Cryptography and Network Security

A Very Hearty Welcome
To Everyone

CONTENTS1. HISTORY
2. INTRODUCTION
2.1 TYPES OF CRYPTOGRAPHY
2.1.1 CODES AND CODE BOOKS
2.1.2 STEGANOGRAPHY
2.1.3 CIPHERS
2.2 COMPUTER CIPHERS AND ENCRYPTION
2.3 CRYPTANALYSIS
3. SECURITY MECHANISMS
3.1 ENCRYPTION
3.2 DIGITAL SIGNATURES
3.3 HASH ALGORITHMS
4. TYPES OF ENCRYPTION
5. SIZE OF ENCRYPTION KEY
6. DIFFERENCE BETWEEN CRYPTOGRAPHY AND STEGNOGRAPHY
7. CRYPTOGRAPHY IN DAILY LIFE
8. ADVANTAGES & DISADVANTAGES
9. PERSONAL COMPUTERS vs COMPUTER HACKERS
9.1 CHALLENGES
9.2 CONCLUSION

1.HISTORY
• How it is used from 1800's to present year.
• Using of cryptography from sending secret messages
between two nations during wars to the modern network
security.
• There are three eras in the history of Cryptography:
– The Manual era
– The Mechanical era
– The Modern era
• Manual era refers to Pen and Paper Cryptography and
dates back to 2000 B.C.
• Mechanical era refers to the invention of cipher machines.
• The Modern era of cryptography refers to computers.

2.INTRODUCTION
• CRYPTOGRAPHY:
“The field of study related to encoded
information (comes from Greek word for
“secret writing”)”.
(or)
• Cryptography is the study of
Secret (crypto-) writing (- Graphy)

COMPONENTS
• The two main components of cryptography
are:
1.ENCRYTION
2.DECRYPTION
Encryption or Encipher or Encode
The process of converting plaintext into cipher text.
Decryption or Decipher or Decode
The process of converting cipher text into plaintext.

BASIC CONCEPTS
Plaintext
The original intelligible message.
Cipher text
The transformed message.
Cipher
An algorithm for transforming an intelligible
message into unintelligible by transposition
and/or substitution

BASIC CONCEPTS
Key
Some critical information used by the cipher,
known only to the sender & receiver.
 Encipher (encode)
The process of converting plaintext to cipher
text.
Decipher (decode)
The process of converting cipher text back into
plaintext.

2.1.1 CODES AND CODEBOOKS
• A well-constructed code can represent phrases and
entire sentences with symbols, such as five-letter
groups, and is often used more for economy than for
secrecy.
• A properly constructed code can give a high degree of
security, but the difficulty of printing and distributing
codebooks—books of known codes—under conditions
of absolute secrecy limits their use to places in which
the books can be effectively guarded.
• In addition, the more a codebook is used, the less
secure it becomes.

2.1.2 STEGANOGRAPHY
• Steganography is a method of hiding the
existence of a message using tools such as
invisible ink, microscopic writing, or hiding
code words within sentences of a message
(such as making every fifth word in a text part
of the message).
• Cryptographers may apply steganography to
electronic communications.
• This application is called transmission security.

2.1.3 CIPHERS
• Ciphers are the secret codes used to encrypt
plaintext messages.
• There are two general types of ciphers.
-Substitution ciphers require a cipher alphabet
to replace plaintext with other letters or
symbols.
-Transposition ciphers use the shuffling of
letters in a word to make the word
incomprehensible.

2.2 COMPUTER CIPHERS &
ENCRYPTION
• As more and more information is transferred over computer
networks, computer scientists continue to develop more secure,
complex algorithms.
• In 1997 the NIST(National Institute of Standards and Technology)
began coordinating development of a replacement for DES
called Advanced Encryption Standard (AES).
• AES will use a more complex algorithm, based on a 128-bit
encryption standard instead of the 64-bit standard of DES.
• This 128-bit algorithm will make AES impossible to decrypt with
current technology.
• Another encryption system based on 128-bit segments is called
International Data Encryption Algorithm, or IDEA.
• The Swiss Federal Institute of Technology developed the IDEA
standard in the 1990s.
• Computer scientists have also proposed alternatives, which use
two types of keys, a public key and a private key.

2.3 CRYPTANALYSIS
• Cryptanalysis: The study of encryption and
encrypted messages, with the goal of finding the
hidden meanings of the messages. (cryptanalyst)
• In other words, cryptanalysis is the opposite of
cryptography.
• It is the breaking of ciphers.
• Today’s cryptanalysis is measured by the number
and speed of computers available to the code
breaker.

