactly opposite to each other.
Biometric characteristics:
1) Physiological
2) Behavioral
Physical biometrics:
➢ Fingerprint
➢ Facial recognition/face location
➢ Hand geometry
➢ Iris scan
➢ Retina scan
Fingerprint recognition
➢ A live acquisition of a person’s fingerprint.
➢ Dots (very small ridges),
➢ Space between two temporarily divergent ridges),
➢ Spurs (a notch protruding from a ridge),

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➢ Bridges (small ridges joining two longer adjacent ridges), crossovers (two ridges that
cross eachother).
Facial Recognition
1. Capture image
2. Find face in image
3. Extract features (store template)
4. Compare templates
5. Declare matches
Hand Geometry
Hand or finger geometry is an automated measurement of many dimensions of the hand and
fingers.
Iris recognition
Iris scanning measures the iris pattern in the colored part of the eye.
Retina recognition
Images back of the eye and compares blood vessels with existing data.
Behavioral biometrics
➢ Speaker/ voice recognition.
➢ Signature/ handwriting.
➢ Keystroke/ patterning.
Speaker / Voice Recognition
➢ Voice or speaker recognition uses vocal characteristics to identify individuals
using a pass-phrase.
➢ A telephone or microphone can serve as a sensor.
Signature Verification
➢ An automated method of measuring an individual’s signature.
➢ This technology examines speed, direction, and pressure of writing; the time that the
stylus is inand out of contact with the “paper’’.
Keystroke dynamics
➢ It is an automated method of examining an individual’s keystrokes on a keyboard.
➢ This technology examines such dynamics as speed and pressure, the total time
taken to typeparticular words, and the time elapsed between hitting certain keys.
APPLICATIONS:
➢ Prevent unauthorized access to ATMs, Cellular phones Desktop PCs.
➢ Criminal identification.
➢ In automobiles biometrics can replace keys with keyless entry devices.
➢ Airport security.

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CHAPTER-7
NETWORK SECURITY AND VPN
TCP/IP Protocol Suite:
• The TCP/IP protocol suite was developed prior to the OSI model. Therefore,
the layers in the TCP/IP protocol suite do not exactly match those in the OSI
model.
• TCP/IP protocol suite is made of five layers: Application Layer,
Transport Layer,Internet Layer, Network Access Layer
• TCP/IP is a hierarchical protocol made up of interactive modules, each of
which provides a specific functionality; however, the modules are not
necessarily interdependent.
• At the transport layer, TCP/IP defines three protocols: Transmission
Control Protocol (TCP), User Datagram Protocol (UDP), and Stream
Control Transmission Protocol (SCTP).
• At the Internet layer, the main protocol defined by TCP/IP is the Internet
Protocol (IP);there are also some other protocols that support data movement in this
layer.
TCP/IP Layers:
TCP segment format:
A packet in TCP is called a segment. The segment consists of a header of 20 to 60

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bytes, followed by data from the application program. The header is 20 bytes if there
are no options and up to 60 bytes if it contains options.
Source port address:
This is a 16-bit field that defines the port number of the application program in the
host that is sending the segment. This serves the same purpose as the source port
address in the UDP.
Destination port address:

This is a 16-bit field that defines the port number of the application program in the
host that is receiving the segment. This serves the same purpose as the destination
port address in the UDP.
Sequence number:
This 32-bit field defines the number assigned to the first byte of data contained in this
segment. As TCP is a stream transport protocol. To ensure connectivity, each byte to
be transmitted is numbered. The sequence number tells the destination which byte in
this sequence is the first byte in the segment. During connection establishment each
party uses a random number generator to create an initial sequence number (ISN),
which is usually different in each direction.
Acknowledgment number:
This 32-bit field defines the byte number that the receiver of the segment is expecting
to receive from the other party. If the receiver of the segment has successfully
received byte number x from the other party, it Returns x+1 as the acknowledgment
number.
Header length:
This 4-bit field indicates the number of 4-byte words in the TCP header. The length
of the header can be between 20 and 60 bytes. Therefore, the value of this field is
always between 5 (5 *4=20) and 15 (15*4=60).
Reserved: This is a 6-bit field reserved for future use.
Control:
This field defines 6 different control bits or flags . One or more of these bits can be
set at a time. These bits enable flow control, connection establishment and
termination, connection abortion, and the mode of Flags from left to right:
Window size:
This field defines the window size of the sending TCP in bytes. Note that the length
of this field is 16 bits, which means that the maximum size of the window is 65,535
bytes.
Checksum:
The 16-bit checksum field is used for error-checking of the header and data.
Urgent pointer:
if the URG flag is set, then this 16-bit field is an offset from the sequence number

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indicating the lasturgent data byte.
IP DATAGRAM FORMAT:
• Packets in the network (internet) layer are called datagram.
• A datagram is a variable-length packet consisting of two parts: header and data.
• The header is 20 to 60 bytes in length and contains information essential
to routing anddelivery.
IP header format:
Version (VER):
This 4-bit field defines the version of the IP protocol. Currently the version is 4(IPv4).

