Cryptography involves encrypting data using mathematical algorithms and decrypting it back to plaintext. Encryption scrambles data into ciphertext while decryption returns it to readable text. Conventional cryptography uses a single key for both functions but public key cryptography uses different keys for encryption and decryption, eliminating the need to share secret keys. Hybrid cryptography combines the strengths of both by using asymmetric keys to distribute a symmetric session key for bulk encryption. Cryptanalysis aims to break secure communication while steganography hides messages within innocent-looking files like images and audio.

1. CRYPOGRAPHY

2. ENCRYPTION and
DECRYPTION

3. Some Basic Terms
 Plain Text/Clear Text :Data that can be read and
understood without any special measure.
 Cipher Text :The unreadable plain text after
encryption.
 Encryption :The method of disguising to hide its
substance.
 Decryption :The method of reverting cipher text to
its original plain text.

4. CRYPTANALYSIS vs. CRYPTOGRAPHY?
 Cryptography is a science of using mathematics to
encrypt and decrypt data. It enable us to store and
transmit sensitive data over unsecure network.
 Cryptanalysis is the science of analyzing and breaking
secure communication.

5. CONVENTIONAL CRYPTOGRAPHY

6.  In conventional cryptography(symmetric key
encryption)one key is used both for encryption and
decryption.
 i.e. Caesar’s cipher
 This cryptography is very fast but is quite expensive
due to difficulty of secure key distribution.

7. PUBLIC KEY CRYPTOGRAPHY

8.  It uses two key, one key for encryption(public key) and
one for decryption(private key).
 We publish the data with the public key to the world
while keeping the private key.
 The need for sender and receiver to share secret key
via some secure channel is eliminated.

9. HYBRID CRYPTOGRAPHY

10. Combines strengths of both methods
Asymmetric distributes symmetric key.
 Also known as a session key(one time
only secret key).
 Symmetric provides bulk encryption
i.e. PGP

11. KEYS
 Work with cryptographic algorithm to produce a
specific cipher text.
 Larger keys are secure for longer period of time.

12. STEGANOGRAPHY
 Greek for “covered writing”
 “The art and science of writing hidden messages in
such a way that no one apart from the intended
recipient even knows that a message has been sent.”
 It makes use of seemingly innocent cover files such as
text, audio, and image files

13. IMAGE BASED TECHNIQUE
 Least Significant Bit Insertion
 Replaces the LSB with the message to be encoded.
 Simple, but susceptible to lossy compression and
image manipulation
 Masking and Filtering
 Masks secret data over the original data by changing
the luminance of particular areas
 During masking, it embed the message within
significant bits of the cover image

14.  Digital Watermarking – provides identification
pertaining to the owner; i.e. license or copyright
information
- Invisible vs. Visible
 Fingerprinting – provides identification of the user;
used to identify and track illegal use of content

15. WATERMARK

16. WEB HOSTING

17.  A web hosting is a type of Internet hosting that allows
individuals and organizations to make their website
accessible via the World Wide Web or locally in the
network.
 The most basic is web page and small-scale file
hosting, where files can be uploaded via File Transfer
Protocol (FTP) on the server.

18. DNS
 A Domain Name Service translates queries for domain
names (which are easier to understand and utilize
when accessing the internet) into IP addresses for the
purpose of locating computer services and devices
worldwide.
 For example, the domain name
www.ethicalpirates.com translates to the addresses
172.16.32.254 (IPv4).

19. APACHE (Web Server)
 Web servers are computers that deliver (serves up)
Web pages. Every Web server has an IP address and
possibly a domain name.
 Any computer can be turned into a Web server by
installing server software and connecting the machine
to the internet

20. FIREWALL

21.  A firewall is a rule or set of rules create to permit or
deny network transmissions based on a set of rules and
is frequently used to protect networks from
unauthorized access while permitting legitimate
communications to pass.
 Firewalls are frequently used to prevent unauthorized
Internet users from accessing private networks
connected to the Internet, especially intranets.
 i.e. Packet Filter, Proxy Server etc.

22. REFERENCES
 www.jjtc.com/stegdoc/steg1995.html
 “Information Hiding: Techniques for Steganography
and Digital Watermarking” – S. Katzenbeisser, F. Petit
colas
 “RSA Security’s Official Guide to Cryptography” by S.
Burnett and S. Paine, Osborne/McGraw-Hill, 2001
 The Code Breaker-David Khan