3.1 ENCRYPTION
• Even if an attacker captures the data , the attacker will
not be able to manipulate it in any meaningful way.
• Roughly speaking, there are two different broad types of
encryption that are used on computers today
– Symmetric encryption relies on keeping keys totally
secret
– Asymmetric encryption actually publicizes one key,
but keeps some information private also
• Neither is really “better” - they just use different
principles.
• In reality, both are vulnerable to attacks.

Symmetric or private key cryptography
• Symmetric algorithms use a single key shared by
two communicating parties.
• The same key is used for both encryption and
decryption
• Most common type is called a block cipher
– Processes the plaintext in fixed sizes blocks
• Examples include DES, 3DES, AES,IDEA
• All require a secret key which is known by both
parties in the communication
• Main issue here: need to securely swap the key.

DES: Data Encryption Standard
• Adopted in 1977 by National Bureau of Standards (now
NIST)
• Divides message into blocks of 64 bits, and uses a key of 56
bits
• Key idea for this: XOR the data with the key
– (Remember XOR? How did it work?)
• In July 1998, DES was officially cracked by a machine built
by the Electronic Frontier Foundation (EFF)
– Total cost: under $250,000
– Total time: 6-8 months
• They then published the details of their approach, which
essentially was a brute force attack(Trying all key values in
the key space)
• Note: 56 bits means 256 keys to try
• Also, not as easy as just trying.

3DES
• Effort to salvage DES
• Main algorithm: repeat DES 3 times with
different keys (so key size is now 168 bits)
• Still very secure - brute force attacks would
take too long, and that is the only way to
attack this algorithm
• Main problem: SLOW

Advanced Encryption Standard (AES)
• In 1997 the NIST began coordinating development of a
replacement for DES called Advanced Encryption Standard
(AES).
• AES will use a more complex algorithm, based on a 128-bit
encryption standard instead of the 64-bit standard of DES.
• This 128-bit algorithm will make AES impossible to decrypt
with current technology.
• Designed in response to a call by NIST in 1998, and officially
adopted in 2001
• Block length is 128 bits, and keys can be 128, 192, or 256 bits.
• Essentially, proceeds in 4 rounds (which are repeated):
– Substitute bytes
– Permute
– Mix columns
– Add round key

Stage 1: substitute bytes
• AES computes a matrix which maps every 8-
bit value to a different 8-bit value
• Computed using properties of finite fields (go
take some math classes to learn more about
this)

Stage 2: permute
• AES then shifts each row, where each row is
shifted a different amount

Stage 3: Mix columns
• Here, the 4 bytes in each column are
combined using a linear transformation
• Essentially, the output of any byte depends on
all the input bytes, so this “mixes” them
together

Stage 4: Add round key
• Use XOR to combine the key with the message

IDEA
• Another encryption system based on 128-bit segments is
called International Data Encryption Algorithm, or IDEA.
• In cryptography, the International Data Encryption
Algorithm (IDEA), originally called Improved Proposed
Encryption Standard (IPES).
• IDEA operates on 64-bit blocks using a 128-bit key.
• IDEA derives much of its security by interleaving operations
from different groups — modular addition and multiplication,
and bitwise eXclusive OR (XOR) — which are algebraically
"incompatible" in some sense.
• Bitwise eXclusive OR (denoted with a blue circled plus ⊕).
• Addition modulo 216 (denoted with a green boxed plus ⊞).
• Multiplication modulo 216+1 (denoted by a red circled dot ⊙).

ASSYMETRIC OR
PUBLIC-KEY CRYPTOGRAPHY
• Public-key cryptography, also known
as asymmetric cryptography, which requires two
separate keys, one of which is secret (or private)
and one of which is public.
• Mathematically related key pairs for encryption
and decryption.
• Public and private keys.
• The public key is used to encrypt plaintext or to
verify a digital signature; whereas the private key
is used to decrypt cipher text or to create a digital
signature.

ASSYMETRIC OR
PUBLIC-KEY CRYPTOGRAPHY
• Asymmetric encryption means there will be two
keys for every user, one is Public key and another
one is Private key.
• Public key is know to any one and private key is
only known to you.
• If you want to send a message to any other you
should encrypt the message with public key of
that person, so that, that person only decrypt the
cipher text he received using private key.
• Asymmetric key algorithm is used in face book.