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Header length (HLEN):

This 4-bit field defines the total length of the datagram header in 4-byte words. This
field is needed because the length of the header is variable (between 20 and 60 bytes).
When there are no options, the header length is 20 bytes, When the option field is at
its maximum size(i.e. 60)
Service type (TOS):
It defines how the datagram should be handled. Part of the field was used to define
the precedence of the datagram; the rest defined the type of service (low delay, high
throughput, and so on).
Total length:
It defines the total length of the datagram including the header in bytes. It is a 16-bit
number so maximum IP size is 216 bytes.
Identification:
This 16-bit field identifies a datagram originating from the source host. The
combination of the identification and source IP address must uniquely define a datagram as
it leaves the source host.
Flags:
This is a three-bit field. The first bit is reserved (not used). The second bit is called
the do not fragment bit. If its value is 1, the machine must not fragment the datagram.
If its value is 0, the datagram can be fragmented if necessary. The third bit is called
the more fragment bit. If its value is 1, it means the datagram is not the last fragment;
there are more fragments after this one. If its value is 0, it means this is the last or
only fragment.
Fragmentation offset:
This 13-bit field shows the relative position of this fragment with respect to the whole
datagram.
Time to live:
A datagram has a limited lifetime in its travel through an internet. This field was
originally designed to hold a timestamp, which was decremented by each visited
router. The datagram was discarded when the value became zero.
Protocol:
This 8-bit field defines the higher-level protocol that uses the services of the
IP layer. An IP datagram can encapsulate data from several higher level protocols
such as TCP, UDP, ICMP, and IGMP. This field specifies the final destination
protocol to which the IP datagram should be delivered.

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Header Checksum:
This fields represents a value that is calculated using an algorithm covering all the
fields in header. This field is used to check the integrity of an IP datagram.
Source address:
This 32-bit field defines the IP address of the source. This field must remain
unchanged during the time the IP datagram travels from the source host to the
destination host.
Destination address:
This 32-bit field defines the IP address of the destination. This field must remain
unchanged during the time the IP datagram travels from the source host to the
destination host.
Firewall:
Firewalls can be used to protect a local system or network of systems (Internal
Network) fromOut-side networks (Internet) from security threats.
➢ Special type of router.
➢ Frequently used to prevent unauthorized internet users from accessing private
networksconnected to the internet, especially intranets.
➢ Controls transmission between internal and external networks. i.e. All
messages entering or leaving the intranet pass through the firewall, which
examines each message and blocks those that do not meet the specified
security criteria.
➢ It is essentially a barrier between two networks that evaluates all incoming or
outgoing traffic to determine whether or not it should be permitted to pass to
the other network. i.e. decides what to allow/disallow.
➢ Can be implemented in both hardware and software, or a combination of both.
➢ At broad level, there are two kind of attacks:
• Most corporations have large amounts of valuable and confidential
data in their networks. Leaking of this critical information to
competitors can be a great setback.
• Apart from the danger of the insider information leaking out, there is a
great danger of the outside elements (such as viruses and worms)
entering a corporate network to create disaster.

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Firewall characteristics/ Design Goals of Firewalls:

A firewall is defined as collection of components placed between two networks that
collectively haveFollowing characteristics:
All traffic from inside to outside, and vice versa, must pass through the firewall.
This is achieved by physically blocking all access to the local network except via
thefirewall.Only authorized traffic, as defined by the local security policy, will be allowed
to pass.
Limitations of Firewalls:
The firewall itself must be strong enough, so as to render attacks on it useless.

