- CRYPTOLOGY. Noun: the study of codes, or the art of writing and solving them.
- - From Ancient Greek: κρυπτός, romanized: kryptós "hidden, secret"; and γράφειν graphein, "to write", or -λογία -logia, "study".
- - A science concerned with data communication and storage in secure and usually secret form. It encompasses both cryptography and cryptanalysis.
- - The people who does cryptography called cryptographer. Their job is to secure computer and information technology systems by creating algorithms and ciphers to encrypt data. They often also carry out the duties of a cryptanalyst, deciphering algorithms and cipher text to decrypt information.
- Cryptology is the mathematics, such as number theory, and the application of formulas and algorithms that underpin cryptography and cryptanalysis. In order for data to be secured for storage or transmission, it must be transformed in such a manner that it would be difficult for an unauthorized individual to be able to discover its true meaning. To do this, certain mathematical equations are used, which are very difficult to solve unless certain strict criteria are met. The level of difficulty of solving a given equation is known as its intractability. These types of equations form the basis of cryptography.
- Words to know:
- - Cryptography. The art and science of making ciphers.
- - Cryptanalysis. The art and science of breaking ciphers.
- - Cryptology. The study of cryptography and cryptanalysis.
- - Cryptosystem. A particular suite of algorithms and protocols for encryption, decryption, and key generation. Examples: Cramer-Shoup cryptosystem, Rabin cryptosystem, Benaloh cryptosystem, RSA cryptosystem.
- - Cryptographic System. Any system that uses cryptography.
- - Cipher. An algorithm used in a cryptosystem.
- Kind of ciphers:
- Here are some useful categories of ciphers. Note that a particular cipher may belong to more than one of these categories.
- - Classical: A cipher easy enough to be performed by hand, usually character-based. Also called manual.
- - Modern: Pretty much any cipher that isn’t classical.
- - Substitution: Each character of the plaintext is replaced with one or more characters to make the ciphertext.
- - Transposition: Characters in the plaintext are rearranged to form the ciphertext.
- - Monoalphabetic: A substitution cipher in which a character of the plaintext is always replaced by the same character.
- - Polyalphabetic: A substitution cipher that essentially uses multiple monoalphabetic substitution mappings.
- - Homophonic: A substitution in which one character can map to one of a set of characters.
- - Polygraphic: A substitution of blocks of characters for blocks of characters.
- - Periodic: A polyalphabetic cipher in which the replacement scheme repeats.
- - Non-periodic: Self-explanatory if you understand periodic.
- - Block: Encryption takes place not per character but per blocks of characters.
- - Stream: A cipher operating on a data stream of unknown length, usually incorporating feedback.
- - Secret Key: A cipher in which ke and kd are the same or trivially derivable from one another; requires the parties to meet in secret to exchange the keys they’ll be using. Also called symmetric.
- - Public Key: A scheme in which everyone’s encryption key is publicly known but their decryption key is kept secre