PUBLIC KEY CRYPTOGRAPHY
SECRET
(or)
PRIVATE
PUBLIC
ASSYMETRIC
CRYPTOGRAPHY
Asymmetric Cryptography

3.2 DIGITAL SIGNATURES
• A digital signature (not to be confused with a digital certificate)
is an electronic (it easy to add your e-signature)
• Used to authenticate the identity of the sender of a message
or the signer of a document, and possibly to ensure that the
original content of the message or document that has been
sent is unchanged.
• Digital signatures can be automatically time-
stamped(declaring time when the folder is created).
• The ability to ensure that the original signed message arrived
means that the sender cannot easily repudiate(reject) it later.
USE: These days, no one is going to stand at a fax machine to
wait for approvals. Being able to electronically sign a PDF.

DIGITAL SIGNATURES
Original text signing signed text verifying verified text

3.3 HASH FUNCTIONS
• A cryptographic hash function is a hash function which is
considered practically impossible to invert, that is, to recreate
the input data from its hash value alone.
• The input data is often called the message, and the hash value
is often called the message digest or simply the digest.
• The ideal cryptographic hash function has four main
properties:
1.It is easy to compute the hash value for any given message
2.It is infeasible to generate a message that has a given hash
3.It is infeasible to modify a message without changing the
hash
4.It is infeasible to find two different messages with the
same hash.

HASH FUNCTIONS
• Cryptographic hash functions have many information
security applications, notably in digital
signatures, message authentication codes (MACs), and
other forms of authentication( authentication is the
process of actually confirming that identity).
• Indeed, in information security contexts, cryptographic
hash values are sometimes called (digital) fingerprints,
or just hash values, even though all these terms stand
for more general functions with rather different
properties and purposes.

HASH FUNCTIONS
Note that even small changes in the source input (here in the word "over")
drastically change the resulting output, by the so-called avalanche effect.

4.FORMS OF ENCRYPTION
 SUBSTITUTION CIPHERS
 CAESAR CIPHERS
 TRANSPOSITION CIPHERS

SUBSTITUTION CIPHERS
• A cipher that substitutes one character with
another.
• These can be as simple as swapping a list, or
can be based on more complex rules.
• These are NOT secure anymore, but they used
to be quite common.

Caesar Cipher
 2000 years ago Julius Caesar used a simple substitution cipher,
now known as the Caesar cipher.
 Replace each letter of message by a letter a
fixed distance away (use the 3rd letter on)
 Reputedly used by Julius Caesar
 Example:
L FDPH L VDZ
I CAME I SAW
D O L H W
A L I E T
 The mapping is
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C

Transposition CipherT O D A Y
+ I S + M
O N D A Y
•Write the letters in a row of five, using '+' as a blank. Encrypt by starting
spiraling inward from the top left moving counter clockwise.
•Encrypt(TODAY IS MONDAY) gives T+ONDAYMYADOIS+
•Decrypt by recreating the grid and reading the letters across the row.
•The key are the dimension of the grid and the route used to encrypt the
data.
• The Rail Fence cipher is a form of transposition cipher .
•In the rail fence cipher, the plaintext is written downwards on successive
"rails" of an imaginary fence, then moving up when we get to the bottom.
The message is then read off in rows. For example, using three "rails" and a
message of 'WE ARE DISCOVERED. FLEE AT ONCE', the cipherer writes out:
• W . . . . . E . . . .C . . . . . . R . . . L . . . . . .T . . . . . E
. E . R . D . .S . O . . E . . E . F . E . . A . O . . C .
. . A . . . I . . . . . V . . . . . D . . . . E . . . . N . .
Then reads off:
• WECRL TEERD SOEEF EAOCA IVDEN

5.SIZE OF ENCRYPTION KEY
• There are several size of encryption keys:
– 64 bit encryption – java, c#, php(Hypertext Processor )
– 128 bit encryption-internet explorer, java, c#, Firefox, android, oracle,
virtualbasic (vb) vb.net, ASP.net
• Active Server Pages ASP.NET is an open source server-side Web
application.
– 256 bit encryption-java, c#, Internet explorer8, php, vb.net
– 512 bit encryption-php, c#
– 1024 bit encryption-c#
• C# is a programming language that is derived from C programming
language andC++ programming language.
• C# is uniquely designed to be used in .NET platform.
• Number indicates the size of the key used to encrypt the
message.
• MD5(message digest) hashed key algorithm is used in
WhatsApp.