o Firewalls cannot stop users from accessing malicious websites, making it vulnerable to
internal threats or attacks.
o Firewalls cannot protect against the transfer of virus-infected files or software.
o Firewalls cannot prevent misuse of passwords.
o Firewalls cannot protect if security rules are misconfigured.
o Firewalls cannot protect against non-technical security risks, such as social engineering.
o Firewalls cannot stop or prevent attackers with modems from dialing in to or out of the
internal network.
o Firewalls cannot secure the system which is already infected.
How Firewall Works
➢ Firewall match the network traffic against the rule set defined in its table. Once the
rule is matched, associate action is applied to the network traffic.
➢ For example, Rules are defined as any employee from HR department cannot access
the data from code server and at the same time another rule is defined like system
administrator can access the data from both HR and technical department.
➢ Rules can be defined on the firewall based on the necessity and security policies of
the organization.
From the perspective of a server, network traffic can be either outgoing or incoming.
Firewall maintains a distinct set of rules for both the cases. Mostly the outgoing
traffic, originated from the server itself, allowed to pass.
➢ Still, setting a rule on outgoing traffic is always better in order to achieve more
security and prevent unwanted communication.
➢ Incoming traffic is treated differently. Most traffic which reaches on the firewall is
one of these three major Transport Layer protocols- TCP, UDP or ICMP. All these
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types have a source address and destination address. Also, TCP and UDP have port
numbers. ICMP uses type code instead of port number which identifies purpose of
that packet.
Types of Firewall
Firewalls are generally of two types: Host-based and Network-based.
1. Host- based Firewalls : Host-based firewall is installed on each network node which
controls each incoming and outgoing packet. It is a software application or suite of
applications, comes as a part of the operating system. Host-based firewalls are needed
because network firewalls cannot provide protection inside a trusted network. Host firewall
protects each host from attacks and unauthorized access.
2. Network-based Firewalls: Network firewall function on network level. In other words,
these firewalls filter all incoming and outgoing traffic across the network. It protects the
internal network by filtering the traffic using rules defined on the firewall. A Network
firewall might have two or more network interface cards (NICs). A network-based firewall is
usually a dedicated system with proprietary software installed.
Virtual Private Network (VPN):
➢ A VPN is thus a mechanism to simulate a private network over a public
network, such as theInternet.
➢ The term virtual signifies that it depends on the use of virtual connections.
➢ These connections are temporary and do not have any Physica1 presence.
They are made upof packets.
➢ Uses the Internet as if it is a private network.
➢ Far less expensive than a leased line.
➢ Uses IPSec protocol.
VPN Architecture:

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We have shown two networks, Network I and Network 2. Network l connects to the
Internet via a firewall named Firewall I. Similarly, Network 2 connects to the Internet with
its own firewall 2.
The two firewalls are virtually connected to each other via the Internet. We have shown
this with the help of a VPN tunnel between the two firewalls.
Let us understand how the VPN protects the traffic passing between any two hosts on the
two different networks. For this, let us assume that host X on Network 1 wants to send a
data packet to host Y on Network 2. This transmission would work as follows.
1.Host X creates the packet, inserts its own IP address as the source address and the IP
address of host Y as the destination address. This is shown in figure. It sends the packet
using the appropriate mechanism.
2. The packet reaches firewall 1. As we know, firewall 1 now adds new headers to the
packet. In these new headers, it changes the source IP address or the packet from that of
host X to its own address (i.e. the IP address of Firewall 1, say F1). It also changes the
destination IP address of the packet from that of host Y to the IP address of Firewall 2. say
F2). This is shown in Fig. It also performs the packet encryption and authentication,
depending on the settings and sends the modified packet over the Internet.

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3. The packet reaches firewall1 2 over the internet, via one more routers, as usual, Firewall
2 discards the outer header and performs the outer header and performs appropriates
decryption and other cryptographic functions as necessary. This yields the original packets,
as was created by host X in step 1. This is shown in fig. It then takes a look the plain text
contents of the packets and realizes that the packet is meant for host Y. Therefore, it
delivers the packet to host Y.
IP Security (IPSec) Protocols:
➢ Before IPSec was initiated, the IP packets were prone to security failure.
➢ The technology that brings secure communications to the internet protocol
layer or networklayer is called IP Security, commonly abbreviated IPSec.
➢ IPSec is a set of services and protocols that provide a complete security
solution for an IPnetwork.
➢ It is a collection of protocols designed by the Internet Engineering Task
Force (IETF) toprovide security in the internet layer.
➢ It can be used in protecting data flows between a pair of host(host-to-host),
between a pair of security gateways(network-to-network), or between a
security and a host(network-to-host).
Applications of IP security: (Important)
➢ IPSec provides the capability to secure communications across a LAN, across

private and public WANs, and across the Internet. Examples of its use
include:
Secure remote access over the Internet:
➢ An end user whose system is equipped with IP security protocols can make a
local call to an Internet Service Provider (ISP) and gain secure access to a
company network. This reduces travelling cost and time wastage of
employees and telecommuters.

