Terminology
Cryptology
Now you'll might be thinking that hey Psycho_Coder promised me a tutorial on Cryptography then what is Cryptology . So here's what cryptology means , Cryptology is the mathematics, such as number theory, and the application of formulas and algorithms, that underpin cryptography and cryptanalysis. Since the cryptanalysis concepts are highly specialized and complex, we concentrate here only on some of the key mathematical concepts behind cryptography . Cryptology can also be defined as the science of study of, or the use of, methods and procedures for translating and interpreting codes and ciphers; cryptanalysis. Therefore , Cryptology is consists of two parts :- a) Cryptography b) Cryptanalysis .
So , in the above defination you came to know about two new terms Cryptography and Cryptanalysis . So what are they , proceed further to know .
Cryptography
Cryptography is a greek word which literally means "secret writing" . Cryptography refers to the art of transforming data and messages to make them secure and immune to attacks .Cryptographycan also be defined as the art of protecting information by transforming it (encrypting it) into an unreadable format, called cipher text. Only those who possess a secret key can decipher (or decrypt) the message into plain text .
Cryptanalysis
Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to loosen" or "to untie") is the art and science of analyzing information systems in order to study the hidden aspects of the systems . Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages , even if the cryptographic key is unknown .
Quote:
Note :- Further tutorials will be based on Cryptography and not Cryptanalysis . I will try to include some attack but don't expect to get most out of it .
Some More Terms :-
Cipher :- A mapping algorithm that is applied to a fixed number of characters at a time with an intent of concealing the contents of the message.
Code :- A mapping algorithm that is applied to a variable number of characters (according to linguistic entities) at a time with an intent of concealing the contents of the message.
Commercial Code :- A code used in business primarily to reduce cost by shortening messages. It involves no secrecy. The prime example is the 'Philips' Code.
Crib :- A word or phrase that might be expected in the plaintext that can be a "wedge" or test for decryption. More...
Deciphering :- The procedure of turning enciphered text into plain text with prior knowledge of the algorithms or keys involved. This is what the intended message receiver does.
Decryption :- The science of turning enciphered text into plain text without prior knowledge of the algorithms or keys involved. This is what the interceptor or 'cracker' does.
Digraphs :- A plaintext character pairing technique that prevents frequency analysis of commonly occurring pairs such as 'qu'. Note that trigraphs (three characters at a time) is an extension of the theme.
Homophones :- Several replacement letters for the same letter in plaintext
Key :- A word or phrase that modifies the enciphering/deciphering process in such a way that knowledge of the algorithm alone is insufficient to decipher an enciphered message.
Monoalphabets :- A single mapping of plaintext letters to ciphertext letters.
Nomenclature :- Half code and half cipher, it was a list of word/syllable substitutions and cipher alphabet with homophones.
Nulls :- Meaningless letters used to confuse by modifying frequency distributions or predictability. Sometimes used to fill a message to a specific length.
Plaintext :- The original message to be encoded or enciphered
Polyalphabets :- A method where several mappings of plaintext letters to ciphertext letters occur in a message.
Steganography :- The art of concealing a message's existence. One example would be through the use of photographic microdots.
Substitution :- Enciphering by replacing one letter by another.
Transmission SecurityThe art of concealing an electrically transmitted message through burst encoding or spread spectrum methods.
Transposition :- Enciphering by shuffling the order of letters.
Purpose Of Cryptography
Cryptography is the science of writing in secret code and is an ancient art; the first documented use of cryptography in writing dates back to circa 1900 B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.
Cryptography, then, not only protects data from theft or alteration, but can also be used for user authentication. There are, in general, three types of cryptographic schemes typically used to accomplish these goals: secret key (or symmetric) cryptography, public-key (or asymmetric) cryptography, and hash functions, each of which is described below. In all cases, the initial unencrypted data is referred to as plaintext. It is encrypted into ciphertext, which will in turn (usually) be decrypted into usable plaintext.
