1.1 Introduction about Cryptography and network security
1. SUBJECT CODE
IV VII
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UNIT NO 1
INTRODUCTION
● Definition
● Terminology
● Applications
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY
(Common to CSE & IT)
20ITPC701
5. Appl
icati
on
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Introduction
Cryptography: Cryptography is a method of storing and transmitting data in a particular form so
that only those for whom it is intended can read and process it. Cryptography is closely related
to the disciplines of cryptology and cryptanalysis. Cryptography includes techniques such as
microdots, merging words with images, and other ways to hide information in storage or transit.
The art and science of concealing the messages to introduce
secrecy in information security is recognized as
cryptography.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
6. Definition
Cryptography is the science of using mathematics to
encrypt and decrypt data.
Phil Zimmermann
Cryptography is the art and science of keeping messages secure.
Bruce Schneier
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
7. Terminologies
A message is plaintext (sometimes called cleartext). The process of
disguising a message in such a way as to hide its substance is encryption. An
encrypted message is ciphertext. The process of turning ciphertext back into
plaintext is decryption.
A cipher (or cypher) is an algorithm for performing encryption or decryption
—a
series of well-defined steps that can be followed as a procedure.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
8. Terminology
A cryptosystem is an implementation of cryptographic techniques
and their accompanying infrastructure to provide information
security services. A cryptosystem is also referred to as a cipher
system. The various components of a basic cryptosystem are as
follows −
§Plaintext §Encryption Algorithm §Ciphertext §Decryption Algorithm
§Encryption Key §Decryption Key
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Terminology
Plaintext: Message that is going to be transmitted or stored is plain text. Anyone
can read plaintext. Encryption: The method by which we can hide the actual
9. meaning of plaintext is called Encryption. Cipher text: The result of encryption
which results in unreadable gibberish is called Cipher text.
Decryption: The method by which the original meaning of cipher text can be
recovered is called Decryption. Simply the process of converting Cipher text to
plaintext is called Decryption.
Key: Key is the secret piece of information which is used for encryption and decryption in
Cryptography.
Cryptanalysis: The science of retrieving the plain text from cipher without
knowing the key. Cryptanalysts: The people who practice cryptanalysis
are called Cryptanalyst.
Cryptosystem: The combination of algorithm, key, and key management functions
used to perform cryptographic operations.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Cryptology
While cryptography is the science of securing data, cryptanalysis is the
science of analyzing and breaking secure communication. Classical
10. cryptanalysis involves an interesting combination of analytical reasoning,
application of mathematical tools, pattern finding, patience, determination,
and luck. Cryptanalysts are also called attackers. Cryptology embraces
both cryptography and cryptanalysis.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
History of Cryptography
➢ As civilizations evolved, human beings got organized in
tribes, groups, and kingdoms. This led to the emergence of
ideas such as power, battles, supremacy, and politics.
11. ➢ These ideas further fueled the natural need of people to
communicate secretly with selective recipient which in
turn ensured the continuous evolution of cryptography
as well.
➢ The roots of cryptography are found in Roman and Egyptian
civilizations.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
•Hieroglyph
•The first known evidence of cryptography can be traced to the use
of ‘hieroglyph’. Some 4000 years ago, the Egyptians used to
communicate by messages written in hieroglyph.
12. 20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE
& IT)
Caesar Shift Cipher
➢ Caesar Shift Cipher, relies on shifting the
letters
of a message by an agreed number (three
was a
common choice), the recipient of this
message
would then shift the letters back by the same
13. number and obtain the original message.
➢ The Caesar cipher is named after Julius Caesar ,
who used it with a shift of three to protect
messages of military significance.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Caesar Shift Cipher
14. Encryption Decryption
PLAINTEXT :
CYPHERTEXT :
internet society ghana
chapter lqwhuqhw vrflhwb
jkdqd fkdswhu
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Goal and Services
Goal: The primary goal of cryptography is to secure important data on
the hard disk or as it passes through a medium that may not be secure
itself. Usually, that medium is a computer network.
15. Services: Cryptography can provide the following services:
•Confidentiality (secrecy)
•Integrity (anti-tampering)
•Authentication
•Non-repudiation.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Confidentiality (secrecy)
•Ensuring that no one can read the message except the
intended receiver
•Data is kept secret from those without the proper
credentials, even if that data travels through an
insecure medium
16. Integrity (anti-tampering)
•Assuring the receiver that the received message has
not been altered in any way from the original.
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY (Common to CSE & IT)
Authentication
Cryptography can help establish identity for
authentication purposes The process of proving
one's identity. (The primary forms of
host-to-host authentication on the
Internet today are name
based or address-based, both of which are
notoriously weak.)
Non-repudiation
17. A mechanism to prove that the sender really sent this message
20ITPC701
CRYPTOGRAPHY AND NETWORK SECURITY
(Common to CSE & IT)1. ATM
2.
Email-
Pass
words
3. E-
Paym