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Secure branch office connectivity over the Internet:

➢ A company can build a secure virtual private network over the Internet or
over a public WAN. This enables connecting all the branches of company.
That will save the costs of creating a private network and network
management overhead.
Establishing extranet and intranet connectivity with partners:
➢ IPSec can be used to secure communication with other organizations,
ensuring authentication and confidentiality and providing a key exchange
mechanism.
Enhancing electronic commerce security:
➢ Even though some Web and electronic commerce applications have built-in
security protocols, the use of IPSec enhances that security.
Benefits of IP security: (Important)
➢ IPSec can be transparent to end users.

• There is no need to train users on security mechanisms.
• No need to issue or cancel keys to and from the users.
➢ When IPSec is implemented in a firewall or router, it provides strong
security that can beapplied to all traffic crossing the perimeter.
• Traffic within a company or workgroup does not have to use IPSec,
thus it minimizethe overhead of security-related processing.
➢ IPSec in a firewall is resistant to bypass if all traffic from the outside must
use IP and thefirewall is the only means of entrance from the Internet into the
organization.
➢ Since IPSec is implemented at network layer, there is no need to make any
changes at theupper layers such as transport layer (TCP, UDP) and
application layer.
➢ IPSec can provide security for individual users if needed. Individuals can
set up a securevirtual sub-network within an organization for sensitive
applications.

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IP security services: (Important)
➢ IPSec provides security services at the IP layer.

➢ Two protocols are used to provide security:
▪ An authentication protocol designated by the header of the protocol,
AuthenticationHeader (AH).
▪ And a combined encryption/ authentication protocol designated by
the format of thepacket for that protocol, Encapsulating Security
Payload (ESP).
➢ Lists the following services:

1. Access control
2. Connectionless integrity
3. Data origin authentication
4. Rejection of replayed packets (a form of partial sequence integrity)
5. Confidentiality (encryption)

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References:
1. Cryptography & Network security by A. Kahate
2. Cryptography & Network Security Principals and Practices by W.Stallings
3. Cryptography & Information security by Pachghare
4. https://en.wikipedia.org
5. https://nptel.ac.in
6. https://www.geeksforgeeks.org/

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CRYPTOGRAPHY & NETWORK SECURITY

S.NO CHAPTER NAME PAGE NO

2 Cryptography Concepts 8-16

3 Symmetric & Asymmetric Key 17-30

4 Digital Certificate & Public Key 31-37

5 Internet Security Protocols 38-42

6 User Authentication 43-49

7 Network Security & VPN 50-60

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NEED FOR SECURITY:

Computer security is important because it keeps your information protected. It's

SECURITY ATTACKS, SERVICES AND MECHANISMS:

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PRINCIPLES OF SECURITY/ SECURITY SERVICES:

The classification of security services are as follows:

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TYPES OF SECURITY ATTACK:

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➢ A denial-of-service (DoS) is a form of cyberattack that prevents legitimate users from

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➢ It is the technique of decoding messages from a non-readable format back to a readable

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Cryptology: Cryptology is a combination of Cryptography and Cryptanalysis.

There are several techniques. They are:

Modified version of Caesar Cipher

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Polyalphabetic Substitution Cipher

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EXAMPLE OF ENCRYPTION AND DECRYPTION IN PLAYFAIR:

Encryption process – it consists of following steps:

1. Before initiating the encryption, break the plain text in

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1) Message is: MY NAME IS ATUL It

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Now translating numbers into alphabets, we get:

It uses a simple algorithm,

1. Writing down the plaintext message into a sequence of diagonals.

Plain Text: meet me Tomorrow

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Simple Columnar Transposition Technique:

Let’s see an example:

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Now, we decide to go with a previous order that is 4,1,3,2.

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Encryption and Decryption:-

Symmetric and Asymmetric Key Cryptography:

Symmetric key Cryptography:-

Asymmetric key Cryptography:-

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Electronic Code book (ECB) Mode:

➢ ECB is a simplest and

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Cipher Block Chaining (CBC) Mode: