19-03-2011, 04:07 PM
PRESENTED BY,
Ayesha Farhin
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Cryptography considered as a branch of both mathematics and computer science.
Affiliated closely with information theory, computer security, and engineering.
Definitions:
Cryptography comes from the Greek words Kryptos, meaning hidden, and Graphen, meaning to write.
Thus Cryptography is the study of secret (crypto-) writing (-graphy)
Cryptography deals with all aspects of secure messaging, authentication, digital signatures, electronic money, and other applications.
The practitioner of Cryptography is called Cryptographer
Cryptography Through History
Cryptography has a history of at least 4000 years.
Ancient Egyptians enciphered some of their hieroglyphic writing on monuments.
Ancient Hebrews enciphered certain words in the scriptures.
2000 years ago Julius Caesar used a simple substitution cipher, now known as the Caesar cipher.
Roger Bacon in the middle ages described several methods in 1200s.
Geoffrey Chaucer included several ciphers in his works (e.g. Canterbury Tales).
Leon Alberti devised a cipher wheel, and described the principles of frequency analysis in the 1460s.
Blaise de Vigenère published a book on cryptology in 1585, & described the polyalphabetic substitution cipher.
Increasing use, especially in diplomacy & war over centuries.
Areas of Study
Computer Security:
Cryptanalysis, Cryptology, Cryptography
Terminologies:
Encryption
Decryption
Plaintext
Cipher Text
Cryptanalaysis
The study of principles and methods of transforming an unintelligible message back into an intelligible message without knowledge of the key is called Cryptanalysis.
Also called “code breaking” sometimes.
Practitioners of cryptanalysis are cryptanalysts.
Cryptology
Cryptology is the branch of mathematics that studies the mathematical foundations of cryptographic methods.
Cryptology is actually the study of codes and ciphers.
Cryptology = both cryptography and cryptanalysis
Definitions:
In cryptographic terminology, the message is called plaintext or cleartext.
Encoding the contents of the message in such a way that hides its contents from outsiders is called encryption.
A method of encryption and decryption is called a cipher - The name cipher originates from the Hebrew word "Saphar," meaning "to number.”
The encrypted message is called the ciphertext.
The process of retrieving the plaintext from the ciphertext is called decryption.
Encryption and decryption usually make use of a key, and the coding method is such that decryption can be performed only by knowing the proper key.
The Key
All modern algorithms use a key to control encryption and decryption; a message can be decrypted only if the key matches the encryption key.
The key used for decryption can be different from the encryption key, but for most algorithms they are the same.