Cryptography is the art and science of securing communication and information by encrypting and decrypting data. It allows for secure transmission of data through both symmetric and asymmetric encryption methods as well as ensuring the integrity, confidentiality and authenticity of digital information. Modern cryptography plays a crucial role in network security through protocols like SSL/TLS that protect internet communication and transactions.

1. Cryptography
Presented To:- Presented By:-
Mr. Anurag Sharma Rohan Jain , CS B ,
1000210077

2. Overview
• Cryptography………………..……….An introduction
• Objectives………………………………….Brief Aspect
• Terminology……………..…..To Make You Familiar
• How………………….…………………….Demonstration
• Methods………………………….......Public & Private
• Implementation………………..Hashing Algorithm
• Cryptography in Networking Security………....…
• Applications……………………………Real Life Scope

3. Introduction
 The Word Cryptology is made up of “Kryptos", which means
hidden and “Logos" which means word.
 In Laymen Words, it is an Art and science of protecting data.
 Technically, It involves logical transformation of information.
 The Principles of Cryptography are today applied to the
encryption of fax ,television, and computer network
communications and many other fields.
 Since the secure exchange of computer data is of great
importance to banking, government, and commercial
communications as well as for individuals.

4. Objectives
1)Confidentiality :-The information cannot be understood by
anyone for whom it was unintended.
2) Integrity :-The information cannot be altered in storage or
transit between sender and intended receiver without the
alteration being detected. (Data Is Not Corrupted).
3)Non-repudiation :-The creator/sender of the information
cannot deny at a later stage his or her intentions in the
creation or transmission of the information.
4) Authentication :-The sender and receiver can confirm each
other’s identity and the origin/destination of the information.
(Source Of Data IS Genuine).

5. Terminology
R O H A N J A I N
Plain Text(Can
Be Variable Length)
Encryption Using Key Using Algorithms
(MD4,MD5,SHA-1,RSA)
Cipher Text
00 B8 3c Ef G0 Xh 99 3d 2f
Using Algorithm (Same As
Decryption Using Same Used To Encrypt the Text)
Keys
R O H A N J A I N

6. HOW…??
A Simple Demonstration:-Substitution Cipher
To Encode:-> S E C R E T
Key :-> Offset the 3rd letter so the alphabets begin with it.
So starting with:-
ABCDEFGHIJKLMNOPQRSTUVWXYZ
and sliding everything by 3, we get:-
DEFGHIJKLMNOPQRSTUVWXYZABC
So D=A, E=B, F=C…..and so on.
Encoded:-> V H F U H W
To Decode:-> Provide anyone the key i.e.,
=>Offset the 3rd letter so the alphabets begin with it.

7. Cryptography Methods : Modern
Cryptography
o Symmetric-Key Cryptography.
o Asymmetric-Key Cryptography.
o Cryptanalysis.

8. Private(Symmetric) Cryptography
In symmetric-key encryption each end already has a secret key
(code) that it can use to encrypt a packet of information before it
is sent over the network to another computer.

9. Private Cryptography Methods:-
DES (Data Encryption Standard) AES(Advanced Encryption Standard)
Older Newer
Breakable Unbreakable
Smaller Key (56-bit Encryption). Bigger Key(128/192bit /256 bit Encryption).
7*10^16 Key Combinations. 3*10^35 Key Combinations.
Smaller Block Size (64 bits). Larger Block Size (128bits).
For DES with 64 bits, the maximum amount For AES with 128 bits, the maximum
of data that can be transferred with a single amount of data that can be transferred
encryption key is 32GB. with a single encryption key is 256 EB.

10. Public/Asymmetric Cryptography
Asymmetric/Public encryption uses two different keys at once
i.e., combination of a private key and a public key. The private
key is known only to your computer while the public key is
given by your computer to any computer that wants to
communicate securely with it.
 To decode an
encrypted Message a
computer must use the
public key provided by
originating computer,
and its own private key

11. Cryptanalysis
 The Study of methods to break Cryptosystems.
 Often targeted at obtaining a key.
 Cryptanalysis Attacks:-
o Brute force
o Trying all key values in the keyspace.
o Frequency Analysis
o Guess values based on frequency of occurrence.
o Dictionary Attack
o Find plaintext based on common words.

12. Implementation of Encryption Keys
:Hash Function
A hash function is any algorithm or subroutine that maps large
data sets of variable length to smaller data sets of a fixed
length. For example, a person's name, having a variable
length, could be hashed to a single integer.
Basic Idea:-
Input Number 10,667
Hashing Function Input# x 143
Hash Value 1,525,381
Public keys generally use more complex algorithms and very
large hash values for encrypting, including 40-bit or even 128-
bit numbers. A 128-bit number has a possible 2128.

13. • The values returned by a hash function are called hash
values, hash codes, digest ,hash sums, checksums or
simply hashes.
• A Cryptographic hash function (specifically, SHA-1) at work.
Note that even small changes in the source input (here in
the word "over") drastically change the resulting output.
V
U

14. Cryptography in Networking
 Transport Layer Security (TLS) and its predecessor, Secure
Sockets Layer (SSL), are cryptographic protocols that
provide communication security over the Internet.
 Several versions of the protocols are in widespread use in
applications such as web browsing, electronic mail, Internet
faxing, instant messaging and voice-over-IP (VoIP).
 When you're accessing sensitive information, such as an
online bank account or a payment transfer service like PayPal
or Google Checkout.

15. The client request the SSL connection by sending the request.
Server provides it’s secure certificate to client to show it’s
authenticity.
Client validates the certificate and request a one time session
with server.
Server completes the SSL handshake and the session begins.

16. Applications
• ATM Cards
• E-Commerce
• Computer Passwords
• Electronic Fund Transfer
• Digital Signatures
• Network Security
• Storage Integrity

17. References
http://en.wikipedia.org/wiki/Cryptography
http://en.wikipedia.org/wiki/Cryptographic_hash
function
http://computer.howstuffworks.com/encryption.ht
m
http://en.wikipedia.org/wiki/Secure_Sockets_Layer

18. Queries ??