6.DIFFERENCE BETWEEN
CRYPTOGRAPHY AND STEGNOGRAPHY
• Cryptography is the study of hiding information, while
Stegnography deals with composing hidden messages so that
only the sender and the receiver know that the message even
exists.
• In Stegnography, only the sender and the receiver know the
existence of the message, whereas in cryptography the
existence of the encrypted message is visible to the world.
• Due to this, Stegnography removes the unwanted attention
coming to the hidden message.
• Cryptographic methods try to protect the content of a
message, while Steganography uses methods that would hide
both the message as well as the content.
• By combining Stegnography and Cryptography one can
achieve better security.

7.CRYPTOGRAPHY IN DAILY LIFE
• A very simple example arises from family lives.
• A family can be considered like a small community
consisting of 2-10 members, depending on what you
call “family”. You go somewhere with your family.
• You need to ask your father when you are going to your
cabana(a small hut built) which stands in a very
beautiful place, and you don’t want others to find out
you’re going there.
• You just ask your old man: “When do we go there?”
And that’s it. You just used cryptography! Why? Only
because others who heard what you’ve just said don’t
know what you’re talking about.

 Emails :
We live in a modern world. We must deliver emails, either for
business, to friends, companies, famous people whose
address we have.
• People deliver around 210 billion emails daily ! When you
deliver an email, it has to get trough the internet - a giant
network consisting of a lot of computers most of which are
unprotected and attackable.
• A lot of people like to steal data from others, sometimes only
for fun, but danger comes when it’s about something else.
• How do emails get protected while they are being sent?
That is done by using data encryption. Generally there would
be two methods for this security.
 PGP (Pretty Good Privacy)-name of a computer program
and the protocol(data transmission between computers)
 MIME Security.

What is MIME?
• Multipurpose Internet Mail Extensions, a
specification for formatting non-ASCII messages
so that they can be sent over the Internet.
• Many e-mail clients now support MIME, which
enables them to send and receive graphics, audio
and video files via the internet mail system.
• In addition, MIME supports messages in
character sets other than ASCII.
• Examples: GIF graphic files.

7.CRYPTOGRAPHY IN DAILY LIFE
• The other solution worked for big distances too.
Assume it was night time, and a ship was sailing
on the sea or on the ocean, fighting a huge storm.
• So if there were people on the ground, 1-2
kilometers away from the ship location, they
could have used a flashlight to guide the ship
safely to the shore.
• The strong point of the flashlight Morse coding
was that it worked even during daytime.

8.ADVANTAGES &
DISADVANTAGES
Advantages of Cryptography are :-
• It hides the message and your privacy is safe.
• No one would be able to know what it says unless
there's a key to the code.
• You can write what ever you want and how ever
you want (any theme any symbol for the code) to
keep your code a secret.
• You are able to use Cryptography during lessons
without the teacher knowing. (BUT WILL TAKE
LONG TO MAKE THE CODE, TO FIGURE IT OUT
AND TO MAKE THE KEY)

ADVANTAGES &
DISADVANTAGES
Disadvantages of Cryptography are:-
• Takes a long time to figure out the code.
• It takes long to create the code.
• If you were to send a code to another person
in the past, it will take long to get to that
person.
• OVERALL CRYPTOGRAPHY IT'S A LONG
PROCESS.

9.PERSONAL COMPUTER vs
COMPUTER HACKERS
• For personal computer users, cryptography
software can perform a lot of different tasks.
-For example, e-mail encryption programs.
• Computer hackers often employ cryptography
software to gain access to other computers. For
example, some programs can uncover passwords
to various networks.
-Hackers can also use software, such as file
shredders(File Shredder is powerful application
to remove unwanted files from your computer
beyond recovery).

9.1 CHALLENGES
• There are two kinds of cryptography in this
world:
cryptography that will stop your kid sister
from reading your files.
cryptography that will stop major
governments from reading your files.

9.2 CONCLUSION
• We’ve seen a lot of different areas of where
cryptography is used in our days or in the past.
• As a common man, you can easily observe
cryptography everywhere around yourself!
• It’s so amazing how far science got, and it keeps going
and going, getting a lot of new knowledge every day.
• Emails and Internet are used by more and more people
every day.
• We just can’t imagine our lives without it. And all of
these work and get secured based on cryptography.

I am
only
Thankful
to
everyone
for being
so kind
to
Me.

THANK YOU GUYS!!!
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