CRYPTOGRAPHY - Basic Concepts

CRYPTOGRAPHY

INTODUCTION TO INFORMATION SECURITY

The internet is not a single network, but a worldwide collection of loosely connected networks that are accessible by individual computer hosts, in a variety of ways, to anyone with a computer and a network connection. Thus, individuals and organizations can reach any point on the internet without regard to national or geographic boundaries or time of day. 
However, along with the convenience and easy access to information come risks. Among them are the risks that valuable information will be lost, stolen, changed, or misused.

COMPONENTS OF INFORMATION SECURITY

Basic Security concepts

Three basic security concepts important to information on the internet are
   -Confidentiality
   -Integrity
   -Availability
The concepts relating to the people who use that information are
   -Authentication
   -Authorization
   -Non repudiation

CRYPTOGRAPHY Basic Concepts 

Cryptography: The art or science encompassing the principles and methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back to its original form.
Plain text: The original intelligible message. 
Cipher text: The transformed message. 
Cipher: An  algorithm  for  transforming  an  intelligible  message  into  one  that  is  unintelligible  by transposition and/or substitution methods 
Key: Some critical information used by the cipher, known only to the sender & receiver 
Encipher (encode): The process of converting plaintext to cipher text using a cipher and a key.
Decipher (decode): The process of converting cipher text back into plaintext using a cipher and a key.
Cryptanalysis: The  study  of  principles  and  methods  of  transforming  an  unintelligible  message back into an intelligible message without knowledge of the key. Also called code breaking.
Cryptology: Both cryptography and cryptanalysis.
Code: An  algorithm  for  transforming  an  intelligible  message  into  an  unintelligible  one  using  a code-book.

Classification of Cryptographic Systems

Cryptographic systems are generally classified along 3 independent dimensions: 
1. Based on the type of operations used for transforming plain text to cipher text.
All the encryption algorithms are based on two general principles:
Substitution Technique: In this technique, each element in the plaintext   is   mapped   into   another   element.
Transposition Technique: In this technique, elements in the plaintext are rearranged. 
2. Based on the number of keys used.
Symmetric key encryption: If the sender and receiver uses same key then it is said to be symmetric key or secret key or single key or conventional encryption. 
Asymmetric key encryption: If the sender and receiver use different keys then it is said to be asymmetric key or public key encryption. 
3. Based on the way in which the plain text is processed.
Block Cipher: It processes the input and block of elements at a time, producing output block for each input block. 
Stream Cipher: It processes the input elements continuously, producing output element one at a time, as it goes along.