Cryptography

CRYPTOGRAPHY

Computer data often travels from one computer to another, leaving the safety of its protected physical
surroundings. Once the data is out of hand, people with bad intention could modify or forge your data,
either for amusement or for their own benefit. Cryptography can reformat and transform our data,
making it safer on its trip between computers. The technology is based on the essentials of secret codes,
augmented by modern mathematics that protects our data in powerful ways.

• Computer Security - generic name for the collection of tools designed to protect data and to thwart
hackers

• Network Security - measures to protect data during their transmission

• Internet Security - measures to protect data during their transmission over a collection of
interconnected networks Security Attacks, Services and Mechanisms To assess the security needs of an
organization effectively, the manager responsible for security needs some systematic way of defining
the requirements for security and characterization of approaches to satisfy those requirements. One
approach is to consider three aspects of information security: Security attack – Any action that
compromises the security of information owned by an organization.

Security mechanism – A mechanism that is designed to detect, prevent or recover from a security
attack.

Security service – A service that enhances the security of the data processing systems and the
information transfers of an organization. The services are intended to counter security attacks and they
make use of one or more security mechanisms to provide the service.

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 Plaintext 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 Cryptography Cryptographic systems are generally
classified along 3 independent dimensions: Type of operations used for transforming plain text to cipher
text All the encryption algorithms are based on two general principles: substitution, in which each
element in the plaintext is mapped into another element, and transposition, in which elements in the
plaintext are rearranged. The number of keys used If the sender and receiver uses same key then it is
said to be symmetric key (or) single key (or) conventional encryption.