Cryptography is a method of protecting information and communications through the use of codes. It involves techniques such as encrypting plaintext into ciphertext using a key, and back again through decryption. Modern cryptography aims for confidentiality, integrity, non-repudiation and authentication of digital information. It uses cryptosystems, keys and algorithms to encrypt and decrypt data between senders and receivers over secure channels.

1. BY
M.LAVANYA,M.Sc(cs)
NADAR SARASWATHI COLLEGE OF ARTS
&SCIENCE THENI

2. CRYPTOGRAPHY
Cryptography 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. The pre-fix "crypt" means
"hidden" or "vault" and the suffix "graph" stands for
"writing."

3. CRYPTOGRAPHY TECHNIQUES
Cryptography techniques
 Cryptography is closely related to the disciplines
of cryptology and cryptanalysis. It includes techniques
such as microdots, merging words with images, and other
ways to hide information in storage or transit. However, in
today's computer-centric world, cryptography is most often
associated with scrambling plaintext (ordinary text,
sometimes referred to as clear text) into cipher text (a
process called encryption), then back again (known as
decryption). Individuals who practice this field are known
as cryptographers.

4. MODERN CRYPTOGRAPHY
Modern cryptography concerns itself with the following four
objectives:
 Confidentiality: the information cannot be understood by
anyone for whom it was unintended
 Integrity: the information cannot be altered in storage or
transit between sender and intended receiver without the
alteration being detected
 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
 Authentication: the sender and receiver can confirm each
other's identity and the origin/destination of the
information

5. BASIC CONCEPTS
 Cryptosystem, plaintext, cipher text, key
 Examples of simple cryptosystems
 To publish or not to publish?
 Secret and open research in cryptology
 Software vs. hardware implementations of
cryptography
 Evolution of cryptography and cryptanalysis.

6.  Consider two parties Alice and Bob. Now, Alice wants to
send a message m to Bob over a secure channel.
So, what happens is as follows.
The sender’s message or sometimes called the Plaintext, is
converted into an unreadable form using a Key k. The
resultant text obtained is called the Cipher text. This
process is known as Encryption. At the time of receival, the
Cipher text is converted back into the plaintext using the
same Key k, so that it can be read by the receiver. This
process is known as Decryption.
 Alice (Sender) Bob (Receiver) C = E (m, k) ----> m = D (C,
k)

7. IMPLEMENTATION OF SECURITY
SERVICES
 Classical (symmetric) vs. public key (asymmetric)
cryptosystems
 Trapdoor one-way functions - main components of public
key cryptosystems
 Features required from today's ciphers
 Implementing security services using cryptographic
transformations
 Block vs. stream ciphers
 Measures of the cipher strength

8. KEY MANAGEMENT
 Session keys and key encrypting keys
 Exchange of keys using Key Distribution Center
 The Diffie-Hellman key exchange protocol
 Exchange of symmetric keys using public key
cryptosystems
 Generation and registration of the public key pair
 Concept of a public key certificate
 Formats of certificates
 Hierarchy of Certification Authorities - Public Key
Infrastructure
 Certificate revocation

9. SECURE INTERNET PROTOCOL
 Secure electronic mail
 S/MIME
 Open PGP
 Secure WWW
 SSL
 Secure payment card protocols
 Secure virtual private networks
 IPSec